Java tutorial
package org.bouncycastle.crypto; /** * A wrapper class that allows block ciphers to be used to process data in * a piecemeal fashion. The BufferedBlockCipher outputs a block only when the * buffer is full and more data is being added, or on a doFinal. * <p> * Note: in the case where the underlying cipher is either a CFB cipher or an * OFB one the last block may not be a multiple of the block size. */ public class BufferedBlockCipher { protected byte[] buf; protected int bufOff; protected boolean forEncryption; protected BlockCipher cipher; protected boolean partialBlockOkay; protected boolean pgpCFB; /** * constructor for subclasses */ protected BufferedBlockCipher() { } /** * Create a buffered block cipher without padding. * * @param cipher the underlying block cipher this buffering object wraps. */ public BufferedBlockCipher(BlockCipher cipher) { this.cipher = cipher; buf = new byte[cipher.getBlockSize()]; bufOff = 0; // // check if we can handle partial blocks on doFinal. // String name = cipher.getAlgorithmName(); int idx = name.indexOf('/') + 1; pgpCFB = (idx > 0 && name.startsWith("PGP", idx)); if (pgpCFB || cipher instanceof StreamCipher) { partialBlockOkay = true; } else { partialBlockOkay = (idx > 0 && (name.startsWith("OpenPGP", idx))); } } /** * return the cipher this object wraps. * * @return the cipher this object wraps. */ public BlockCipher getUnderlyingCipher() { return cipher; } /** * initialise the cipher. * * @param forEncryption if true the cipher is initialised for * encryption, if false for decryption. * @param params 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(forEncryption, params); } /** * return the blocksize for the underlying cipher. * * @return the blocksize for the underlying cipher. */ public int getBlockSize() { return cipher.getBlockSize(); } /** * 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; if (pgpCFB) { if (forEncryption) { leftOver = total % buf.length - (cipher.getBlockSize() + 2); } else { leftOver = total % buf.length; } } else { leftOver = total % buf.length; } return total - leftOver; } /** * return the size of the output buffer required for an update plus a * doFinal with an input of 'length' bytes. * * @param length the length of the input. * @return the space required to accommodate a call to update and doFinal * with 'length' bytes of input. */ public int getOutputSize(int length) { // Note: Can assume partialBlockOkay is true for purposes of this calculation return length + bufOff; } /** * process a single byte, producing an output block if necessary. * * @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; buf[bufOff++] = in; if (bufOff == buf.length) { resultLen = cipher.processBlock(buf, 0, out, outOff); bufOff = 0; } return resultLen; } /** * 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 OutputLengthException("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); bufOff = 0; len -= gapLen; inOff += gapLen; while (len > buf.length) { resultLen += cipher.processBlock(in, inOff, out, outOff + resultLen); len -= blockSize; inOff += blockSize; } } System.arraycopy(in, inOff, buf, bufOff, len); bufOff += len; if (bufOff == buf.length) { resultLen += cipher.processBlock(buf, 0, out, outOff + resultLen); bufOff = 0; } return resultLen; } /** * 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, or the input is not block size aligned and should be. * @exception IllegalStateException if the underlying cipher is not * initialised. * @exception InvalidCipherTextException if padding is expected and not found. * @exception DataLengthException if the input is not block size * aligned. */ public int doFinal(byte[] out, int outOff) throws DataLengthException, IllegalStateException, InvalidCipherTextException { try { int resultLen = 0; if (outOff + bufOff > out.length) { throw new OutputLengthException("output buffer too short for doFinal()"); } if (bufOff != 0) { if (!partialBlockOkay) { throw new DataLengthException("data not block size aligned"); } cipher.processBlock(buf, 0, buf, 0); resultLen = bufOff; bufOff = 0; System.arraycopy(buf, 0, out, outOff, resultLen); } return resultLen; } finally { reset(); } } /** * Reset the buffer and cipher. After resetting the object is in the same * state as it was after the last init (if there was one). */ public void reset() { // // clean the buffer. // for (int i = 0; i < buf.length; i++) { buf[i] = 0; } bufOff = 0; // // reset the underlying cipher. // cipher.reset(); } }