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Cryptanalysis of Lee-Kim-Yoo password-based key agreement scheme

This paper analyzes the Lee-Kim-Yoo password-based key agreement scheme and identifies its vulnerabilities, particularly in terms of the incompleteness of the key computation process and susceptibility to offline dictionary attacks.

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Cryptanalysis of Lee-Kim-Yoo password-based key agreement scheme

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  1. Cryptanalysis of Lee-Kim-Yoo password-based key agreement scheme From：Applied Mathematics and Computation, Volume 168, Issue 2, 15, Pages 858-865 Author：Jeoung Ok Kwon, Jung Yeon Hwang, Changwook Kim and Dong Hoon Lee Present by che-yuan chang Data：2006/12/13

  2. Outline • Introduction • Related work • LKY overview • Incompleteness of a key-computation process • Off-line dictionary attack • Conclusion

  3. Introduction • Password-based Authenticated Key Agreement (PAKA) • Diffie–Hellman scheme • The function of Password • authenticate each other • establish a session key • Drawback • Passwords are weak (password guessing attack ) • LKY • Incompleteness of a key-computation process • Off-line dictionary attack

  4. Related work(1/2) • Seo and Sweeney (1999) • Slight modification of the Diffie–Hellman scheme, and based on a preshared password method for user authentication • drawback：replay attack • Tseng (2000) • drawback：backward replay attack and modification attack • Ku and Wang (2000) • drawback：modification attack

  5. Related work(2/2) • Hsu (2003) • drawback：modification attack • Lee and Lee (2004) • drawback：password guessing attack • Lee (2004) • drawback：password guessing attack • Author (2005)

  6. LKY overview(1/4) • There are two phases：Key establishment phase and Key confirmation phase • share a common password P before the protocol is executed • n is a large prime and g is a generator of order n-1 in GF(n) • h is an one-way hash function • random number a、b

  7. LKY overview(2/4) Share P,n,g And random a Share P,n,g And random b

  8. LKY overview(3/4) • Incompleteness of a key-computation process • session key1 session key2 • Example • Solution • computes X1 omitting the last modular operation mod n. • Alice always checks if X1 ≦n-1 ≠

  9. LKY overview() • Incompleteness of a key-computation process • the probability Pr[Large] of incompleteness of LKY is at least • Pr[Large] is non-negligible if the difference between k and l is bounded by

  10. LKY overview(4/4) • Off-line dictionary attack • discover the password of Alice and Bob running the scheme LKY • Example • success probability of the attack is • Solution • Let is smaller than n in the mth bitposition for some m ( < m ≦ )

  11. Conclusion • LKY still vulnerable to an off-line dictionary attack by using two different types of group operations, a bit-wise XOR and a modular multiplication • we described a method which eliminates an useful redundancy that could be used by the adversary performing a dictionary attack

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