https://openjdk.java.net/ 
/*
 * Copyright (c) 2004, 2011, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package com.sun.crypto.provider;

import java.security.*;
import java.security.spec.*;
import javax.crypto.*;
import javax.crypto.spec.*;


Author:Valerie Peng
See Also:
/**
 * This class implements the CMS DESede KeyWrap algorithm as defined
 * in <a href=http://www.w3.org/TR/xmlenc-core/#sec-Alg-SymmetricKeyWrap>
 * "XML Encryption Syntax and Processing" section 5.6.2
 * "CMS Triple DES Key Wrap".
 * Note: only <code>CBC</code> mode and <code>NoPadding</code> padding
 * scheme can be used for this algorithm.
 *
 * @author Valerie Peng
 *
 *
 * @see DESedeCipher
 */
public final class DESedeWrapCipher extends CipherSpi {

    private static final byte[] IV2 = {
        (byte) 0x4a, (byte) 0xdd, (byte) 0xa2, (byte) 0x2c,
        (byte) 0x79, (byte) 0xe8, (byte) 0x21, (byte) 0x05
    };

    /*
     * internal cipher object which does the real work.
     */
    private FeedbackCipher cipher;

    /*
     * iv for (re-)initializing the internal cipher object.
     */
    private byte[] iv = null;

    /*
     * key for re-initializing the internal cipher object.
     */
    private Key cipherKey = null;

    /*
     * are we encrypting or decrypting?
     */
    private boolean decrypting = false;

    
Creates an instance of CMS DESede KeyWrap cipher with default
mode, i.e. "CBC" and padding scheme, i.e. "NoPadding".

/**
     * Creates an instance of CMS DESede KeyWrap cipher with default
     * mode, i.e. "CBC" and padding scheme, i.e. "NoPadding".
     */
    public DESedeWrapCipher() {
        cipher = new CipherBlockChaining(new DESedeCrypt());
    }

    
Sets the mode of this cipher. Only "CBC" mode is accepted for this
cipher.

Params:
  • mode – the cipher mode.
Throws:
/**
     * Sets the mode of this cipher. Only "CBC" mode is accepted for this
     * cipher.
     *
     * @param mode the cipher mode.
     *
     * @exception NoSuchAlgorithmException if the requested cipher mode
     * is not "CBC".
     */
    protected void engineSetMode(String mode)
        throws NoSuchAlgorithmException {
        if (!mode.equalsIgnoreCase("CBC")) {
            throw new NoSuchAlgorithmException(mode + " cannot be used");
        }
    }

    
Sets the padding mechanism of this cipher. Only "NoPadding" schmem
is accepted for this cipher.

Params:
  • padding – the padding mechanism.
Throws:
/**
     * Sets the padding mechanism of this cipher. Only "NoPadding" schmem
     * is accepted for this cipher.
     *
     * @param padding the padding mechanism.
     *
     * @exception NoSuchPaddingException if the requested padding mechanism
     * is not "NoPadding".
     */
    protected void engineSetPadding(String padding)
        throws NoSuchPaddingException {
        if (!padding.equalsIgnoreCase("NoPadding")) {
            throw new NoSuchPaddingException(padding + " cannot be used");
        }
    }

    
Returns the block size (in bytes), i.e. 8 bytes.

Returns:the block size (in bytes), i.e. 8 bytes.
/**
     * Returns the block size (in bytes), i.e. 8 bytes.
     *
     * @return the block size (in bytes), i.e. 8 bytes.
     */
    protected int engineGetBlockSize() {
        return DESConstants.DES_BLOCK_SIZE;
    }

    
Returns the length in bytes that an output buffer would need to be
given the input length inputLen (in bytes).

The actual output length of the next update or
doFinal call may be smaller than the length returned
by this method.

