APPENDIX B Some Elementary Tips for Frequency Analysis
1. Begin by counting up the frequencies of all the letters in the ciphertext. About five of the letters should have a frequency of less than 1 percent, and these probably represent j, k, q, x and z. One of the letters should have a frequency greater than 10 percent, and it probably represents e. If the ciphertext does not obey this distribution of frequencies, then consider the possibility that the original message was not written in English. You can identify the language by analyzing the distribution of frequencies in the ciphertext. For example, typically in Italian there are three letters with a frequency greater than 10 percent, and nine letters have frequencies less than 1 percent. In German, the letter e has the extraordinarily high frequency of 19 percent, so any ciphertext containing one letter with such a high frequency is quite possibly German. Once you have identified the language you should use the appropriate table of frequencies for that language for your frequency analysis. It is often possible to unscramble ciphertexts in an unfamiliar language, as long as you have the appropriate frequency table. 2. If the correlation is sympathetic with English but the plaintext does not reveal itself immediately, which is often the 246