RijndaelManaged的AES OFB加密

我需要通过OFB模式下的加密消息从C＃应用程序通信到另一个应用程序。 我知道RijndaelManaged不支持AES OFB模式。 有没有比我更有经验的人知道使用OFB模式加密/解密的任何其他方法？

Answer 1

以下流通过使用由零馈送CBC密码流生成的密钥流来实现OFB。

 public class OFBStream : Stream { private const int BLOCKS = 16; private const int EOS = 0; // the goddess of dawn is found at the end of the stream private Stream parent; private CryptoStream cbcStream; private CryptoStreamMode mode; private byte[] keyStreamBuffer; private int keyStreamBufferOffset; private byte[] readWriteBuffer; public OFBStream (Stream parent, SymmetricAlgorithm algo, CryptoStreamMode mode) { if (algo.Mode != CipherMode.CBC) algo.Mode = CipherMode.CBC; if (algo.Padding != PaddingMode.None) algo.Padding = PaddingMode.None; this.parent = parent; this.cbcStream = new CryptoStream (new ZeroStream (), algo.CreateEncryptor (), CryptoStreamMode.Read); this.mode = mode; keyStreamBuffer = new byte[algo.BlockSize * BLOCKS]; readWriteBuffer = new byte[keyStreamBuffer.Length]; } public override int Read (byte[] buffer, int offset, int count) { if (!CanRead) { throw new NotSupportedException (); } int toRead = Math.Min (count, readWriteBuffer.Length); int read = parent.Read (readWriteBuffer, 0, toRead); if (read == EOS) return EOS; for (int i = 0; i < read; i++) { // NOTE could be optimized (branches for each byte) if (keyStreamBufferOffset % keyStreamBuffer.Length == 0) { FillKeyStreamBuffer (); keyStreamBufferOffset = 0; } buffer [offset + i] = (byte)(readWriteBuffer [i] ^ keyStreamBuffer [keyStreamBufferOffset++]); } return read; } public override void Write (byte[] buffer, int offset, int count) { if (!CanWrite) { throw new NotSupportedException (); } int readWriteBufferOffset = 0; for (int i = 0; i < count; i++) { if (keyStreamBufferOffset % keyStreamBuffer.Length == 0) { FillKeyStreamBuffer (); keyStreamBufferOffset = 0; } if (readWriteBufferOffset % readWriteBuffer.Length == 0) { parent.Write (readWriteBuffer, 0, readWriteBufferOffset); readWriteBufferOffset = 0; } readWriteBuffer [readWriteBufferOffset++] = (byte)(buffer [offset + i] ^ keyStreamBuffer [keyStreamBufferOffset++]); } parent.Write (readWriteBuffer, 0, readWriteBufferOffset); } private void FillKeyStreamBuffer () { int read = cbcStream.Read (keyStreamBuffer, 0, keyStreamBuffer.Length); // NOTE undocumented feature // only works if keyStreamBuffer.Length % blockSize == 0 if (read != keyStreamBuffer.Length) throw new InvalidOperationException ("Implementation error: could not read all bytes from CBC stream"); } public override bool CanRead { get { return mode == CryptoStreamMode.Read; } } public override bool CanWrite { get { return mode == CryptoStreamMode.Write; } } public override void Flush () { // should never have to be flushed, implementation empty } public override bool CanSeek { get { return false; } } public override long Seek (long offset, System.IO.SeekOrigin origin) { throw new NotSupportedException (); } public override long Position { get { throw new NotSupportedException (); } set { throw new NotSupportedException (); } } public override long Length { get { throw new NotSupportedException (); } } public override void SetLength (long value) { throw new NotSupportedException (); } } 

ZeroStream需要额外的类OFBStream

 class ZeroStream : System.IO.Stream { public override int Read (byte[] buffer, int offset, int count) { for (int i = 0; i < count; i++) { buffer [offset + i] = 0; } return count; } public override bool CanRead { get { return true; } } ... the rest is not implemented } 

你可以像我对测试向量一样使用它：

 // NIST CAVP test vector F.4.1: OFB-AES128.Encrypt from NIST SP 800-38A RijndaelManaged aes = new RijndaelManaged (); aes.Key = FromHex ("2b7e151628aed2a6abf7158809cf4f3c"); aes.IV = FromHex ("000102030405060708090A0B0C0D0E0F"); MemoryStream testVectorStream = new MemoryStream (FromHex ( "6bc1bee22e409f96e93d7e117393172aae2d8a571e03ac9c9eb76fac45af8e5130c81c46a35ce411e5fbc1191a0a52eff69f2445df4f9b17ad2b417be66c3710")); OFBStream testOFBStream = new OFBStream (testVectorStream, aes, CryptoStreamMode.Read); MemoryStream cipherTextStream = new MemoryStream (); testOFBStream.CopyTo (cipherTextStream); Console.WriteLine (ToHex (cipherTextStream.ToArray ())); 

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请注意，流处理尚未完全测试（尚未）。