crypt -- Command

Encrypt/decrypt text
crypt [password]

The command  crypt encrypts data.  It  emulates a rotor-encryption machine,
such as the Enigma or Hagelin C-48 cipher machines.  Unlike these machines,
crypt  uses only  one rotor,  with  a 256-character  alphabet and  a keying
sequence of period 2^32.

crypt  reads text  from standard  input  and writes  the encrypted  text to
standard output.   password is used  to construct the model  of the machine
and to start  the keying sequence.  If no password  is given, crypt prompts
for a  password on the terminal  and disables echo while  it is being typed
in.  The password may be up  to ten characters long, but must not be empty;
all characters  past the first ten are ignored.   All characters are legal,
although  it may  not  be possible  to  input certain  characters from  the
terminal.

crypt  uses the  same  password for  both encryption  and decryption.   For
example, the commands

    crypt COHERENT <file1 >file2
    crypt COHERENT <file2 >file3

leave file3 identical to file1.

Encrypted files produced by ed with its -x option may be read by crypt, and
vice versa, as ed uses crypt to perform its encryption.

Security of a cryptosystem depends on several factors:

1. Brute-force  attempts   to  break  the  system   should  be  infeasible.
   Passwords  should  be  at  least  five  characters  long;  although  the
   construction of the machine  model from the password takes a substantial
   fraction of  a second, it is still plausible  that encrypted files could
   be read by a brute-force search of a portion of the password space (say,
   all passwords less than four characters long).

2. Cryptanalysis  of  the  basic encryption  scheme  should  be very  hard.
   Analysis of  rotor machines  is understood, but  it is difficult  and in
   most cases probably not worth the trouble.

3. Passwords must be kept secret.  crypt erases password as soon as it can,
   to avoid the possibility that it could appear in the output of ps.

4. Privileged access  to the system  must be guarded.   Under COHERENT, the
   security of crypt can be no better than the security governing access to
   superuser  status, because  the superuser  can do  practically anything.
   This is probably crypt's most vulnerable point.

Files

/dev/tty -- Typed passwords

See Also

commands,
passwd,
security,
shadow

© 2012 by Stephen A. Ness