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CFBBlockCipher.javaAPI DocAzureus 3.0.3.47689Tue Jun 08 05:12:58 BST 2004org.bouncycastle.crypto.modes

CFBBlockCipher

public class CFBBlockCipher extends Object implements org.bouncycastle.crypto.BlockCipher
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
private boolean
encrypting
Constructors Summary
public CFBBlockCipher(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 intdecryptBlock(byte[] in, int inOff, byte[] out, int outOff)
Do the appropriate processing for CFB mode decryption.

param
in the array containing the data to be decrypted.
param
inOff offset into the in array the data starts at.
param
out the array the encrypted 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);

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

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

        return blockSize;
    
public intencryptBlock(byte[] in, int inOff, byte[] out, int outOff)
Do the appropriate processing for CFB mode encryption.

param
in the array containing the data to be encrypted.
param
inOff offset into the in array the data starts at.
param
out the array the encrypted 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 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;
    
public org.bouncycastle.crypto.BlockCiphergetUnderlyingCipher()
return the underlying block cipher that we are wrapping.

return
the underlying block cipher that we are wrapping.

        return cipher;
    
public voidinit(boolean encrypting, 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
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
IllegalArgumentException if the params argument is inappropriate.

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

                if (iv.length < IV.length)
                {
					// prepend the supplied IV with zeros (per FIPS PUB 81)
                    System.arraycopy(iv, 0, IV, IV.length - iv.length, iv.length);
					for (int i = 0; i < IV.length - iv.length; i++)
					{
						IV[i] = 0;
					}
                }
                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.

        return (encrypting) ? encryptBlock(in, inOff, out, outOff) : decryptBlock(in, inOff, out, outOff);
    
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();