1 files changed, 273 insertions, 0 deletions
diff --git a/Crypto/src/crypto/encodings/ISO9796d1Encoding.cs b/Crypto/src/crypto/encodings/ISO9796d1Encoding.cs
new file mode 100644
index 000000000..30e988356
--- /dev/null
+++ b/Crypto/src/crypto/encodings/ISO9796d1Encoding.cs
@@ -0,0 +1,273 @@
+using System;
+using Org.BouncyCastle.Crypto;
+using Org.BouncyCastle.Crypto.Parameters;
+using Org.BouncyCastle.Math;
+
+namespace Org.BouncyCastle.Crypto.Encodings
+{
+	/**
+	* ISO 9796-1 padding. Note in the light of recent results you should
+	* only use this with RSA (rather than the "simpler" Rabin keys) and you
+	* should never use it with anything other than a hash (ie. even if the
+	* message is small don't sign the message, sign it's hash) or some "random"
+	* value. See your favorite search engine for details.
+	*/
+	public class ISO9796d1Encoding
+		: IAsymmetricBlockCipher
+	{
+		private static readonly BigInteger Sixteen = BigInteger.ValueOf(16);
+		private static readonly BigInteger Six = BigInteger.ValueOf(6);
+
+		private static readonly byte[] shadows = { 0xe, 0x3, 0x5, 0x8, 0x9, 0x4, 0x2, 0xf,
+			0x0, 0xd, 0xb, 0x6, 0x7, 0xa, 0xc, 0x1 };
+		private static readonly byte[] inverse = { 0x8, 0xf, 0x6, 0x1, 0x5, 0x2, 0xb, 0xc,
+			0x3, 0x4, 0xd, 0xa, 0xe, 0x9, 0x0, 0x7 };
+
+		private readonly IAsymmetricBlockCipher engine;
+		private bool forEncryption;
+		private int bitSize;
+		private int padBits = 0;
+		private BigInteger modulus;
+
+		public ISO9796d1Encoding(
+			IAsymmetricBlockCipher   cipher)
+		{
+			this.engine = cipher;
+		}
+
+		public string AlgorithmName
+		{
+			get { return engine.AlgorithmName + "/ISO9796-1Padding"; }
+		}
+
+		public IAsymmetricBlockCipher GetUnderlyingCipher()
+		{
+			return engine;
+		}
+
+		public void Init(
+			bool				forEncryption,
+			ICipherParameters	parameters)
+		{
+			RsaKeyParameters kParam;
+			if (parameters is ParametersWithRandom)
+			{
+				ParametersWithRandom rParam = (ParametersWithRandom)parameters;
+				kParam = (RsaKeyParameters)rParam.Parameters;
+			}
+			else
+			{
+				kParam = (RsaKeyParameters)parameters;
+			}
+
+			engine.Init(forEncryption, parameters);
+
+			modulus = kParam.Modulus;
+			bitSize = modulus.BitLength;
+
+			this.forEncryption = forEncryption;
+		}
+
+		/**
+		* return the input block size. The largest message we can process
+		* is (key_size_in_bits + 3)/16, which in our world comes to
+		* key_size_in_bytes / 2.
+		*/
+		public int GetInputBlockSize()
+		{
+			int baseBlockSize = engine.GetInputBlockSize();
+
+			if (forEncryption)
+			{
+				return (baseBlockSize + 1) / 2;
+			}
+			else
+			{
+				return baseBlockSize;
+			}
+		}
+
+		/**
+		* return the maximum possible size for the output.
+		*/
+		public int GetOutputBlockSize()
+		{
+			int baseBlockSize = engine.GetOutputBlockSize();
+
+			if (forEncryption)
+			{
+				return baseBlockSize;
+			}
+			else
+			{
+				return (baseBlockSize + 1) / 2;
+			}
+		}
+
+		/**
+		* set the number of bits in the next message to be treated as
+		* pad bits.
+		*/
+		public void SetPadBits(
+			int     padBits)
+		{
+			if (padBits > 7)
+			{
+				throw new ArgumentException("padBits > 7");
+			}
+
+			this.padBits = padBits;
+		}
+
+		/**
+		* retrieve the number of pad bits in the last decoded message.
