The next generation of the Teknik Services. Written in ASP.NET. https://www.teknik.io/
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using System;
using System.Security.Cryptography;
namespace Teknik.Utilities.Cryptography
{
public class AesCounterMode : SymmetricAlgorithm
{
// Internal Variables
private const int _BlockSize = 16;
private readonly byte[] _Counter;
private readonly AesManaged _Algo;
public AesCounterMode() : this(new byte[_BlockSize]) { }
public AesCounterMode(byte[] counter)
{
if (counter == null) throw new ArgumentNullException("counter");
if (counter.Length != _BlockSize)
throw new ArgumentException(String.Format("Counter size must be same as block size (actual: {0}, expected: {1})",
counter.Length, _BlockSize));
// Generate a new instance of the Aes Algorithm in ECB mode with no padding
_Algo = new AesManaged
{
Mode = CipherMode.ECB,
Padding = PaddingMode.None
};
// Set the internal variables
_Counter = new byte[counter.Length];
counter.CopyTo(_Counter, 0);
}
public override ICryptoTransform CreateEncryptor(byte[] key, byte[] iv)
{
return new CounterModeCryptoTransform(_Algo, key, iv, _Counter);
}
public override ICryptoTransform CreateDecryptor(byte[] key, byte[] iv)
{
return new CounterModeCryptoTransform(_Algo, key, iv, _Counter);
}
public override void GenerateKey()
{
_Algo.GenerateKey();
}
public override void GenerateIV()
{
_Algo.GenerateIV();
}
}
public class CounterModeCryptoTransform : ICryptoTransform
{
private readonly byte[] _IV;
private readonly byte[] _Counter;
private readonly ICryptoTransform _CounterEncryptor;
private readonly SymmetricAlgorithm _SymmetricAlgorithm;
// Stateful Fields
private byte[] _EncryptedCounter;
private int _Iterations;
public int Iterations
{
get
{
return _Iterations;
}
}
private int _CounterPosition;
public int CounterPosition
{
get
{
return _CounterPosition;
}
set
{
if (value >= 0 && value < _EncryptedCounter.Length)
{
_CounterPosition = value;
}
}
}
public CounterModeCryptoTransform(SymmetricAlgorithm symmetricAlgorithm, byte[] key, byte[] iv, byte[] counter)
{
if (symmetricAlgorithm == null) throw new ArgumentNullException("symmetricAlgorithm");
if (key == null) throw new ArgumentNullException("key");
if (iv == null) throw new ArgumentNullException("iv");
if (counter == null) throw new ArgumentNullException("counter");
// Check lengths
if (counter.Length != symmetricAlgorithm.BlockSize / 8)
throw new ArgumentException(String.Format("Counter size must be same as block size (actual: {0}, expected: {1})",
counter.Length, symmetricAlgorithm.BlockSize / 8));
_SymmetricAlgorithm = symmetricAlgorithm;
// Initialize the encrypted counter
_EncryptedCounter = new byte[_SymmetricAlgorithm.BlockSize / 8];
_IV = new byte[iv.Length];
iv.CopyTo(_IV, 0);
_Counter = new byte[counter.Length];
counter.CopyTo(_Counter, 0);
_CounterEncryptor = symmetricAlgorithm.CreateEncryptor(key, iv);
// Initialize State
_CounterPosition = 0;
_Iterations = 0;
// Encrypt the counter
EncryptCounter();
// Initial Increment
IncrementCounter();
}
public byte[] TransformFinalBlock(byte[] inputBuffer, int inputOffset, int inputCount)
{
var output = new byte[inputCount];
TransformBlock(inputBuffer, inputOffset, inputCount, output, 0);
return output;
}
public int TransformBlock(byte[] inputBuffer, int inputOffset, int inputCount, byte[] outputBuffer, int outputOffset)
{
for (var i = 0; i < inputCount; i++)
{
// Encrypt the counter if we have reached the end, or
if (_CounterPosition >= _EncryptedCounter.Length)
{
//Reset current counter position
_CounterPosition = 0;
// Encrypt the counter
EncryptCounter();
// Increment the counter for the next batch
IncrementCounter();
}
// XOR the encrypted counter with the input plain text
outputBuffer[outputOffset + i] = (byte)(_EncryptedCounter[_CounterPosition] ^ inputBuffer[inputOffset + i]);
// Move the counter position
_CounterPosition++;
}
return inputCount;
}
public void EncryptCounter()
{
// Clear the encrypted counter
Array.Clear(_EncryptedCounter, 0, _EncryptedCounter.Length);
// Encrypt the current counter to the encrypted counter
_CounterEncryptor.TransformBlock(_Counter, 0, _Counter.Length, _EncryptedCounter, 0);
}
public void ResetCounter()
{
Array.Clear(_Counter, 0, _Counter.Length);
_IV.CopyTo(_Counter, 0);
_Iterations = 0;
}
public void IncrementCounter()
{
int j = _Counter.Length;
while (--j >= 0 && ++_Counter[j] == 0)
{
}
_Iterations++;
}
public int InputBlockSize { get { return _SymmetricAlgorithm.BlockSize / 8; } }
public int OutputBlockSize { get { return _SymmetricAlgorithm.BlockSize / 8; } }
public bool CanTransformMultipleBlocks { get { return true; } }
public bool CanReuseTransform { get { return false; } }
public void Dispose()
{
}
}
}