What sort of encryption do you need?

For public key encryption (where the public key encrypts and the private key decrypts), I like Crypt::OpenPGP (though it has a massive ammount of dependencies, including the annoying-to-install Math::Pari).

For good-old block cipher encryption, you probably want Crypt::CBC using Crypt::Rijndael as the underlieing block cipher. Unless you have a need for another cipher mode (if you don't know what this means, look it up, or just use CBC).

For stream ciphers, there is Crypt::RC4. RC4 might have some problems, but there aren't really any better stream ciphers (though most of the time you can drop in a block cipher instead).

If you're just storing some passwords, you probably only need a digest, not a cipher. Try Digest::SHA1.

what Crypt module would be good to use

The absolute answer is: "It depends!"

My personal preference is Crypt::Blowfish in terms of ease of use. If I am interested in using some sort of public key/private key scheme then Crypt::GPG is going to get considered.

Blowfish rocks and you just gotta love the name.....

I gave an example in Re: Data File Encryption that should provide you with a good starting point for consideration.

Here are a couple of examples:

#!/usr/bin/perl
use Crypt::RC4;

$passphrase = "rumpelstiltskin";

$plaintext= qw(qqq"""""""''''''';;;;;qwweeerrrtttyyyy); 
 
$encrypted = RC4( $passphrase, $plaintext ); 
$decrypt = RC4( $passphrase, $encrypted ); 
 
print "$plaintext\n$encrypted\n$decrypt\n";
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or

#!/usr/bin/perl
use Crypt::RC5;

$key = 'e726f4a56b3e4f';
$rc5 = new Crypt::RC5($key, '12' );

open (FH,"< /etc/passwd");
while(<FH>){
$file .= $_ }
close FH;
print "$file\n";


$cipher = $rc5->encrypt($file);

$rc5d = new Crypt::RC5($key, '12' );

$plain = $rc5d->decrypt($cipher);

print "$plain\n";
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or

#!/usr/bin/perl
use Crypt::Rijndael;

$key = chr(0) x 32; #key is all nulls here 
substr($key, 0, 1) = chr(1); #put 1 chr(1)in key just for fun 

print "key->$key\n";

$plaintext= "adrqwqqqqqqqqqqqqqqqqqqqqqqwrxcq4gfq3g2q45g2q43g5";
print "plaintext->$plaintext\n";
$plaintext16= get16($plaintext);
print "plaintext16->$plaintext16\n";


$cbc = new Crypt::Rijndael $key, Crypt::Rijndael::MODE_CBC;
$crypted = $cbc->encrypt($plaintext16);
print 'crypted->',"$crypted\n"; #keep encrypted string in different pr
+int string 
                                #to avoid character corruption of prec
+eding string 

$cbc = new Crypt::Rijndael $key, Crypt::Rijndael::MODE_CBC;
$decrypted = $cbc->decrypt($crypted);
print "decrypted->$decrypted\n";

#this sub makes all data blocksize of 16 bytes. 
sub get16 {
    my $data = shift;
    print "data=$data\n";
      return "\0" x ( 16 - length($data)%16 ) . $data;
      }

exit;
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$cipher = $rc5->encrypt($file); This encrypts in ECB mode. Don't do that. IMAO, don't use any crypto module by Kurt Kincaid.

If you're on WinXP, maybe you don't have a compiler, so you either need to find a precompiled crypto module (in .ppm format, maybe), or use a pure perl implementation. Those are usually named with _PP or ::Perl on the end. They're slower, but it won't matter much for short strings.

IMAO, don't use any crypto module by Kurt Kincaid.

Explain arrogant opinion.

I'd use some GPG module and use a client from http://www.gnupg.org as standalone client.

That's a pretty wide open question, but you could try out Digest::MD5 as a start.

How would you decrypt a MD5-encrypted string? ;)

Update: MD5 is one-way hash, and therefore, you aren't able to "decrypt" something you "encrypted" with MD5. This can be useful for passwords (and some operating systems use MD5 for their password file). You make a MD5 hash of the password once and store that output. When, later, a user types in his/her password, you MD5 that string too and compare the results. But since you specifically spoke about decrypting, this type (MD5) doesn't seem valid here. (Thanks to Limbic~Region for pointing out the lacking explanation)

Update: changed terminology a bit

--
b10m

D'Oh! I looked at the post carefully and registered 'encryption' only. Need more coffee, clearly.

Alex / talexb / Toronto

Life is short: get busy!

How would you decrypt a MD5-encrypted string?

By being very, very patient.

----
I wanted to explore how Perl's closures can be manipulated, and ended up creating an object system by accident.
-- Schemer

: () { :|:& };:

Note: All code is untested, unless otherwise stated

How would you decrypt a MD5-encrypted string? ;)

Well I work for NSA and with a CRAY and the right hooks you can turn 128bits into the complete works of Shakespere ;)