Cryptography Pseudorandomness

though random numbers needed in cryptography, use of pseudorandom number generators (whether hardware or software or combination) insecure. when random values required in cryptography, goal make message hard crack possible, eliminating or obscuring parameters used encrypt message (the key) message or context in carried. pseudorandom sequences deterministic , reproducible; required in order discover , reproduce pseudorandom sequence algorithm used generate , initial seed. entire sequence of numbers powerful randomly chosen parts - algorithm , seed, seed.

there many examples in cryptographic history of ciphers, otherwise excellent, in random choices not random enough , security lost direct consequence. world war ii japanese purple cipher machine used diplomatic communications example. consistently broken throughout world war ii, because key values used insufficiently random. had patterns, , patterns made intercepted traffic readily decryptable. had keys (i.e. initial settings of stepping switches in machine) been made unpredictably (i.e. randomly), traffic have been harder break, , perhaps secure in practice.

users , designers of cryptography cautioned treat randomness needs utmost care. absolutely nothing has changed era of computerized cryptography, except patterns in pseudorandom data easier discover ever before. randomness is, if anything, more important ever.