/* Sha256.java -- 
Copyright (C) 2003, 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
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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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As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
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package com.classpath.hash;

/**
 * Implementation of SHA2-1 [SHA-256] per the IETF Draft Specification.
 * <p>
 * References:
 * <ol>
 *    <li><a href="http://ftp.ipv4.heanet.ie/pub/ietf/internet-drafts/draft-ietf-ipsec-ciph-aes-cbc-03.txt">
 *    Descriptions of SHA-256, SHA-384, and SHA-512</a>,</li>
 *    <li>http://csrc.nist.gov/cryptval/shs/sha256-384-512.pdf</li>
 * </ol>
 */
public class Sha256
	extends BaseHash
{
	private static final int[] k =
	{
		0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5,
		0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
		0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3,
		0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
		0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc,
		0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
		0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7,
		0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
		0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13,
		0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
		0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3,
		0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
		0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5,
		0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
		0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208,
		0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2
	};
	private static final int BLOCK_SIZE = 64; // inner block size in bytes
	private static final String DIGEST0 =
		"BA7816BF8F01CFEA414140DE5DAE2223B00361A396177A9CB410FF61F20015AD";
	private static final int[] w = new int[64];
	/** caches the result of the correctness test, once executed. */
	private static Boolean valid;
	/** 256-bit interim result. */
	private int h0, h1, h2, h3, h4, h5, h6, h7;

	/** Trivial 0-arguments constructor. */
	public Sha256()
	{
		super(32, BLOCK_SIZE);
	}

	public static final int[] G(int hh0, int hh1, int hh2, int hh3, int hh4,
		int hh5, int hh6, int hh7, byte[] in, int offset)
	{
		return sha(hh0, hh1, hh2, hh3, hh4, hh5, hh6, hh7, in, offset);
	}

	protected void transform(byte[] in, int offset)
	{
		int[] result = sha(h0, h1, h2, h3, h4, h5, h6, h7, in, offset);
		h0 = result[0];
		h1 = result[1];
		h2 = result[2];
		h3 = result[3];
		h4 = result[4];
		h5 = result[5];
		h6 = result[6];
		h7 = result[7];
	}

	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,
				(byte) (h5 >>> 24), (byte) (h5 >>> 16), (byte) (h5 >>> 8), (byte) h5,
				(byte) (h6 >>> 24), (byte) (h6 >>> 16), (byte) (h6 >>> 8), (byte) h6,
				(byte) (h7 >>> 24), (byte) (h7 >>> 16), (byte) (h7 >>> 8), (byte) h7
			};
	}

	protected void resetContext()
	{
		// magic SHA-256 initialisation constants
		h0 = 0x6a09e667;
		h1 = 0xbb67ae85;
		h2 = 0x3c6ef372;
		h3 = 0xa54ff53a;
		h4 = 0x510e527f;
		h5 = 0x9b05688c;
		h6 = 0x1f83d9ab;
		h7 = 0x5be0cd19;
	}

	public boolean selfTest()
	{
		if(valid == null)
		{
			Sha256 md = new Sha256();
			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, int hh5,
		int hh6, int hh7, byte[] in,
		int offset)
	{
		int A = hh0;
		int B = hh1;
		int C = hh2;
		int D = hh3;
		int E = hh4;
		int F = hh5;
		int G = hh6;
		int H = hh7;
		int r, T, T2;
		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 < 64; r++)
		{
			T = w[r - 2];
			T2 = w[r - 15];
			w[r] = ((((T >>> 17) | (T << 15)) ^ ((T >>> 19) | (T << 13)) ^ (T >>> 10))
				+ w[r - 7]
				+ (((T2 >>> 7) | (T2 << 25))
				^ ((T2 >>> 18) | (T2 << 14))
				^ (T2 >>> 3)) + w[r - 16]);
		}
		for(r = 0; r < 64; r++)
		{
			T = (H
				+ (((E >>> 6) | (E << 26))
				^ ((E >>> 11) | (E << 21))
				^ ((E >>> 25) | (E << 7)))
				+ ((E & F) ^ (~E & G)) + k[r] + w[r]);
			T2 = ((((A >>> 2) | (A << 30))
				^ ((A >>> 13) | (A << 19))
				^ ((A >>> 22) | (A << 10))) + ((A & B) ^ (A & C) ^ (B & C)));
			H = G;
			G = F;
			F = E;
			E = D + T;
			D = C;
			C = B;
			B = A;
			A = T + T2;
		}
		return new int[]
			{
				hh0 + A, hh1 + B, hh2 + C, hh3 + D,
				hh4 + E, hh5 + F, hh6 + G, hh7 + H
			};
	}
}
