ccrypt is a utility for encrypting and decrypting files and streams. It was designed as a replacement for the standard unix crypt utility, which is notorious for using a very weak encryption algorithm. It is based on the Rijndael cipher, which is the U.S. government's chosen candidate for the Advanced Encryption Standard. This cipher is believed to provide very strong security.

Encryption and decryption depends on a keyword (or key phrase) supplied by the user. By default, the user is prompted to enter a keyword from the terminal. Keywords can consist of any number of characters, and all characters are significant (although ccrypt internally hashes the key to 256 bits). Longer keywords provide better security than short ones, since they are less likely to be discovered by exhaustive search.