package org.minicastle.crypto.modes;
import org.minicastle.crypto.BlockCipher;
import org.minicastle.crypto.CipherParameters;
import org.minicastle.crypto.DataLengthException;
/**
* 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.
* <p>
* For further info see <a href="http://www.ietf.org/rfc/rfc2440.html">RFC 2440</a>.
*/
public class OpenPGPCFBBlockCipher
implements BlockCipher
{
private byte[] IV;
private byte[] FR;
private byte[] FRE;
private byte[] tmp;
private BlockCipher cipher;
private int count;
private int blockSize;
private boolean forEncryption;
/**
* Basic constructor.
*
* @param cipher the block cipher to be used as the basis of the
* feedback mode.
*/
public OpenPGPCFBBlockCipher(
BlockCipher cipher)
{
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];
}
/**
* return the underlying block cipher that we are wrapping.
*
* @return the underlying block cipher that we are wrapping.
*/
public BlockCipher getUnderlyingCipher()
{
return cipher;
}
/**
* return the algorithm name and mode.
*
* @return the name of the underlying algorithm followed by "/PGPCFB"
* and the block size in bits.
*/
public String getAlgorithmName()
{
return cipher.getAlgorithmName() + "/OpenPGPCFB";
}
/**
* return the block size we are operating at.
*
* @return the block size we are operating at (in bytes).
*/
public int getBlockSize()
{
return cipher.getBlockSize();
}
/**
* 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.
*/
public int processBlock(
byte[] in,
int inOff,
byte[] out,
int outOff)
throws DataLengthException, IllegalStateException
{
return (forEncryption) ? encryptBlock(in, inOff, out, outOff) : decryptBlock(in, inOff, out, outOff);
}
/**
* reset the chaining vector back to the IV and reset the underlying
* cipher.
*/
public void reset()
{
count = 0;
for (int i = 0; i != FR.length; i++)
{
FR[i] = IV[i];
}
cipher.reset();
}
/**
* 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.
*/
public void init(
boolean forEncryption,
CipherParameters params)
throws IllegalArgumentException
{
this.forEncryption = forEncryption;
reset();
cipher.init(true, params);
}
/**
* 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
*/
private byte encryptByte(byte data, int blockOff)
{
return (byte)(FRE[blockOff] ^ data);
}
/**
* 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.
*/
private int encryptBlock(
byte[] in,
int inOff,
byte[] out,
int outOff)
throws DataLengthException, IllegalStateException
{
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;
}
/**
* 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.
*/
private int decryptBlock(
byte[] in,
int inOff,
byte[] out,
int outOff)
throws DataLengthException, IllegalStateException
{
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;
}
}