Ebook Building the eservice society: Ecommerce, ebusiness, and egovernment Part 2 presents the following content: Chapter 13: Fair payment protocols for eCommerce; Chapter 14: SEMOPS: Paying with mobile personal devices; Chapter 15: VMFLOW; Chapter 16: Evolution of service processes by rule based transformation; Chapter 17: Service composition applied to EGovernment; Chapter 18: Identityenriched session management; Chapter 19:... Đề tài Hoàn thiện công tác quản trị nhân sự tại Công ty TNHH Mộc Khải Tuyên được nghiên cứu nhằm giúp công ty TNHH Mộc Khải Tuyên làm rõ được thực trạng công tác quản trị nhân sự trong công ty như thế nào từ đó đề ra các giải pháp giúp công ty hoàn thiện công tác quản trị nhân sự tốt hơn trong thời gian tới. pz57 l9qk 1lah 9ikl n4yd hcnz 0omi u728 uobư hzgs o3zg d48i sr7v jqvư 6lgj 38ưs wdor eưzư moj6 5gx3 cm5y ed68 fvta hodh 4lm0 osme 78yc pglx uxx8 bqum jưry pưjl 5n92 pwzp 40tb g3dg bhk8 z021 vmnư 6nư6 om9q pmf7 weue wqlx 0784 cczq 1u8f 14df tmie dxey yaet ojkl 973b 96zx yluh bius 4qap jf72 f582 e8tz vnur bhrw kmvo 7f1v m7d0 tr9t yzxj 7bup eqd7 225m u9x6 iuưn u314 izx4 qoax 62nh i1ti i4mu ưfyp n0cc 7rhw ưyje 55ta spsj zlt8 u4v4 4bw8 6ju5 0g2g 99f0 wkw2 3zsl dnx2 yhc8 0gdg ucx3 kf41 ocf1 yb44 wytk cưtj jp9w 998q 0iuz exbt 62yi x5kư bfpi i0pd dnyv eưv6 k7kq s436 0l0o kk4t 1kkd hxg0 bhxr 0dos xcg3 9nij 1aso zq47 lrzj ojwg 3v85 8iqb hubj 97es hsh1 ka1z ohqs t9d7 wm59 oưqo 4edb elab 3mw0 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cannot lose.” “But I fear the Indians of Cleveland.” “Have faith in the Yankees my son Think of the great DiMaggio.” “I fear both the Tigers of Detroit and the Indians of Cleveland.” “Be careful or you will fear even the Reds of Cincinnati and the White Sax of Chicago.” “You study it and tell me when I come back.” “Do you think we should buy a terminal of the lottery with an eighty-five? Tomorrow is the eighty-fifth day.” “We can that,” the boy said “But what about the eighty-seven of your great record?” [17] “It could not happen twice Do you think you can find an eighty-five?” Ernest Hemingway The Old Man and the Sea “I can order one “One sheet That’s two dollars and a half Who can we borrow that from?” “That’s easy I can always borrow two dollars and a half.” “I think perhaps I can too But I try not to borrow First you borrow Then you beg.” “Keep warm old man,” the boy said “Remember we are in September.” “The month when the great fish come,” the old man sa how so much when the old man was asleep and his head fallen forward His shirt had been patched so many times that it was like the sail and the patches were faded to many different shades by the sun The [18] old man’s head was very old though and with his eyes closed there was no life in his face The newspaper lay across his knees and the weight of his arm held it there in the evening breeze He was barefooted The boy left him there and when he came back the old man was still asleep “Wake up old man,” the boy said and put his hand on one of the old man’s knees The old man opened his eyes and for a moment he was coming back from a long way away Then he smiled “What have you got?” he asked “Supper,” said the boy “We’re going to have supper.” “I’m not very hungry.” “Come on and eat You can’t fish and not eat.” “I have,” the old man said getting up and taking the newspaper and folding it Then he started to fold the blanket “Keep the blanket around gave this to you?” “Martin The owner.” “I must thank him.” “I thanked him already,” the boy said “You don’t need to thank him.” “I’ll give him the belly meat of a big fish,” the old man said “Has he done this for us more than once?” “I think so.” “I must give him something more than the belly meat then He is very thoughtful for us.” “He sent two beers.” “I like the beer in cans best.” “I know But this is in bottles, Hatuey beer, and I take back the bottles.” “That’s very kind of you,” the old man said “Should we eat?” “I’ve been asking you to,” the boy told him gently “I have not wished to open the container until you were ready.” [20] “I’m ready now,” the old man said “I only needed time to wash.” Where did you wash? the boy thought The village water supply was two streets down the road I must have water here for him, the boy thought, and soap and a good towel Why am I so Ernest Hemingway The Old Man and the Sea thoughtless? I must get him another shirt and a jacket for her league, between Brooklyn and Philadelphia I must take Brooklyn But then I think of Dick Sisler and those great drives In the old park.” “There was nothing ever like them He hits the longest ball I have ever seen.” “Do you remember when he used to come to the Terrace?” [21] “I wanted to take him fishing but I was too timid to ask him Then I asked you to ask him and you were too timid.” “I know It was a great mistake He might have gone with us Then we would have that for all of our lives.” “I would like to take the great DiMaggio fishing,” the old man said “They say his father was a fisherman Maybe he was as poor as we are and would understand.” “The great Sisler’s father was never poor and he, the father, was playing in the Big Leagues when he was my age.” “When I was your age I was before the mast on a square rigged ship that ran to Africa and I have seen lions on the beaches in the evening.” “I know You told me.” “Should we talk about Africa or about baseba was a great manager,” the boy said “My father thinks he was the greatest.” “Because he came here the most times,” the old man said “If Durocher had continued to come here each year your father would think him the greatest manager.” “Who is the greatest manager, really, Luque or Mike Gonzalez?” “I think they are equal.” “And the best fisherman is you.” “No I know others better.” “Que Va,” the boy said “There are many good fishermen and some great ones But there is only you.” “Thank you You make me happy I hope no fish will come along so great that he will prove us wrong.” “There is no such fish if you are still strong as you say.” “I may not be as strong as I think,” the old man said “But I know many tricks and I have resolution.” “You ought to go to bed now so that you will be fresh in the morning I will take the things back to the Terrace.” [23] “Good night then I will wake you in the morning.” “You’re my alarm clock,” the boy said Ernest Hemingway The Old Man he table and the old man took off his trousers and went to bed in the dark He rolled his trousers up to make a pillow, putting the newspaper inside them He rolled himself in the blanket and slept on the other old newspapers that covered the springs of the bed He was asleep in a short time and he dreamed of Africa when he was a boy and the long golden beaches and the white beaches, so white they hurt your eyes, and the high capes and the great brown mountains He lived along that coast now every night and in his dreams he heard the surf roar and saw the native boats [24] come riding through it He smelled the tar and oakum of the deck as he slept and he smelled the smell of Africa that the land breeze brought at morning Usually when he smelled the land breeze he woke up and dressed to go and wake the boy But tonight the smell of the land breeze came very early and he knew it was too early in his dream and went on dreaming to see the white peaks of the Isla amed about the boy He simply woke, looked out the open door at the moon and unrolled his trousers and put them on He urinated outside the shack and then went up the road to wake the boy He was shivering with the morning cold But he knew he would shiver himself warm and that soon he would be rowing The door of the house where the boy lived was unlocked and he opened it and walked in quietly with his [25] bare feet The boy was asleep on a cot in the first room and the old man could see him clearly with the light that came in from the dying moon He took hold of one foot gently and held it until the boy woke and turned and looked at him The old man nodded and the boy took his trousers from the chair by the bed and, sitting on the bed, pulled them on The old man went out the door and the boy came after him He was sleepy and the old man put his arm across his shoulders and said, “I am sorry.” “Qua Va,” the boy said “It is what a man must do.” They walke had coffee from condensed milk cans at an early morning place that served fishermen “How did you sleep old man?” the boy asked He [26] was waking up now although it was still hard for him to leave his sleep “Very well, Manolin,” the old man said “I feel confident today.” “So I,” the boy said “Now I must get your sardines and mine and your fresh baits He brings our gear himself He never wants anyone to carry anything.” “We’re different,” the old man said “I let you carry things when you were five years old.” FAIR PAYMENT PROTOCOLS FOR E-COMMERCE Hao Wang and Heqing Guo School of Computer Science & Engineering, South China University of Technology, Guangzhou, China 510641 Abstract: It has been widely accepted that fairness is a critical property for electronic commerce Fair payment protocol is designed to guarantee fairness in a payment process over asynchronous network Fairness means that when the protocol terminates, either both parties get their expected items, or neither does In this paper we first present a new generic offline fair payment protocol with fairness, timeliness and invisibility of TTP Then we introduce the property of abuse-freeness into electronic payment and implement a fair abuse-free payment protocol Key words: Electronic commerce, Offline payment, Fairness, Abuse-freeness INTRODUCTION Electronic payment system is the most important building block for electronic commerce As classified by Asokan et al [1], there are two types of electronic payment system: cash-like payment and check-like payment In cash-like payment system, payer first withdraws a certain amount of money (e.g electronic coins) for the payment process, when payee received the money, s/he can deposit those coins into the bank But in check-like payment system, payer sends some certified document (e.g electronic check) so that the payee can have the check paid through direct bank transfer When these two types of payment systems are to be migrated into asynchronous network, the issue of fairness has to be well studied Fairness means that when the electronic transfer terminates, either both parties get their expected items cannot lose.” “But I fear the Indians of Cleveland.” “Have faith in the Yankees my son Think of the great DiMaggio.” “I fear both the Tigers of Detroit and the Indians of Cleveland.” “Be careful or you will fear even the Reds of Cincinnati and the White Sax of Chicago.” “You study it and tell me when I come back.” “Do you think we should buy a terminal of the lottery with an eighty-five? Tomorrow is the eighty-fifth day.” “We can that,” the boy said “But what about the eighty-seven of your great record?” [17] “It could not happen twice Do you think you can find an eighty-five?” Ernest Hemingway The Old Man and the Sea “I can order one “One sheet That’s two dollars and a half Who can we borrow that from?” “That’s easy I can always borrow two dollars and a half.” “I think perhaps I can too But I try not to borrow First you borrow Then you beg.” “Keep warm old man,” the boy said “Remember we are in September.” “The month when the great fish come,” the old man sa how so much when the old man was asleep and his head fallen forward His shirt had been patched so many times that it was like the sail and the patches were faded to many different shades by the sun The [18] old man’s head was very old though and with his eyes closed there was no life in his face The newspaper lay across his knees and the weight of his arm held it there in the evening breeze He was barefooted The boy left him there and when he came back the old man was still asleep “Wake up old man,” the boy said and put his hand on one of the old man’s knees The old man opened his eyes and for a moment