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package com.sun.crypto.provider;

import java.security.InvalidKeyException;

import jdk.internal.vm.annotation.IntrinsicCandidate;
import sun.security.util.ArrayUtil;

This class represents ciphers in counter (CTR) mode.

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:Andreas Sterbenz
Since:1.4.2
/** * This class represents ciphers in counter (CTR) mode. * * <p>This mode is implemented independently of a particular cipher. * Ciphers to which this mode should apply (e.g., DES) must be * <i>plugged-in</i> using the constructor. * * <p>NOTE: This class does not deal with buffering or padding. * * @author Andreas Sterbenz * @since 1.4.2 */
class CounterMode extends FeedbackCipher { // current counter value final byte[] counter; // encrypted bytes of the previous counter value private final byte[] encryptedCounter; // number of bytes in encryptedCounter already used up private int used; // variables for save/restore calls private byte[] counterSave = null; private byte[] encryptedCounterSave = null; private int usedSave = 0; CounterMode(SymmetricCipher embeddedCipher) { super(embeddedCipher); counter = new byte[blockSize]; encryptedCounter = new byte[blockSize]; }
Gets the name of the feedback mechanism
Returns:the name of the feedback mechanism
/** * Gets the name of the feedback mechanism * * @return the name of the feedback mechanism */
String getFeedback() { return "CTR"; }
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).
/** * 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, counter, 0, blockSize); used = blockSize; }
Save the current content of this cipher.
/** * Save the current content of this cipher. */
void save() { if (counterSave == null) { counterSave = new byte[blockSize]; encryptedCounterSave = new byte[blockSize]; } System.arraycopy(counter, 0, counterSave, 0, blockSize); System.arraycopy(encryptedCounter, 0, encryptedCounterSave, 0, blockSize); usedSave = used; }
Restores the content of this cipher to the previous saved one.
/** * Restores the content of this cipher to the previous saved one. */
void restore() { System.arraycopy(counterSave, 0, counter, 0, blockSize); System.arraycopy(encryptedCounterSave, 0, encryptedCounter, 0, blockSize); used = usedSave; }
Initializes the cipher in the specified mode with the given key and iv.
Params:
  • decrypting – flag indicating encryption or decryption
  • algorithm – the algorithm name
  • key – the key
  • iv – the iv
Throws:
/** * 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(); // always encrypt mode for embedded cipher embeddedCipher.init(false, algorithm, key); }
Performs encryption operation.

The input plain text plain, starting at plainOffset and ending at (plainOffset + len - 1), is encrypted. The result is stored in cipher, starting at cipherOffset.

Params:
  • in – the buffer with the input data to be encrypted
  • inOff – the offset in plain
  • len – the length of the input data
  • out – the buffer for the result
  • outOff – the offset in cipher
Returns:the length of the encrypted data
/** * Performs encryption operation. * * <p>The input plain text <code>plain</code>, starting at * <code>plainOffset</code> and ending at * <code>(plainOffset + len - 1)</code>, is encrypted. * The result is stored in <code>cipher</code>, starting at * <code>cipherOffset</code>. * * @param in the buffer with the input data to be encrypted * @param inOff the offset in <code>plain</code> * @param len the length of the input data * @param out the buffer for the result * @param outOff the offset in <code>cipher</code> * @return the length of the encrypted data */
int encrypt(byte[] in, int inOff, int len, byte[] out, int outOff) { return crypt(in, inOff, len, out, outOff); } // CTR encrypt and decrypt are identical int decrypt(byte[] in, int inOff, int len, byte[] out, int outOff) { return crypt(in, inOff, len, out, outOff); }
Increment the counter value.
/** * Increment the counter value. */
private static void increment(byte[] b) { int n = b.length - 1; while ((n >= 0) && (++b[n] == 0)) { n--; } }
Do the actual encryption/decryption operation. Essentially we XOR the input plaintext/ciphertext stream with a keystream generated by encrypting the counter values. Counter values are encrypted on demand.
/** * Do the actual encryption/decryption operation. * Essentially we XOR the input plaintext/ciphertext stream with a * keystream generated by encrypting the counter values. Counter values * are encrypted on demand. */
private int crypt(byte[] in, int inOff, int len, byte[] out, int outOff) { if (len == 0) { return 0; } ArrayUtil.nullAndBoundsCheck(in, inOff, len); ArrayUtil.nullAndBoundsCheck(out, outOff, len); return implCrypt(in, inOff, len, out, outOff); } // Implementation of crpyt() method. Possibly replaced with a compiler intrinsic. @IntrinsicCandidate private int implCrypt(byte[] in, int inOff, int len, byte[] out, int outOff) { int result = len; while (len-- > 0) { if (used >= blockSize) { embeddedCipher.encryptBlock(counter, 0, encryptedCounter, 0); increment(counter); used = 0; } out[outOff++] = (byte)(in[inOff++] ^ encryptedCounter[used++]); } return result; } }