Params:
  • inputLen – the input length (in bytes).
Returns:the required output buffer size (in bytes).
/**
     * Returns the length in bytes that an output buffer would need to be
     * given the input length <code>inputLen</code> (in bytes).
     *
     * <p>The actual output length of the next <code>update</code> or
     * <code>doFinal</code> call may be smaller than the length returned
     * by this method.
     *
     * @param inputLen the input length (in bytes).
     *
     * @return the required output buffer size (in bytes).
     */
    protected int engineGetOutputSize(int inputLen) {
        // can only return an upper-limit if not initialized yet.
        int result = 0;
        if (decrypting) {
            result = inputLen - 16;
        } else {
            result = CipherCore.addExact(inputLen, 16);
        }
        return (result < 0? 0:result);
    }

    
Returns the initialization vector (IV) in a new buffer.

Returns:the initialization vector, or null if the underlying
algorithm does not use an IV, or if the IV has not yet
been set.
/**
     * Returns the initialization vector (IV) in a new buffer.
     *
     * @return the initialization vector, or null if the underlying
     * algorithm does not use an IV, or if the IV has not yet
     * been set.
     */
    protected byte[] engineGetIV() {
        return (iv == null) ? null : iv.clone();
    }

    
Initializes this cipher with a key and a source of randomness.

The cipher only supports the following two operation modes:
Cipher.WRAP_MODE, and 
Cipher.UNWRAP_MODE.

For modes other than the above two, UnsupportedOperationException
will be thrown.

If this cipher requires an initialization vector (IV), it will get
it from random.

Params:
  • opmode – the operation mode of this cipher. Only
WRAP_MODE or UNWRAP_MODE) are accepted.
  • key – the secret key.
  • random – the source of randomness.
Throws:
  • InvalidKeyException – if the given key is inappropriate
or if parameters are required but not supplied.
/**
     * Initializes this cipher with a key and a source of randomness.
     *
     * <p>The cipher only supports the following two operation modes:<b>
     * Cipher.WRAP_MODE, and <b>
     * Cipher.UNWRAP_MODE.
     * <p>For modes other than the above two, UnsupportedOperationException
     * will be thrown.
     * <p>If this cipher requires an initialization vector (IV), it will get
     * it from <code>random</code>.
     *
     * @param opmode the operation mode of this cipher. Only
     * <code>WRAP_MODE</code> or <code>UNWRAP_MODE</code>) are accepted.
     * @param key the secret key.
     * @param random the source of randomness.
     *
     * @exception InvalidKeyException if the given key is inappropriate
     * or if parameters are required but not supplied.
     */
    protected void engineInit(int opmode, Key key, SecureRandom random)
        throws InvalidKeyException {
        try {
            engineInit(opmode, key, (AlgorithmParameterSpec) null, random);
        } catch (InvalidAlgorithmParameterException iape) {
            // should never happen
            InvalidKeyException ike =
                new InvalidKeyException("Parameters required");
            ike.initCause(iape);
            throw ike;
        }
    }

    
Initializes this cipher with a key, a set of algorithm parameters,
and a source of randomness.

The cipher only supports the following two operation modes:
Cipher.WRAP_MODE, and 
Cipher.UNWRAP_MODE.

For modes other than the above two, UnsupportedOperationException
will be thrown.

If this cipher requires an initialization vector (IV), it will get
it from random.