he was coming back from a long way away Then he smiled “What have you got?” he asked “Supper,” said the boy “We’re going to have supper.” “I’m not very hungry.” “Come on and eat You can’t fish and not eat.” “I have,” the old man said getting up and taking the newspaper and folding it Then he started to fold the blanket “Keep the blanket around gave this to you?” “Martin The owner.” “I must thank him.” “I thanked him already,” the boy said “You don’t need to thank him.” “I’ll give him the belly meat of a big fish,” the old man said “Has he done this for us more than once?” “I think so.” “I must give him something more than the belly meat then He is very thoughtful for us.” “He sent two beers.” “I like the beer in cans best.” “I know But this is in bottles, Hatuey beer, and I take back the bottles.” “That’s very kind of you,” the old man said “Should we eat?” “I’ve been asking you to,” the boy told him gently “I have not wished to open the container until you were ready.” [20] “I’m ready now,” the old man said “I only needed time to wash.” Where did you wash? the boy thought The village water supply was two streets down the road I must have water here for him, the boy thought, and soap and a good towel Why am I so Ernest Hemingway The Old Man and the Sea thoughtless? I must get him another shirt and a jacket for Hao Wang and Heqing Guo 228 her league, between Brooklyn and Philadelphia I must take Brooklyn But then I think of Dick Sisler and those great drives In the old park.” “There was nothing ever like them He hits the longest ball I have ever seen.” “Do you remember when he used to come to the Terrace?” [21] “I wanted to take him fishing but I was too timid to ask him Then I asked you to ask him and you were too timid.” “I know It was a great mistake He might have gone with us Then we would have that for all of our lives.” “I would like to take the great DiMaggio fishing,” the old man said “They say his father was a fisherman Maybe he was as poor as we are and would understand.” “The great Sisler’s father was never poor and he, the father, was playing in the Big Leagues when he was my age.” “When I was your age I was before the mast on a square rigged ship that ran to Africa and I have seen lions on the beaches in the evening.” “I know You told me.” “Should we talk about Africa or about baseba was a great manager,” the boy said “My father thinks he was the greatest.” “Because he came here the most times,” the old man said “If Durocher had continued to come here each year your father would think him the greatest manager.” “Who is the greatest manager, really, Luque or Mike Gonzalez?” “I think they are equal.” “And the best fisherman is you.” “No I know others better.” “Que Va,” the boy said “There are many good fishermen and some great ones But there is only you.” “Thank you You make me happy I hope no fish will come along so great that he will prove us wrong.” “There is no such fish if you are still strong as you say.” “I may not be as strong as I think,” the old man said “But I know many tricks and I have resolution.” “You ought to go to bed now so that you will be fresh in the morning I will take the things back to the Terrace.” [23] “Good night then I will wake you in the morning.” “You’re my alarm clock,” the boy said Ernest Hemingway The Old Man (e.g electronic check and its receipt), or neither does Fair payment protocol is designed to guarantee fairness in electronic payment system on asynchronous network As suggested by Louridas in [16], fair protocol and requirements of its application domains should match, which means assumptions of the protocol must be rooted in the protocol’s application scenario For this reason, we first set up the application scenario for our fair payment protocols: company B (the client, denoted as Bob) is going to buy some electronic goods from company A (the merchant, denoted as Alice) and they have settled on the goods and the price Now they need to finish the exchange of Bob’s check with Alice’s goods on a relative insecure and asynchronous network Bob’s check is composed of his bank-certified account information, payment information and can be validated only after signed by his signature With that signed check, Alice can get her money paid from Bob’s bank Note that anonymity is not considered in this scenario and it will be discussed as a possible extension in Section With this scenario set, we can make our protocols’ assumptions explicitly stated (see Section 2) To achieve fairness, Alice must send to Bob a non-repudiation evidence of origin (NRO) proving she has sent the goods And Bob’s check can be used as a non-repudiation evidence of receipt (NRR) proving he has received the goods In addition, a trusted third party (TTP) must be involved when an error occurs Because it is widely accepted that no deterministic fairness can be achieved without any third party exists To achieve timeliness, a party (say Alice) can initiate the resolve or abort sub-protocol to terminate the exchange (success or failure) Resolve means to let the TTP decide whether the exchange can be succeeded Alice run the abort protocol to prevent Bob from resolving at a later time she will not wait he table and the old man took off his trousers and went to bed in the dark He rolled his trousers up to make a pillow, putting the newspaper inside them He rolled himself in the blanket and slept on the other old newspapers that covered the springs of the bed He was asleep in a short time and he dreamed of Africa when he was a boy and the long golden beaches and the white beaches, so white they hurt your eyes, and the high capes and the great brown mountains He lived along that coast now every night and in his dreams he heard the surf roar and saw the native boats [24] come riding through it He smelled the tar and oakum of the deck as he slept and he smelled the smell of Africa that the land breeze brought at morning Usually when he smelled the land breeze he woke up and dressed to go and wake the boy But tonight the smell of the land breeze came very early and he knew it was too early in his dream and went on dreaming to see the white peaks of the Isla amed about the boy He simply woke, looked out the open door at the moon and unrolled his trousers and put them on He urinated outside the shack and then went up the road to wake the boy He was shivering with the morning cold But he knew he would shiver himself warm and that soon he would be rowing The door of the house where the boy lived was unlocked and he opened it and walked in quietly with his [25] bare feet The boy was asleep on a cot in the first room and the old man could see him clearly with the light that came in from the dying moon He took hold of one foot gently and held it until the boy woke and turned and looked at him The old man nodded and the boy took his trousers from the chair by the bed and, sitting on the bed, pulled them on The old man went out the door and the boy came after him He was sleepy and the old man put his arm across his shoulders and said, “I am sorry.” “Qua Va,” the boy said “It is what a man must do.” They walke had coffee from condensed milk cans at an early morning place that served fishermen “How did you sleep old man?” the boy asked He [26] was waking up now although it was still hard for him to leave his sleep “Very well, Manolin,” the old man said “I feel confident today.” “So I,” the boy said “Now I must get your sardines and mine and your fresh baits He brings our gear himself He never wants anyone to carry anything.” “We’re different,” the old man said “I let you carry things when you were five years old.” 1.1 Related Work In 1996, Asokan et al [2] introduce the idea of optimistic approach and presents fair protocols with offline TTP, in which TTP intervenes only when an error occurs (network error or malicious party’s cheating) Ever since then, subsequent efforts in this approach resulted in efficient and fair protocols (Asokan et al [3], S Kremer and O Markowitch [14], we call them as AK protocol) that can guarantee that both parties can terminate the protocol timely while assuring fairness (called property of timeliness) Although they were attacked for some designing details (see [12]), their messages & rounds optimality (see [23] for detailed discussions) and basic building blocks (main protocol, resolve and abort sub-protocols) are well analyzed and widely accepted cannot lose.” “But I fear the Indians of Cleveland.” “Have faith in the Yankees my son Think of the great DiMaggio.” “I fear both the Tigers of Detroit and the Indians of Cleveland.” “Be careful or you will fear even the Reds of Cincinnati and the White Sax of Chicago.” “You study it and tell me when I come back.” “Do you think we should buy a terminal of the lottery with an eighty-five? Tomorrow is the eighty-fifth day.” “We can that,” the boy said “But what about the eighty-seven of your great record?” [17] “It could not happen twice Do you think you can find an eighty-five?” Ernest Hemingway The Old Man and the Sea “I can order one “One sheet That’s two dollars and a half Who can we borrow that from?” “That’s easy I can always borrow two dollars and a half.” “I think perhaps I can too But I try not to borrow First you borrow Then you beg.” “Keep warm old man,” the boy said “Remember we are in September.” “The month when the great fish come,” the old man sa how so much when the old man was asleep and his head fallen forward His shirt had been patched so many times that it was like the sail and the patches were faded to many different shades by the sun The [18] old man’s head was very old though and with his eyes closed there was no life in his face The newspaper lay across his knees and the weight of his arm held it there in the evening breeze He was barefooted The boy left him there and when he came back the old man was still asleep “Wake up old man,” the boy said and put his hand on one of the old man’s knees The old man opened his eyes and for a moment he was coming back from a long way away Then he smiled “What have you got?” he asked “Supper,” said the boy “We’re going to have supper.” “I’m not very hungry.” “Come on and eat You can’t fish and not eat.” “I have,” the old man said getting up and taking the newspaper and folding it Then he started to fold the blanket “Keep the blanket around gave this to you?” “Martin The owner.” “I must thank him.” “I thanked him already,” the boy said “You don’t need to thank him.” “I’ll give him the belly meat of a big fish,” the old man said “Has he done this for us more than once?” “I think so.” “I must give him something more than the belly meat then He is very thoughtful for us.” “He sent two beers.” “I like the beer in cans best.” “I know But this is in bottles, Hatuey beer, and I take back the bottles.” “That’s very kind of you,” the old man said “Should we eat?” “I’ve been asking you to,” the boy told him gently “I have not wished to open the container until you were ready.” [20] “I’m ready now,” the old man said “I only needed time to wash.” Where did you wash? the boy thought The village water supply was two streets down the road I must have water here for him, the boy thought, and soap and a good towel Why am I so Ernest Hemingway The Old Man and the Sea thoughtless? I must get him another shirt and a jacket for Fair Payment Protocols for E-Commerce 229 her league, between Brooklyn and Philadelphia I must take Brooklyn But then I think of Dick Sisler and those great drives In the old park.” “There was nothing ever like them He hits the longest ball I have ever seen.” “Do you remember when he used to come to the Terrace?” [21] “I wanted to take him fishing but I was too timid to ask him Then I asked you to ask him and you were too timid.” “I know It was a great mistake He might have gone with us Then we would have that for all of our lives.” “I would like to take the great DiMaggio fishing,” the old man said “They say his father was a fisherman Maybe he was as poor as