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The Apache Commons Codec package contains simple encoder and decoders for various formats such as Base64 and Hexadecimal. In addition to these widely used encoders and decoders, the codec package also maintains a collection of phonetic encoding utilities.
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/* ====================================================================
   Licensed to the Apache Software Foundation (ASF) under one or more
   contributor license agreements.  See the NOTICE file distributed with
   this work for additional information regarding copyright ownership.
   The ASF licenses this file to You 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 org.apache.poi.poifs.crypt.cryptoapi;

import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.IOException;
import java.io.OutputStream;
import java.security.GeneralSecurityException;
import java.security.MessageDigest;
import java.security.SecureRandom;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;

import javax.crypto.Cipher;
import javax.crypto.SecretKey;

import org.apache.poi.EncryptedDocumentException;
import org.apache.poi.poifs.crypt.ChunkedCipherOutputStream;
import org.apache.poi.poifs.crypt.CryptoFunctions;
import org.apache.poi.poifs.crypt.EncryptionInfo;
import org.apache.poi.poifs.crypt.Encryptor;
import org.apache.poi.poifs.crypt.HashAlgorithm;
import org.apache.poi.poifs.crypt.cryptoapi.CryptoAPIDecryptor.StreamDescriptorEntry;
import org.apache.poi.poifs.filesystem.DirectoryNode;
import org.apache.poi.poifs.filesystem.DocumentInputStream;
import org.apache.poi.poifs.filesystem.Entry;
import org.apache.poi.poifs.filesystem.POIFSFileSystem;
import org.apache.poi.util.IOUtils;
import org.apache.poi.util.LittleEndian;
import org.apache.poi.util.StringUtil;

public class CryptoAPIEncryptor extends Encryptor {

    private int chunkSize = 512;

    CryptoAPIEncryptor() {}

    CryptoAPIEncryptor(CryptoAPIEncryptor other) {
        super(other);
        chunkSize = other.chunkSize;
    }

    @Override
    public void confirmPassword(String password) {
        Random r = new SecureRandom();
        byte[] salt = new byte[16];
        byte[] verifier = new byte[16];
        r.nextBytes(salt);
        r.nextBytes(verifier);
        confirmPassword(password, null, null, verifier, salt, null);
    }

    @Override
    public void confirmPassword(String password, byte[] keySpec,
                                byte[] keySalt, byte[] verifier, byte[] verifierSalt,
                                byte[] integritySalt) {
        assert(verifier != null && verifierSalt != null);
        CryptoAPIEncryptionVerifier ver = (CryptoAPIEncryptionVerifier)getEncryptionInfo().getVerifier();
        ver.setSalt(verifierSalt);
        SecretKey skey = CryptoAPIDecryptor.generateSecretKey(password, ver);
        setSecretKey(skey);
        try {
            Cipher cipher = initCipherForBlock(null, 0);
            byte[] encryptedVerifier = new byte[verifier.length];
            cipher.update(verifier, 0, verifier.length, encryptedVerifier);
            ver.setEncryptedVerifier(encryptedVerifier);
            HashAlgorithm hashAlgo = ver.getHashAlgorithm();
            MessageDigest hashAlg = CryptoFunctions.getMessageDigest(hashAlgo);
            byte[] calcVerifierHash = hashAlg.digest(verifier);
            byte[] encryptedVerifierHash = cipher.doFinal(calcVerifierHash);
            ver.setEncryptedVerifierHash(encryptedVerifierHash);
        } catch (GeneralSecurityException e) {
            throw new EncryptedDocumentException("Password confirmation failed", e);
        }
    }

    /**
     * Initializes a cipher object for a given block index for encryption
     *
     * @param cipher may be null, otherwise the given instance is reset to the new block index
     * @param block the block index, e.g. the persist/slide id (hslf)
     * @return a new cipher object, if cipher was null, otherwise the reinitialized cipher
     * @throws GeneralSecurityException when the cipher can't be initialized
     */
    public Cipher initCipherForBlock(Cipher cipher, int block)
    throws GeneralSecurityException {
        return CryptoAPIDecryptor.initCipherForBlock(cipher, block, getEncryptionInfo(), getSecretKey(), Cipher.ENCRYPT_MODE);
    }

    @Override
    public ChunkedCipherOutputStream getDataStream(DirectoryNode dir) throws IOException {
        throw new IOException("not supported");
    }

    @Override
    public CryptoAPICipherOutputStream getDataStream(OutputStream stream, int initialOffset)
    throws IOException, GeneralSecurityException {
        return new CryptoAPICipherOutputStream(stream);
    }

