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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.IOException;

import org.apache.poi.EncryptedDocumentException;
import org.apache.poi.poifs.crypt.ChainingMode;
import org.apache.poi.poifs.crypt.CipherAlgorithm;
import org.apache.poi.poifs.crypt.CipherProvider;
import org.apache.poi.poifs.crypt.HashAlgorithm;
import org.apache.poi.poifs.crypt.standard.StandardEncryptionHeader;
import org.apache.poi.util.LittleEndianInput;

public class CryptoAPIEncryptionHeader extends StandardEncryptionHeader {

    public CryptoAPIEncryptionHeader(LittleEndianInput is) throws IOException {
        super(is);
    }

    protected CryptoAPIEncryptionHeader(CryptoAPIEncryptionHeader other) {
        super(other);
    }

    protected CryptoAPIEncryptionHeader(CipherAlgorithm cipherAlgorithm,
            HashAlgorithm hashAlgorithm, int keyBits, int blockSize,
            ChainingMode chainingMode) {
        super(cipherAlgorithm, hashAlgorithm, keyBits, blockSize, chainingMode);
    }

    @Override
    public void setKeySize(int keyBits) {
        // Microsoft Base Cryptographic Provider is limited up to 40 bits
        // http://msdn.microsoft.com/en-us/library/windows/desktop/aa375599(v=vs.85).aspx
        boolean found = false;
        for (int size : getCipherAlgorithm().allowedKeySize) {
            if (size == keyBits) {
                found = true;
                break;
            }
        }
        if (!found) {
            throw new EncryptedDocumentException("invalid keysize "+keyBits+" for cipher algorithm "+getCipherAlgorithm());
        }
        super.setKeySize(keyBits);
        if (keyBits > 40) {
            setCspName("Microsoft Enhanced Cryptographic Provider v1.0");
        } else {
            setCspName(CipherProvider.rc4.cipherProviderName);
        }
    }

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