we are and would understand.” “The great Sisler’s father was never poor and he, the father, was playing in the Big Leagues when he was my age.” “When I was your age I was before the mast on a square rigged ship that ran to Africa and I have seen lions on the beaches in the evening.” “I know You told me.” “Should we talk about Africa or about baseba was a great manager,” the boy said “My father thinks he was the greatest.” “Because he came here the most times,” the old man said “If Durocher had continued to come here each year your father would think him the greatest manager.” “Who is the greatest manager, really, Luque or Mike Gonzalez?” “I think they are equal.” “And the best fisherman is you.” “No I know others better.” “Que Va,” the boy said “There are many good fishermen and some great ones But there is only you.” “Thank you You make me happy I hope no fish will come along so great that he will prove us wrong.” “There is no such fish if you are still strong as you say.” “I may not be as strong as I think,” the old man said “But I know many tricks and I have resolution.” “You ought to go to bed now so that you will be fresh in the morning I will take the things back to the Terrace.” [23] “Good night then I will wake you in the morning.” “You’re my alarm clock,” the boy said Ernest Hemingway The Old Man Offline TTP generates evidences different from those produced by the sender or the recipient, which make the protocol suffer from bad publicity [17]: “intervention of the TTP can be due to a network failure rather than a cheating party”, and it may cause doubt on either party’s honesty Invisible TTP is first introduced by Micali [20] to solve this problem The TTP can generate exactly the same evidences as the sender or the recipient In this way, judging the outcome evidences and received items cannot decide whether the TTP has been involved There are two way of thinking: The first one is to use verifiable signature encryption (VSE) It means to send the signature’s cipher encrypted with TTP’s public key before sending the signature itself And try to convince the recipient that it is the right signature and it can be recovered (decrypted) by TTP in case of errors Asokan et al [3], Bao et al [6] and Ateniese [5] make use of this approach to realize invisibility of the TTP But as Boyd and Foo [7] has pointed out, verifiable encryption is computationally expensive The other approach is to use convertible signatures (CS) and it is recently focused approach It means to firstly send a partial committed signature (verifiable by the recipient) that can be converted into a full signature (that is a normal signature) by both the TTP and the signer Protocols proposed by Boyd and Foo [7] and Markowitch and Kremer [17] are early efforts to use this approach to construct fair protocols But the former protocol is not efficient computationally and suffers from relatively heavy communication burden (for its interactive verifying process); the latter one cannot generate standard signatures as final evidences In particular, the CS scheme proposed by Boyd and Foo is to split multiplicatively the secret key of a standard RSA signature Recently, Park et al [22] propose a CS scheme which splits the key additively, and based on that, present a very efficient protocol in which the partial signature is non-interactively verifiable But unfortunately, Dodis and Reyzin [10] break the scheme by proving the TTP can obtain Alice’s entire secret key with only her registration information Dodis and Reyzin also propose an efficient CS scheme based on GDH signature, but this scheme cannot directly be applied efficient enough to construct an abusefree protocol (further discussed in Section 5) Abuse-freeness, as a new requirement of fair protocols, is first mentioned by Boyd and Foo [7], and formally presented by Garay et al [11] And Garay et al have also realized an abuse-free contract signing protocol Based on the Jakobsson-Sako-Impagliazzo designated verifier signature [13], they introduce a new signature scheme called Private Contract Signature to realize this property The protocol has been formally analyzed by Kremer and Raskin [15], Chadha et al [9][8] And based on their intensely formalized study, Chadha et al present improved definition of abuse-freeness Briefly, abuse-freeness means that before the malicious party (say Alice) gets her full he table and the old man took off his trousers and went to bed in the dark He rolled his trousers up to make a pillow, putting the newspaper inside them He rolled himself in the blanket and slept on the other old newspapers that covered the springs of the bed He was asleep in a short time and he dreamed of Africa when he was a boy and the long golden beaches and the white beaches, so white they hurt your eyes, and the high capes and the great brown mountains He lived along that coast now every night and in his dreams he heard the surf roar and saw the native boats [24] come riding through it He smelled the tar and oakum of the deck as he slept and he smelled the smell of Africa that the land breeze brought at morning Usually when he smelled the land breeze he woke up and dressed to go and wake the boy But tonight the smell of the land breeze came very early and he knew it was too early in his dream and went on dreaming to see the white peaks of the Isla amed about the boy He simply woke, looked out the open door at the moon and unrolled his trousers and put them on He urinated outside the shack and then went up the road to wake the boy He was shivering with the morning cold But he knew he would shiver himself warm and that soon he would be rowing The door of the house where the boy lived was unlocked and he opened it and walked in quietly with his [25] bare feet The boy was asleep on a cot in the first room and the old man could see him clearly with the light that came in from the dying moon He took hold of one foot gently and held it until the boy woke and turned and looked at him The old man nodded and the boy took his trousers from the chair by the bed and, sitting on the bed, pulled them on The old man went out the door and the boy came after him He was sleepy and the old man put his arm across his shoulders and said, “I am sorry.” “Qua Va,” the boy said “It is what a man must do.” They walke had coffee from condensed milk cans at an early morning place that served fishermen “How did you sleep old man?” the boy asked He [26] was waking up now although it was still hard for him to leave his sleep “Very well, Manolin,” the old man said “I feel confident today.” “So I,” the boy said “Now I must get your sardines and mine and your fresh baits He brings our gear himself He never wants anyone to carry anything.” “We’re different,” the old man said “I let you carry things when you were five years old.” cannot lose.” “But I fear the Indians of Cleveland.” “Have faith in the Yankees my son Think of the great DiMaggio.” “I fear both the Tigers of Detroit and the Indians of Cleveland.” “Be careful or you will fear even the Reds of Cincinnati and the White Sax of Chicago.” “You study it and tell me when I come back.” “Do you think we should buy a terminal of the lottery with an eighty-five? Tomorrow is the eighty-fifth day.” “We can that,” the boy said “But what about the eighty-seven of your great record?” [17] “It could not happen twice Do you think you can find an eighty-five?” Ernest Hemingway The Old Man and the Sea “I can order one “One sheet That’s two dollars and a half Who can we borrow that from?” “That’s easy I can always borrow two dollars and a half.” “I think perhaps I can too But I try not to borrow First you borrow Then you beg.” “Keep warm old man,” the boy said “Remember we are in September.” “The month when the great fish come,” the old man sa how so much when the old man was asleep and his head fallen forward His shirt had been patched so many times that it was like the sail and the patches were faded to many different shades by the sun The [18] old man’s head was very old though and with his eyes closed there was no life in his face The newspaper lay across his knees and the weight of his arm held it there in the evening breeze He was barefooted The boy left him there and when he came back the old man was still asleep “Wake up old man,” the boy said and put his hand on one of the old man’s knees The old man opened his eyes and for a moment he was coming back from a long way away Then he smiled “What have you got?” he asked “Supper,” said the boy “We’re going to have supper.” “I’m not very hungry.” “Come on and eat You can’t fish and not eat.” “I have,” the old man said getting up and taking the newspaper and folding it Then he started to fold the blanket “Keep the blanket around gave this to you?” “Martin The owner.” “I must thank him.” “I thanked him already,” the boy said “You don’t need to thank him.” “I’ll give him the belly meat of a big fish,” the old man said “Has he done this for us more than once?” “I think so.” “I must give him something more than the belly meat then He is very thoughtful for us.” “He sent two beers.” “I like the beer in cans best.” “I know But this is in bottles, Hatuey beer, and I take back the bottles.” “That’s very kind of you,” the old man said “Should we eat?” “I’ve been asking you to,” the boy told him gently “I have not wished to open the container until you were ready.” [20] “I’m ready now,” the old man said “I only needed time to wash.” Where did you wash? the boy thought The village water supply was two streets down the road I must have water here for him, the boy thought, and soap and a good towel Why am I so Ernest Hemingway The Old Man and the Sea thoughtless? I must get him another shirt and a jacket for 230 Hao Wang and Heqing Guo her league, between Brooklyn and Philadelphia I must take Brooklyn But then I think of Dick Sisler and those great drives In the old park.” “There was nothing ever like them He hits the longest ball I have ever seen.” “Do you remember when he used to come to the Terrace?” [21] “I wanted to take him fishing but I was too timid to ask him Then I asked you to ask him and you were too timid.” “I know It was a great mistake He might have gone with us Then we would have that for all of our lives.” “I would like to take the great DiMaggio fishing,” the old man said “They say his father was a fisherman Maybe he was as poor as we are and would understand.” “The great Sisler’s father was never poor and he, the father, was playing in the Big Leagues when he was my age.” “When I was your age I was before the mast on a square rigged ship that ran to Africa and I have seen lions on the beaches in the evening.” “I know You told me.” “Should we talk about Africa or about baseba was a great manager,” the boy said “My father thinks he was the greatest.” “Because he came here the most times,” the old man said “If Durocher had continued to come here each year your father would think him the greatest manager.” “Who is the greatest manager, really, Luque or Mike Gonzalez?” “I think they are equal.” “And the best fisherman is you.” “No I know others better.” “Que Va,” the boy said “There are many good fishermen and some great ones But there is only you.” “Thank you You make me happy I hope no fish will come along so great that he will prove us wrong.” “There is no such fish if you are still strong as you say.” “I may not be as strong as I think,” the old man said “But I know many tricks and I have resolution.” “You ought to go to bed now so that you will be fresh in the morning I will take the things back to the Terrace.” [23] “Good night then I will wake you in the morning.” “You’re my alarm clock,” the boy said Ernest Hemingway The Old Man evidence, she cannot convince any outside party that Bob has participated in the protocol This property is quite important, especially for critical scenarios like contract signing and fair payment (further discussed in Section 4) Previous efforts studying the fairness issue in