diff options
Diffstat (limited to 'libjava/classpath/gnu/javax/crypto/mode/ICM.java')
| -rw-r--r-- | libjava/classpath/gnu/javax/crypto/mode/ICM.java | 139 |
1 files changed, 46 insertions, 93 deletions
diff --git a/libjava/classpath/gnu/javax/crypto/mode/ICM.java b/libjava/classpath/gnu/javax/crypto/mode/ICM.java index d37908b5dfd..833ddb18f7f 100644 --- a/libjava/classpath/gnu/javax/crypto/mode/ICM.java +++ b/libjava/classpath/gnu/javax/crypto/mode/ICM.java @@ -44,75 +44,66 @@ import gnu.javax.crypto.cipher.IBlockCipher; import java.math.BigInteger; /** - * <p>An implementation of <i>David McGrew</i> Integer Counter Mode (ICM) as an - * {@link IMode}.</p> - * - * <p>ICM is a way to define a pseudorandom keystream generator using a block - * cipher. The keystream can be used for additive encryption, key derivation, - * or any other application requiring pseudorandom data. In the case of this - * class, it is used as additive encryption, XOR-ing the keystream with the - * input text --for both encryption and decryption.</p> - * - * <p>In ICM, the keystream is logically broken into segments. Each segment is + * An implementation of <i>David McGrew</i> Integer Counter Mode (ICM) as an + * {@link IMode}. + * <p> + * ICM is a way to define a pseudorandom keystream generator using a block + * cipher. The keystream can be used for additive encryption, key derivation, or + * any other application requiring pseudorandom data. In the case of this class, + * it is used as additive encryption, XOR-ing the keystream with the input text + * --for both encryption and decryption. + * <p> + * In ICM, the keystream is logically broken into segments. Each segment is * identified with a segment index, and the segments have equal lengths. This * segmentation makes ICM especially appropriate for securing packet-based * protocols. ICM also allows a variety of configurations based, among other - * things, on two parameters: the <i>block index length</i> and the - * <i>segment index length</i>. A constraint on those two values exists: The sum - * of <i>segment index length</i> and <i>block index length</i> <b>must not</b> - * half the <i>block size</i> of the underlying cipher. This requirement protects - * the ICM keystream generator from potentially failing to be pseudorandom.</p> - * - * <p>For simplicity, this implementation, fixes these two values to the - * following:</p> - * + * things, on two parameters: the <i>block index length</i> and the <i>segment + * index length</i>. A constraint on those two values exists: The sum of + * <i>segment index length</i> and <i>block index length</i> <b>must not</b> + * half the <i>block size</i> of the underlying cipher. This requirement + * protects the ICM keystream generator from potentially failing to be + * pseudorandom. + * <p> + * For simplicity, this implementation, fixes these two values to the following: * <ul> - * <li>block index length: is half the underlying cipher block size, and</li> - * <li>segment index length: is zero.</li> + * <li>block index length: is half the underlying cipher block size, and</li> + * <li>segment index length: is zero.</li> * </ul> - * - * <p>For a 128-bit block cipher, the above values imply a maximum keystream - * length of 295,147,905,179,352,825,856 octets, since in ICM, each segment must - * not exceed the value <code>(256 ^ <i>block index length</i>) * <i>block length</i></code> - * octets.</p> - * - * <p>Finally, for this implementation of the ICM, the IV placeholder will be - * used to pass the value of the <i>Offset</i> in the keystream segment.</p> - * - * <p>References:</p> - * + * <p> + * For a 128-bit block cipher, the above values imply a maximum keystream length + * of 295,147,905,179,352,825,856 octets, since in ICM, each segment must not + * exceed the value + * <code>(256 ^ <i>block index length</i>) * <i>block length</i></code> + * octets. + * <p> + * Finally, for this implementation of the ICM, the IV placeholder will be used + * to pass the value of the <i>Offset</i> in the keystream segment. + * <p> + * References: * <ol> - * <li><a href="http://www.ietf.org/internet-drafts/draft-mcgrew-saag-icm-00.txt"> - * Integer Counter Mode</a>, David A. McGrew.