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One time pad used twise

  1. Jun 1, 2006 #1
    Hi everyone

    I've been given a challenge and i was wondering if you guys could shed some light on it...

    i have been given two ciphertexts that have been encrypted with the same one time pad... the ciphertexts start the same (message header), but im not given any more information about it...

    the ciphertexts are split up into the same number of blocks so i think padding may have been used...

    im assuming xor, they havent given us any information (im also assuming one time pad used twice, because of the message headers)...

    heres the cipher texts so you see what i mean

    3:17am :
    UWCHR IFLFK AFFTG WVOOM SZYUJ
    QVGBR LZFSC CWAXZ KCIUE KDZEA
    RIAAY HHJTN DLCWV CIIJE WARON
    JEDZO IKFNM AFJJL FVSZE MEFOM

    4:29am :
    UWCHR IFLFK AFFTG WVOHI LDOQX
    NYQUE PHRSC BDIBB FHMTI VKVOA
    RHMTQ EZACG INLDH ALTHI ISGHV
    AGSPI WPJML BSICH BKZNX TAFGE

    so they start the same, each cipher text has exactly 100 characters in it, i've xor'd the ciphertexts but im not quite sure what to do next.

    Also there is a hint from one guy who has solved this cipher:

    just look at the time at which the ciphertext was sent: 3:17( = 3x60+17 = 197) and 4:29 ( = 4x60 + 29 = 269), both of these are primes.

    any help would be great!!
     
  2. jcsd
  3. Jun 1, 2006 #2
    Two primes are used in the RSA algorithm, so that's my guess.
     
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