+		*/
+		public int GetPadBits()
+		{
+			return padBits;
+		}
+
+		public byte[] ProcessBlock(
+			byte[]	input,
+			int		inOff,
+			int		length)
+		{
+			if (forEncryption)
+			{
+				return EncodeBlock(input, inOff, length);
+			}
+			else
+			{
+				return DecodeBlock(input, inOff, length);
+			}
+		}
+
+		private byte[] EncodeBlock(
+			byte[]	input,
+			int		inOff,
+			int		inLen)
+		{
+			byte[]  block = new byte[(bitSize + 7) / 8];
+			int     r = padBits + 1;
+			int     z = inLen;
+			int     t = (bitSize + 13) / 16;
+
+			for (int i = 0; i < t; i += z)
+			{
+				if (i > t - z)
+				{
+					Array.Copy(input, inOff + inLen - (t - i),
+						block, block.Length - t, t - i);
+				}
+				else
+				{
+					Array.Copy(input, inOff, block, block.Length - (i + z), z);
+				}
+			}
+
+			for (int i = block.Length - 2 * t; i != block.Length; i += 2)
+			{
+				byte val = block[block.Length - t + i / 2];
+
+				block[i] = (byte)((shadows[(uint) (val & 0xff) >> 4] << 4)
+					| shadows[val & 0x0f]);
+				block[i + 1] = val;
+			}
+
+			block[block.Length - 2 * z] ^= (byte) r;
+			block[block.Length - 1] = (byte)((block[block.Length - 1] << 4) | 0x06);
+
+			int maxBit = (8 - (bitSize - 1) % 8);
+			int offSet = 0;
+
+			if (maxBit != 8)
+			{
+				block[0] &= (byte) ((ushort) 0xff >> maxBit);
+				block[0] |= (byte) ((ushort) 0x80 >> maxBit);
+			}
+			else
+			{
+				block[0] = 0x00;
+				block[1] |= 0x80;
+				offSet = 1;
+			}
+
+			return engine.ProcessBlock(block, offSet, block.Length - offSet);
+		}
+
+		/**
+		* @exception InvalidCipherTextException if the decrypted block is not a valid ISO 9796 bit string
+		*/
+		private byte[] DecodeBlock(
+			byte[]	input,
+			int		inOff,
+			int		inLen)
+		{
+			byte[]  block = engine.ProcessBlock(input, inOff, inLen);
+			int     r = 1;
+			int     t = (bitSize + 13) / 16;
+
+			BigInteger iS = new BigInteger(1, block);
+			BigInteger iR;
+			if (iS.Mod(Sixteen).Equals(Six))
+			{
+				iR = iS;
+			}
+			else
+			{
+				iR = modulus.Subtract(iS);
+
+				if (!iR.Mod(Sixteen).Equals(Six))
+					throw new InvalidCipherTextException("resulting integer iS or (modulus - iS) is not congruent to 6 mod 16");
+			}
+
+			block = iR.ToByteArrayUnsigned();
+
+			if ((block[block.Length - 1] & 0x0f) != 0x6)
+				throw new InvalidCipherTextException("invalid forcing byte in block");
+
+			block[block.Length - 1] =
+				(byte)(((ushort)(block[block.Length - 1] & 0xff) >> 4)
+				| ((inverse[(block[block.Length - 2] & 0xff) >> 4]) << 4));
+
+			block[0] = (byte)((shadows[(uint) (block[1] & 0xff) >> 4] << 4)
+				| shadows[block[1] & 0x0f]);
+
+			bool boundaryFound = false;
+			int boundary = 0;
+
+			for (int i = block.Length - 1; i >= block.Length - 2 * t; i -= 2)
+			{
+				int val = ((shadows[(uint) (block[i] & 0xff) >> 4] << 4)
+					| shadows[block[i] & 0x0f]);
+
+				if (((block[i - 1] ^ val) & 0xff) != 0)
+				{
+					if (!boundaryFound)
+					{
+						boundaryFound = true;
+						r = (block[i - 1] ^ val) & 0xff;
+						boundary = i - 1;
+					}
+					else
+					{
+						throw new InvalidCipherTextException("invalid tsums in block");
+					}
+				}
+			}
+
+			block[boundary] = 0;
+
+			byte[] nblock = new byte[(block.Length - boundary) / 2];
+
+			for (int i = 0; i < nblock.Length; i++)
+			{
+				nblock[i] = block[2 * i + boundary + 1];
+			}
+
+			padBits = r - 1;
+
+			return nblock;
+		}
+	}
+}