static byte[] MakeAuthentication(JToken token)
{
var cipher = token.ToObject <byte[]> ();
using (var aes = new System.Security.Cryptography.AesManaged()) {
using (var key = Sas.SecureHelper.APP_KEY)
aes.Key = key.GetByte(Convert.FromBase64String);
using (var iv = Sas.SecureHelper.APP_IV)
aes.IV = iv.GetByte(Convert.FromBase64String);
using (var question = aes.Decrypt(cipher.ToArray())) {
var val = SasUtil.Evaluate(question.GetByte(b => b));
question.AppendChar('=');
foreach (var ch in val.ToString())
{
question.AppendChar(ch);
}
return(question.GetByte(aes.Encrypt));
}
}
}
/// <summary>
/// Returns a binary array of decrypted data for the given parameters.
/// </summary>
/// <param name="source">Binary array of data to decrypt.</param>
/// <param name="startIndex">Offset into <paramref name="source"/> buffer.</param>
/// <param name="length">Number of bytes in <paramref name="source"/> buffer to decrypt starting from <paramref name="startIndex"/> offset.</param>
/// <param name="key">Encryption key to use to decrypt data.</param>
/// <param name="iv">Initialization vector to use to decrypt data.</param>
/// <param name="strength">Cryptographic strength to use when decrypting data.</param>
/// <returns>A decrypted version of the source data.</returns>
public static byte[] Decrypt(this byte[] source, int startIndex, int length, byte[] key, byte[] iv, CipherStrength strength)
{
if (strength == CipherStrength.None)
return source;
AesManaged symmetricAlgorithm = new AesManaged();
symmetricAlgorithm.KeySize = (int)strength;
return symmetricAlgorithm.Decrypt(source, startIndex, length, key, iv);
}
