package org.postgresql.util;

/*
 * MD5-based utility function to obfuscate passwords before network transmission
 *
 * @author Jeremy Wohl
 *
 */

import java.security.*;

public class MD5Digest
{
	private MD5Digest()
	{}


	/*
	 * Encodes user/password/salt information in the following way:
	 *	 MD5(MD5(password + user) + salt)
	 *
	 * @param user		The connecting user.
	 * @param password	The connecting user's password.
	 * @param salt		A four-character string sent by the server.
	 *
	 * @return	A 35-byte array, comprising the string "md5", followed by an MD5 digest.
	 */
	public static byte[] encode(String user, String password, String salt)
	{
		MessageDigest md;
		byte[] temp_digest, pass_digest;
		byte[] hex_digest = new byte[35];

		try
		{
			md = MessageDigest.getInstance("MD5");

			md.update(password.getBytes());
			md.update(user.getBytes());
			temp_digest = md.digest();

			bytesToHex(temp_digest, hex_digest, 0);
			md.update(hex_digest, 0, 32);
			md.update(salt.getBytes());
			pass_digest = md.digest();

			bytesToHex(pass_digest, hex_digest, 3);
			hex_digest[0] = (byte) 'm';
			hex_digest[1] = (byte) 'd';
			hex_digest[2] = (byte) '5';
		}
		catch (Exception e)
		{
			; // "MessageDigest failure; " + e
		}

		return hex_digest;
	}


	/*
	 * Turn 16-byte stream into a human-readable 32-byte hex string
	 */
	private static void bytesToHex(byte[] bytes, byte[] hex, int offset)
	{
		final char lookup[] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
								'a', 'b', 'c', 'd', 'e', 'f' };

		int i, c, j, pos = offset;

		for (i = 0; i < 16; i++)
		{
			c = bytes[i] & 0xFF;
			j = c >> 4;
			hex[pos++] = (byte) lookup[j];
			j = (c & 0xF);
			hex[pos++] = (byte) lookup[j];
		}
	}
}
