com.healthmarketscience.jackcess.impl.office.ECMAStandardEncryptionProvider.java Source code

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Here is the source code for com.healthmarketscience.jackcess.impl.office.ECMAStandardEncryptionProvider.java

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/*
Copyright (c) 2013 James Ahlborn
    
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
    
http://www.apache.org/licenses/LICENSE-2.0
    
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package com.healthmarketscience.jackcess.impl.office;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.util.Arrays;
import java.util.EnumSet;
import java.util.Set;

import com.healthmarketscience.jackcess.impl.ByteUtil;
import com.healthmarketscience.jackcess.impl.PageChannel;
import org.bouncycastle.crypto.BlockCipher;
import org.bouncycastle.crypto.BufferedBlockCipher;
import org.bouncycastle.crypto.Digest;
import org.bouncycastle.crypto.digests.SHA1Digest;
import org.bouncycastle.crypto.engines.AESEngine;
import org.bouncycastle.crypto.params.KeyParameter;

/**
 *
 * @author James Ahlborn
 */
public class ECMAStandardEncryptionProvider extends BlockCipherProvider {
    private static final Set<EncryptionHeader.CryptoAlgorithm> VALID_CRYPTO_ALGOS = EnumSet.of(
            EncryptionHeader.CryptoAlgorithm.AES_128, EncryptionHeader.CryptoAlgorithm.AES_192,
            EncryptionHeader.CryptoAlgorithm.AES_256);
    private static final Set<EncryptionHeader.HashAlgorithm> VALID_HASH_ALGOS = EnumSet
            .of(EncryptionHeader.HashAlgorithm.SHA1);
    private static final int HASH_ITERATIONS = 50000;

    private final EncryptionHeader _header;
    private final EncryptionVerifier _verifier;
    private final byte[] _baseHash;
    private final int _encKeyByteSize;

    public ECMAStandardEncryptionProvider(PageChannel channel, byte[] encodingKey, ByteBuffer encProvBuf,
            byte[] pwdBytes) throws IOException {
        super(channel, encodingKey);

        // OC: 2.3.4.6
        _header = EncryptionHeader.read(encProvBuf, VALID_CRYPTO_ALGOS, VALID_HASH_ALGOS);

        _verifier = new EncryptionVerifier(encProvBuf, _header.getCryptoAlgorithm());

        // OC: 2.3.4.7 (part 1)
        _baseHash = hash(getDigest(), _verifier.getSalt(), pwdBytes);
        _encKeyByteSize = bits2bytes(_header.getKeySize());
    }

    @Override
    protected Digest initDigest() {
        return new SHA1Digest();
    }

    @Override
    protected BlockCipher initCipher() {
        return new AESEngine();
    }

    @Override
    protected KeyParameter computeCipherParams(int pageNumber) {
        // when actually decrypting pages, we incorporate the "encoding key"
        return computeEncryptionKey(getEncodingKey(pageNumber));
    }

    @Override
    protected boolean verifyPassword(byte[] pwdBytes) {

        // OC: 2.3.4.9
        BufferedBlockCipher cipher = decryptInit(getBlockCipher(), computeEncryptionKey(int2bytes(0)));

        byte[] verifier = decryptBytes(cipher, _verifier.getEncryptedVerifier());
        byte[] verifierHash = fixToLength(decryptBytes(cipher, _verifier.getEncryptedVerifierHash()),
                _verifier.getVerifierHashSize());

        byte[] testHash = fixToLength(hash(getDigest(), verifier), _verifier.getVerifierHashSize());

        return Arrays.equals(verifierHash, testHash);
    }

    private KeyParameter computeEncryptionKey(byte[] blockBytes) {
        byte[] encKey = cryptDeriveKey(_baseHash, blockBytes, HASH_ITERATIONS, _encKeyByteSize);
        return new KeyParameter(encKey);
    }

    private byte[] cryptDeriveKey(byte[] baseHash, byte[] blockBytes, int iterations, int keyByteLen) {
        Digest digest = getDigest();

        // OC: 2.3.4.7 (after part 1)
        byte[] iterHash = iterateHash(baseHash, iterations);

        byte[] finalHash = hash(digest, iterHash, blockBytes);

        byte[] x1 = hash(digest, genXBytes(finalHash, 0x36));
        byte[] x2 = hash(digest, genXBytes(finalHash, 0x5C));

        return fixToLength(ByteUtil.concat(x1, x2), keyByteLen);
    }

    private static byte[] genXBytes(byte[] finalHash, int code) {
        byte[] x = fill(new byte[64], code);

        for (int i = 0; i < finalHash.length; ++i) {
            x[0] ^= finalHash[i];
        }

        return x;
    }
}