NAME

crypt − encode/decode

SYNOPSIS

crypt [ password ]

DESCRIPTION

Crypt reads from the standard input and writes on the standard output.  The password is a key that selects a particular transformation.  If no password is given, crypt demands a key from the terminal and turns off printing while the key is being typed in.  Crypt encrypts and decrypts with the same key:

crypt key <clear >cypher
crypt key <cypher | pr

will print the clear. 

Files encrypted by crypt are compatible with those treated by the editor ed in encryption mode. 

The security of encrypted files depends on three factors: the fundamental method must be difficult to solve; direct search of the key space must be infeasible; ‘sneak paths’ by which keys or cleartext can become visible must be minimized. 

Crypt 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 not widely known moreover, infiltration requires a large amount of work. 

The transformation of a key into the internal settings of the machine is deliberately designed to be expensive, (i.e., to take a substantial fraction of a second to compute).  However, if keys are restricted (e.g., three lower-case letters), then encrypted files can be read by expending only a substantial fraction of five minutes of machine time. 

Since the key is an argument to the crypt command, it is potentially visible to users executing ps(1) or a derivative. To minimize this possibility, crypt destroys any record of the key immediately upon entry.  The choice of keys and key security are the most vulnerable aspect of crypt. 

FILES

/dev/ttyfor typed key

SEE ALSO

ed(1), makekey(8)

BUGS

There is no warranty of merchantability or fitness for a particular purpose, nor any other warranty, either expressed or implied, as to the accuracy of the enclosed materials or their suitability for any particular purpose.  Accordingly, Bell Telephone Laboratories assumes no responsibility for their use by the recipient.   Further, Bell Laboratories assumes no obligation to furnish any assistance of any kind whatsoever, or to furnisD any additional information or documentation. 

October 20, 1983  —  @(#)crypt.11.1%Q%%Y%