This page contains a number of on-line tools for working with ciphers. These could be of use in tackling challenges such as the National Cipher Challenge.

The tools work with capital letter codes in English.

#### Letter Frequency Analysis

The best place to start cryptanalysis is to run a frequency counting programme. This may give you some clues. There are three letter frequency tools to the left on this page. The single letter frequency tool is quick but if you set out to count double letter combinations (bi-grams), or even triple letter combinations (tri-grams) then the amont of processing increases exponentially. (This is an NP and not an P problem.)

#### Letter Guessing

Following a frequency analysis you may want to see what the cipher looks like with some letters substituted for guesses. Use the Substitution Tool.

#### Ceasar Shift

If the letter frequency graph suggest all letters cycled on through the alphabet by a fixed number. Use the Ceasar Shift Decoder by entering the number by which the alphabet has been shifted.

#### Affine Shift

If the letter frequency graph suggests that the cipher is not a simple shift, it may be that the cipher is an Affine Shift. Use frequency analysis to make a guess at E (most frequent letter) and T (occurs in most frequent double/triple letter combinations) and use the Affine Shit Decoder.