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  1. using System;
  2. using System.Collections.Generic;
  3. using System.IO;
  4. using System.Security.Cryptography;
  5. using System.Text;
  6.  
  7. public class Test
  8. {
  9. 	public static void Main()
  10. 	{
  11. 		byte[] key = Convert.FromBase64String("DWsCdkYUwgXUPLRYWV/11mj56HsbS9Qw1EGYrygLETw=");
  12. 		byte[] iv = Convert.FromBase64String("120AY/Oe+jLhXiPd8vBcUQ==");
  13. 		byte[] cipher = Convert.FromBase64String("zfpqy8EVXg9xbBc=");
  14. 		var provider = new CounterModeCryptoTransform(new AesManaged { Mode = CipherMode.ECB, Padding = PaddingMode.PKCS7 }, key, iv);
  15. 		byte[] plain = provider.TransformFinalBlock(cipher, 0, cipher.Length);
  16. 		Console.WriteLine(Encoding.UTF8.GetString(plain));
  17. 	}
  18. }
  19.  
  20. public class CounterModeCryptoTransform : ICryptoTransform
  21. {
  22.     private readonly byte[] _counter;
  23.     private readonly ICryptoTransform _counterEncryptor;
  24.     private readonly Queue<byte> _xorMask = new Queue<byte>();
  25.     private readonly SymmetricAlgorithm _symmetricAlgorithm;
  26.  
  27.     public CounterModeCryptoTransform(SymmetricAlgorithm symmetricAlgorithm, byte[] key, byte[] counter)
  28.     {
  29.         if (symmetricAlgorithm == null) throw new ArgumentNullException("symmetricAlgorithm");
  30.         if (key == null) throw new ArgumentNullException("key");
  31.         if (counter == null) throw new ArgumentNullException("counter");
  32.         if (counter.Length != symmetricAlgorithm.BlockSize / 8)
  33.             throw new ArgumentException(String.Format("Counter size must be same as block size (actual: {0}, expected: {1})",
  34.                 counter.Length, symmetricAlgorithm.BlockSize / 8));
  35.  
  36.         _symmetricAlgorithm = symmetricAlgorithm;
  37.         _counter = counter;
  38.  
  39.         var zeroIv = new byte[_symmetricAlgorithm.BlockSize / 8];
  40.         _counterEncryptor = symmetricAlgorithm.CreateEncryptor(key, zeroIv);
  41.     }
  42.  
  43.     public byte[] TransformFinalBlock(byte[] inputBuffer, int inputOffset, int inputCount)
  44.     {
  45.         var output = new byte[inputCount];
  46.         TransformBlock(inputBuffer, inputOffset, inputCount, output, 0);
  47.         return output;
  48.     }
  49.  
  50.     public int TransformBlock(byte[] inputBuffer, int inputOffset, int inputCount, byte[] outputBuffer, int outputOffset)
  51.     {
  52.         for (var i = 0; i < inputCount; i++)
  53.         {
  54.             if (NeedMoreXorMaskBytes()) EncryptCounterThenIncrement();
  55.  
  56.             var mask = _xorMask.Dequeue();
  57.             outputBuffer[outputOffset + i] = (byte)(inputBuffer[inputOffset + i] ^ mask);
  58.         }
  59.  
  60.         return inputCount;
  61.     }
  62.  
  63.     private bool NeedMoreXorMaskBytes()
  64.     {
  65.         return _xorMask.Count == 0;
  66.     }
  67.  
  68.     private void EncryptCounterThenIncrement()
  69.     {
  70.         var counterModeBlock = new byte[_symmetricAlgorithm.BlockSize / 8];
  71.  
  72.         _counterEncryptor.TransformBlock(_counter, 0, _counter.Length, counterModeBlock, 0);
  73.         IncrementCounter();
  74.  
  75.         foreach (var b in counterModeBlock)
  76.         {
  77.             _xorMask.Enqueue(b);
  78.         }
  79.     }
  80.  
  81.     private void IncrementCounter()
  82.     {
  83.         for (var i = _counter.Length - 1; i >= 0; i--)
  84.         {
  85.             if (++_counter[i] != 0)
  86.                 break;
  87.         }
  88.     }
  89.  
  90.     public int InputBlockSize { get { return _symmetricAlgorithm.BlockSize / 8; } }
  91.     public int OutputBlockSize { get { return _symmetricAlgorithm.BlockSize / 8; } }
  92.     public bool CanTransformMultipleBlocks { get { return true; } }
  93.     public bool CanReuseTransform { get { return false; } }
  94.  
  95.     public void Dispose()
  96.     {
  97.     }
  98. }
Success #stdin #stdout 0.03s 26844KB
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Standard input is empty
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Test string
https://ideone.com/3U1WN4
language:
C# (gmcs 5.20.1)
created:
5 days ago
visibility:
public

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