Params:
  • opmode – the operation mode of this cipher. Only
WRAP_MODE or UNWRAP_MODE) are accepted.
  • key – the secret key.
  • params – the algorithm parameters.
  • random – the source of randomness.
Throws:
/**
     * Initializes this cipher with a key, a set of algorithm parameters,
     * and a source of randomness.
     *
     * <p>The cipher only supports the following two operation modes:<b>
     * Cipher.WRAP_MODE, and <b>
     * Cipher.UNWRAP_MODE.
     * <p>For modes other than the above two, UnsupportedOperationException
     * will be thrown.
     * <p>If this cipher requires an initialization vector (IV), it will get
     * it from <code>random</code>.
     *
     * @param opmode the operation mode of this cipher. Only
     * <code>WRAP_MODE</code> or <code>UNWRAP_MODE</code>) are accepted.
     * @param key the secret key.
     * @param params the algorithm parameters.
     * @param random the source of randomness.
     *
     * @exception InvalidKeyException if the given key is inappropriate.
     * @exception InvalidAlgorithmParameterException if the given algorithm
     * parameters are inappropriate for this cipher.
     */
    protected void engineInit(int opmode, Key key,
                              AlgorithmParameterSpec params,
                              SecureRandom random)
        throws InvalidKeyException, InvalidAlgorithmParameterException {
        byte[] currIv = null;
        if (opmode == Cipher.WRAP_MODE) {
            decrypting = false;
            if (params == null) {
                iv = new byte[8];
                if (random == null) {
                    random = SunJCE.RANDOM;
                }
                random.nextBytes(iv);
            }
            else if (params instanceof IvParameterSpec) {
                iv = ((IvParameterSpec) params).getIV();
            } else {
                throw new InvalidAlgorithmParameterException
                    ("Wrong parameter type: IV expected");
            }
            currIv = iv;
        } else if (opmode == Cipher.UNWRAP_MODE) {
            if (params != null) {
                throw new InvalidAlgorithmParameterException
                    ("No parameter accepted for unwrapping keys");
            }
            iv = null;
            decrypting = true;
            currIv = IV2;
        } else {
            throw new UnsupportedOperationException("This cipher can " +
                "only be used for key wrapping and unwrapping");
        }
        cipher.init(decrypting, key.getAlgorithm(), key.getEncoded(),
                    currIv);
        cipherKey = key;
    }

    
Initializes this cipher with a key, a set of algorithm parameters,
and a source of randomness.

The cipher only supports the following two operation modes:
Cipher.WRAP_MODE, and 
Cipher.UNWRAP_MODE.

For modes other than the above two, UnsupportedOperationException
will be thrown.

If this cipher requires an initialization vector (IV), it will get
it from random.

Params:
  • opmode – the operation mode of this cipher. Only
WRAP_MODE or UNWRAP_MODE) are accepted.
  • key – the secret key.
  • params – the algorithm parameters.
  • random – the source of randomness.
Throws:
/**
     * Initializes this cipher with a key, a set of algorithm parameters,
     * and a source of randomness.
     *
     * <p>The cipher only supports the following two operation modes:<b>
     * Cipher.WRAP_MODE, and <b>
     * Cipher.UNWRAP_MODE.
     * <p>For modes other than the above two, UnsupportedOperationException
     * will be thrown.
     * <p>If this cipher requires an initialization vector (IV), it will get
     * it from <code>random</code>.
     *
     * @param opmode the operation mode of this cipher. Only
     * <code>WRAP_MODE</code> or <code>UNWRAP_MODE</code>) are accepted.
     * @param key the secret key.
     * @param params the algorithm parameters.
     * @param random the source of randomness.
     *
     * @exception InvalidKeyException if the given key is inappropriate.
     * @exception InvalidAlgorithmParameterException if the given algorithm
     * parameters are inappropriate for this cipher.
     */
    protected void engineInit(int opmode, Key key,
                              AlgorithmParameters params,
                              SecureRandom random)
        throws InvalidKeyException, InvalidAlgorithmParameterException {
        IvParameterSpec ivSpec = null;
        if (params != null) {
            try {
                DESedeParameters paramsEng = new DESedeParameters();
                paramsEng.engineInit(params.getEncoded());
                ivSpec = paramsEng.engineGetParameterSpec(IvParameterSpec.class);
            } catch (Exception ex) {
                InvalidAlgorithmParameterException iape =
                    new InvalidAlgorithmParameterException
                        ("Wrong parameter type: IV expected");
                iape.initCause(ex);
                throw iape;
            }
        }
        engineInit(opmode, key, ivSpec, random);
    }

    
This operation is not supported by this cipher.
Since it's impossible to initialize this cipher given the
current Cipher.engineInit(...) implementation,
IllegalStateException will always be thrown upon invocation.

Params:
  • in – the input buffer.
  • inOffset – the offset in in where the input
starts.
  • inLen – the input length.
Throws:
Returns:n/a.
/**
     * This operation is not supported by this cipher.
     * Since it's impossible to initialize this cipher given the
     * current Cipher.engineInit(...) implementation,
     * IllegalStateException will always be thrown upon invocation.
     *
     * @param in the input buffer.
     * @param inOffset the offset in <code>in</code> where the input
     * starts.
     * @param inLen the input length.
     *
     * @return n/a.
     *
     * @exception IllegalStateException upon invocation of this method.
     */
    protected byte[] engineUpdate(byte[] in, int inOffset, int inLen) {
        throw new IllegalStateException("Cipher has not been initialized");
    }

    
This operation is not supported by this cipher.
Since it's impossible to initialize this cipher given the
current Cipher.engineInit(...) implementation,
IllegalStateException will always be thrown upon invocation.

