It seems you don't need the Crypt::CBC module since you can use Crypt::Rijndael directly configured in CBC mode, as the following example (taken from the manual) shows:

use Crypt::Rijndael;

 # keysize() is 32, but 24 and 16 are also possible
 # blocksize() is 16

 $cipher = Crypt::Rijndael->new( "a" x 32, Crypt::Rijndael::MODE_CBC()
+ ); # <-- key and CBC-MODE

 $cipher->set_iv($iv);  # <-- here's your I-Vector
 $crypted = $cipher->encrypt($plaintext);
        # - OR -
 $plaintext = $cipher->decrypt($crypted);
[download]

Actually I just find the solution. The problem was that the PasswordDeriveByte System from C# don't create the same kind of Key/IV that the Perl CBC system (that uses openssl system). However, here is the C# code to generate de Key and IV

private void GenerateKeyIV(string strKey, byte[] bSalt, out byte[] bEn
+cKey, out byte[] bEncIV)
        {
            // Extracted from http://www.jensign.com/JavaScience/dotne
+t/DeriveKeyM/
            // by Michel Gallant

            int HASHLENGTH = 16;
            byte[] bKey = Encoding.UTF8.GetBytes(strKey);
            int count = 1;
            int miter = 3;

            byte[] keymaterial = new byte[HASHLENGTH * miter];

            byte[] data00 = new byte[bKey.Length + bSalt.Length];
            Array.Copy(bKey, data00, bKey.Length);
            Array.Copy(bSalt, 0, data00, bKey.Length, bSalt.Length);


            MD5 md5 = new MD5CryptoServiceProvider();
            byte[] result = null;
            byte[] hashtarget = new byte[HASHLENGTH + data00.Length];

            for (int j = 0; j < miter; j++)
            {
                if (j == 0)
                    result = data00;
                else
                {
                    Array.Copy(result, hashtarget, result.Length);
                    Array.Copy(data00, 0, hashtarget, result.Length, d
+ata00.Length);
                    result = hashtarget;
                }

                for (int i = 0; i < count; i++)
                    result = md5.ComputeHash(result);

                Array.Copy(result, 0, keymaterial, j * HASHLENGTH, res
+ult.Length);
            }

            bEncKey = new byte[32];
            bEncIV = new byte[16];

            Array.Copy(keymaterial, 0, bEncKey, 0, 32);
            Array.Copy(keymaterial, 32, bEncIV, 0, 16);
        }
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Your snippet doesn't handle padding.

There's no reason not to use Crypt::CBC.

There's no reason not to use Crypt::CBC.

Unless performance is important.

use strict;
use warnings;

use Crypt::CBC;
use Crypt::Rijndael;
use Crypt::GCrypt;

my $cbc = Crypt::CBC->new(
    -key    => 'a' x 32,
    -cipher => 'Rijndael'
);
$cbc->start('encrypting');
my $rij = Crypt::Rijndael->new( 'a' x 32, Crypt::Rijndael::MODE_CBC );
my $gcry = Crypt::GCrypt->new(
    type      => 'cipher',
    algorithm => 'rijndael',
    mode      => 'cbc'
);
$gcry->start('encrypting');
$gcry->setkey( 'a' x 32 );
$gcry->setiv( 'b' x 16 );

my $plaintext = 'plain text' x 8192;

use Benchmark qw( cmpthese );

cmpthese - 10,
  {
    'Crypt::CBC'      => sub { $cbc->crypt($plaintext); },
    'Crypt::Rijndael' => sub { $rij->encrypt($plaintext); },
    'Crypt::GCrypt'   => sub { $gcry->encrypt($plaintext); },
  };

$cbc->finish;
$gcry->finish;
__END__
                  Rate      Crypt::CBC Crypt::Rijndael   Crypt::GCrypt
Crypt::CBC      74.2/s              --            -83%            -89%
Crypt::Rijndael  430/s            479%              --            -39%
Crypt::GCrypt    704/s            849%             64%              --
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Upd: fix to improve Crypt::CBC performance

I think you should first decode message, extract salt and iv, and after that provide them to Crypt::CBC->new. Though I'm not sure that schemes used by Crypt::CBC and C# are compatible.

That shouldn't be the problem because if you do the encrypt with the perl function it work whith the decrypt code.

Have a look onto Crypt::CBC source, particularly onto _generate_iv_and_cipher_from_datastream and _salted_key_and_iv functions. Crypt::CBC doesn't read IV from encrypted data, it computes IV from the salt and passphrase. Note, that C# implementation may use another algorithm to compute encryption key from the salt and passphrase.