    /**
     * Encrypt the Document-/SummaryInformation and other optionally streams.
     * Opposed to other crypto modes, cryptoapi is record based and can't be used
     * to stream-encrypt a whole file
     *
     * @see 2.3.5.4 RC4 CryptoAPI Encrypted Summary Stream
     */
    public void setSummaryEntries(DirectoryNode dir, String encryptedStream, POIFSFileSystem entries)
    throws IOException, GeneralSecurityException {
        CryptoAPIDocumentOutputStream bos = new CryptoAPIDocumentOutputStream(this); // NOSONAR
        byte[] buf = new byte[8];

        bos.write(buf, 0, 8); // skip header
        List descList = new ArrayList<>();

        int block = 0;
        for (Entry entry : entries.getRoot()) {
            if (entry.isDirectoryEntry()) {
                continue;
            }
            StreamDescriptorEntry descEntry = new StreamDescriptorEntry();
            descEntry.block = block;
            descEntry.streamOffset = bos.size();
            descEntry.streamName = entry.getName();
            descEntry.flags = StreamDescriptorEntry.flagStream.setValue(0, 1);
            descEntry.reserved2 = 0;

            bos.setBlock(block);
            DocumentInputStream dis = dir.createDocumentInputStream(entry);
            IOUtils.copy(dis, bos);
            dis.close();

            descEntry.streamSize = bos.size() - descEntry.streamOffset;
            descList.add(descEntry);

            block++;
        }

        int streamDescriptorArrayOffset = bos.size();

        bos.setBlock(0);
        LittleEndian.putUInt(buf, 0, descList.size());
        bos.write(buf, 0, 4);

        for (StreamDescriptorEntry sde : descList) {
            LittleEndian.putUInt(buf, 0, sde.streamOffset);
            bos.write(buf, 0, 4);
            LittleEndian.putUInt(buf, 0, sde.streamSize);
            bos.write(buf, 0, 4);
            LittleEndian.putUShort(buf, 0, sde.block);
            bos.write(buf, 0, 2);
            LittleEndian.putUByte(buf, 0, (short)sde.streamName.length());
            bos.write(buf, 0, 1);
            LittleEndian.putUByte(buf, 0, (short)sde.flags);
            bos.write(buf, 0, 1);
            LittleEndian.putUInt(buf, 0, sde.reserved2);
            bos.write(buf, 0, 4);
            byte[] nameBytes = StringUtil.getToUnicodeLE(sde.streamName);
            bos.write(nameBytes, 0, nameBytes.length);
            LittleEndian.putShort(buf, 0, (short)0); // null-termination
            bos.write(buf, 0, 2);
        }

        int savedSize = bos.size();
        int streamDescriptorArraySize = savedSize - streamDescriptorArrayOffset;
        LittleEndian.putUInt(buf, 0, streamDescriptorArrayOffset);
        LittleEndian.putUInt(buf, 4, streamDescriptorArraySize);

        bos.reset();
        bos.setBlock(0);
        bos.write(buf, 0, 8);
        bos.setSize(savedSize);

        dir.createDocument(encryptedStream, new ByteArrayInputStream(bos.getBuf(), 0, savedSize));
    }

//    protected int getKeySizeInBytes() {
//        return getEncryptionInfo().getHeader().getKeySize() / 8;
//    }

    @Override
    public void setChunkSize(int chunkSize) {
        this.chunkSize = chunkSize;
    }

    @Override
    public CryptoAPIEncryptor copy() {
        return new CryptoAPIEncryptor(this);
    }

    protected class CryptoAPICipherOutputStream extends ChunkedCipherOutputStream {

        @Override
        protected Cipher initCipherForBlock(Cipher cipher, int block, boolean lastChunk)
        throws IOException, GeneralSecurityException {
            flush();
            return initCipherForBlockNoFlush(cipher, block, lastChunk);
        }

        @Override
        protected Cipher initCipherForBlockNoFlush(Cipher existing, int block, boolean lastChunk)
        throws GeneralSecurityException {
            EncryptionInfo ei = getEncryptionInfo();
            SecretKey sk = getSecretKey();
            return CryptoAPIDecryptor.initCipherForBlock(existing, block, ei, sk, Cipher.ENCRYPT_MODE);
        }

        @Override
        protected void calculateChecksum(File file, int i) {
        }

        @Override
        protected void createEncryptionInfoEntry(DirectoryNode dir, File tmpFile) {
            throw new EncryptedDocumentException("createEncryptionInfoEntry not supported");
        }

        CryptoAPICipherOutputStream(OutputStream stream)
        throws IOException, GeneralSecurityException {
            super(stream, CryptoAPIEncryptor.this.chunkSize);
        }

        @Override
        public void flush() throws IOException {
            writeChunk(false);
            super.flush();
        }
    }

}