ENCRYPT(1)

NAME
encrypt, decrypt - encrypt or decrypt a message or file

SYNOPSIS
encrypt [ -p ] [ password ]
decrypt [ -p ] [ password ]

DESCRIPTION
Encrypt ( decrypt ) reads from the standard input and writes on the standard output. The password is a key, up to 127 characters in length, which selects a particular transformation. If no password is given, encrypt demands a key from the terminal (without echoing what the user types). If the wrong key is given to decrypt, it will usually exit without writing on standard output.

If the -p option is specified, the ciphertext will be encoded into printing characters only; suitable for sending through mail. In this mode, decrypt ignores any lines that do not have a special prefix (added by encrypt ), so messages received in the mail can be read without having to edit out headers.

Encryption takes place in three layers. The first addresses traffic analysis threats by hiding the size of the message and insuring that if the same message is send repeatedly with the same password the ciphertext will be entirely different each time. The second layer is the proposed Data Encryption Standard (DES) used in Cipher Block Chaining (CBC) mode. Finally, a key-dependent character transposition is applied to the ciphertext which impedes the assembly of corresponding pairs of DES blocks under a known-plaintext attack.

The user is encouraged to use a lengthy password. A short sequence of words chosen at random from a dictionary and committed to memory is a good plan.

FILES
/dev/tty for typed key

AUTHOR
D.P.Mitchell

BUGS
This encryption program is not provably secure, and the author gives no guarantee that it cannot be broken.