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213
iTechSharp/srcbc/crypto/macs/CbcBlockCipherMac.cs
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213
iTechSharp/srcbc/crypto/macs/CbcBlockCipherMac.cs
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using System;
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using Org.BouncyCastle.Crypto.Modes;
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using Org.BouncyCastle.Crypto.Paddings;
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namespace Org.BouncyCastle.Crypto.Macs
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{
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/**
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* standard CBC Block Cipher MAC - if no padding is specified the default of
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* pad of zeroes is used.
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*/
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public class CbcBlockCipherMac
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: IMac
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{
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private byte[] mac;
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private byte[] Buffer;
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private int bufOff;
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private IBlockCipher cipher;
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private IBlockCipherPadding padding;
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private int macSize;
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/**
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* create a standard MAC based on a CBC block cipher. This will produce an
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* authentication code half the length of the block size of the cipher.
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*
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* @param cipher the cipher to be used as the basis of the MAC generation.
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*/
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public CbcBlockCipherMac(
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IBlockCipher cipher)
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: this(cipher, (cipher.GetBlockSize() * 8) / 2, null)
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{
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}
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/**
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* create a standard MAC based on a CBC block cipher. This will produce an
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* authentication code half the length of the block size of the cipher.
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*
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* @param cipher the cipher to be used as the basis of the MAC generation.
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* @param padding the padding to be used to complete the last block.
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*/
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public CbcBlockCipherMac(
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IBlockCipher cipher,
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IBlockCipherPadding padding)
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: this(cipher, (cipher.GetBlockSize() * 8) / 2, padding)
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{
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}
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/**
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* create a standard MAC based on a block cipher with the size of the
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* MAC been given in bits. This class uses CBC mode as the basis for the
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* MAC generation.
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* <p>
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* Note: the size of the MAC must be at least 24 bits (FIPS Publication 81),
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* or 16 bits if being used as a data authenticator (FIPS Publication 113),
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* and in general should be less than the size of the block cipher as it reduces
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* the chance of an exhaustive attack (see Handbook of Applied Cryptography).
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* </p>
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* @param cipher the cipher to be used as the basis of the MAC generation.
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* @param macSizeInBits the size of the MAC in bits, must be a multiple of 8.
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*/
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public CbcBlockCipherMac(
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IBlockCipher cipher,
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int macSizeInBits)
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: this(cipher, macSizeInBits, null)
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{
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}
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/**
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* create a standard MAC based on a block cipher with the size of the
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* MAC been given in bits. This class uses CBC mode as the basis for the
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* MAC generation.
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* <p>
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* Note: the size of the MAC must be at least 24 bits (FIPS Publication 81),
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* or 16 bits if being used as a data authenticator (FIPS Publication 113),
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* and in general should be less than the size of the block cipher as it reduces
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* the chance of an exhaustive attack (see Handbook of Applied Cryptography).
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* </p>
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* @param cipher the cipher to be used as the basis of the MAC generation.
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* @param macSizeInBits the size of the MAC in bits, must be a multiple of 8.
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* @param padding the padding to be used to complete the last block.
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*/
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public CbcBlockCipherMac(
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IBlockCipher cipher,
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int macSizeInBits,
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IBlockCipherPadding padding)
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{
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if ((macSizeInBits % 8) != 0)
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throw new ArgumentException("MAC size must be multiple of 8");
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this.cipher = new CbcBlockCipher(cipher);
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this.padding = padding;
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this.macSize = macSizeInBits / 8;
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mac = new byte[cipher.GetBlockSize()];
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Buffer = new byte[cipher.GetBlockSize()];
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bufOff = 0;
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}
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public string AlgorithmName
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{
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get { return cipher.AlgorithmName; }
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}
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public void Init(
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ICipherParameters parameters)
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{
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Reset();
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cipher.Init(true, parameters);
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}
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public int GetMacSize()
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{
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return macSize;
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}
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public void Update(
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byte input)
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{
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if (bufOff == Buffer.Length)
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{
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cipher.ProcessBlock(Buffer, 0, mac, 0);
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bufOff = 0;
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}
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Buffer[bufOff++] = input;
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}
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public void BlockUpdate(
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byte[] input,
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int inOff,
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int len)
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{
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if (len < 0)
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throw new ArgumentException("Can't have a negative input length!");
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int blockSize = cipher.GetBlockSize();
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int resultLen = 0;
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int gapLen = blockSize - bufOff;
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if (len > gapLen)
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{
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Array.Copy(input, inOff, Buffer, bufOff, gapLen);
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resultLen += cipher.ProcessBlock(Buffer, 0, mac, 0);
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bufOff = 0;
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len -= gapLen;
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inOff += gapLen;
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while (len > blockSize)
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{
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resultLen += cipher.ProcessBlock(input, inOff, mac, 0);
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len -= blockSize;
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inOff += blockSize;
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}
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}
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Array.Copy(input, inOff, Buffer, bufOff, len);
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bufOff += len;
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}
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public int DoFinal(
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byte[] output,
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int outOff)
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{
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int blockSize = cipher.GetBlockSize();
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if (padding == null)
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{
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// pad with zeroes
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while (bufOff < blockSize)
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{
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Buffer[bufOff++] = 0;
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}
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}
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else
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{
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if (bufOff == blockSize)
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{
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cipher.ProcessBlock(Buffer, 0, mac, 0);
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bufOff = 0;
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}
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padding.AddPadding(Buffer, bufOff);
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}
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cipher.ProcessBlock(Buffer, 0, mac, 0);
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Array.Copy(mac, 0, output, outOff, macSize);
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Reset();
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return macSize;
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}
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/**
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* Reset the mac generator.
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*/
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public void Reset()
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{
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// Clear the buffer.
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Array.Clear(Buffer, 0, Buffer.Length);
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bufOff = 0;
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// Reset the underlying cipher.
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cipher.Reset();
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}
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}
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}
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