[willdye] 'Dunno why this old man page is in the Tcl Wiki, but if you're 
looking for a way to perform the crypt function in Tcl, then the link
you want is probably "crypt in pure tcl", at:  http://wiki.tcl.tk/1070

[JMN] 2005-08-31 The "crypt in pure tcl" above is packaged as 'tclcrypt' in the [TclHttpd] distribution.

In the non-starkit TclHttpd distribution, there is also the much faster binary version packaged as 'crypt'.

These are also available separately here: http://vectorstream.com/tcl/packages/ 

The [trf] package also provides the crypt function, but apparently not on the Windows platform at least.

While on the general subject - beware that at least one crypt implementation (crypt.exe in Cygwin on Windows) takes its 'password & salt' arguments in the reverse order to that of the Tcl implementations mentioned above.

The man page below appears to be from a different unix crypt function - i.e not the one commonly used for encrypting passwords for HTTP.
----
 
User Commands                                            crypt(1)

NAME
     crypt - encode or decode a file

SYNOPSIS
     crypt [ password ]

DESCRIPTION
     crypt encrypts and decrypts the contents of  a  file.  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:

          example% crypt key<clear.file> encrypted.file
          example% crypt key<encrypted.file | pr

     will print the contents of  clear.file.

     Files encrypted by crypt are compatible with  those  treated
     by the editors ed(1), ex(1), and vi(1) 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  widely  known,  thus
     crypt 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 substantial fraction of a second  to  compute.
     However,  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 derivative
     command.  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

SunOS 5.8           Last change: 14 May 1997                    1

User Commands                                            crypt(1)

ATTRIBUTES
     See attributes(5) for descriptions of the  following  attri-
     butes:

     ____________________________________________________________
    |       ATTRIBUTE TYPE        |       ATTRIBUTE VALUE       |
    |_____________________________|_____________________________|
    | Availability                | SUNWcsu                     |
    |_____________________________|_____________________________|

SEE ALSO
     ed(1), ex(1), ps(1), vi(1), attributes (5)

SunOS 5.8           Last change: 14 May 1997                    2