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OpenPGPCFBBlockCipher.javaAPI DocAzureus 3.0.3.49667Tue Jun 08 05:12:58 BST 2004org.bouncycastle.crypto.modes

OpenPGPCFBBlockCipher

public class OpenPGPCFBBlockCipher extends Object implements org.bouncycastle.crypto.BlockCipher
Implements OpenPGP's rather strange version of Cipher-FeedBack (CFB) mode on top of a simple cipher. This class assumes the IV has been prepended to the data stream already, and just accomodates the reset after (blockSize + 2) bytes have been read.

For further info see RFC 2440.

Fields Summary
private byte[]
IV
private byte[]
FR
private byte[]
FRE
private byte[]
tmp
private org.bouncycastle.crypto.BlockCipher
cipher
private int
count
private int
blockSize
private boolean
forEncryption
Constructors Summary
public OpenPGPCFBBlockCipher(org.bouncycastle.crypto.BlockCipher cipher)
Basic constructor.

param
cipher the block cipher to be used as the basis of the feedback mode.

        this.cipher = cipher;

        this.blockSize = cipher.getBlockSize();
        this.IV = new byte[blockSize];
        this.FR = new byte[blockSize];
        this.FRE = new byte[blockSize];
        this.tmp = new byte[blockSize];
Methods Summary
private intdecryptBlock(byte[] in, int inOff, byte[] out, int outOff)
Do the appropriate processing for CFB IV 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");
        }
        
        if (count > blockSize)
        {
            // copy in buffer so that this mode works if in and out are the same 
            System.arraycopy(in, inOff, tmp, 0, blockSize);

            out[outOff + 0] = encryptByte(tmp[0], blockSize - 2);
            out[outOff + 1] = encryptByte(tmp[1], blockSize - 1);

            System.arraycopy(tmp, 0, FR, blockSize - 2, 2);

            cipher.processBlock(FR, 0, FRE, 0);
            
            for (int n = 2; n < blockSize; n++) 
            {
                out[outOff + n] = encryptByte(tmp[n], n - 2);
            }
            
            System.arraycopy(tmp, 2, FR, 0, blockSize - 2);
        } 
        else if (count == 0)
        {
			cipher.processBlock(FR, 0, FRE, 0);
			
            for (int n = 0; n < blockSize; n++) 
            {
                FR[n] = in[inOff + n];
                out[n] = encryptByte(in[inOff + n], n);
            }
            
            count += blockSize;
        }
        else if (count == blockSize)
        {
			System.arraycopy(in, inOff, tmp, 0, blockSize);
			
			cipher.processBlock(FR, 0, FRE, 0);

			out[outOff + 0] = encryptByte(tmp[0], 0);
			out[outOff + 1] = encryptByte(tmp[1], 1);
			
            System.arraycopy(FR, 2, FR, 0, blockSize - 2);
            
            FR[blockSize - 2] = tmp[0];
            FR[blockSize - 1] = tmp[1];

            cipher.processBlock(FR, 0, FRE, 0);

            for (int n = 2; n < blockSize; n++) 
            {
                FR[n - 2] = in[inOff + n];
                out[outOff + n] = encryptByte(in[inOff + n], n - 2);
            }

            count += blockSize;;
        }
        
        return blockSize;
private intencryptBlock(byte[] in, int inOff, byte[] out, int outOff)
Do the appropriate processing for CFB IV 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");
        }
        
        if (count > blockSize)
        {
            FR[blockSize - 2] = out[outOff] = encryptByte(in[inOff], blockSize - 2);
            FR[blockSize - 1] = out[outOff + 1] = encryptByte(in[inOff + 1], blockSize - 1);

            cipher.processBlock(FR, 0, FRE, 0);

            for (int n = 2; n < blockSize; n++) 
            {
                out[outOff + n] = encryptByte(in[inOff + n], n - 2);
            }
            
            System.arraycopy(out, outOff + 2, FR, 0, blockSize - 2);
        }
        else if (count == 0)
        {
            cipher.processBlock(FR, 0, FRE, 0);

            for (int n = 0; n < blockSize; n++) 
            {
                out[outOff + n] = encryptByte(in[inOff + n], n);
            }
            
            System.arraycopy(out, outOff, FR, 0, blockSize);

            count += blockSize;
        }
        else if (count == blockSize)
        {
            cipher.processBlock(FR, 0, FRE, 0);

            out[outOff] = encryptByte(in[inOff], 0);
            out[outOff + 1] = encryptByte(in[inOff + 1], 1);

            //
            // do reset
            //
            System.arraycopy(FR, 2, FR, 0, blockSize - 2);
            System.arraycopy(out, outOff, FR, blockSize - 2, 2);

            cipher.processBlock(FR, 0, FRE, 0);

            for (int n = 2; n < blockSize; n++) 
            {
                out[outOff + n] = encryptByte(in[inOff + n], n - 2);
            }

            System.arraycopy(out, outOff + 2, FR, 0, blockSize - 2);

            count += blockSize;
        }
        
        return blockSize;
private byteencryptByte(byte data, int blockOff)
Encrypt one byte of data according to CFB mode.

param
data the byte to encrypt
param
where am i in the current block, determines when to resync the block
returns
the encrypted byte

        return (byte)(FRE[blockOff] ^ data);
public java.lang.StringgetAlgorithmName()
return the algorithm name and mode.

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

        return cipher.getAlgorithmName() + "/OpenPGPCFB";
public intgetBlockSize()
return the block size we are operating at.

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

        return cipher.getBlockSize();
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 forEncryption, 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.forEncryption = forEncryption;
     
        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 (forEncryption) ? 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.

        count = 0;

        for (int i = 0; i != FR.length; i++)
        {
            FR[i] = IV[i];
        }

        cipher.reset();