Real-Time Communication Security IPsec & SSL Issues

Real-Time Communication SecurityIPsec & SSL Issues CS 519 Cryptography and Network Security Instructor: Ali Aydin Selcuk Real-Time Communication Issues

The Internet A packet-switched network: • Data to be transmitted is divided into “packets” • Each packet is forwarded by “routers” towards the destination ... ... Real-Time Communication Issues

Security of TCP/IP Communications The TCP/IP reference model: IP: delivery of packets to the destination TCP: reliability of the communication • ordering the packets • error detection & recovery • congestion control UDP: basic transport protocol Application Layer (HTTP, FTP, SMTP, etc.) Transport Layer (TCP, UDP) Network Layer (IP) Data Link Layer (PPP, Ethernet, etc.) Physical Layer Real-Time Communication Issues

Securing TCP/IP Layer 3: • can secure all IP comm., transparent to applications • must be built into the OS Layer 4: • doesn’t require OS modification; deployment easy Application L. Layer 4 (SSL/TLS) Transport L. Layer 3 (IPsec) Network L. Data Link L. Physical L. Real-Time Communication Issues

Real-Time Protocol Issues • Interactive session security (unlike e-mail) • End-to-end security (encryption/authentication) requires layer 3 or 4 (or, layer 3.5 & 4.5) protection Real-Time Communication Issues

TCP Header 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Port | Destination Port | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Acknowledgment Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Data | |U|A|P|R|S|F| | | Offset| Reserved |R|C|S|S|Y|I| Window | | | |G|K|H|T|N|N| | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Checksum | Urgent Pointer | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Options | Padding | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Real-Time Communication Issues

UDP Header 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Port | Destination Port | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Real-Time Communication Issues

Layer 4 (SSL) • Implemented on top of layer 4, between TCP & application • Doesn’t require any modifications to OS(deployment made easy!) Real-Time Communication Issues

Layer 3 (IPsec) • Implemented between IP & TCP • Each IP packet authenticated separately • Built in the OS • Can secure all IP communication • Host-to-host and network-to-networkapplication is common;process-to-process also possible Real-Time Communication Issues

Session Key Establishment • Message authentication with a session key is needed against connection hijacking • Sequence numbers needed against packet replays (different from TCP seq.no.) • Session key reset before seq.no. wraps around • For freshness guarantee, both parties should contribute to the session key Real-Time Communication Issues

Perfect Forward Secrecy • PFS: Compromise of long-term secrets doesn’t compromise session keys • Example: DH with RSA authentication • Non-PFS examples: • Kerberos • Session key transport with RSA encryption • By-product: Escrow preventionConversations can’t be decrypted by authorities holding copies of long-term private keys Real-Time Communication Issues

DoS Protection • If attacker can make server do DH exponentiation by just initiating a session, DoS is made easy • Protection: • cookies • puzzles Real-Time Communication Issues

DoS Protection – Cookie Solution • Server responds to session requests with a random number (cookie).Initiator has to respond back with that cookie to continue • Attacker would either • reveal its address • or, abort the attack • Stateless cookies: cookie is H(IP address, secret); server doesn’t remember it. Real-Time Communication Issues

DoS Protection – Puzzle Solution • Server requires initiator to solve a puzzleE.g., MD5(x) = …, x = ?, for an n-bit x. • Solving is slow, verification fast. • Can be made adaptive to increasing load. (how?) • Can be made stateless. (how?) • Can be used against spam as well Real-Time Communication Issues

Identity Hiding • Hiding the parties’ identities from eavesdroppers • Do DH without authentication.Then send the authentication info encrypted under the session key. • Passive attacker can’t learn identities Real-Time Communication Issues

Live Partner Assurance • Against replays, different DH exponents must be used in different sessions • DH exponentiation is expensive; problem for servers, low-end clients • Solution: Constant DH exponents, different nonces. Incorporate nonces into the session key. E.g., K = H(gab mod p, nonces) Real-Time Communication Issues

Other Issues • Session resumption: Use previously established session keys to bypass public-key authentication • Deniability: Don’t use signatures for authentication. Use encryption with public keys. (e.g., the SKEME protocol) • Crypto negotiations: Key exchange protocols negotiate the algorithms to be used as well Real-Time Communication Issues

Real-Time Communication Security IPsec & SSL Issues