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240
iTechSharp/srcbc/crypto/macs/CMac.cs
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240
iTechSharp/srcbc/crypto/macs/CMac.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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* CMAC - as specified at www.nuee.nagoya-u.ac.jp/labs/tiwata/omac/omac.html
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* <p>
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* CMAC is analogous to OMAC1 - see also en.wikipedia.org/wiki/CMAC
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* </p><p>
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* CMAC is a NIST recomendation - see
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* csrc.nist.gov/CryptoToolkit/modes/800-38_Series_Publications/SP800-38B.pdf
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* </p><p>
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* CMAC/OMAC1 is a blockcipher-based message authentication code designed and
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* analyzed by Tetsu Iwata and Kaoru Kurosawa.
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* </p><p>
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* CMAC/OMAC1 is a simple variant of the CBC MAC (Cipher Block Chaining Message
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* Authentication Code). OMAC stands for One-Key CBC MAC.
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* </p><p>
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* It supports 128- or 64-bits block ciphers, with any key size, and returns
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* a MAC with dimension less or equal to the block size of the underlying
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* cipher.
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* </p>
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*/
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public class CMac
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: IMac
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{
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private const byte CONSTANT_128 = (byte)0x87;
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private const byte CONSTANT_64 = (byte)0x1b;
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private byte[] ZEROES;
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private byte[] mac;
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private byte[] buf;
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private int bufOff;
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private IBlockCipher cipher;
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private int macSize;
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private byte[] L, Lu, Lu2;
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/**
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* create a standard MAC based on a CBC block cipher (64 or 128 bit block).
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* This will produce an authentication code the length of the block size
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* 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 CMac(
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IBlockCipher cipher)
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: this(cipher, cipher.GetBlockSize() * 8)
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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.
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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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*
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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 and @lt;= 128.
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*/
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public CMac(
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IBlockCipher cipher,
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int macSizeInBits)
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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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if (macSizeInBits > (cipher.GetBlockSize() * 8))
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{
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throw new ArgumentException(
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"MAC size must be less or equal to "
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+ (cipher.GetBlockSize() * 8));
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}
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if (cipher.GetBlockSize() != 8 && cipher.GetBlockSize() != 16)
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{
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throw new ArgumentException(
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"Block size must be either 64 or 128 bits");
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}
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this.cipher = new CbcBlockCipher(cipher);
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this.macSize = macSizeInBits / 8;
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mac = new byte[cipher.GetBlockSize()];
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buf = new byte[cipher.GetBlockSize()];
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ZEROES = 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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private byte[] doubleLu(
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byte[] inBytes)
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{
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int FirstBit = (inBytes[0] & 0xFF) >> 7;
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byte[] ret = new byte[inBytes.Length];
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for (int i = 0; i < inBytes.Length - 1; i++)
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{
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ret[i] = (byte)((inBytes[i] << 1) + ((inBytes[i + 1] & 0xFF) >> 7));
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}
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ret[inBytes.Length - 1] = (byte)(inBytes[inBytes.Length - 1] << 1);
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if (FirstBit == 1)
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{
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ret[inBytes.Length - 1] ^= inBytes.Length == 16 ? CONSTANT_128 : CONSTANT_64;
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}
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return ret;
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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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//initializes the L, Lu, Lu2 numbers
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L = new byte[ZEROES.Length];
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cipher.ProcessBlock(ZEROES, 0, L, 0);
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Lu = doubleLu(L);
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Lu2 = doubleLu(Lu);
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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 == buf.Length)
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{
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cipher.ProcessBlock(buf, 0, mac, 0);
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bufOff = 0;
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}
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buf[bufOff++] = input;
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}
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public void BlockUpdate(
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byte[] inBytes,
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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 gapLen = blockSize - bufOff;
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if (len > gapLen)
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{
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Array.Copy(inBytes, inOff, buf, bufOff, gapLen);
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cipher.ProcessBlock(buf, 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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cipher.ProcessBlock(inBytes, 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(inBytes, inOff, buf, bufOff, len);
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bufOff += len;
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}
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public int DoFinal(
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byte[] outBytes,
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int outOff)
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{
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int blockSize = cipher.GetBlockSize();
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byte[] lu;
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if (bufOff == blockSize)
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{
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lu = Lu;
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}
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else
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{
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new ISO7816d4Padding().AddPadding(buf, bufOff);
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lu = Lu2;
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}
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for (int i = 0; i < mac.Length; i++)
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{
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buf[i] ^= lu[i];
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}
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cipher.ProcessBlock(buf, 0, mac, 0);
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Array.Copy(mac, 0, outBytes, 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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/*
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* clean the buffer.
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*/
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Array.Clear(buf, 0, buf.Length);
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bufOff = 0;
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/*
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* Reset the underlying cipher.
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*/
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cipher.Reset();
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}
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}
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}
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