Tag: cryptanalysis
The History of Cryptography (4) — The Arab Cryptanalysts
by FOX on 03:59 PM, under History
How many different simple substitution ciphers exists? We can count them by enumerating all the possible values of each single plain-text letter. First we assign a to one of the 26 possible cipher text letters from A to Z, then assign b to the rest 25 cause one of the letter in cipher alphabet has been occupied by letter a; then there are 26*25 = 650 possible ways to assign a and b. Thus the total number of ways to assign 26 plain-text letters to 26 cipher-text letters by using each cipher-text once, is
26*25*24*23…*3*2*1 = 26! = 403291461126605635584000000
there are more than 10 26 possibilities for a code-breaker, those who were attempting crack the substitution cipher. if they just simply test each possible keys. If a code-breaker is able to check one million keys per second, it takes him/her 1013 years to finish all jobs. It’s even longer than the life of universe. So, is there an efficient way to break it?
