Kim Yoonjeong wrote:
Hello, all ! With given a unknown DES system with 64 bits plaintext p, ciphertext c, can there be MORE THAN ONE keys ?
I don't think so: I you look closely to 1-Round DES, you can have this case: Let p=LR (plaintext) and K=key (without parity check) When computing f(R,k) in 1-Round DES I can have the same input (and output) in the S-Boxes with: p=LR, with k ; and p=L(R'), with k' (k' denotes 1-complement of k) You have _two_ different (plaintext,key) pairs with the same input using f(R,k) and f(R',k').
From this, you can prove that:
if y=DES(p,k) then y'=DES(p',k') wich is what everyone really wants: a beautiful chance of using a trapdoor in DES. Did you like it? - Don't use DES: It's not reliable. -- Iñigo González - ADV Internet Technical Advisor <nexus@adv.es> "Never say anything online that you wouldn't want to see on the front page of The New York Times." - alt.2600.moderated Posting