diff options
Diffstat (limited to 'libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/modes/CTSBlockCipher.java')
| -rw-r--r-- | libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/modes/CTSBlockCipher.java | 287 |
1 files changed, 287 insertions, 0 deletions
diff --git a/libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/modes/CTSBlockCipher.java b/libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/modes/CTSBlockCipher.java new file mode 100644 index 000000000..d56fd10bc --- /dev/null +++ b/libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/modes/CTSBlockCipher.java @@ -0,0 +1,287 @@ +package org.spongycastle.crypto.modes; + +import org.spongycastle.crypto.BlockCipher; +import org.spongycastle.crypto.BufferedBlockCipher; +import org.spongycastle.crypto.DataLengthException; +import org.spongycastle.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. + */ +public class CTSBlockCipher + extends BufferedBlockCipher +{ + private int blockSize; + + /** + * 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) || (cipher instanceof SICBlockCipher)) + { + // TODO: This is broken - need to introduce marker interface to differentiate block cipher primitive from mode? + 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. + * + * @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. + * + * @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 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; + + 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. + * + * @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. + * + * @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) + { + if (bufOff < blockSize) + { + throw new DataLengthException("need at least one block of input for CTS"); + } + + cipher.processBlock(buf, 0, block, 0); + + if (bufOff > blockSize) + { + 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 + { + System.arraycopy(block, 0, out, outOff, blockSize); + } + } + else + { + if (bufOff < blockSize) + { + throw new DataLengthException("need at least one block of input for CTS"); + } + + byte[] lastBlock = new byte[blockSize]; + + if (bufOff > 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); + } + else + { + cipher.processBlock(buf, 0, block, 0); + + System.arraycopy(block, 0, out, outOff, blockSize); + } + } + + int offset = bufOff; + + reset(); + + return offset; + } +} |