In cryptography, the one-time pad (OTP) is an encryption technique that cannot be cracked, but requires the use of a one-time pre-shared key the same size as, or longer than, the message being sent.

This is a native C implementation of OTP that encrypts a file or pipe input. Every byte/character of the input is encrypted with a generated (pseudo-)random byte/character key. The result output (encrypted file and key file or pipe output and key file) contains the encrypted bytes/characters and the key bytes/characters of same size of the input. The source-code can be compiled with any POSIX-compiler including the platforms pthread-library and with Microsofts Visual-C++-compiler.