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/**
 * Copyright 2003-2016 SSHTOOLS Limited. All Rights Reserved.
 *
 * For product documentation visit https://www.sshtools.com/
 *
 * This file is part of J2SSH Maverick.
 *
 * J2SSH Maverick is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * J2SSH Maverick 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 for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with J2SSH Maverick.  If not, see .
 */
package com.sshtools.publickey;

import java.io.IOException;
import java.io.UnsupportedEncodingException;

import com.sshtools.ssh.SshException;
import com.sshtools.ssh.SshIOException;
import com.sshtools.ssh.components.ComponentManager;
import com.sshtools.ssh.components.Digest;

class PEM {
	/**  */
	public final static String DSA_PRIVATE_KEY = "DSA PRIVATE KEY";

	/**  */
	public final static String RSA_PRIVATE_KEY = "RSA PRIVATE KEY";

	/**  */
	protected final static String PEM_BOUNDARY = "-----";

	/**  */
	protected final static String PEM_BEGIN = PEM_BOUNDARY + "BEGIN ";

	/**  */
	protected final static String PEM_END = PEM_BOUNDARY + "END ";

	/**  */
	protected final static int MAX_LINE_LENGTH = 75;

	/**  */
	protected final static char[] HEX_CHARS = "0123456789ABCDEF".toCharArray();
	private final static int MD5_HASH_BYTES = 0x10;

	/**
	 * 
	 * 
	 * @param passphrase
	 * @param iv
	 * @param keySize
	 * 
	 * @return byte[]
	 */
	protected static byte[] getKeyFromPassphrase(String passphrase, byte[] iv,
			int keySize) throws IOException {
		try {
			byte[] passphraseBytes;

			try {
				passphraseBytes = passphrase == null ? new byte[0] : passphrase
						.getBytes("UTF-8");
			} catch (UnsupportedEncodingException e) {
				throw new IOException(
						"Mandatory US-ASCII character encoding is not supported by the VM");
			}

			/*
			 * hash is MD5 h(0) <- hash(passphrase, iv); h(n) <- hash(h(n-1),
			 * passphrase, iv); key <- (h(0),...,h(n))[0,..,key.length];
			 */
			Digest hash = (Digest) ComponentManager.getInstance()
					.supportedDigests().getInstance("MD5");

			byte[] key = new byte[keySize];

			int hashesSize = keySize & 0xfffffff0;

			if ((keySize & 0xf) != 0) {
				hashesSize += MD5_HASH_BYTES;
			}

			byte[] hashes = new byte[hashesSize];

			byte[] previous;

			for (int index = 0; (index + MD5_HASH_BYTES) <= hashes.length; hash
					.putBytes(previous, 0, previous.length)) {
				hash.putBytes(passphraseBytes, 0, passphraseBytes.length);
				hash.putBytes(iv, 0, 8);
				previous = hash.doFinal();
				System.arraycopy(previous, 0, hashes, index, previous.length);
				index += previous.length;
			}

			System.arraycopy(hashes, 0, key, 0, key.length);

			return key;
		} catch (SshException e) {
			throw new SshIOException(e);
		}
	}
}