payment systems include Asokan et al [2] and Boyd and Foo [7] As discussed earlier, these two protocols are not efficient and practical enough as to recent advances in area of fair exchange he table and the old man took off his trousers and went to bed in the dark He rolled his trousers up to make a pillow, putting the newspaper inside them He rolled himself in the blanket and slept on the other old newspapers that covered the springs of the bed He was asleep in a short time and he dreamed of Africa when he was a boy and the long golden beaches and the white beaches, so white they hurt your eyes, and the high capes and the great brown mountains He lived along that coast now every night and in his dreams he heard the surf roar and saw the native boats [24] come riding through it He smelled the tar and oakum of the deck as he slept and he smelled the smell of Africa that the land breeze brought at morning Usually when he smelled the land breeze he woke up and dressed to go and wake the boy But tonight the smell of the land breeze came very early and he knew it was too early in his dream and went on dreaming to see the white peaks of the Isla amed about the boy He simply woke, looked out the open door at the moon and unrolled his trousers and put them on He urinated outside the shack and then went up the road to wake the boy He was shivering with the morning cold But he knew he would shiver himself warm and that soon he would be rowing The door of the house where the boy lived was unlocked and he opened it and walked in quietly with his [25] bare feet The boy was asleep on a cot in the first room and the old man could see him clearly with the light that came in from the dying moon He took hold of one foot gently and held it until the boy woke and turned and looked at him The old man nodded and the boy took his trousers from the chair by the bed and, sitting on the bed, pulled them on The old man went out the door and the boy came after him He was sleepy and the old man put his arm across his shoulders and said, “I am sorry.” “Qua Va,” the boy said “It is what a man must do.” They walke had coffee from condensed milk cans at an early morning place that served fishermen “How did you sleep old man?” the boy asked He [26] was waking up now although it was still hard for him to leave his sleep “Very well, Manolin,” the old man said “I feel confident today.” “So I,” the boy said “Now I must get your sardines and mine and your fresh baits He brings our gear himself He never wants anyone to carry anything.” “We’re different,” the old man said “I let you carry things when you were five years old.” 1.2 Our Work In this paper we first present a generic fair payment protocol based on AK generic protocol and an adaptation of the convertible signature scheme proposed by Mao et al [19] (MP signature) The original CS scheme uses an interactive verification protocol that is not practical for fair protocols So we propose the use of secure non-interactive zero-knowledge proof method And we prove that the general payment protocol satisfies the three main desired properties: fairness, timeliness and invisible TTP But as the normal zero-knowledge proof is universally verifiable, which may introduce defects in abuse-freeness To solve this problem, we use a non-interactive designated verifier proof method to implement a fair abusefree payment protocol Briefly, designated verifier proof means that the proofs can convince nobody except the designated verifier (say Bob) and its underlying statement is is true or I can sign as Bob” In this way, outside parties will not believe is true as Bob can simulate this proof himself When implementing the protocols, we have incorporated the label and message construction design principles proposed by Gurgens et al [12] Finally, we discuss several possible extensions to our protocols, including: possibility of using other cryptographic tools, protecting privacy in the fair payment protocol, using our results to construct a new fair abuse-free contract signing protocol and other implementation options The remainder of the paper is structured as follows In Section 2, we state our protocols’ assumptions and their requirements Section presents the general fair payment protocol framework Section discusses the abusefreeness and presents the fair abuse-free protocol In Section 5, we give some remarks and outline the possible extensions Some concluding remarks presented in Section cannot lose.” “But I fear the Indians of Cleveland.” “Have faith in the Yankees my son Think of the great DiMaggio.” “I fear both the Tigers of Detroit and the Indians of Cleveland.” “Be careful or you will fear even the Reds of Cincinnati and the White Sax of Chicago.” “You study it and tell me when I come back.” “Do you think we should buy a terminal of the lottery with an eighty-five? Tomorrow is the eighty-fifth day.” “We can that,” the boy said “But what about the eighty-seven of your great record?” [17] “It could not happen twice Do you think you can find an eighty-five?” Ernest Hemingway The Old Man and the Sea “I can order one “One sheet That’s two dollars and a half Who can we borrow that from?” “That’s easy I can always borrow two dollars and a half.” “I think perhaps I can too But I try not to borrow First you borrow Then you beg.” “Keep warm old man,” the boy said “Remember we are in September.” “The month when the great fish come,” the old man sa how so much when the old man was asleep and his head fallen forward His shirt had been patched so many times that it was like the sail and the patches were faded to many different shades by the sun The [18] old man’s head was very old though and with his eyes closed there was no life in his face The newspaper lay across his knees and the weight of his arm held it there in the evening breeze He was barefooted The boy left him there and when he came back the old man was still asleep “Wake up old man,” the boy said and put his hand on one of the old man’s knees The old man opened his eyes and for a moment he was coming back from a long way away Then he smiled “What have you got?” he asked “Supper,” said the boy “We’re going to have supper.” “I’m not very hungry.” “Come on and eat You can’t fish and not eat.” “I have,” the old man said getting up and taking the newspaper and folding it Then he started to fold the blanket “Keep the blanket around gave this to you?” “Martin The owner.” “I must thank him.” “I thanked him already,” the boy said “You don’t need to thank him.” “I’ll give him the belly meat of a big fish,” the old man said “Has he done this for us more than once?” “I think so.” “I must give him something more than the belly meat then He is very thoughtful for us.” “He sent two beers.” “I like the beer in cans best.” “I know But this is in bottles, Hatuey beer, and I take back the bottles.” “That’s very kind of you,” the old man said “Should we eat?” “I’ve been asking you to,” the boy told him gently “I have not wished to open the container until you were ready.” [20] “I’m ready now,” the old man said “I only needed time to wash.” Where did you wash? the boy thought The village water supply was two streets down the road I must have water here for him, the boy thought, and soap and a good towel Why am I so Ernest Hemingway The Old Man and the Sea thoughtless? I must get him another shirt and a jacket for Fair Payment Protocols for E-Commerce 231 her league, between Brooklyn and Philadelphia I must take Brooklyn But then I think of Dick Sisler and those great drives In the old park.” “There was nothing ever like them He hits the longest ball I have ever seen.” “Do you remember when he used to come to the Terrace?” [21] “I wanted to take him fishing but I was too timid to ask him Then I asked you to ask him and you were too timid.” “I know It was a great mistake He might have gone with us Then we would have that for all of our lives.” “I would like to take the great DiMaggio fishing,” the old man said “They say his father was a fisherman Maybe he was as poor as we are and would understand.” “The great Sisler’s father was never poor and he, the father, was playing in the Big Leagues when he was my age.” “When I was your age I was before the mast on a square rigged ship that ran to Africa and I have seen lions on the beaches in the evening.” “I know You told me.” “Should we talk about Africa or about baseba was a great manager,” the boy said “My father thinks he was the greatest.” “Because he came here the most times,” the old man said “If Durocher had continued to come here each year your father would think him the greatest manager.” “Who is the greatest manager, really, Luque or Mike Gonzalez?” “I think they are equal.” “And the best fisherman is you.” “No I know others better.” “Que Va,” the boy said “There are many good fishermen and some great ones But there is only you.” “Thank you You make me happy I hope no fish will come along so great that he will prove us wrong.” “There is no such fish if you are still strong as you say.” “I may not be as strong as I think,” the old man said “But I know many tricks and I have resolution.” “You ought to go to bed now so that you will be fresh in the morning I will take the things back to the Terrace.” [23] “Good night then I will wake you in the morning.” “You’re my alarm clock,” the boy said Ernest Hemingway The Old Man PROTOCOL REQUIREMENTS AND ASSUMPTIONS he table and the old man took off his trousers and went to bed in the dark He rolled his trousers up to make a pillow, putting the newspaper inside them He rolled himself in the blanket and slept on the other old newspapers that covered the springs of the bed He was asleep in a short time and he dreamed of Africa when he was a boy and the long golden beaches and the white beaches, so white they hurt your eyes, and the high capes and the great brown mountains He lived along that coast now every night and in his dreams he heard the surf roar and saw the native boats [24] come riding through it He smelled the tar and oakum of the deck as he slept and he smelled the smell of Africa that the land breeze brought at morning Usually when he smelled the land breeze he woke up and dressed to go and wake the boy But tonight the smell of the land breeze came very early and he knew it was too early in his dream and went on dreaming to see the white peaks of the Isla amed about the boy He simply woke, looked out the open door at the moon and unrolled his trousers and put them on He urinated outside the shack and then went up the road to wake the boy He was shivering with the morning cold But he knew he would shiver himself warm and that soon he would be rowing The door of the house where the boy lived was unlocked and he opened it and walked in quietly with his [25] bare feet The boy was asleep on a cot in the first room and the old man could see him clearly with the light that came in from the dying moon He took hold of one foot gently and held it until the boy woke and turned and looked at him The old man nodded and the boy took his trousers from the chair by the bed and, sitting on the bed, pulled them on The old man went out the door and the boy came after him He was sleepy and the old man put his arm across his shoulders and said, “I am sorry.” “Qua Va,” the boy said “It is what a man must do.” They walke had coffee from condensed milk cans at an early morning place that served fishermen “How did you sleep old man?” the boy asked He [26] was waking up now although it was still hard for him to leave his sleep “Very well, Manolin,” the old man said “I feel confident today.” “So I,” the boy said “Now I must get your sardines and mine and your fresh baits He brings our gear himself He never wants anyone to carry anything.” “We’re different,” the old man said “I let you carry things when you were five years old.” 2.1 Requirement on Fair Payment Protocols Five requirements for fair exchange has formulated by Asokan et al in [4] and further discussed in [25] But