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ECE 454/599 Computer and Network Security

ECE 454/599 Computer and Network Security. Dr. Jinyuan (Stella) Sun Dept. of Electrical Engineering and Computer Science University of Tennessee Fall 2012. IPsec: IKE. Photuris and SKIP PHASE 1 IKE PHASE 2 IKE. Security Association Issues. How is SA established?

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ECE 454/599 Computer and Network Security

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  1. ECE 454/599 Computer and Network Security Dr. Jinyuan (Stella) Sun Dept. of Electrical Engineering and Computer Science University of Tennessee Fall 2012

  2. IPsec: IKE Photuris and SKIP PHASE 1 IKE PHASE 2 IKE

  3. Security Association Issues • How is SA established? • How do parties negotiate a common set of cryptographic algorithms and keys to use? • More than one SA can apply to a packet! • E.g., end-to-end authentication (AH) and additional encryption (ESP) on the public part of the network

  4. IKE: Internet Key Exchange • Purpose • Mutual Authentication • Shared Secret Establishment • Crypto Algorithms Negotiation • Security Association Establishment

  5. IPsec Key Management • Data transmitted needs to be secured • IPsec SA, session keys, AH or ESP • Messages for establishing IPsec SA need to be secured • IKE SA, negotiated secret • Negotiation for establishing IKE SA need to be authenticated • Pre-shared secret key • Public/private keys

  6. Review: Cookies • Clogging attacks • An opponent forges the source address of a legitimate user and send a public Diffie-Hellman key to the victim; The victim then performs a modular exponentiation to compute the secret key; Repeated messages of this type can clog the victim’s system with useless work. • First proposed in Photuris; Cookie • A number chosen by responder; When receiving a request from S, send the cookie to S in clear; start the processing after the cookie comes back from the initiator. • Stateless cookies • The responder does not have to remember (store) the cookies he sent out; The cookie is a function of the IP address and a secret known to the responder

  7. A Stateless Cookie Protocol

  8. Photuris

  9. Features of Photuris • Denial of service protection: • Stateless cookie CB in message 2 • Signed Diffie-Hellman exchange • Signature on the previous message in message 5 and 6 • Identity hiding • Anonymous Diffie-Hellman • Identities are encrypted in message 5 and 6 (for active man-in-the-middle, the initiator’s identity is revealed, but not the responder)

  10. SKIP: Simple Key Management for Internet Protocols • SKIP uses Diffie-Hellman public keys • Alice finds Bob’s public key (gB mod p ) via a certificate from Bob or a directory. Bob finds Alice’s public key (gA mod p ). Then they will have a common secret (gAB mod p). • Data encryption • The D-H common secret should not be used to encrypt data. Instead each message has a SKIP header where the long term secret is used to encrypt a short-term data encryption key, which is used to encrypt the message.

  11. IKE Phases • Phase One • Mutual authentication • Session key establishment • ISAKMP SA/IKE SA • Phase Two • Negotiating IPsec SAs (AH, ESP)

  12. Why two phases? • ISAKMP would be used by other protocols to set up SAs, not only to set up IPsec SAs. • Phase 1 exchange is relatively expensive. ISAKMP/IKE SA has a longer timeout period. It can be used to negotiate multiple phase 2 IPsec SAs, which reduces the usage of pre-shared secret or private key.

  13. Phase 1 IKE • Two modes • Aggressive mode • 3 messages • Mutual authentication • Session key establishment • Main Mode • 6 messages • Mutual authentication • Session key establishment • Hiding endpoint identity • Negotiating cryptographic algorithms

  14. Phase 1: Aggressive Mode

  15. Phase 1: Main Mode

  16. Negotiating Cryptographic Parameters • Encryption algorithm (e.g., DES, 3DES, IDEA) • Hash algorithm (e.g., MD5, SHA) • Authentication method (e.g., pre-shared keys, RSA public key signature, DSS, RSA public key encryption) • Diffie-Hellman group (e.g., g and p)

  17. Crypto Proposals • Alice sends Bob a list of proposals, each consisting of an encryption algorithm, a hash algorithm, authentication method, and a Diffie-Hellman group. • Bob replies one as the accepted proposal. • The parameters in the proposal are used in Phase 1 and Phase 2 (IKE SA), with hash algorithm used for various purposes.

  18. Key Types • Mutual authentication based on • Pre-shared secret key • Public encryption key • Original protocol design • Improved Protocol design • Public signature key

  19. Cookie Issues • IKE is stateful, starting from the first message. • Alice’s crypto proposal is in the identity proof • ISAKMP requires randomly chosen cookies • Identifier: <initiator cookie, responder cookie>

  20. Session Keys • After Diffie-Hellman key exchange, each side knows gxy mod p • Encryption key and Integrity key for the rest of IKE SA • Keys for IPSec SAs

  21. Session Keys • Pseudo Random function – prf(key, data), e.g., CBC residue, HMAC • SKEYID • For signature public keys, prf(nonces, gxy) • For encryption public keys, prf(hash(nonces), cookies) • For pre-shared secret keys, prf(pre-shared secret key, nonces) • SKEYID_d: secret bits used to create other keys • prf(SKEYID, gxy | cookies | 0) • SKEYID_a: the integrity protection key • prf(SKEYID, SKEYID_d | gxy | cookies | 1) • SKEYID_e: the encryption key • prf(SKEYID, SKEYID_d | gxy | cookies | 2)

  22. Proof of Identity • Proof of the key associated with the identity • pre-shared secret key • private encryption key • private signature key • Integrity-check on the previous messages, such as identity, Diffie-Hellman values, nonce, Alice’s crypto proposal, and the cookies.

  23. Proof of Identity (Cont’d) • Alice’s proof of identity • prf ( SKEYID, gx | gy | cookies | Alice’s initial proposals | Alice’s identity ) • Bob’s proof of identity • prf ( SKEYID, gx | gy | cookies | Alice’s initial proposal | Bob’s identity )

  24. IKE phase 1 protocols • 8 phase-1 protocols • 2 modes • 4 types of keys • Common features • Message 1 starts with Alice’s cookie • All other messages start with (initiator cookie, responder cookie), which serves as the IKE connection identifier

  25. Phase 1: Public Signature Keys, Main Mode

  26. Phase 1: Public Signature Keys, Aggressive Mode

  27. Phase 1: Public Encryption Keys, Main Mode, Original

  28. Phase 1: Public Encryption Keys, Aggressive Mode, Original

  29. Phase 1: Public Encryption Keys, Main Mode, Revised

  30. Phase 1: Public Encryption Keys, Aggressive Mode, Revised

  31. Phase 1: Pre-Shared Secret Keys, Main Mode

  32. Phase 1: Pre-Shared Secret Keys, Aggressive Mode

  33. Phase 2, Quick Mode • Establish IPSec SAs (e.g., ESP and/or AH) • Crypto parameters • Diffie-Hellman numbers (optional) • Traffic type (optional) • All messages (except X,Y) encrypted and integrity protected

  34. Reading Assignment • [Kaufman] Chapter 18

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