Decrypt SOAP Body encrypted with X.509 certificate with WS-Security (C#).

decrypt

//decrypt the encryptedKey to get the session key:
//==================================================
string wrappingKey = "put here the value base64 CipherValue under the encryptedKey element";
X509Certificate2 serverCert = new X509Certificate2(File.ReadAllBytes(@"c:\temp\xws-security-server.p12"), "changeit");
RSACryptoServiceProvider rsa = (RSACryptoServiceProvider)serverCert.PrivateKey;
var enckey = rsa.Decrypt(Convert.FromBase64String(wrappingKey), true);
return enckey;


//decrypt the soap body using the session key (aes128):
//=====================================================

internal static byte[] ExtractIVAndDecrypt(SymmetricAlgorithm algorithm, byte[] cipherText, int offset, int count)
{
    byte[] buffer2;
    if (cipherText == null)
    {
        throw new Exception();
    }
    if ((count < 0) || (count > cipherText.Length))
    {
        throw new Exception();
    }
    if ((offset < 0) || (offset > (cipherText.Length - count)))
    {
        throw new Exception();
    }
    int num = algorithm.BlockSize / 8;
    byte[] dst = new byte[num];
    Buffer.BlockCopy(cipherText, offset, dst, 0, dst.Length);
    algorithm.Padding = PaddingMode.ISO10126;
    algorithm.Mode = CipherMode.CBC;
    try
    {
        using (ICryptoTransform transform = algorithm.CreateDecryptor(algorithm.Key, dst))
        {
            buffer2 = transform.TransformFinalBlock(cipherText, offset + dst.Length, count - dst.Length);
        }
    }
    catch (CryptographicException exception)
    {
        throw new Exception();
    }
    return buffer2;
}

//the IV is the first 16 byes (in our case) of the encrypted cipher (not key)
 private byte[] GetIV( byte[] cypher)
{            
    byte[] IV = new byte[16];
    Array.Copy(cypher, IV, 16);
    return IV;
}

//note the cipher contains the iv inside it but we do not remove it since the methods expect to get the cipher with iv and ic separately
byte[] cypher = Convert.FromBase64String("put here the base64 encrypted cipherValue under the encrypted body");

byte[] key =this.key; //we are assumed to know the key. for example we decrypted it using the method above.
byte[] iv = GetIV(cypher);


var AesManagedAlg = new AesCryptoServiceProvider();
AesManagedAlg.KeySize = 128;
AesManagedAlg.Key = key;
AesManagedAlg.IV = iv;

var body = ExtractIVAndDecrypt(AesManagedAlg, cypher, 0, cypher.Length);

System.Out.Print("decrypted body is: " + UTF8Encoding.UTF8.GetString(body));