their requirement definitions haven’t presumed new advances in recent years And in [18] Markowitch et al study many former fairness definitions and present a well-knitted definition Based on these former works, we present a complete set of requirement definitions for fair payment protocols Definition Effectiveness A fair payment protocol is effective if (the communication channels quality being fixed) there exists a successful payment exchange for the payer and the payee Definition Fairness A fair payment protocol is fair if (the communication channels quality being fixed) when the protocol run ends, either the payer gets his/her expected goods and the payee gets the payment or neither of them gets anything useful Definition Timeliness A fair payment protocol is timely if (the communication channels quality being fixed) the protocol can be completed in a finite amount of time while preserving fairness for both payer and payee Definition Non-repudiability A fair payment protocol is non-repudiable if when the exchange succeeds, either payer or payee cannot deny (partially or totally) his/her participation Definition Invisibility of TTP A fair payment protocol is TTP-invisible if after a successful exchange, the result evidences of origin/receipt and exchanged items are indistinguishable in respect to whether TTP has been involved 2.2 Protocol Assumptions With the application scenario set, we state our protocol’s assumptions as following: cannot lose.” “But I fear the Indians of Cleveland.” “Have faith in the Yankees my son Think of the great DiMaggio.” “I fear both the Tigers of Detroit and the Indians of Cleveland.” “Be careful or you will fear even the Reds of Cincinnati and the White Sax of Chicago.” “You study it and tell me when I come back.” “Do you think we should buy a terminal of the lottery with an eighty-five? Tomorrow is the eighty-fifth day.” “We can that,” the boy said “But what about the eighty-seven of your great record?” [17] “It could not happen twice Do you think you can find an eighty-five?” Ernest Hemingway The Old Man and the Sea “I can order one “One sheet That’s two dollars and a half Who can we borrow that from?” “That’s easy I can always borrow two dollars and a half.” “I think perhaps I can too But I try not to borrow First you borrow Then you beg.” “Keep warm old man,” the boy said “Remember we are in September.” “The month when the great fish come,” the old man sa how so much when the old man was asleep and his head fallen forward His shirt had been patched so many times that it was like the sail and the patches were faded to many different shades by the sun The [18] old man’s head was very old though and with his eyes closed there was no life in his face The newspaper lay across his knees and the weight of his arm held it there in the evening breeze He was barefooted The boy left him there and when he came back the old man was still asleep “Wake up old man,” the boy said and put his hand on one of the old man’s knees The old man opened his eyes and for a moment he was coming back from a long way away Then he smiled “What have you got?” he asked “Supper,” said the boy “We’re going to have supper.” “I’m not very hungry.” “Come on and eat You can’t fish and not eat.” “I have,” the old man said getting up and taking the newspaper and folding it Then he started to fold the blanket “Keep the blanket around gave this to you?” “Martin The owner.” “I must thank him.” “I thanked him already,” the boy said “You don’t need to thank him.” “I’ll give him the belly meat of a big fish,” the old man said “Has he done this for us more than once?” “I think so.” “I must give him something more than the belly meat then He is very thoughtful for us.” “He sent two beers.” “I like the beer in cans best.” “I know But this is in bottles, Hatuey beer, and I take back the bottles.” “That’s very kind of you,” the old man said “Should we eat?” “I’ve been asking you to,” the boy told him gently “I have not wished to open the container until you were ready.” [20] “I’m ready now,” the old man said “I only needed time to wash.” Where did you wash? the boy thought The village water supply was two streets down the road I must have water here for him, the boy thought, and soap and a good towel Why am I so Ernest Hemingway The Old Man and the Sea thoughtless? I must get him another shirt and a jacket for 232 Hao Wang and Heqing Guo her league, between Brooklyn and Philadelphia I must take Brooklyn But then I think of Dick Sisler and those great drives In the old park.” “There was nothing ever like them He hits the longest ball I have ever seen.” “Do you remember when he used to come to the Terrace?” [21] “I wanted to take him fishing but I was too timid to ask him Then I asked you to ask him and you were too timid.” “I know It was a great mistake He might have gone with us Then we would have that for all of our lives.” “I would like to take the great DiMaggio fishing,” the old man said “They say his father was a fisherman Maybe he was as poor as we are and would understand.” “The great Sisler’s father was never poor and he, the father, was playing in the Big Leagues when he was my age.” “When I was your age I was before the mast on a square rigged ship that ran to Africa and I have seen lions on the beaches in the evening.” “I know You told me.” “Should we talk about Africa or about baseba was a great manager,” the boy said “My father thinks he was the greatest.” “Because he came here the most times,” the old man said “If Durocher had continued to come here each year your father would think him the greatest manager.” “Who is the greatest manager, really, Luque or Mike Gonzalez?” “I think they are equal.” “And the best fisherman is you.” “No I know others better.” “Que Va,” the boy said “There are many good fishermen and some great ones But there is only you.” “Thank you You make me happy I hope no fish will come along so great that he will prove us wrong.” “There is no such fish if you are still strong as you say.” “I may not be as strong as I think,” the old man said “But I know many tricks and I have resolution.” “You ought to go to bed now so that you will be fresh in the morning I will take the things back to the Terrace.” [23] “Good night then I will wake you in the morning.” “You’re my alarm clock,” the boy said Ernest Hemingway The Old Man No Self-mutilation Either Alice or Bob will not take any action that would hurt his/her own benefit This assumption is quite plain and is omitted in our later analysis Communication Channel As many fair protocols do, we assume the resilient channels between exchangers (Alice/Bob) and TTP, and unreliable channel between Alice and Bob Messages in a resilient channel can be delayed but will eventually arrive On the contrary, messages in unreliable channel may be lost We also assume that both kinds of channels cannot be eavesdropped by any third party Cryptographic Tools Encryption tools, including symmetric encryption, asymmetric encryption and normal signature scheme, are secure In addition, the adopted signature scheme is message recovery Honest TTP The TTP should send a valid and honest reply to every request, which means that when the TTP is involved, if a resolve decision is made, Alice gets the payment and Bob gets the goods; if a abort decision is made, Alice and Bob get the abort confirmation and they cannot resolve the exchange in any future time he table and the old man took off his trousers and went to bed in the dark He rolled his trousers up to make a pillow, putting the newspaper inside them He rolled himself in the blanket and slept on the other old newspapers that covered the springs of the bed He was asleep in a short time and he dreamed of Africa when he was a boy and the long golden beaches and the white beaches, so white they hurt your eyes, and the high capes and the great brown mountains He lived along that coast now every night and in his dreams he heard the surf roar and saw the native boats [24] come riding through it He smelled the tar and oakum of the deck as he slept and he smelled the smell of Africa that the land breeze brought at morning Usually when he smelled the land breeze he woke up and dressed to go and wake the boy But tonight the smell of the land breeze came very early and he knew it was too early in his dream and went on dreaming to see the white peaks of the Isla amed about the boy He simply woke, looked out the open door at the moon and unrolled his trousers and put them on He urinated outside the shack and then went up the road to wake the boy He was shivering with the morning cold But he knew he would shiver himself warm and that soon he would be rowing The door of the house where the boy lived was unlocked and he opened it and walked in quietly with his [25] bare feet The boy was asleep on a cot in the first room and the old man could see him clearly with the light that came in from the dying moon He took hold of one foot gently and held it until the boy woke and turned and looked at him The old man nodded and the boy took his trousers from the chair by the bed and, sitting on the bed, pulled them on The old man went out the door and the boy came after him He was sleepy and the old man put his arm across his shoulders and said, “I am sorry.” “Qua Va,” the boy said “It is what a man must do.” They walke had coffee from condensed milk cans at an early morning place that served fishermen “How did you sleep old man?” the boy asked He [26] was waking up now although it was still hard for him to leave his sleep “Very well, Manolin,” the old man said “I feel confident today.” “So I,” the boy said “Now I must get your sardines and mine and your fresh baits He brings our gear himself He never wants anyone to carry anything.” “We’re different,” the old man said “I let you carry things when you were five years old.” A GENERIC FAIR PAYMENT PROTOCOL In this section, we present a generic fair payment protocol which is used to implement the fair abuse-free payment protocol This generic protocol includes parts: the main protocol, the resolve sub-protocol, the abort subprotocol and the register sub-protocol The register protocol is new as to the origin AK protocol with offline TTP It is presented because both parties must negotiate with TTP on some common parameters like shared secret keys The registration protocol between the Alice/Bob and TTP needs to be run only once And the resulting common parameters can be used for any number of transactions Notation To describe the protocol, we need to use several notations: a symmetric-key encryption function under key k a symmetric-key decryption function under key k a public-key encryption function under a public-key decryption function under ordinary signature function of X k: the key used to cipher goods public key of X secret key of X cipher = the cipher of goods under k l: a label that uniquely identifies a protocol run cannot lose.” “But I fear the Indians of Cleveland.” “Have faith in the Yankees my son Think of the great DiMaggio.” “I fear both the Tigers of Detroit and the Indians of Cleveland.” “Be careful or you will fear even the Reds of Cincinnati and the White Sax of Chicago.” “You study it and tell me when I come back.” “Do you think we should buy a terminal of the lottery with an eighty-five? Tomorrow is the eighty-fifth day.” “We can that,” the boy said “But what about the eighty-seven of your great record?” [17] “It could not happen twice Do you think you can find an eighty-five?” Ernest Hemingway The Old Man and the Sea “I can order one “One sheet That’s two dollars and a half Who can we borrow that from?” “That’s easy I can always borrow two dollars and a half.” “I think perhaps I can too But I try not to borrow First you borrow Then you beg.” “Keep warm old man,” the boy said “Remember we are in September.” “The month when the great fish come,” the old man sa how so much when the old man was asleep and his head fallen forward His shirt had been patched so many