Decryption of an 8-bit code

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Katherine Brideau
Katherine Brideau on 27 Mar 2013
I'm trying to crack a code that's concatenated ascii codes, encrypted by xor'ing each ascii code with an 8 bit key. Decoding it is apparently an xor operation, however I've hit a brick wall.
My algorithm is 1) create a decrypt code 2) xor each letter with code 3) translate back to a number 4) change number to letter 5) print out message
3,4, and 5 a straightforward, but I can't move past 1 and 2
My code so far is
encrypted = '11111111111111111011101111100000000100000000101000101000000001000100010111101001001010111010100011100101';
z = reshape(encrypted, length(encrypted)/8,8)
key = dec2bin(0:255,8)
Basically I'm going to use brute force to crack it, and split things off into groups of 8.
If anyone has any suggestions I would really appreciate it!
Thank you
  1 Comment
Walter Roberson
Walter Roberson on 27 Mar 2013
You probably want
z = reshape(encrypted .', 8, length(encrypted)/8).' ;

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Answers (1)

Walter Roberson
Walter Roberson on 27 Mar 2013
You cannot reliably break xor codes using brute force. You cannot, for example, determine whether the original source was
IBM
or
HAL
(as in 2001's HAL 9000 computer)

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