Params:
  • in – the input buffer.
  • inOffset – the offset in in where the input
starts.
  • inLen – the input length.
  • out – the buffer for the result.
  • outOffset – the offset in out where the result
is stored.
Throws:
Returns:n/a.
/**
     * This operation is not supported by this cipher.
     * Since it's impossible to initialize this cipher given the
     * current Cipher.engineInit(...) implementation,
     * IllegalStateException will always be thrown upon invocation.
     *
     * @param in the input buffer.
     * @param inOffset the offset in <code>in</code> where the input
     * starts.
     * @param inLen the input length.
     * @param out the buffer for the result.
     * @param outOffset the offset in <code>out</code> where the result
     * is stored.
     *
     * @return n/a.
     *
     * @exception IllegalStateException upon invocation of this method.
     */
    protected int engineUpdate(byte[] in, int inOffset, int inLen,
                               byte[] out, int outOffset)
        throws ShortBufferException {
        throw new IllegalStateException("Cipher has not been initialized");
    }

    
This operation is not supported by this cipher.
Since it's impossible to initialize this cipher given the
current Cipher.engineInit(...) implementation,
IllegalStateException will always be thrown upon invocation.

Params:
  • in – the input buffer.
  • inOffset – the offset in in where the input
starts.
  • inLen – the input length.
Throws:
Returns:the new buffer with the result.
/**
     * This operation is not supported by this cipher.
     * Since it's impossible to initialize this cipher given the
     * current Cipher.engineInit(...) implementation,
     * IllegalStateException will always be thrown upon invocation.
     *
     * @param in the input buffer.
     * @param inOffset the offset in <code>in</code> where the input
     * starts.
     * @param inLen the input length.
     *
     * @return the new buffer with the result.
     *
     * @exception IllegalStateException upon invocation of this method.
     */
    protected byte[] engineDoFinal(byte[] in, int inOffset, int inLen)
        throws IllegalBlockSizeException, BadPaddingException {
        throw new IllegalStateException("Cipher has not been initialized");
    }

    
This operation is not supported by this cipher.
Since it's impossible to initialize this cipher given the
current Cipher.engineInit(...) implementation,
IllegalStateException will always be thrown upon invocation.

Params:
  • in – the input buffer.
  • inOffset – the offset in in where the input
starts.
  • inLen – the input length.
  • out – the buffer for the result.
  • outOffset – the ofset in out where the result
is stored.
Throws:
Returns:the number of bytes stored in out.
/**
     * This operation is not supported by this cipher.
     * Since it's impossible to initialize this cipher given the
     * current Cipher.engineInit(...) implementation,
     * IllegalStateException will always be thrown upon invocation.
     *
     * @param in the input buffer.
     * @param inOffset the offset in <code>in</code> where the input
     * starts.
     * @param inLen the input length.
     * @param out the buffer for the result.
     * @param outOffset the ofset in <code>out</code> where the result
     * is stored.
     *
     * @return the number of bytes stored in <code>out</code>.
     *
     * @exception IllegalStateException upon invocation of this method.
     */
    protected int engineDoFinal(byte[] input, int inputOffset, int inputLen,
                                byte[] output, int outputOffset)
        throws IllegalBlockSizeException, ShortBufferException,
               BadPaddingException {
        throw new IllegalStateException("Cipher has not been initialized");
    }

    
Returns the parameters used with this cipher.
Note that null maybe returned if this cipher does not use any
parameters or when it has not be set, e.g. initialized with
UNWRAP_MODE but wrapped key data has not been given.