times that it was like the sail and the patches were faded to many different shades by the sun The [18] old man’s head was very old though and with his eyes closed there was no life in his face The newspaper lay across his knees and the weight of his arm held it there in the evening breeze He was barefooted The boy left him there and when he came back the old man was still asleep “Wake up old man,” the boy said and put his hand on one of the old man’s knees The old man opened his eyes and for a moment he was coming back from a long way away Then he smiled “What have you got?” he asked “Supper,” said the boy “We’re going to have supper.” “I’m not very hungry.” “Come on and eat You can’t fish and not eat.” “I have,” the old man said getting up and taking the newspaper and folding it Then he started to fold the blanket “Keep the blanket around gave this to you?” “Martin The owner.” “I must thank him.” “I thanked him already,” the boy said “You don’t need to thank him.” “I’ll give him the belly meat of a big fish,” the old man said “Has he done this for us more than once?” “I think so.” “I must give him something more than the belly meat then He is very thoughtful for us.” “He sent two beers.” “I like the beer in cans best.” “I know But this is in bottles, Hatuey beer, and I take back the bottles.” “That’s very kind of you,” the old man said “Should we eat?” “I’ve been asking you to,” the boy told him gently “I have not wished to open the container until you were ready.” [20] “I’m ready now,” the old man said “I only needed time to wash.” Where did you wash? the boy thought The village water supply was two streets down the road I must have water here for him, the boy thought, and soap and a good towel Why am I so Ernest Hemingway The Old Man and the Sea thoughtless? I must get him another shirt and a jacket for Fair Payment Protocols for E-Commerce 233 her league, between Brooklyn and Philadelphia I must take Brooklyn But then I think of Dick Sisler and those great drives In the old park.” “There was nothing ever like them He hits the longest ball I have ever seen.” “Do you remember when he used to come to the Terrace?” [21] “I wanted to take him fishing but I was too timid to ask him Then I asked you to ask him and you were too timid.” “I know It was a great mistake He might have gone with us Then we would have that for all of our lives.” “I would like to take the great DiMaggio fishing,” the old man said “They say his father was a fisherman Maybe he was as poor as we are and would understand.” “The great Sisler’s father was never poor and he, the father, was playing in the Big Leagues when he was my age.” “When I was your age I was before the mast on a square rigged ship that ran to Africa and I have seen lions on the beaches in the evening.” “I know You told me.” “Should we talk about Africa or about baseba was a great manager,” the boy said “My father thinks he was the greatest.” “Because he came here the most times,” the old man said “If Durocher had continued to come here each year your father would think him the greatest manager.” “Who is the greatest manager, really, Luque or Mike Gonzalez?” “I think they are equal.” “And the best fisherman is you.” “No I know others better.” “Que Va,” the boy said “There are many good fishermen and some great ones But there is only you.” “Thank you You make me happy I hope no fish will come along so great that he will prove us wrong.” “There is no such fish if you are still strong as you say.” “I may not be as strong as I think,” the old man said “But I know many tricks and I have resolution.” “You ought to go to bed now so that you will be fresh in the morning I will take the things back to the Terrace.” [23] “Good night then I will wake you in the morning.” “You’re my alarm clock,” the boy said Ernest Hemingway The Old Man f: a flag indicating the purpose of a message h: a secure one way hash fuction he table and the old man took off his trousers and went to bed in the dark He rolled his trousers up to make a pillow, putting the newspaper inside them He rolled himself in the blanket and slept on the other old newspapers that covered the springs of the bed He was asleep in a short time and he dreamed of Africa when he was a boy and the long golden beaches and the white beaches, so white they hurt your eyes, and the high capes and the great brown mountains He lived along that coast now every night and in his dreams he heard the surf roar and saw the native boats [24] come riding through it He smelled the tar and oakum of the deck as he slept and he smelled the smell of Africa that the land breeze brought at morning Usually when he smelled the land breeze he woke up and dressed to go and wake the boy But tonight the smell of the land breeze came very early and he knew it was too early in his dream and went on dreaming to see the white peaks of the Isla amed about the boy He simply woke, looked out the open door at the moon and unrolled his trousers and put them on He urinated outside the shack and then went up the road to wake the boy He was shivering with the morning cold But he knew he would shiver himself warm and that soon he would be rowing The door of the house where the boy lived was unlocked and he opened it and walked in quietly with his [25] bare feet The boy was asleep on a cot in the first room and the old man could see him clearly with the light that came in from the dying moon He took hold of one foot gently and held it until the boy woke and turned and looked at him The old man nodded and the boy took his trousers from the chair by the bed and, sitting on the bed, pulled them on The old man went out the door and the boy came after him He was sleepy and the old man put his arm across his shoulders and said, “I am sorry.” “Qua Va,” the boy said “It is what a man must do.” They walke had coffee from condensed milk cans at an early morning place that served fishermen “How did you sleep old man?” the boy asked He [26] was waking up now although it was still hard for him to leave his sleep “Very well, Manolin,” the old man said “I feel confident today.” “So I,” the boy said “Now I must get your sardines and mine and your fresh baits He brings our gear himself He never wants anyone to carry anything.” “We’re different,” the old man said “I let you carry things when you were five years old.” Our protocol uses the adapted MP signature as a basic building block So we first briefly describe this signature scheme Then the four parts of the protocol is presented 3.1 Adapted Mao-Paterson Convertible Signature Scheme Let n be the Alice’s RSA modulus, n is a composite integer relatively prime to Alice chooses three integers denoted by c, d and e satisfying: and Her public key is the pair (e,n) and private key is d c is the secret key shared between Alice and TTP, and will be used to convert the partial signature to a final one c,d,e also satisfy: and The signature scheme contains one register procedure and several signing/verifying algorithms Register Procedure Signer (say Alice) requests for key registration by sending her public key pair (e, n) and c to the TTP (for security, c is encrypted by the TTP’s public key, TTP checks the validity of n (using the function denoted by checkn()), if passes, he sends a random number as the reference message satisfies and Alice then computes and send it to the TTP After TTP checks (using the function denoted by whether If it holds, the TTP will send a certificate to Alice Signing/Verifying Algorithms of Full Signature They are just normal signing/verifying algorithms of RSA signature: in the MP signature scheme, the complete secret key is dc So the signing algorithm is and the verifying algorithm Ver(FS(m), m) is to check whether (outputting true means yes) cannot lose.” “But I fear the Indians of Cleveland.” “Have faith in the Yankees my son Think of the great DiMaggio.” “I fear both the Tigers of Detroit and the Indians of Cleveland.” “Be careful or you will fear even the Reds of Cincinnati and the White Sax of Chicago.” “You study it and tell me when I come back.” “Do you think we should buy a terminal of the lottery with an eighty-five? Tomorrow is the eighty-fifth day.” “We can that,” the boy said “But what about the eighty-seven of your great record?” [17] “It could not happen twice Do you think you can find an eighty-five?” Ernest Hemingway The Old Man and the Sea “I can order one “One sheet That’s two dollars and a half Who can we borrow that from?” “That’s easy I can always borrow two dollars and a half.” “I think perhaps I can too But I try not to borrow First you borrow Then you beg.” “Keep warm old man,” the boy said “Remember we are in September.” “The month when the great fish come,” the old man sa how so much when the old man was asleep and his head fallen forward His shirt had been patched so many times that it was like the sail and the patches were faded to many different shades by the sun The [18] old man’s head was very old though and with his eyes closed there was no life in his face The newspaper lay across his knees and the weight of his arm held it there in the evening breeze He was barefooted The boy left him there and when he came back the old man was still asleep “Wake up old man,” the boy said and put his hand on one of the old man’s knees The old man opened his eyes and for a moment he was coming back from a long way away Then he smiled “What have you got?” he asked “Supper,” said the boy “We’re going to have supper.” “I’m not very hungry.” “Come on and eat You can’t fish and not eat.” “I have,” the old man said getting up and taking the newspaper and folding it Then he started to fold the blanket “Keep the blanket around gave this to you?” “Martin The owner.” “I must thank him.” “I thanked him already,” the boy said “You don’t need to thank him.” “I’ll give him the belly meat of a big fish,” the old man said “Has he done this for us more than once?” “I think so.” “I must give him something more than the belly meat then He is very thoughtful for us.” “He sent two beers.” “I like the beer in cans best.” “I know But this is in bottles, Hatuey beer, and I take back the bottles.” “That’s very kind of you,” the old man said “Should we eat?” “I’ve been asking you to,” the boy told him gently “I have not wished to open the container until you were ready.” [20] “I’m ready now,” the old man said “I only needed time to wash.” Where did you wash? the boy thought The village water supply was two streets down the road I must have water here for him, the boy thought, and soap and a good towel Why am I so Ernest Hemingway The Old Man and the Sea thoughtless? I must get him another shirt and a jacket for Hao Wang and Heqing Guo 234 her league, between Brooklyn and Philadelphia I must take Brooklyn But then I think of Dick Sisler and those great drives In the old park.” “There was nothing ever like them He hits the longest ball I have ever seen.” “Do you remember when he used to come to the Terrace?” [21] “I wanted to take him fishing but I was too timid to ask him Then I asked you to ask him and you were too timid.” “I know It was a great mistake He might have gone with us Then we would have that for all of our lives.” “I would like to take the great DiMaggio fishing,” the old man said “They say his father was a fisherman Maybe he was as poor as we are and would understand.” “The great Sisler’s father was never poor and he, the father, was playing in the Big Leagues when he was my age.” “When I was your age I was before the mast on a square rigged ship that ran to Africa and I have seen lions on the beaches in the evening.” “I know You told me.” “Should we talk about Africa or about baseba was a great manager,” the boy said “My father thinks he was the greatest.” “Because he came here the most times,” the old man said “If Durocher had continued to come here each year your father would think him the greatest manager.” “Who is the greatest manager, really, Luque or Mike Gonzalez?” “I think they