crypt(1)crypt(1)NAMEcrypt - encode and decode files
reads from the standard input and writes on the standard output. pass‐
word is a key that selects a particular transformation. If no password
is given, demands a key from the terminal and turns off printing while
the key is being typed in. encrypts and decrypts with the same key:
The latter command decrypts the file and prints the clear version.
Files encrypted by are compatible with those treated by the editor in
encryption mode (see ed(1)).
Security of encrypted files depends on three factors: the fundamental
method must be hard to solve; direct search of the key space must be
infeasible; "sneak paths" by which keys or clear text can become visi‐
ble must be minimized.
implements a one-rotor machine designed along the lines of the German
Enigma, but with a 256-element rotor. Methods of attack on such
machines are widely known; thus provides minimal security.
The transformation of a key into the internal settings of the machine
is deliberately designed to be expensive; that is, to take a substan‐
tial fraction of a second to compute. However, if keys are restricted
to, for example, three lowercase letters, then encrypted files can be
read by expending only a substantial fraction of five minutes of
Since the key is an argument to the command, it is potentially visible
to users executing the or a derivative (see ps(1)). The choice of keys
and key security are the most vulnerable aspect of
The following example demonstrates the use of to edit a file that the
user wants to keep strictly confidential:
Note that the option is the encryption mode of and prompts the user for
the same key with which the file was encrypted.
If output is piped to and the encryption key is given on the command
line, can leave terminal modes in a strange state (see nroff(1) and
If two or more files encrypted with the same key are concatenated and
an attempt is made to decrypt the result, only the the first of the
original files is decrypted correctly.
for typed key
SEE ALSOed(1), makekey(1), stty(1).