Hexcellents CTF Wiki

Classical ciphers

  • Substitution / Caesar / Vigenere
    • Easy to break if the underlying language and alphabet is known
    • Alphabet can consist of grouped letters
    • Caesar ciphers can be cracked immediately in the command line using 'caesar' from the bsd-games package
        for i in {0..25}; do echo "Ackkmaa" |  /usr/games/bin/caesar $i ; done 
    • Substitution can be cracked using Cryptool using letter frequency, digram/trigram frequency and word frequency but a large portion of text must be given as input
    • Vigenere can also be cracked using Cryptool (for English and German texts)
  • Xor / Vernam
    • Strings/files xored with a random key cannot be cracked if length(key) == length(text)
    • If length(key) << length(string) xortool can be used to infer key length and possible keys given the most common byte: (0x20 for text and 0x00 for binary)
    • Autocorrelation can be used in Cryptool as well

Tools for analysis

kb/crypto/classical.txt ยท Last modified: 2013/10/06 17:35 by rcaragea
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