/* Sha160.java -- 
Copyright (C) 2001, 2002, 2006 Free Software Foundation, Inc.

This file is a part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or (at
your option) any later version.

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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.

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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
USA

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
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permission to link this library with independent modules to produce an
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package com.classpath.hash;

/**
 * The Secure Hash Algorithm (SHA-1) is required for use with the Digital
 * Signature Algorithm (DSA) as specified in the Digital Signature Standard
 * (DSS) and whenever a secure hash algorithm is required for federal
 * applications. For a message of length less than 2^64 bits, the SHA-1
 * produces a 160-bit condensed representation of the message called a message
 * digest. The message digest is used during generation of a signature for the
 * message. The SHA-1 is also used to compute a message digest for the received
 * version of the message during the process of verifying the signature. Any
 * change to the message in transit will, with very high probability, result in
 * a different message digest, and the signature will fail to verify.
 * <p>
 * The SHA-1 is designed to have the following properties: it is
 * computationally infeasible to find a message which corresponds to a given
 * message digest, or to find two different messages which produce the same
 * message digest.
 * <p>
 * References:
 * <ol>
 *    <li><a href="http://www.itl.nist.gov/fipspubs/fip180-1.htm">SECURE HASH
 *    STANDARD</a><br>
 *    Federal Information, Processing Standards Publication 180-1, 1995 April 17.
 *    </li>
 * </ol>
 */
public class Sha160
	extends BaseHash
{
	private static final int BLOCK_SIZE = 64; // inner block size in bytes
	private static final String DIGEST0 = "A9993E364706816ABA3E25717850C26C9CD0D89D";
	private static final int[] w = new int[80];
	/** caches the result of the correctness test, once executed. */
	private static Boolean valid;
	/** 160-bit interim result. */
	private int h0, h1, h2, h3, h4;

	/** Trivial 0-arguments constructor. */
	public Sha160()
	{
		super(20, BLOCK_SIZE);
	}

	public static final int[] G(int hh0, int hh1, int hh2, int hh3, int hh4,
		byte[] in, int offset)
	{
		return sha(hh0, hh1, hh2, hh3, hh4, in, offset);
	}

	protected void transform(byte[] in, int offset)
	{
		int[] result = sha(h0, h1, h2, h3, h4, in, offset);
		h0 = result[0];
		h1 = result[1];
		h2 = result[2];
		h3 = result[3];
		h4 = result[4];
	}

	protected byte[] padBuffer()
	{
		int n = (int) (count % BLOCK_SIZE);
		int padding = (n < 56) ? (56 - n) : (120 - n);
		byte[] result = new byte[padding + 8];
		// padding is always binary 1 followed by binary 0s
		result[0] = (byte) 0x80;
		// save number of bits, casting the long to an array of 8 bytes
		long bits = count << 3;
		result[padding++] = (byte) (bits >>> 56);
		result[padding++] = (byte) (bits >>> 48);
		result[padding++] = (byte) (bits >>> 40);
		result[padding++] = (byte) (bits >>> 32);
		result[padding++] = (byte) (bits >>> 24);
		result[padding++] = (byte) (bits >>> 16);
		result[padding++] = (byte) (bits >>> 8);
		result[padding] = (byte) bits;
		return result;
	}

	protected byte[] getResult()
	{
		return new byte[]
			{
				(byte) (h0 >>> 24), (byte) (h0 >>> 16), (byte) (h0 >>> 8), (byte) h0,
				(byte) (h1 >>> 24), (byte) (h1 >>> 16), (byte) (h1 >>> 8), (byte) h1,
				(byte) (h2 >>> 24), (byte) (h2 >>> 16), (byte) (h2 >>> 8), (byte) h2,
				(byte) (h3 >>> 24), (byte) (h3 >>> 16), (byte) (h3 >>> 8), (byte) h3,
				(byte) (h4 >>> 24), (byte) (h4 >>> 16), (byte) (h4 >>> 8), (byte) h4
			};
	}

	protected void resetContext()
	{
		// magic SHA-1/RIPEMD160 initialisation constants
		h0 = 0x67452301;
		h1 = 0xEFCDAB89;
		h2 = 0x98BADCFE;
		h3 = 0x10325476;
		h4 = 0xC3D2E1F0;
	}

	public boolean selfTest()
	{
		if(valid == null)
		{
			Sha160 md = new Sha160();
			md.update((byte) 0x61); // a
			md.update((byte) 0x62); // b
			md.update((byte) 0x63); // c
			String result = HashUtil.toString(md.digest());
			valid = new Boolean(DIGEST0.equals(result));
		}
		return valid.booleanValue();
	}

	private static synchronized final int[] sha(int hh0, int hh1, int hh2,
		int hh3, int hh4, byte[] in,
		int offset)
	{
		int A = hh0;
		int B = hh1;
		int C = hh2;
		int D = hh3;
		int E = hh4;
		int r, T;
		for(r = 0; r < 16; r++)
		{
			w[r] = in[offset++] << 24
				| (in[offset++] & 0xFF) << 16
				| (in[offset++] & 0xFF) << 8
				| (in[offset++] & 0xFF);
		}
		for(r = 16; r < 80; r++)
		{
			T = w[r - 3] ^ w[r - 8] ^ w[r - 14] ^ w[r - 16];
			w[r] = T << 1 | T >>> 31;
		}
		for(r = 0; r < 20; r++) // rounds 0-19
		{
			T = (A << 5 | A >>> 27) + ((B & C) | (~B & D)) + E + w[r] + 0x5A827999;
			E = D;
			D = C;
			C = B << 30 | B >>> 2;
			B = A;
			A = T;
		}
		for(r = 20; r < 40; r++) // rounds 20-39
		{
			T = (A << 5 | A >>> 27) + (B ^ C ^ D) + E + w[r] + 0x6ED9EBA1;
			E = D;
			D = C;
			C = B << 30 | B >>> 2;
			B = A;
			A = T;
		}
		for(r = 40; r < 60; r++) // rounds 40-59
		{
			T = (A << 5 | A >>> 27) + (B & C | B & D | C & D) + E + w[r] + 0x8F1BBCDC;
			E = D;
			D = C;
			C = B << 30 | B >>> 2;
			B = A;
			A = T;
		}
		for(r = 60; r < 80; r++) // rounds 60-79
		{
			T = (A << 5 | A >>> 27) + (B ^ C ^ D) + E + w[r] + 0xCA62C1D6;
			E = D;
			D = C;
			C = B << 30 | B >>> 2;
			B = A;
			A = T;
		}
		return new int[]
			{
				hh0 + A, hh1 + B, hh2 + C, hh3 + D, hh4 + E
			};
	}
}
