Substitution ciphers are vulnerable to english letter frequency attacks. If you find the most common letter in the text then you can suppose it would be the letter “e” and so forth. From there you can use digrams and trigrams with the same heuristic. I.e “an” “th” are most likely to be found next to each other. If it’s not a substituion cipher it’s probably a vigenere cipher. If it is, you’ll have a hell of a time cracking it w/o any software but it’s still possible esp if you know the key-length.
Alex Roman • Jan 8, 2014 at 12:46 pm
Substitution ciphers are vulnerable to english letter frequency attacks. If you find the most common letter in the text then you can suppose it would be the letter “e” and so forth. From there you can use digrams and trigrams with the same heuristic. I.e “an” “th” are most likely to be found next to each other. If it’s not a substituion cipher it’s probably a vigenere cipher. If it is, you’ll have a hell of a time cracking it w/o any software but it’s still possible esp if you know the key-length.