</li> + * <li><a + * href="http://www.ietf.org/internet-drafts/draft-mcgrew-saag-icm-00.txt"> + * Integer Counter Mode</a>, David A. McGrew.</li> * </ol> */ -public class ICM extends BaseMode implements Cloneable +public class ICM + extends BaseMode + implements Cloneable { - - // Constants and variables - // ------------------------------------------------------------------------- - /** The integer value 256 as a BigInteger. */ private static final BigInteger TWO_FIFTY_SIX = new BigInteger("256"); - /** Maximum number of blocks per segment. */ private BigInteger maxBlocksPerSegment; - /** A work constant. */ private BigInteger counterRange; - /** The initial counter for a given keystream segment. */ private BigInteger C0; - /** The index of the next block for a given keystream segment. */ private BigInteger blockNdx; - // Constructor(s) - // ------------------------------------------------------------------------- - /** - * <p>Trivial package-private constructor for use by the Factory class.</p> - * + * Trivial package-private constructor for use by the Factory class. + * * @param underlyingCipher the underlying cipher implementation. * @param cipherBlockSize the underlying cipher block size to use. */ @@ -122,8 +113,8 @@ public class ICM extends BaseMode implements Cloneable } /** - * <p>Private constructor for cloning purposes.<p> - * + * Private constructor for cloning purposes. + * * @param that the instance to clone. */ private ICM(ICM that) @@ -131,27 +122,15 @@ public class ICM extends BaseMode implements Cloneable this((IBlockCipher) that.cipher.clone(), that.cipherBlockSize); } - // Class methods - // ------------------------------------------------------------------------- - - // Cloneable interface implementation - // ------------------------------------------------------------------------- - public Object clone() { return new ICM(this); } - // Implementation of abstract methods in BaseMode - // ------------------------------------------------------------------------- - public void setup() { if (modeBlockSize != cipherBlockSize) - { - throw new IllegalArgumentException(); - } - + throw new IllegalArgumentException(); counterRange = TWO_FIFTY_SIX.pow(cipherBlockSize); maxBlocksPerSegment = TWO_FIFTY_SIX.pow(cipherBlockSize / 2); BigInteger r = new BigInteger(1, iv); @@ -177,35 +156,13 @@ public class ICM extends BaseMode implements Cloneable icm(in, i, out, o); } - // Instance methods - // ------------------------------------------------------------------------- - private void icm(byte[] in, int inOffset, byte[] out, int outOffset) { if (blockNdx.compareTo(maxBlocksPerSegment) >= 0) throw new RuntimeException("Maximum blocks for segment reached"); - - // encrypt the counter for the current blockNdx - // C[i] = (C[0] + i) modulo (256^BLOCK_LENGTH). - BigInteger Ci = C0.add(blockNdx).modPow(BigInteger.ONE, counterRange); byte[] result = Ci.toByteArray(); int limit = result.length; - // if (limit < cipherBlockSize) { - // byte[] data = new byte[cipherBlockSize]; - // System.arraycopy(result, 0, data, cipherBlockSize-limit, limit); - // result = data; - // } else if (limit > cipherBlockSize) { - // byte[] data = new byte[cipherBlockSize]; - // System.arraycopy(result, limit-cipherBlockSize, data, 0, cipherBlockSize); - // result = data; - // } - // - // cipher.encryptBlock(result, 0, result, 0); - // blockNdx = blockNdx.add(BigInteger.ONE); // increment blockNdx - // for (int i = 0; i < modeBlockSize; ) { // xor result with input block - // out[outOffset++] = (byte)(in[inOffset++] ^ result[i++]); - // } int ndx = 0; if (limit < cipherBlockSize) { @@ -214,15 +171,11 @@ public class ICM extends BaseMode implements Cloneable result = data; } else if (limit > cipherBlockSize) - { - ndx = limit - cipherBlockSize; - } + ndx = limit - cipherBlockSize; cipher.encryptBlock(result, ndx, result, ndx); blockNdx = blockNdx.add(BigInteger.ONE); // increment blockNdx - for (int i = 0; i < modeBlockSize; i++) - { // xor result with input block - out[outOffset++] = (byte) (in[inOffset++] ^ result[ndx++]); - } + for (int i = 0; i < modeBlockSize; i++) // xor result with input block + out[outOffset++] = (byte)(in[inOffset++] ^ result[ndx++]); } -}
\ No newline at end of file +} |
