1 files changed, 178 insertions, 0 deletions
diff --git a/Crypto/src/crypto/modes/OfbBlockCipher.cs b/Crypto/src/crypto/modes/OfbBlockCipher.cs
new file mode 100644
index 000000000..9408a74d4
--- /dev/null
+++ b/Crypto/src/crypto/modes/OfbBlockCipher.cs
@@ -0,0 +1,178 @@
+using System;
+
+using Org.BouncyCastle.Crypto.Parameters;
+
+namespace Org.BouncyCastle.Crypto.Modes
+{
+    /**
+    * implements a Output-FeedBack (OFB) mode on top of a simple cipher.
+    */
+    public class OfbBlockCipher
+		: IBlockCipher
+    {
+        private byte[]	IV;
+        private byte[]	ofbV;
+        private byte[]	ofbOutV;
+
+        private readonly int			blockSize;
+        private readonly IBlockCipher	cipher;
+
+        /**
+        * Basic constructor.
+        *
+        * @param cipher the block cipher to be used as the basis of the
+        * feedback mode.
+        * @param blockSize the block size in bits (note: a multiple of 8)
+        */
+        public OfbBlockCipher(
+            IBlockCipher cipher,
+            int         blockSize)
+        {
+            this.cipher = cipher;
+            this.blockSize = blockSize / 8;
+
+            this.IV = new byte[cipher.GetBlockSize()];
+            this.ofbV = new byte[cipher.GetBlockSize()];
+            this.ofbOutV = new byte[cipher.GetBlockSize()];
+        }
+
+        /**
+        * return the underlying block cipher that we are wrapping.
+        *
+        * @return the underlying block cipher that we are wrapping.
+        */
+        public IBlockCipher GetUnderlyingCipher()
+        {
+            return cipher;
+        }
+
+        /**
+        * Initialise the cipher and, possibly, the initialisation vector (IV).
+        * If an IV isn't passed as part of the parameter, the IV will be all zeros.
+        * An IV which is too short is handled in FIPS compliant fashion.
+        *
+        * @param forEncryption if true the cipher is initialised for
+        *  encryption, if false for decryption.
+        * @param param the key and other data required by the cipher.
+        * @exception ArgumentException if the parameters argument is
+        * inappropriate.
+        */
+        public void Init(
+            bool				forEncryption, //ignored by this OFB mode
+            ICipherParameters	parameters)
+        {
+			if (parameters is ParametersWithIV)
+            {
+                ParametersWithIV ivParam = (ParametersWithIV)parameters;
+                byte[] iv = ivParam.GetIV();
+
+                if (iv.Length < IV.Length)
+                {
+                    // prepend the supplied IV with zeros (per FIPS PUB 81)
+                    Array.Copy(iv, 0, IV, IV.Length - iv.Length, iv.Length);
+                    for (int i = 0; i < IV.Length - iv.Length; i++)
+                    {
+                        IV[i] = 0;
+                    }
+                }
+                else
+                {
+                    Array.Copy(iv, 0, IV, 0, IV.Length);
+                }
+
+				parameters = ivParam.Parameters;
+            }
+
+			Reset();
+
+			cipher.Init(true, parameters);
+        }
+
+		/**
+        * return the algorithm name and mode.
+        *
+        * @return the name of the underlying algorithm followed by "/OFB"
+        * and the block size in bits
+        */
+        public string AlgorithmName
+        {
+            get { return cipher.AlgorithmName + "/OFB" + (blockSize * 8); }
+        }
+
+		public bool IsPartialBlockOkay
+		{
+			get { return true; }
+		}
+
+		/**
+        * return the block size we are operating at (in bytes).
+        *
+        * @return the block size we are operating at (in bytes).
+        */
+        public int GetBlockSize()
+        {
+            return blockSize;
+        }
+
+        /**
+        * Process one block of input from the array in and write it to
+        * the out array.
+        *
+        * @param in the array containing the input data.
+        * @param inOff offset into the in array the data starts at.
+        * @param out the array the output data will be copied into.
+        * @param outOff the offset into the out array the output will start at.
+        * @exception DataLengthException if there isn't enough data in in, or
+        * space in out.
+        * @exception InvalidOperationException if the cipher isn't initialised.
+        * @return the number of bytes processed and produced.
+        */
+        public int ProcessBlock(
+            byte[]	input,
+            int		inOff,
+            byte[]	output,
+            int		outOff)
+        {
+            if ((inOff + blockSize) > input.Length)
+            {
+                throw new DataLengthException("input buffer too short");
+            }
+
+            if ((outOff + blockSize) > output.Length)
+            {
+                throw new DataLengthException("output buffer too short");
+            }
+
+            cipher.ProcessBlock(ofbV, 0, ofbOutV, 0);
+
+            //
+            // XOR the ofbV with the plaintext producing the cipher text (and
+            // the next input block).
+            //
+            for (int i = 0; i < blockSize; i++)
+            {
+                output[outOff + i] = (byte)(ofbOutV[i] ^ input[inOff + i]);
+            }
+
+            //
+            // change over the input block.
+            //
+            Array.Copy(ofbV, blockSize, ofbV, 0, ofbV.Length - blockSize);
+            Array.Copy(ofbOutV, 0, ofbV, ofbV.Length - blockSize, blockSize);
+
+            return blockSize;
+        }
+
+        /**
+        * reset the feedback vector back to the IV and reset the underlying
+        * cipher.
+        */
+        public void Reset()
+        {
+            Array.Copy(IV, 0, ofbV, 0, IV.Length);
+
+            cipher.Reset();
+        }
+    }
+
+}