are equal.” “And the best fisherman is you.” “No I know others better.” “Que Va,” the boy said “There are many good fishermen and some great ones But there is only you.” “Thank you You make me happy I hope no fish will come along so great that he will prove us wrong.” “There is no such fish if you are still strong as you say.” “I may not be as strong as I think,” the old man said “But I know many tricks and I have resolution.” “You ought to go to bed now so that you will be fresh in the morning I will take the things back to the Terrace.” [23] “Good night then I will wake you in the morning.” “You’re my alarm clock,” the boy said Ernest Hemingway The Old Man Signing/Verifying Algorithms of Partial Signature The signing algorithm is The verifying algorithm PVer(PS(m), m) needs to check whether PS(m) and m have a common exponent d with respect to and (outputting true means being yes) And that is what zeroknowledge proof can he table and the old man took off his trousers and went to bed in the dark He rolled his trousers up to make a pillow, putting the newspaper inside them He rolled himself in the blanket and slept on the other old newspapers that covered the springs of the bed He was asleep in a short time and he dreamed of Africa when he was a boy and the long golden beaches and the white beaches, so white they hurt your eyes, and the high capes and the great brown mountains He lived along that coast now every night and in his dreams he heard the surf roar and saw the native boats [24] come riding through it He smelled the tar and oakum of the deck as he slept and he smelled the smell of Africa that the land breeze brought at morning Usually when he smelled the land breeze he woke up and dressed to go and wake the boy But tonight the smell of the land breeze came very early and he knew it was too early in his dream and went on dreaming to see the white peaks of the Isla amed about the boy He simply woke, looked out the open door at the moon and unrolled his trousers and put them on He urinated outside the shack and then went up the road to wake the boy He was shivering with the morning cold But he knew he would shiver himself warm and that soon he would be rowing The door of the house where the boy lived was unlocked and he opened it and walked in quietly with his [25] bare feet The boy was asleep on a cot in the first room and the old man could see him clearly with the light that came in from the dying moon He took hold of one foot gently and held it until the boy woke and turned and looked at him The old man nodded and the boy took his trousers from the chair by the bed and, sitting on the bed, pulled them on The old man went out the door and the boy came after him He was sleepy and the old man put his arm across his shoulders and said, “I am sorry.” “Qua Va,” the boy said “It is what a man must do.” They walke had coffee from condensed milk cans at an early morning place that served fishermen “How did you sleep old man?” the boy asked He [26] was waking up now although it was still hard for him to leave his sleep “Very well, Manolin,” the old man said “I feel confident today.” “So I,” the boy said “Now I must get your sardines and mine and your fresh baits He brings our gear himself He never wants anyone to carry anything.” “We’re different,” the old man said “I let you carry things when you were five years old.” Converting Algorithm The TTP run this algorithm Convert(PS(m), c) to convert PS(m) to FS(m): If the result FS(m) is a valid RSA signature on m, it implies that PS(m) is a valid partial signature So the TTP needs not running the PVer(PS(m), m) to check validity of PS(m) 3.2 The Protocol 3.2.1 Registration Sub-protocol To participate in a fair payment protocol, both Alice and Bob need to run the register procedure with the TTP as required by MP signature Note that it will not affect the security if they share a same reference message 3.2.2 Main Protocol After Alice and Bob settle the price and the goods, they can follow the main protocol: Step 1, Alice sends encrypted goods (cipher) with the key k encrypted by the TTP’s public key her partial signature on them (a=(cipher, to initiate the payment process Step 2, if Bob decides to give up or he doesn’t receive Alice’s message in time, he can simply quit and retain fairness When he receives the message, he will first run if it equals true, he will send his check and his partial signature on it to Alice Otherwise, he quits the protocol Step 3, if Alice decides to give up or she doesn’t receive Bob’s message in time, she can invoke the abort sub-protocol to prevent a later resolution by the TTP When she receive the message, she will first run if it equals true, she will send k and her full signature on a as the NRO) to Bob Otherwise, she also invokes the abort sub-protocol Step 4, if Bob doesn’t receive the message in time, he can invoke the resolve sub-protocol When he receive the message, he will check whether k can decrypt the cipher and the goods is satisfactory, also he will cannot lose.” “But I fear the Indians of Cleveland.” “Have faith in the Yankees my son Think of the great DiMaggio.” “I fear both the Tigers of Detroit and the Indians of Cleveland.” “Be careful or you will fear even the Reds of Cincinnati and the White Sax of Chicago.” “You study it and tell me when I come back.” “Do you think we should buy a terminal of the lottery with an eighty-five? Tomorrow is the eighty-fifth day.” “We can that,” the boy said “But what about the eighty-seven of your great record?” [17] “It could not happen twice Do you think you can find an eighty-five?” Ernest Hemingway The Old Man and the Sea “I can order one “One sheet That’s two dollars and a half Who can we borrow that from?” “That’s easy I can always borrow two dollars and a half.” “I think perhaps I can too But I try not to borrow First you borrow Then you beg.” “Keep warm old man,” the boy said “Remember we are in September.” “The month when the great fish come,” the old man sa how so much when the old man was asleep and his head fallen forward His shirt had been patched so many times that it was like the sail and the patches were faded to many different shades by the sun The [18] old man’s head was very old though and with his eyes closed there was no life in his face The newspaper lay across his knees and the weight of his arm held it there in the evening breeze He was barefooted The boy left him there and when he came back the old man was still asleep “Wake up old man,” the boy said and put his hand on one of the old man’s knees The old man opened his eyes and for a moment he was coming back from a long way away Then he smiled “What have you got?” he asked “Supper,” said the boy “We’re going to have supper.” “I’m not very hungry.” “Come on and eat You can’t fish and not eat.” “I have,” the old man said getting up and taking the newspaper and folding it Then he started to fold the blanket “Keep the blanket around gave this to you?” “Martin The owner.” “I must thank him.” “I thanked him already,” the boy said “You don’t need to thank him.” “I’ll give him the belly meat of a big fish,” the old man said “Has he done this for us more than once?” “I think so.” “I must give him something more than the belly meat then He is very thoughtful for us.” “He sent two beers.” “I like the beer in cans best.” “I know But this is in bottles, Hatuey beer, and I take back the bottles.” “That’s very kind of you,” the old man said “Should we eat?” “I’ve been asking you to,” the boy told him gently “I have not wished to open the container until you were ready.” [20] “I’m ready now,” the old man said “I only needed time to wash.” Where did you wash? the boy thought The village water supply was two streets down the road I must have water here for him, the boy thought, and soap and a good towel Why am I so Ernest Hemingway The Old Man and the Sea thoughtless? I must get him another shirt and a jacket for Fair Payment Protocols for E-Commerce 235 her league, between Brooklyn and Philadelphia I must take Brooklyn But then I think of Dick Sisler and those great drives In the old park.” “There was nothing ever like them He hits the longest ball I have ever seen.” “Do you remember when he used to come to the Terrace?” [21] “I wanted to take him fishing but I was too timid to ask him Then I asked you to ask him and you were too timid.” “I know It was a great mistake He might have gone with us Then we would have that for all of our lives.” “I would like to take the great DiMaggio fishing,” the old man said “They say his father was a fisherman Maybe he was as poor as we are and would understand.” “The great Sisler’s father was never poor and he, the father, was playing in the Big Leagues when he was my age.” “When I was your age I was before the mast on a square rigged ship that ran to Africa and I have seen lions on the beaches in the evening.” “I know You told me.” “Should we talk about Africa or about baseba was a great manager,” the boy said “My father thinks he was the greatest.” “Because he came here the most times,” the old man said “If Durocher had continued to come here each year your father would think him the greatest manager.” “Who is the greatest manager, really, Luque or Mike Gonzalez?” “I think they are equal.” “And the best fisherman is you.” “No I know others better.” “Que Va,” the boy said “There are many good fishermen and some great ones But there is only you.” “Thank you You make me happy I hope no fish will come along so great that he will prove us wrong.” “There is no such fish if you are still strong as you say.” “I may not be as strong as I think,” the old man said “But I know many tricks and I have resolution.” “You ought to go to bed now so that you will be fresh in the morning I will take the things back to the Terrace.” [23] “Good night then I will wake you in the morning.” “You’re my alarm clock,” the boy said Ernest Hemingway The Old Man run if all these checking pass, he will send his check and his full signature on it to Alice Otherwise, he will invokes the resolve sub-protocol Step 5, if Alice doesn’t receive the message in time, she can invoke the resolve sub-protocol When she receives the message, she will run if it equals true, she will accept the check Otherwise, she will invoke the resolve sub-protocol he table and the old man took off his trousers and went to bed in the dark He rolled his trousers up to make a pillow, putting the newspaper inside them He rolled himself in the blanket and slept on the other old newspapers that covered the springs of the bed He was asleep in a short time and he dreamed of Africa when he was a boy and the long golden beaches and the white beaches, so white they hurt your eyes, and the high capes and the great brown mountains He lived along that coast now every night and in his dreams he heard the surf roar and saw the native boats [24] come riding through it He smelled the tar and oakum of the deck as he slept and he smelled the smell of Africa that the land breeze brought at morning Usually when he smelled the land breeze he woke up and dressed to go and wake the boy But tonight the smell of the land breeze came very early and he knew it was too early in his dream and went on dreaming to see the white peaks of the Isla amed about the boy He simply woke, looked out the open door at the moon and unrolled his trousers and put them on He urinated outside the shack and then went up the road to wake the boy He was shivering with the morning cold But he knew he would shiver himself warm and that soon he would be rowing The door of the house where the boy lived was unlocked and he opened it and walked in quietly with his [25] bare feet The boy was asleep on a cot in the first room and the old man could see him clearly with the light that came in from the dying moon He took hold of one foot gently and held it until the boy woke and turned and looked at him The old man nodded and the boy took his trousers from the chair by the bed