Quote from: Banjo on April 18, 2012, 10:51 pmBook ciphers are just as vulnerable to frequency analysis as any other primitive method of cryptography. While admittedly something fun to do for the sake of understanding the history of cryptography, it would be extremely foolish and naive to use this for any actual security purpose. If you have a lot of long, complicated passwords that you need to remember, don't write them down and "encrypt" them with this method. Instead, put them in a file on a flash drive, and encrypt that file using a program like GPG or TrueCrypt.And what password would you use to protect that file? You see the dilemma? Passwords that are easy to remember are shorter and/or based on dictionary words which are vulnerable to a brute force attack. Strong passwords conversely contain mixtures of upper and lower case letters, symbols and numbers. It's true you could have a file containing many such passwords protected by a single weak one but this is simply restating the problem as once the weak password is cracked every single one of your passwords will be exposed!The way I have suggested using a book cipher works to compliment your existing security methods, not replace them. Also it is not vulnerable to frequency analysis if you're using it to encipher a strong password which in the nature of things would be a random combinations of letters, symbols and numbers from a text. Frequency analysis would also only be possible on a significant portion of text, not a password of say 20 characters.If you require proof of this I would suggest you Google the "Beale Ciphers" which were based on a book cipher and have eluded the finest Cryptographers in the country, including staff from the NSA. The strength of the cipher lies in the fact that any piece of text can be used - you could even write an essay yourself on Abraham Lincoln for instance and use that as the key text.Moreover, I would suggest that anyone interested in the field of Cryptography in general should take an interest in classic ciphers for the other reason I mentioned, which is that you may well find yourself in a situation where you need to send a message secretly but are unable to use a computer to do so!V.