package org.bouncycastle.crypto.modes;

import org.bouncycastle.crypto.BlockCipher;
import org.bouncycastle.crypto.BufferedBlockCipher;
import org.bouncycastle.crypto.DataLengthException;
import org.bouncycastle.crypto.InvalidCipherTextException;

A Cipher Text Stealing (CTS) mode cipher. CTS allows block ciphers to be used to produce cipher text which is the same length as the plain text.
/** * A Cipher Text Stealing (CTS) mode cipher. CTS allows block ciphers to * be used to produce cipher text which is the same length as the plain text. */
public class CTSBlockCipher extends BufferedBlockCipher { private int blockSize;
Create a buffered block cipher that uses Cipher Text Stealing
Params:
  • cipher – the underlying block cipher this buffering object wraps.
/** * Create a buffered block cipher that uses Cipher Text Stealing * * @param cipher the underlying block cipher this buffering object wraps. */
public CTSBlockCipher( BlockCipher cipher) { if ((cipher instanceof OFBBlockCipher) || (cipher instanceof CFBBlockCipher)) { throw new IllegalArgumentException("CTSBlockCipher can only accept ECB, or CBC ciphers"); } this.cipher = cipher; blockSize = cipher.getBlockSize(); buf = new byte[blockSize * 2]; bufOff = 0; }
return the size of the output buffer required for an update an input of len bytes.
Params:
  • len – the length of the input.
Returns:the space required to accommodate a call to update with len bytes of input.
/** * return the size of the output buffer required for an update * an input of len bytes. * * @param len the length of the input. * @return the space required to accommodate a call to update * with len bytes of input. */
public int getUpdateOutputSize( int len) { int total = len + bufOff; int leftOver = total % buf.length; if (leftOver == 0) { return total - buf.length; } return total - leftOver; }
return the size of the output buffer required for an update plus a doFinal with an input of len bytes.
Params:
  • len – the length of the input.
Returns:the space required to accommodate a call to update and doFinal with len bytes of input.
/** * return the size of the output buffer required for an update plus a * doFinal with an input of len bytes. * * @param len the length of the input. * @return the space required to accommodate a call to update and doFinal * with len bytes of input. */
public int getOutputSize( int len) { return len + bufOff; }
process a single byte, producing an output block if neccessary.
Params:
  • in – the input byte.
  • out – the space for any output that might be produced.
  • outOff – the offset from which the output will be copied.
Throws:
Returns:the number of output bytes copied to out.
/** * process a single byte, producing an output block if neccessary. * * @param in the input byte. * @param out the space for any output that might be produced. * @param outOff the offset from which the output will be copied. * @return the number of output bytes copied to out. * @exception DataLengthException if there isn't enough space in out. * @exception IllegalStateException if the cipher isn't initialised. */
public int processByte( byte in, byte[] out, int outOff) throws DataLengthException, IllegalStateException { int resultLen = 0; if (bufOff == buf.length) { resultLen = cipher.processBlock(buf, 0, out, outOff); System.arraycopy(buf, blockSize, buf, 0, blockSize); bufOff = blockSize; } buf[bufOff++] = in; return resultLen; }
process an array of bytes, producing output if necessary.
Params:
  • in – the input byte array.
  • inOff – the offset at which the input data starts.
  • len – the number of bytes to be copied out of the input array.
  • out – the space for any output that might be produced.
  • outOff – the offset from which the output will be copied.
Throws:
Returns:the number of output bytes copied to out.
/** * process an array of bytes, producing output if necessary. * * @param in the input byte array. * @param inOff the offset at which the input data starts. * @param len the number of bytes to be copied out of the input array. * @param out the space for any output that might be produced. * @param outOff the offset from which the output will be copied. * @return the number of output bytes copied to out. * @exception DataLengthException if there isn't enough space in out. * @exception IllegalStateException if the cipher isn't initialised. */
public int processBytes( byte[] in, int inOff, int len, byte[] out, int outOff) throws DataLengthException, IllegalStateException { if (len < 0) { throw new IllegalArgumentException("Can't have a negative input length!"); } int blockSize = getBlockSize(); int length = getUpdateOutputSize(len); if (length > 0) { if ((outOff + length) > out.length) { throw new DataLengthException("output buffer too short"); } } int resultLen = 0; int gapLen = buf.length - bufOff; if (len > gapLen) { System.arraycopy(in, inOff, buf, bufOff, gapLen); resultLen += cipher.processBlock(buf, 0, out, outOff); System.arraycopy(buf, blockSize, buf, 0, blockSize); bufOff = blockSize; len -= gapLen; inOff += gapLen; while (len > blockSize) { System.arraycopy(in, inOff, buf, bufOff, blockSize); resultLen += cipher.processBlock(buf, 0, out, outOff + resultLen); System.arraycopy(buf, blockSize, buf, 0, blockSize); len -= blockSize; inOff += blockSize; } } System.arraycopy(in, inOff, buf, bufOff, len); bufOff += len; return resultLen; }
Process the last block in the buffer.
Params:
  • out – the array the block currently being held is copied into.
  • outOff – the offset at which the copying starts.
Throws:
Returns:the number of output bytes copied to out.
/** * Process the last block in the buffer. * * @param out the array the block currently being held is copied into. * @param outOff the offset at which the copying starts. * @return the number of output bytes copied to out. * @exception DataLengthException if there is insufficient space in out for * the output. * @exception IllegalStateException if the underlying cipher is not * initialised. * @exception InvalidCipherTextException if cipher text decrypts wrongly (in * case the exception will never get thrown). */
public int doFinal( byte[] out, int outOff) throws DataLengthException, IllegalStateException, InvalidCipherTextException { if (bufOff + outOff > out.length) { throw new DataLengthException("output buffer to small in doFinal"); } int blockSize = cipher.getBlockSize(); int len = bufOff - blockSize; byte[] block = new byte[blockSize]; if (forEncryption) { cipher.processBlock(buf, 0, block, 0); if (bufOff < blockSize) { throw new DataLengthException("need at least one block of input for CTS"); } for (int i = bufOff; i != buf.length; i++) { buf[i] = block[i - blockSize]; } for (int i = blockSize; i != bufOff; i++) { buf[i] ^= block[i - blockSize]; } if (cipher instanceof CBCBlockCipher) { BlockCipher c = ((CBCBlockCipher)cipher).getUnderlyingCipher(); c.processBlock(buf, blockSize, out, outOff); } else { cipher.processBlock(buf, blockSize, out, outOff); } System.arraycopy(block, 0, out, outOff + blockSize, len); } else { byte[] lastBlock = new byte[blockSize]; if (cipher instanceof CBCBlockCipher) { BlockCipher c = ((CBCBlockCipher)cipher).getUnderlyingCipher(); c.processBlock(buf, 0, block, 0); } else { cipher.processBlock(buf, 0, block, 0); } for (int i = blockSize; i != bufOff; i++) { lastBlock[i - blockSize] = (byte)(block[i - blockSize] ^ buf[i]); } System.arraycopy(buf, blockSize, block, 0, len); cipher.processBlock(block, 0, out, outOff); System.arraycopy(lastBlock, 0, out, outOff + blockSize, len); } int offset = bufOff; reset(); return offset; } }