Network systems security by mort anvari lecture10

Ethernet Network Systems Security Mort Anvari Ethernet     Most widely used LAN technology Low cost and high flexibility Versions of different speed: 10Mbps, 100Mbps, Gigabit Use globally unique media access control (MAC) address (hardware address) for every interface card 9/28/2004 Use of Hardware Address     Need an address to send a message to receiver on same Ethernet IP address is not usable because network layer does not listen to wire Use hardware address to identify receiver’s interface Need to resolve receiver’s hardware address from receiver’s IP address 9/28/2004 Address Resolution Protocol   Protocol maps each IP address to corresponding hardware address in subnetwork For computer i to get hardware address of computer j, i broadcasts a rqst message with IP address of j to the subnetwork i rqst(ipa.j) switch default router r Internet j 9/28/2004 Address Resolution  If j sees a rqst message from i with its IP address, j sends a rply message with its IP address and hardware address to i i rply(ipa.j,hda.j) switch default router r Internet j 9/28/2004 Functions of ARP  Three functions of ARP    Resolving IP addresses Supporting dynamic assignment of addresses Detecting destination failures 9/28/2004 ARP Spoofing Attack  To stop traffic from i to j, an adversary sends to i a spoofed rply message with IP address of j and a non-existent hardware address i switch default router r Internet j A 9/28/2004 rply(ipa.j,hda.x) Another ARP Spoofing Attack  To stop traffic from i to default router r, an adversary sends to i a spoofed rply message with IP address of r and its own hardware address i switch default router r Internet j A 9/28/2004 rply(ipa.r,hda.A) Countering ARP Spoofing Attacks  Proposed solutions include ARPWATCH and static ARP caches   ARPWATCH monitors transmission of rqst and rply messages over Ethernet and check them against a database of (IP addr, hardware addr) pairings Static ARP cache stores permanent (IP addr, hardware addr) pairings of trusted hosts to avoid sending rqst and rply messages over Ethernet 9/28/2004 Insufficiencies of Proposed Solutions   ARPWATCH does not support dynamic assignment of IP addresses Static ARP caches does not support dynamic assignment of IP addresses and detection of destination failures 9/28/2004 10 Need for Secure Address Resolution   When a computer receives a message m, it needs to determine whether m was indeed sent by claimed source, or was inserted, modified, or replayed by an adversary Use secure address resolution protocol between each computer and a secure server 9/28/2004 11 Architecture of Secure Address Resolution Protocol h[i] s Applications Transport Network Applications Transport Network Subnetwork hn[i] hr[i] Interface  invite-accept protocol request-reply protocol Subnetwork sn write arrays ipa, hda, valid sr Interface Ethernet 9/28/2004 12 Adversary  The adversary can perform three types of actions to disrupt communication between server s and any computer h[i] on the Ethernet    Message loss Message modification Message replay 9/28/2004 13 Secure Address Resolution Protocol  Use three mechanisms to counter adversary actions    timeouts to counter message loss shared secrets to counter message modification nonces to counter message replay 9/28/2004 14 Invite-Accept Protocol    Periodically, server s sends out an invt message to every computer on Ethernet Every up computer is required to send back an acpt message including its IP address and hardware address s updates its address database according to received acpt messages 9/28/2004 15 Invite-Accept Protocol s  h[0 n-1]: invt(nc, md) where md=MD(nc;scr[0])||MD(nc;scr[1])||…|| MD(nc;scr[n-1]) h[i]  s: acpt(nc, ipa[i], hda[i], d) where d=MD(nc;ipa[i];hda[i];scr[i]) 9/28/2004 16 Request-Reply Protocol    When a computer needs to resolve a destination’s hardware address, it sends a rqst message to server s If destination’s hardware address is still valid, s sends back a rply message with address information If destination’s hardware address is not valid anymore, s sends back a rply message with no address information 9/28/2004 17 Request-Reply Protocol h[i]  s: rqst(nc, ipa[j], d) where d=MD(nc;ipa[j];scr[i]) If found, s  h[i]: rply(nc, ipa[j], hda[j], d) where d=MD(nc;ipa[j];hda[j];scr[i]) If not found, s  h[i]: rply(nc, ipa[j], 0, d) where d=MD(nc;ipa[j];0;scr[i]) 9/28/2004 18 Extensions  Four extensions of secure address resolution protocol     Insecure address resolution Backup server System diagnosis Address resolution across multiple Ethernets 9/28/2004 19 Next Class  IPsec    Authentication Header (AH) Encapsulation Security Payload (ESP) key management 9/28/2004 20 ... Protocol h[i] s Applications Transport Network Applications Transport Network Subnetwork hn[i] hr[i] Interface  invite-accept protocol request-reply protocol Subnetwork sn write arrays ipa, hda,... receives a message m, it needs to determine whether m was indeed sent by claimed source, or was inserted, modified, or replayed by an adversary Use secure address resolution protocol between each... corresponding hardware address in subnetwork For computer i to get hardware address of computer j, i broadcasts a rqst message with IP address of j to the subnetwork i rqst(ipa.j) switch default