Problem with Crypt::CBC

[Kevin]

I know I'm missing something, but I'll be damned if I can figure it out...

I want to create a simple sub-routine to encrypt and (later) decrypt a
variable length string. The key for encryption and decryption is
absolutely known to be the same; it is created from the concatenation of
some other data which does not change. However, the key will be unique to
each instance of the encrypt/decrypt.

The goal is to store the encrypted string in a Mysql database, and have
the ability to use the decryption sub-routine to decrypt it at a future
time.

I've tried making the "$key" a reference in the $cipher creation hash
(i.e., 'key' => \$key), but that didn't help.

And yes, Crypt::Blowfish is installed. :-)

Here is the code I have:

#==============================#
# Encrypt
#==============================#
#! /usr/local/bin/perl -w
use strict;
use Crypt::CBC;

my $key = <some key>;
my $cipher = Crypt::CBC->new( {
'key' => $key,
'cipher' => 'Blowfish',
'prepend_iv' => 0,
'regenerate_key' => 0,
'padding' => 'null'});

my $encrypted = $cipher->encrypt($ARGV[0]);

open (FH, "> string.txt");
print FH $encrypted;
close FH;

exit;


#==============================#
# Decrypt
#==============================#
#! /usr/local/bin/perl -w
use strict;
use Crypt::CBC;

my $key = <some key>;
my $cipher = Crypt::CBC->new( {
'key' => $key,
'cipher' => 'Blowfish',
'prepend_iv' => 0,
'regenerate_key' => 0,
'padding' => 'null'});

my $encrypted = $cipher->encrypt($ARGV[0]);

open (FH, "< string.txt");
def $/;
my $encrypted = <FH>;
close FH;

my $decrypted = $cipher->decrypt($encrypted);

print $decrypted, "\n";

exit;

The encrypted string never looks the same twice; consequently, the
decrypted string that gets returned is not the same as the original input
string.

Thoughts, anyone?

KJJ

[Sisyphus]

Kevin wrote:

>
> Here is the code I have:
>
> #==============================#
> # Encrypt
> #==============================#
> #! /usr/local/bin/perl -w
> use strict;
> use Crypt::CBC;
>
> my $key = <some key>;
> my $cipher = Crypt::CBC->new( {
> 'key' => $key,
> 'cipher' => 'Blowfish',
> 'prepend_iv' => 0,
> 'regenerate_key' => 0,
> 'padding' => 'null'});
>
> my $encrypted = $cipher->encrypt($ARGV[0]);
>
> open (FH, "> string.txt");
> print FH $encrypted;
> close FH;
>
> exit;
>

That way you're getting a random (different) iv each time you run the
script. Hence you get different cyphertext each time. Specify an 'iv' in
the new() constructor (there's an example at the start of the Crypt::CBC
documentation) and you will get the same cyphertext each time.

Cheers,
Rob


--
To reply by email u have to take out the u in kalinaubears.

[Thomas Kratz]

Kevin wrote:

> I know I'm missing something, but I'll be damned if I can figure it out...
>
> I want to create a simple sub-routine to encrypt and (later) decrypt a
> variable length string. The key for encryption and decryption is
> absolutely known to be the same; it is created from the concatenation of
> some other data which does not change. However, the key will be unique to
> each instance of the encrypt/decrypt.

That should work out of the box with Crypt::CBC.

>
> The goal is to store the encrypted string in a Mysql database, and have
> the ability to use the decryption sub-routine to decrypt it at a future
> time.

Be careful: you have to make sure you are (re)storing binary data.
You can use pack/unpack with 'H*' or MIME::Base64 to convert to text.

[...]

> Here is the code I have:
>
> #==============================#
> # Encrypt
> #==============================#
> #! /usr/local/bin/perl -w
> use strict;
> use Crypt::CBC;
>
> my $key = <some key>;
> my $cipher = Crypt::CBC->new( {
> 'key' => $key,
> 'cipher' => 'Blowfish',
> 'prepend_iv' => 0,
> 'regenerate_key' => 0,
> 'padding' => 'null'});

Get rid of all the unneccessary parameters. A simple:

my $cipher = Crypt::CBC->new({
key => $key,
cipher => 'Blowfish',
}) or return;

will do. (Your problem is the prepend_iv set to 0).

[rest of code snipped]

>
> The encrypted string never looks the same twice; consequently, the
> decrypted string that gets returned is not the same as the original input
> string.

You got that wrong. The encrypted data should not be the same for
different calls to encrypt(). This is by design.

Thomas

--
open STDIN,"<&DATA";$=+=14;$%=50;while($_=(seek( #J~.> a>n~>>e~.......>r.
STDIN,$:*$=+$,+$%,0),getc)){/\./&&last;/\w| /&&( #.u.t.^..oP..r.>h>a~.e..
print,$_=$~);/~/&&++$:;/\^/&&--$:;/>/&&++$,;/</ #.>s^~h<t< ..~. ...c.^..
&&--$,;$:%=4;$,%=23;$~=$_;++$i==1?++$,:_;}__END__#.... >>e>r^..>l^...>k^..