#!/usr/bin/perl -0777  --

# $0 key infile > outfile
# symmetric works both ways

use strict;
use warnings;

my @k = map { ord($_) } split //, shift;

my ( @s, $x, $y );
$y = 0;
for ( my @t = @s = 0 .. 255 ) {
    $y = ( $k[ $_ % @k ] + $s[ $x = $_ ] + $y ) % 256;
    &S;
}

$x = $y = 0;

for ( unpack( 'C*', <> ) ) {
    $x++;
    $y = ( $s[ $x %= 256 ] + $y ) % 256;
    &S;
    print pack( 'C', $_ ^= $s[ ( $s[$x] + $s[$y] ) % 256 ] );
}

sub S { @s[ $x, $y ] = @s[ $y, $x ] }
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This looks Neat, Thanks Guys !!

yes

Shortest answer ever?

e.g. UnixCrypt for a Perl only crypt module. But there are several, see CPAN! What are your requirements?

Udate
Crypt::Lite is an option but not if you're looking for STRONG encryption.

Well i m browsing a website using Mechanize.I m authenticating myself by entering my login credentials. Now the login password is stored in clear text and i want to get rid of that.So i thought if i could store the encryted password somewhere and later retreive and decrypt it and then use it in my script, i could achieve the same.

Let me know if there is a more elegant way to do the same

I would follow the same approach. Of course don't hard code the password/key in the script, then you would gain little compared to your current approach.