Slide an toàn và hệ thống bảo mật thông tin chapter 4 cryptography symmetric modern dec

.c om cu u du o ng th an co ng SYMMETRIC CIPHERS CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om Contents Block Cipher Principles 2) Feistel Cipher 3) Data Encryption Standard (DEC) cu u du o ng th an co ng 1) CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om ng CRYPTOLOGY an co CRYPTOGRAPHY Transposition ng du o u Substitution ASYMMETRIC MODERN Block ciphers cu CLASSICAL th SYMMETRIC CRYPTANALYSIS Stream ciphers CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om cu u du o ng th an co ng Block Cipher Principles CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om Stream Ciphers and Block Ciphers  A stream cipher is a type pf symmetric encryption in which input data is cu u du o ng th an co ng encrypted one bit (byte) at a time CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om Stream Ciphers and Block Ciphers  Block Ciphers is one in which the plaintext is divided in blocks and one cu  Block size? u du o ng th an co ng block is encrypted at a time producing a ciphertext of equal length CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om cu u du o ng th an co ng Feistel Cipher CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om The Feistel Cipher  Horst Feistel devised the feistel cipher co ng  Most symmetric block ciphers are based on a feistel cipher structure an  Feistel proposed the use of a cipher that alternates substitutions and ng th permutations, where these terms are defined as follows: du o  Substitution: Each plaintext element or group of elements is uniquely replaced cu u by a corresponding ciphertext element or group of elements  Permutation: A sequence of plaintext elements is replaced by a permutation of that sequence CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om Feistel Cipher Structure ng  The Plaintext block: 2w bits co  The plaintext block is divided into two halves, th an L0 and R0 du o ng  L, R pass through n rounds of processing and u then combine to produce the ciphertext block cu  Each round i (1->16): CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om Feistel Cipher Principles The exact realization of a Feistel network depends on the choice of the co ng following parameters and design features: th an  Block size: Larger block sizes mean greater security but reduced du o ng encryption/decryption speed for a given algorithm  Key size: Larger key size means greater security but may decrease cu u encryption/decryption speed  Number of rounds: increase number improves security, but slows cipher CuuDuongThanCong.com https://fb.com/tailieudientucntt cu u du o ng th an co ng c om S-Boxes (cont.) CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om ng co an th ng du o u cu CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om ng co an th ng du o u cu CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om S-Boxes (cont.) ng  The input to S-box is 100011 What is the output? cu u du o ng th an co  The input to S-box is 000000 What is the output? CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om Permutation Function (P)  The 32-bit output is permutated as defined in the permutation table also to cu u du o ng th an co ng produce the output CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om ng co an th ng du o u cu CuuDuongThanCong.com https://fb.com/tailieudientucntt cu u du o ng th an co ng c om Key Generation CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om Key Generation (cont.)  Permuted Choice One (PC-1): co ng  Input: 64-bit cu u du o ng th an  Ouput: 56-bit (Discard the parity-check bits) CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om Key Generation (cont.)  The resulting 56-bit key is then treated as co ng two 28-bit quantities, labeled C0 and D0 th an  At each round, Ci-1 and Di-1 are separately ng subjected to a circular left shift or (rotation) u cu calculation table du o of or bits governed by the DES key CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om ng co an th ng du o u cu CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om Permuted Choice Two (PC-2) cu u du o ng th an co ng  PC-2 changes the 58 bits to 48 bits, which are used as a key for a round CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om The Strength Of Des  Brute-force attack: With a key length of 56 bits, there are 256 possible co ng keys, which is approximately 7.2 * 106 keys th an  1997 on alarge network of computers in afew months ng  1998 on dedicated H/W in a few days du o  1999 aboved combined in 22 hours (DES cracker + 100,000 computers) cu u  => double DES, triple DES, AES CuuDuongThanCong.com https://fb.com/tailieudientucntt cu u du o ng th an co ng c om Double DES CuuDuongThanCong.com https://fb.com/tailieudientucntt cu u du o ng th an co ng c om Triple DES CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om ng co an th ng du o u cu CuuDuongThanCong.com https://fb.com/tailieudientucntt ... Encryption Standard (DEC) cu u du o ng th an co ng 1) CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om ng CRYPTOLOGY an co CRYPTOGRAPHY Transposition ng du o u Substitution ASYMMETRIC MODERN. .. cryptanalysis th an  Round function F: greater complexity generally means greater resistance cu u du o ng to cryptanalysis CuuDuongThanCong.com https://fb.com/tailieudientucntt cu u du o ng th an. .. Data Encryption Standard - DEC  The Data Encryption Standard (DES) is a symmetric- key block cipher co ng published by the National Institute of Standards and Technology (NIST) th an  A block cipher