Examples for decrypting message
using System;
using System.Linq;
using System.Text;
using Org.BouncyCastle.Crypto.Engines;
using Org.BouncyCastle.Crypto.Modes;
using Org.BouncyCastle.Crypto.Parameters;
namespace DecryptionExample
{
// You need to install bccrypto-csharp from BouncyCastle. Please see BouncyCastle page.
class Program
{
static void Main(string[] args)
{
string keyFromConfiguration = "000102030405060708090a0b0c0d0e0f000102030405060708090a0b0c0d0e0f";
// Data from server
string ivFromHttpHeader = "000000000000000000000000";
string authTagFromHttpHeader = "CE573FB7A41AB78E743180DC83FF09BD";
string httpBody = "0A3471C72D9BE49A8520F79C66BBD9A12FF9";
// Convert data to process
byte[] key = ToByteArray(keyFromConfiguration);
byte[] iv = ToByteArray(ivFromHttpHeader);
byte[] authTag = ToByteArray(authTagFromHttpHeader);
byte[] encryptedText = ToByteArray(httpBody);
byte[] cipherText = encryptedText.Concat(authTag).ToArray();
// Prepare decryption
GcmBlockCipher cipher = new GcmBlockCipher(new AesFastEngine());
AeadParameters parameters = new AeadParameters(new KeyParameter(key), 128, iv);
cipher.Init(false, parameters);
// Decrypt
var plainText = new byte[cipher.GetOutputSize(cipherText.Length)];
var len = cipher.ProcessBytes(cipherText, 0, cipherText.Length, plainText, 0);
cipher.DoFinal(plainText, len);
Console.WriteLine(Encoding.ASCII.GetString(plainText));
}
static byte[] ToByteArray(string HexString)
{
int NumberChars = HexString.Length;
byte[] bytes = new byte[NumberChars / 2];
for (int i = 0; i < NumberChars; i += 2)
{
bytes[i / 2] = Convert.ToByte(HexString.Substring(i, 2), 16);
}
return bytes;
}
}
}
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