John's Secret-Code Systems A working bench for classical and modern ciphers: run every method, open a famous cipher and watch it come apart, or let the solvers have a go at something new.

Classic counters

Kasiski examination

Repeated sequences of 3 or more letters and the distances between them. A key length tends to divide most of the distances.

Crib tool

Slide a known word along the ciphertext. At each position the tool shows the key letters it would imply under three tableau rules. Real key fragments look like words, or repeat at the key period.

Text comparison

Two texts are laid side by side; matching characters at the same position are kept, everything else becomes a dot.

Sum-log frequency

One candidate per line. Higher (less negative) totals look more like English at the single-letter level; the quadgram column is the stronger test.