Returns:the parameters used with this cipher; can be null.
/**
     * Returns the parameters used with this cipher.
     * Note that null maybe returned if this cipher does not use any
     * parameters or when it has not be set, e.g. initialized with
     * UNWRAP_MODE but wrapped key data has not been given.
     *
     * @return the parameters used with this cipher; can be null.
     */
    protected AlgorithmParameters engineGetParameters() {
        AlgorithmParameters params = null;
        if (iv != null) {
            String algo = cipherKey.getAlgorithm();
            try {
                params = AlgorithmParameters.getInstance(algo, "SunJCE");
            } catch (NoSuchAlgorithmException nsae) {
                // should never happen
                throw new RuntimeException("Cannot find " + algo +
                    " AlgorithmParameters implementation in SunJCE provider");
            } catch (NoSuchProviderException nspe) {
                // should never happen
                throw new RuntimeException("Cannot find SunJCE provider");
            }
            try {
                params.init(new IvParameterSpec(iv));
            } catch (InvalidParameterSpecException ipse) {
                // should never happen
                throw new RuntimeException("IvParameterSpec not supported");
            }
        }
        return params;
    }

    
Returns the key size of the given key object in number of bits.
This cipher always return the same key size as the DESede ciphers.

Params:
  • key – the key object.
Throws:
Returns:the "effective" key size of the given key object.
/**
     * Returns the key size of the given key object in number of bits.
     * This cipher always return the same key size as the DESede ciphers.
     *
     * @param key the key object.
     *
     * @return the "effective" key size of the given key object.
     *
     * @exception InvalidKeyException if <code>key</code> is invalid.
     */
    protected int engineGetKeySize(Key key) throws InvalidKeyException {
        byte[] encoded = key.getEncoded();
        if (encoded.length != 24) {
            throw new InvalidKeyException("Invalid key length: " +
                encoded.length + " bytes");
        }
        // Return the effective key length
        return 112;
    }

    
Wrap a key.

Params:
  • key – the key to be wrapped.
Throws:
  • IllegalBlockSizeException – if this cipher is a block
cipher, no padding has been requested, and the length of the
encoding of the key to be wrapped is not a
multiple of the block size.
  • InvalidKeyException – if it is impossible or unsafe to
wrap the key with this cipher (e.g., a hardware protected key is
being passed to a software only cipher).
Returns:the wrapped key.
/**
     * Wrap a key.
     *
     * @param key the key to be wrapped.
     *
     * @return the wrapped key.
     *
     * @exception IllegalBlockSizeException if this cipher is a block
     * cipher, no padding has been requested, and the length of the
     * encoding of the key to be wrapped is not a
     * multiple of the block size.
     *
     * @exception InvalidKeyException if it is impossible or unsafe to
     * wrap the key with this cipher (e.g., a hardware protected key is
     * being passed to a software only cipher).
     */
    protected byte[] engineWrap(Key key)
        throws IllegalBlockSizeException, InvalidKeyException {
        byte[] keyVal = key.getEncoded();
        if ((keyVal == null) || (keyVal.length == 0)) {
            throw new InvalidKeyException("Cannot get an encoding of " +
                                          "the key to be wrapped");
        }

        byte[] cks = getChecksum(keyVal);
        byte[] out = new byte[CipherCore.addExact(iv.length,
                CipherCore.addExact(keyVal.length, cks.length))];

        System.arraycopy(keyVal, 0, out, iv.length, keyVal.length);
        System.arraycopy(cks, 0, out,
                CipherCore.addExact(iv.length, keyVal.length), cks.length);

        cipher.encrypt(out, iv.length,
                CipherCore.addExact(keyVal.length, cks.length), out, iv.length);

        System.arraycopy(iv, 0, out, 0, iv.length);
        // reverse the array content
        for (int i = 0; i < out.length/2; i++) {
            byte temp = out[i];
            out[i] = out[out.length-1-i];
            out[out.length-1-i] = temp;
        }
        try {
            cipher.init(false, cipherKey.getAlgorithm(),
                        cipherKey.getEncoded(), IV2);
        } catch (InvalidKeyException ike) {
            // should never happen
            throw new RuntimeException("Internal cipher key is corrupted");
        }
        cipher.encrypt(out, 0, out.length, out, 0);

        // restore cipher state to prior to this call
        try {
            cipher.init(decrypting, cipherKey.getAlgorithm(),
                        cipherKey.getEncoded(), iv);
        } catch (InvalidKeyException ike) {
            // should never happen
            throw new RuntimeException("Internal cipher key is corrupted");
        }
        return out;
    }

    
Unwrap a previously wrapped key.

