adfgvx cipher affine cipher alberti cipher alphabet atbash autocorrelation autokey cipher bible code bifid cipher block cipher book cipher caesar cipher correlation cryptanalysis cryptogram cryptographic hash function cryptographically secure pseudorandom number generator cryptography encryption english language expected value four-square cipher frequency analysis great cipher hill cipher history of cryptography kasiski examination keyword cipher letter frequencies message authentication code military cryptanalytics natural language nihilist cipher null hypothesis online computer library center permutation cipher pigpen cipher plaintext playfair cipher polyalphabetic cipher polybius square public-key cryptography rail fence cipher reihenschieber reservehandverfahren running key cipher scytale smithy code steganography straddling checkerboard stream cipher substitution cipher symmetric-key algorithm tabula recta tap code telegraphy topics in cryptography transposition cipher trifid cipher two-square cipher vic cipher