and, sitting on the bed, pulled them on The old man went out the door and the boy came after him He was sleepy and the old man put his arm across his shoulders and said, “I am sorry.” “Qua Va,” the boy said “It is what a man must do.” They walke had coffee from condensed milk cans at an early morning place that served fishermen “How did you sleep old man?” the boy asked He [26] was waking up now although it was still hard for him to leave his sleep “Very well, Manolin,” the old man said “I feel confident today.” “So I,” the boy said “Now I must get your sardines and mine and your fresh baits He brings our gear himself He never wants anyone to carry anything.” “We’re different,” the old man said “I let you carry things when you were five years old.” 3.2.3 Resolve Sub-protocol Whenever necessary, Alice/Bob (noted by X) will invoke the resolve protocol to let the TTP decide whether finish or abort the payment process Step 1, X sends to the TTP to initiate a resolve process Because of the resilient channel between X and the TTP, this message will eventually arrives the TTP Step 2, when the TTP receive the message, it will first check whether the protocol has already been resolved or aborted, if so, it will stop because it is sure that both parties have got the resolved items or the abort confirmation Then it will decrypt with its secret key if succeeds, it will run and If both equals true, the TTP will run and send the to Alice and & k to Bob If any checking fails, it will abort the protocol and send confirmations to Alice and Bob 3.2.4 Abort Sub-protocol In step of the main protocol, Alice can invoke this sub-protocol to make the TTP abort this payment protocol run Step 1, Alice sends an abort request to the TTP Because of the resilient channel between X and the TTP, this message will eventually arrives the TTP Step 2, if the protocol has not been resolved or aborted, the TTP will abort the protocol and send confirmations to both parties 3.3 Analysis of the Protocol Following is the analysis with respect to requirement definitions in Section 2.1 CLAIM Assuming the channel between Alice and Bob is unreliable and adopted cryptographic tools are secure, the protocol satisfies the effectiveness requirement cannot lose.” “But I fear the Indians of Cleveland.” “Have faith in the Yankees my son Think of the great DiMaggio.” “I fear both the Tigers of Detroit and the Indians of Cleveland.” “Be careful or you will fear even the Reds of Cincinnati and the White Sax of Chicago.” “You study it and tell me when I come back.” “Do you think we should buy a terminal of the lottery with an eighty-five? Tomorrow is the eighty-fifth day.” “We can that,” the boy said “But what about the eighty-seven of your great record?” [17] “It could not happen twice Do you think you can find an eighty-five?” Ernest Hemingway The Old Man and the Sea “I can order one “One sheet That’s two dollars and a half Who can we borrow that from?” “That’s easy I can always borrow two dollars and a half.” “I think perhaps I can too But I try not to borrow First you borrow Then you beg.” “Keep warm old man,” the boy said “Remember we are in September.” “The month when the great fish come,” the old man sa how so much when the old man was asleep and his head fallen forward His shirt had been patched so many times that it was like the sail and the patches were faded to many different shades by the sun The [18] old man’s head was very old though and with his eyes closed there was no life in his face The newspaper lay across his knees and the weight of his arm held it there in the evening breeze He was barefooted The boy left him there and when he came back the old man was still asleep “Wake up old man,” the boy said and put his hand on one of the old man’s knees The old man opened his eyes and for a moment he was coming back from a long way away Then he smiled “What have you got?” he asked “Supper,” said the boy “We’re going to have supper.” “I’m not very hungry.” “Come on and eat You can’t fish and not eat.” “I have,” the old man said getting up and taking the newspaper and folding it Then he started to fold the blanket “Keep the blanket around gave this to you?” “Martin The owner.” “I must thank him.” “I thanked him already,” the boy said “You don’t need to thank him.” “I’ll give him the belly meat of a big fish,” the old man said “Has he done this for us more than once?” “I think so.” “I must give him something more than the belly meat then He is very thoughtful for us.” “He sent two beers.” “I like the beer in cans best.” “I know But this is in bottles, Hatuey beer, and I take back the bottles.” “That’s very kind of you,” the old man said “Should we eat?” “I’ve been asking you to,” the boy told him gently “I have not wished to open the container until you were ready.” [20] “I’m ready now,” the old man said “I only needed time to wash.” Where did you wash? the boy thought The village water supply was two streets down the road I must have water here for him, the boy thought, and soap and a good towel Why am I so Ernest Hemingway The Old Man and the Sea thoughtless? I must get him another shirt and a jacket for 236 Hao Wang and Heqing Guo her league, between Brooklyn and Philadelphia I must take Brooklyn But then I think of Dick Sisler and those great drives In the old park.” “There was nothing ever like them He hits the longest ball I have ever seen.” “Do you remember when he used to come to the Terrace?” [21] “I wanted to take him fishing but I was too timid to ask him Then I asked you to ask him and you were too timid.” “I know It was a great mistake He might have gone with us Then we would have that for all of our lives.” “I would like to take the great DiMaggio fishing,” the old man said “They say his father was a fisherman Maybe he was as poor as we are and would understand.” “The great Sisler’s father was never poor and he, the father, was playing in the Big Leagues when he was my age.” “When I was your age I was before the mast on a square rigged ship that ran to Africa and I have seen lions on the beaches in the evening.” “I know You told me.” “Should we talk about Africa or about baseba was a great manager,” the boy said “My father thinks he was the greatest.” “Because he came here the most times,” the old man said “If Durocher had continued to come here each year your father would think him the greatest manager.” “Who is the greatest manager, really, Luque or Mike Gonzalez?” “I think they are equal.” “And the best fisherman is you.” “No I know others better.” “Que Va,” the boy said “There are many good fishermen and some great ones But there is only you.” “Thank you You make me happy I hope no fish will come along so great that he will prove us wrong.” “There is no such fish if you are still strong as you say.” “I may not be as strong as I think,” the old man said “But I know many tricks and I have resolution.” “You ought to go to bed now so that you will be fresh in the morning I will take the things back to the Terrace.” [23] “Good night then I will wake you in the morning.” “You’re my alarm clock,” the boy said Ernest Hemingway The Old Man PROOF: When both Alice and Bob are honest, thus they will follow the protocol to send messages If the probability of successful transmission in the unreliable channel is then the probability of successful execution of one main protocol run will roughly be Even it’s small, but it means that successful execution without TTP’s involvement is still possible Thus the protocol satisfies the effectiveness requirement he table and the old man took off his trousers and went to bed in the dark He rolled his trousers up to make a pillow, putting the newspaper inside them He rolled himself in the blanket and slept on the other old newspapers that covered the springs of the bed He was asleep in a short time and he dreamed of Africa when he was a boy and the long golden beaches and the white beaches, so white they hurt your eyes, and the high capes and the great brown mountains He lived along that coast now every night and in his dreams he heard the surf roar and saw the native boats [24] come riding through it He smelled the tar and oakum of the deck as he slept and he smelled the smell of Africa that the land breeze brought at morning Usually when he smelled the land breeze he woke up and dressed to go and wake the boy But tonight the smell of the land breeze came very early and he knew it was too early in his dream and went on dreaming to see the white peaks of the Isla amed about the boy He simply woke, looked out the open door at the moon and unrolled his trousers and put them on He urinated outside the shack and then went up the road to wake the boy He was shivering with the morning cold But he knew he would shiver himself warm and that soon he would be rowing The door of the house where the boy lived was unlocked and he opened it and walked in quietly with his [25] bare feet The boy was asleep on a cot in the first room and the old man could see him clearly with the light that came in from the dying moon He took hold of one foot gently and held it until the boy woke and turned and looked at him The old man nodded and the boy took his trousers from the chair by the bed and, sitting on the bed, pulled them on The old man went out the door and the boy came after him He was sleepy and the old man put his arm across his shoulders and said, “I am sorry.” “Qua Va,” the boy said “It is what a man must do.” They walke had coffee from condensed milk cans at an early morning place that served fishermen “How did you sleep old man?” the boy asked He [26] was waking up now although it was still hard for him to leave his sleep “Very well, Manolin,” the old man said “I feel confident today.” “So I,” the boy said “Now I must get your sardines and mine and your fresh baits He brings our gear himself He never wants anyone to carry anything.” “We’re different,” the old man said “I let you carry things when you were five years old.” CLAIM Assuming the channels between the TTP and exchangers (Alice and Bob) are resilient, adopted cryptographic tools are secure and the TTP is honest, the protocol satisfies the fairness requirement PROOF: The first part of fairness requirement implies two aspects: fairness for Alice and fairness for Bob Fairness for Alice Assuming Alice is honest, then risks she may face include: 1) She did not receive any message or the message is invalid in step She can request abort to prevent that Bob may call a recovery later If Bob’s recovery request arrives to the TTP before her abort request, the TTP still will send the recovered item and evidence to her Thus will not affect her benefit 2) She did not receive any message or the message is invalid in step She can submit a recovery request, because the TTP is honest, the exchange will be forced to complete If Bob sent a recovery request during this period, the result will be the same; if Bob sent an abort request which arrived before Alice’s recovery request, the exchange will be aborted by the TTP, and no party can gain advantage Fairness for Bob Assuming Bob is honest, then risks he may face include: 1) He did not receive any message or the message is invalid in step He can simply stop without any risk And at this time, Alice cannot call recovery 2) He did not receive any message or the message is invalid in step He can request recovery and the exchange will be forced to complete If Alice request recovery at the same time, the result will be the same CLAIM Assuming the channels between the TTP and exchangers (Alice and Bob) are resilient, adopted cryptographic tools are secure and the TTP is honest, the protocol satisfies timeliness requirement PROOF: Alice can conclude the protocol in one of the two ways: requesting abort before sending the message of step requesting recovery in any other time Bob can conclude the protocol in one of the three ways: stopping at any time before sending the message of step requesting recovery in any other time