ccrypt
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. ccrypt is based on the Rijndael block cipher, a version of which is also used in the Advanced Encryption Standard (AES, see http://www.nist.gov/aes). This cipher is believed to provide very strong security. Unlike unix crypt, the algorithm provided by ccrypt is not symmetric, i.e., one must specify whether to encrypt or decrypt. The most common way to invoke ccrypt is via the commands ccencrypt and ccdecrypt. There is also a ccat command for decrypting a file directly to the terminal, thus reducing the likelihood of leaving temporary plaintext files around. In addition, there is a compatibility mode for decrypting legacy unix crypt files. An emacs mode is also supplied for editing encrypted text files. 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. For a detailed description of the encryption algorithm used by ccrypt, see the man page.
