This mode is implemented independently of a particular cipher. * Ciphers to which this mode should apply (e.g., DES) must be * plugged-in using the constructor. * *
NOTE: This class does not deal with buffering or padding.
*
* @author Gigi Ankeny
*/
class CipherBlockChaining extends FeedbackCipher {
/*
* random bytes that are initialized with iv
*/
protected byte[] r;
/*
* output buffer
*/
private byte[] k;
// variables for save/restore calls
private byte[] rSave = null;
CipherBlockChaining(SymmetricCipher embeddedCipher) {
super(embeddedCipher);
k = new byte[blockSize];
r = new byte[blockSize];
}
/**
* Gets the name of this feedback mode.
*
* @return the string CBC
*/
String getFeedback() {
return "CBC";
}
/**
* Initializes the cipher in the specified mode with the given key
* and iv.
*
* @param decrypting flag indicating encryption or decryption
* @param algorithm the algorithm name
* @param key the key
* @param iv the iv
*
* @exception InvalidKeyException if the given key is inappropriate for
* initializing this cipher
*/
void init(boolean decrypting, String algorithm, byte[] key, byte[] iv)
throws InvalidKeyException {
if ((key == null) || (iv == null) || (iv.length != blockSize)) {
throw new InvalidKeyException("Internal error");
}
this.iv = iv;
reset();
embeddedCipher.init(decrypting, algorithm, key);
}
/**
* Resets the iv to its original value.
* This is used when doFinal is called in the Cipher class, so that the
* cipher can be reused (with its original iv).
*/
void reset() {
System.arraycopy(iv, 0, r, 0, blockSize);
}
/**
* Save the current content of this cipher.
*/
void save() {
if (rSave == null) {
rSave = new byte[blockSize];
}
System.arraycopy(r, 0, rSave, 0, blockSize);
}
/**
* Restores the content of this cipher to the previous saved one.
*/
void restore() {
System.arraycopy(rSave, 0, r, 0, blockSize);
}
/**
* Performs encryption operation.
*
*
The input plain text plain, starting at
* plainOffset and ending at
* (plainOffset + plainLen - 1), is encrypted.
* The result is stored in cipher, starting at
* cipherOffset.
*
* @param plain the buffer with the input data to be encrypted
* @param plainOffset the offset in plain
* @param plainLen the length of the input data
* @param cipher the buffer for the result
* @param cipherOffset the offset in cipher
* @exception ProviderException if len is not
* a multiple of the block size
* @return the length of the encrypted data
*/
int encrypt(byte[] plain, int plainOffset, int plainLen,
byte[] cipher, int cipherOffset) {
if (plainLen <= 0) {
return plainLen;
}
cryptBlockSizeCheck(plainLen);
cryptNullAndBoundsCheck(plain, plainOffset, plainLen);
cryptNullAndBoundsCheck(cipher, cipherOffset, plainLen);
return implEncrypt(plain, plainOffset, plainLen,
cipher, cipherOffset);
}
private int implEncrypt(byte[] plain, int plainOffset, int plainLen,
byte[] cipher, int cipherOffset)
{
int endIndex = plainOffset + plainLen;
for (; plainOffset < endIndex;
plainOffset += blockSize, cipherOffset += blockSize) {
for (int i = 0; i < blockSize; i++) {
k[i] = (byte)(plain[i + plainOffset] ^ r[i]);
}
embeddedCipher.encryptBlock(k, 0, cipher, cipherOffset);
System.arraycopy(cipher, cipherOffset, r, 0, blockSize);
}
return plainLen;
}
/**
* Performs decryption operation.
*
*
The input cipher text cipher, starting at
* cipherOffset and ending at
* (cipherOffset + cipherLen - 1), is decrypted.
* The result is stored in plain, starting at
* plainOffset.
*
*
It is also the application's responsibility to make sure that
* init has been called before this method is called.
* (This check is omitted here, to avoid double checking.)
*
* @param cipher the buffer with the input data to be decrypted
* @param cipherOffset the offset in cipherOffset
* @param cipherLen the length of the input data
* @param plain the buffer for the result
* @param plainOffset the offset in plain
* @exception ProviderException if len is not
* a multiple of the block size
* @return the length of the decrypted data
*/
int decrypt(byte[] cipher, int cipherOffset, int cipherLen,
byte[] plain, int plainOffset) {
if (cipherLen <= 0) {
return cipherLen;
}
cryptBlockSizeCheck(cipherLen);
cryptNullAndBoundsCheck(cipher, cipherOffset, cipherLen);
cryptNullAndBoundsCheck(plain, plainOffset, cipherLen);
return implDecrypt(cipher, cipherOffset, cipherLen, plain, plainOffset);
}
private int implDecrypt(byte[] cipher, int cipherOffset, int cipherLen,
byte[] plain, int plainOffset)
{
int endIndex = cipherOffset + cipherLen;
for (; cipherOffset < endIndex;
cipherOffset += blockSize, plainOffset += blockSize) {
embeddedCipher.decryptBlock(cipher, cipherOffset, k, 0);
for (int i = 0; i < blockSize; i++) {
plain[i + plainOffset] = (byte)(k[i] ^ r[i]);
}
System.arraycopy(cipher, cipherOffset, r, 0, blockSize);
}
return cipherLen;
}
private void cryptBlockSizeCheck(int len) {
if ((len % blockSize) != 0) {
throw new ProviderException("Internal error in input buffering");
}
}
private static void cryptNullAndBoundsCheck(byte[] array, int offset, int len) {
Objects.requireNonNull(array);
if (offset < 0 || offset >= array.length) {
throw new ArrayIndexOutOfBoundsException(offset);
}
int endIndex = offset + len - 1;
if (endIndex < 0 || endIndex >= array.length) {
throw new ArrayIndexOutOfBoundsException(endIndex);
}
}
}