Page "Timeline of algorithms" Paragraph 11

* c. 1400-Ahmad al-Qalqashandi gives a list of ciphers in his Subh al-a ' sha which include both substitution and transposition, and for the first time, a cipher with multiple substitutions for each plaintext letter ; he also gives an exposition on and worked example of cryptanalysis, including the use of tables of letter frequencies and sets of letters which can not occur together in one word