Params:
  • wrappedKey – the key to be unwrapped.
  • wrappedKeyAlgorithm – the algorithm the wrapped key is for.
  • wrappedKeyType – the type of the wrapped key.
This is one of Cipher.SECRET_KEY,
Cipher.PRIVATE_KEY, or Cipher.PUBLIC_KEY.
Throws:
  • NoSuchAlgorithmException – if no installed providers
can create keys of type wrappedKeyType for the
wrappedKeyAlgorithm.
  • InvalidKeyException – if wrappedKey does not
represent a wrapped key of type wrappedKeyType for
the wrappedKeyAlgorithm.
Returns:the unwrapped key.
/**
     * Unwrap a previously wrapped key.
     *
     * @param wrappedKey the key to be unwrapped.
     *
     * @param wrappedKeyAlgorithm the algorithm the wrapped key is for.
     *
     * @param wrappedKeyType the type of the wrapped key.
     * This is one of <code>Cipher.SECRET_KEY</code>,
     * <code>Cipher.PRIVATE_KEY</code>, or <code>Cipher.PUBLIC_KEY</code>.
     *
     * @return the unwrapped key.
     *
     * @exception NoSuchAlgorithmException if no installed providers
     * can create keys of type <code>wrappedKeyType</code> for the
     * <code>wrappedKeyAlgorithm</code>.
     *
     * @exception InvalidKeyException if <code>wrappedKey</code> does not
     * represent a wrapped key of type <code>wrappedKeyType</code> for
     * the <code>wrappedKeyAlgorithm</code>.
     */
    protected Key engineUnwrap(byte[] wrappedKey,
                               String wrappedKeyAlgorithm,
                               int wrappedKeyType)
        throws InvalidKeyException, NoSuchAlgorithmException {
        if (wrappedKey.length == 0) {
            throw new InvalidKeyException("The wrapped key is empty");
        }
        byte[] buffer = new byte[wrappedKey.length];
        cipher.decrypt(wrappedKey, 0, wrappedKey.length, buffer, 0);

        // reverse array content
        for (int i = 0; i < buffer.length/2; i++) {
            byte temp = buffer[i];
            buffer[i] = buffer[buffer.length-1-i];
            buffer[buffer.length-1-i] = temp;
        }
        iv = new byte[IV2.length];
        System.arraycopy(buffer, 0, iv, 0, iv.length);
        cipher.init(true, cipherKey.getAlgorithm(), cipherKey.getEncoded(),
                    iv);
        cipher.decrypt(buffer, iv.length, buffer.length-iv.length,
                       buffer, iv.length);
        int origLen = buffer.length - iv.length - 8;
        byte[] cks = getChecksum(buffer, iv.length, origLen);
        int offset = iv.length + origLen;
        for (int i = 0; i < cks.length; i++) {
            if (buffer[offset + i] != cks[i]) {
                throw new InvalidKeyException("Checksum comparison failed");
            }
        }
        // restore cipher state to prior to this call
        cipher.init(decrypting, cipherKey.getAlgorithm(),
                    cipherKey.getEncoded(), IV2);
        byte[] out = new byte[origLen];
        System.arraycopy(buffer, iv.length, out, 0, out.length);
        return ConstructKeys.constructKey(out, wrappedKeyAlgorithm,
                                          wrappedKeyType);
    }

    private static final byte[] getChecksum(byte[] in) {
        return getChecksum(in, 0, in.length);
    }
    private static final byte[] getChecksum(byte[] in, int offset, int len) {
        MessageDigest md = null;
        try {
            md = MessageDigest.getInstance("SHA1");
        } catch (NoSuchAlgorithmException nsae) {
            throw new RuntimeException("SHA1 message digest not available");
        }
        md.update(in, offset, len);
        byte[] cks = new byte[8];
        System.arraycopy(md.digest(), 0, cks, 0, cks.length);
        return cks;
    }
}