private static byte[] Decode(byte[] cipherData, byte[] key, byte[] initVector)
{
    MemoryStream memoryStream = new MemoryStream();
    Rijndael algorythmus = Rijndael.Create();
    algorythmus .Key = key;
    algorythmus .IV = initVector;
    
    CryptoStream cs = new CryptoStream(memoryStream, algorythmus .CreateDecryptor(), CryptoStreamMode.Write);
    cs.Write(cipherData, 0, cipherData.Length);
    cs.Close();
    
    byte[] decryptedData = memoryStream.ToArray();

    return decryptedData;
}

#!/usr/bin/perl -w
use strict;
use Crypt::Rijndael;
use Crypt::CBC;
use Convert::Base64;

my $encodedString = 'AI8Xv81IsklU/SLZDV8sW4EqUWKh4yiOm/y0WE5PPmXrciz1NyP3zDzirY1vq0/2wPD0m8ZlTHeGL4Cpygs7/CJAS9pyEz47/Apnn5qix45YpH7m2OXxug/04UyuOFnH';
my @keyArray = (231, 216, 3, 26, 247, 91, 73, 223, 222, 174, 20, 122, 30, 27, 240, 211, 219, 51, 217, 212, 22, 94, 219, 239, 147, 12, 164, 230, 73, 168, 72, 247);
my @ivArray = (222, 174, 20, 122, 30, 27, 240, 211, 95, 191, 236, 203, 64, 122, 254, 71);

my $key = CreateString(@keyArray);
my $initVector = CreateString(@ivArray);

my $decryptedString = Encode::decode("UTF-16LE",Decrypt($encodedString, $key, $initVector));
print $decryptedString;

sub Decrypt {
    my $encodedString = shift;
    my $key = shift;
    my $initVector = shift;
        
    #1. Schritt
    #Das Array mit den korrekten Daten
    #my @cipherData =(0, 143, 23, 191, 205, 72, 178, 73, 84, 253, 34, 217, 13, 95, 44, 91, 129, 42, 81, 98, 161, 227, 40, 142, 155, 252, 180, 88, 78, 79, 62, 101, 235, 114, 44, 245, 55, 35, 247, 204, 60, 226, 173, 141, 111, 171, 79, 246, 192, 240, 244, 155, 198, 101, 76, 119, 134, 47, 128, 169, 202, 11, 59, 252, 34, 64, 75, 218, 114, 19, 62, 59, 252, 10, 103, 159, 154, 162, 199, 142, 88, 164, 126, 230, 216, 229, 241, 186, 15, 244, 225, 76, 174, 56, 89, 199);
    my @cipherData = DecodeBase64ToArray($encodedString);
    
    #2. Schritt
    my @decryptedData = ();
    #Das Array mit den korrekten Daten
    #@decryptedData = (80, 0, 101, 0, 114, 0, 108, 0, 32, 0, 117, 0, 110, 0, 100, 0, 32, 0, 67, 0, 35, 0, 32, 0, 115, 0, 105, 0, 110, 0, 100, 0, 32, 0, 99, 0, 111, 0, 111, 0, 108, 0, 101, 0, 32, 0, 80, 0, 114, 0, 111, 0, 103, 0, 114, 0, 97, 0, 109, 0, 109, 0, 105, 0, 101, 0, 114, 0, 115, 0, 112, 0, 114, 0, 97, 0, 99, 0, 104, 0, 101, 0, 110, 0, 33, 0);

    #Hier mit string als Test
    my $base64String = DecodeBase64ToString($encodedString);
    
    my $cipher = Crypt::CBC->new(
    {
        key             => $key,            #The encryption/decryption key (required)
        cipher          => 'Rijndael',      #The cipher algorithm (defaults to Crypt::DES), or a preexisting cipher object.
        iv              => $initVector,     #The initialization vector (IV)
        header          => 'none',          #What type of header to prepend to ciphertext. One of 'salt'   -- use OpenSSL-compatible salted header 'randomiv' -- Randomiv-compatible "RandomIV" header 'none'   -- prepend no header at all
        padding         => 'standard',      #The padding method, one of "standard" (default), "space", "oneandzeroes", "rijndael_compat", "null", or "none" (default "standard").
        literal_key     => 0,               #If true, the key provided by "key" is used directly for encryption/decryption. Otherwise the actual key used will be a hash of the provided key. (default false)
        pcbc            => 0,               #Whether to use the PCBC chaining algorithm rather than the standard CBC algorithm (default false)
        keysize         => 32,              #Force the cipher keysize to the indicated number of bytes.
        blocksize       => 16               #Force the cipher blocksize to the indicated number of bytes.
    }
    );

    foreach my $value (@cipherData) {
        push(@decryptedData, $cipher->decrypt($value));
    }
    
    #Hier mit string als Test
    my $decodedString = $cipher->decrypt($base64String);
    
    #3. Schritt
    my $unicodeString = ConvertToUnicode(@decryptedData);

 return $unicodeString;
}

sub ConvertToUnicode {
    my @byteArray = @_;
    
    return join('', map chr, @byteArray);
}

sub DecodeBase64ToArray {
    my $encodedString = shift;
    
    my @base64decoded = ();
    
    my $base64string = unpack("H*",decode_base64($encodedString));
    my @base64HexDecoded = $base64string =~ /\w{2}/g;
   
    @base64decoded = ConvertToDecimal(@base64HexDecoded);
    
    return @base64decoded;
}

sub DecodeBase64ToString {
    my $encodedString = shift;
    
    return decode_base64($encodedString);
}

sub ConvertToDecimal {
    my @hexArray = @_;
    
    my @returnArray = ();
    
    foreach my $hexValue (@hexArray) {
        push(@returnArray, hex($hexValue));
    }
    return @returnArray;
}

sub CreateString {
    my @array = @_;
    
    my @chars = ();
    
    foreach my $value (@array) {
        push(@chars, chr($value));
    }
    
    return join('', @chars);
}