From: jmount+@CS.CMU.EDU (John Mount)
Newsgroups: sci.crypt
Subject: Re: Unix compatible crypt utility needed
Keywords: encryption
Date: 27 Aug 92 13:52:20 GMT
Organization: Carnegie Mellon University

In article <phil.714897700@adam.adelaide.edu.au>, phil@adam.adelaide.edu.au (Phil Kernick) writes:
|> exukev@exu.ericsson.se (Kevin Autrey) writes:
|> 
|> >I've got some files I've encrypted on a Unix workstation that I want
|> >to decrypt on my Amiga.  They were encrypted using "crypt" on the Sun
|> >(which, I believe, uses the DES encryption scheme).  Does any Amiga
|> >utility decrypt data encrypted with Unix's "crypt"?
|> 
|> I think that you may not quite understand how crypt works.
|>
|> If they have been encrypted by DES then this is a one way algorithm, and
|> hence you can't get the text back.
|> 
|> All you could do is encrypt another section of text and compare the crypted
|> version.

No I don't think you understand how crypt works (or have it confused with
the unix password encryption scheme, which is intended to be one way).  Crypt
doesn't use DES (see below man page), it is a wimpy Enigma machine.  DES 
IS invertible (ie. people do decrypt DES messages).


CRYPT(1)            UNIX Programmer's Manual             CRYPT(1)



NAME
     crypt - encode/decode

SYNOPSIS
     crypt [ password ]

DESCRIPTION
     Crypt reads from the standard input and writes on the stan-
     dard output.  The password is a key that selects a particu-
     lar 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 hard 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 known, but not
     widely; moreover the amount of work required is likely to be
     large.

     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.  How-
     ever, if keys are restricted to (say) 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 deriva-
     tive.  To minimize this possibility, crypt takes care to
     destroy any record of the key immediately upon entry.  No
     doubt the choice of keys and key security are the most
     vulnerable aspect of crypt.

FILES
     /dev/tty for typed key

SEE ALSO
     ed(1), makekey(8)

BUGS
     There is no warranty of merchantability nor any warranty of
     fitness for a particular purpose nor any other warranty,
     either express or implied, as to the accuracy of the
     enclosed materials or as to their suitability for any par-
     ticular 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 furnish any
     additional information or documentation.

-- 
--- It is kind of strange being in CS theory, given computers really do exist.
John Mount: jmount+@cs.cmu.edu               (412)268-6247
School of Computer Science, Carnegie Mellon University, 
5000 Forbes Ave., Pittsburgh PA 15213-3891
Newsgroups: sci.crypt