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.\" ========================================================================
.\"
.IX Title "UnixCrypt 3"
.TH UnixCrypt 3 "1999-10-20" "perl v5.22.0" "User Contributed Perl Documentation"
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.SH "NAME"
Crypt::UnixCrypt \- perl\-only implementation of the "crypt" function.
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 2
\&  use Crypt::UnixCrypt;
\&  $hashed = crypt($plaintext,$salt);
\&
\&  # always use this module\*(Aqs crypt
\&  BEGIN { $Crypt::UnixCrpyt::OVERRIDE_BUILTIN = 1 }
\&  use Crypt::UnixCrypt;
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This module is for all those poor souls whose perl port answers to the
use of \f(CW\*(C`crypt()\*(C'\fR with the message `The \fIcrypt()\fR function is unimplemented
due to excessive paranoia.'.
.PP
This module won't overload a built-in \f(CW\*(C`crypt()\*(C'\fR unless forced by a true
value of the variable \f(CW$Crypt::UnixCrypt::OVERRIDE_BUILTIN\fR.
.PP
If you use this module, you probably neither have a built-in \f(CW\*(C`crypt()\*(C'\fR
function nor a \fIcrypt\fR\|(3) manpage; so I'll supply the appropriate portions
of its description (from my Linux system) here:
.PP
crypt is the password encryption function. It is based on the Data
Encryption Standard algorithm with variations intended (among other
things) to discourage use of hardware implementations of a key search.
.PP
\&\f(CW$plaintext\fR is a user's typed password.
.PP
\&\f(CW$salt\fR is a two-character string chosen from the set [a\-zA\-Z0\-9./]. This
string is used to perturb the algorithm in one of 4096 different ways.
.PP
By taking the lowest 7 bit of each character of \f(CW$plaintext\fR (filling it up
to 8 characters with zeros, if needed), a 56\-bit key is obtained. This
56\-bit key is used to encrypt repeatedly a constant string (usually a
string consisting of all zeros). The returned value points to the
encrypted password, a series of 13 printable \s-1ASCII\s0 characters (the first
two characters represent the salt itself).
.PP
Warning: The key space consists of 2**56 equal 7.2e16 possible values.
Exhaustive searches of this key space are possible using massively
parallel computers. Software, such as \fIcrack\fR\|(1), is available which will
search the portion of this key space that is generally used by humans
for passwords. Hence, password selection should, at minimum, avoid
common words and names. The use of a \fIpasswd\fR\|(1) program that checks for
crackable passwords during the selection process is recommended.
.PP
The \s-1DES\s0 algorithm itself has a few quirks which make the use of the
\&\fIcrypt\fR\|(3) interface a very poor choice for anything other than password
authentication. If you are planning on using the \fIcrypt\fR\|(3) interface for
a cryptography project, don't do it: get a good book on encryption and
one of the widely available \s-1DES\s0 libraries.
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
This module is free software; you may redistribute it and/or modify it
under the same terms as Perl itself.
.SH "AUTHORS"
.IX Header "AUTHORS"
Written by Martin Vorlaender, martin@radiogaga.harz.de, 11\-DEC\-1997.
Based upon Java source code written by jdumas@zgs.com, which in turn is
based upon C source code written by Eric Young, eay@psych.uq.oz.au.
.SH "CAVEATS"
.IX Header "CAVEATS"
In extreme situations, this function doesn't behave like \f(CWcrypt(3)\fR,
e.g. when called with a salt not in [A\-Za\-z0\-9./]{2}.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fIperl\fR\|(1), \fIperlfunc\fR\|(1), \fIcrypt\fR\|(3).