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CFBBlockCipherMac.javaAPI DocAndroid 1.5 API10859Wed May 06 22:41:06 BST 2009org.bouncycastle.crypto.macs

MacCFBBlockCipher

public class MacCFBBlockCipher extends Object
implements a Cipher-FeedBack (CFB) mode on top of a simple cipher.

Fields Summary
private byte[]
IV
private byte[]
cfbV
private byte[]
cfbOutV
private int
blockSize
private org.bouncycastle.crypto.BlockCipher
cipher
Constructors Summary
public MacCFBBlockCipher(org.bouncycastle.crypto.BlockCipher cipher, int bitBlockSize)
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)


                                      
     
                 
                         
    
        this.cipher = cipher;
        this.blockSize = bitBlockSize / 8;

        this.IV = new byte[cipher.getBlockSize()];
        this.cfbV = new byte[cipher.getBlockSize()];
        this.cfbOutV = new byte[cipher.getBlockSize()];
Methods Summary
public java.lang.StringgetAlgorithmName()
return the algorithm name and mode.

return
the name of the underlying algorithm followed by "/CFB" and the block size in bits.

        return cipher.getAlgorithmName() + "/CFB" + (blockSize * 8);
public intgetBlockSize()
return the block size we are operating at.

return
the block size we are operating at (in bytes).

        return blockSize;
voidgetMacBlock(byte[] mac)

        cipher.processBlock(cfbV, 0, mac, 0);
public voidinit(org.bouncycastle.crypto.CipherParameters params)
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
param the key and other data required by the cipher.
exception
IllegalArgumentException if the params argument is inappropriate.

        if (params instanceof ParametersWithIV)
        {
                ParametersWithIV ivParam = (ParametersWithIV)params;
                byte[]      iv = ivParam.getIV();

                if (iv.length < IV.length)
                {
                    System.arraycopy(iv, 0, IV, IV.length - iv.length, iv.length);
                }
                else
                {
                    System.arraycopy(iv, 0, IV, 0, IV.length);
                }

                reset();

                cipher.init(true, ivParam.getParameters());
        }
        else
        {
                reset();

                cipher.init(true, params);
        }
public intprocessBlock(byte[] in, int inOff, byte[] out, int outOff)
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
IllegalStateException if the cipher isn't initialised.
return
the number of bytes processed and produced.

        if ((inOff + blockSize) > in.length)
        {
            throw new DataLengthException("input buffer too short");
        }

        if ((outOff + blockSize) > out.length)
        {
            throw new DataLengthException("output buffer too short");
        }

        cipher.processBlock(cfbV, 0, cfbOutV, 0);

        //
        // XOR the cfbV with the plaintext producing the cipher text
        //
        for (int i = 0; i < blockSize; i++)
        {
            out[outOff + i] = (byte)(cfbOutV[i] ^ in[inOff + i]);
        }

        //
        // change over the input block.
        //
        System.arraycopy(cfbV, blockSize, cfbV, 0, cfbV.length - blockSize);
        System.arraycopy(out, outOff, cfbV, cfbV.length - blockSize, blockSize);

        return blockSize;
public voidreset()
reset the chaining vector back to the IV and reset the underlying cipher.

        System.arraycopy(IV, 0, cfbV, 0, IV.length);

        cipher.reset();