GHASH.cpp

/*
 * Copyright (C) 2015 Southern Storm Software, Pty Ltd.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 */
 
#include "GHASH.h"
#include "GF128.h"
#include "Crypto.h"
#include <string.h>
 
GHASH::GHASH()
{
    state.posn = 0;
}
 
GHASH::~GHASH()
{
    clean(state);
}
 
void GHASH::reset(const void *key)
{
    GF128::mulInit(state.H, key);
    memset(state.Y, 0, sizeof(state.Y));
    state.posn = 0;
}
 
void GHASH::update(const void *data, size_t len)
{
    // XOR the input with state.Y in 128-bit chunks and process them.
    const uint8_t *d = (const uint8_t *)data;
    while (len > 0) {
        uint8_t size = 16 - state.posn;
        if (size > len)
            size = len;
        uint8_t *y = ((uint8_t *)state.Y) + state.posn;
        for (uint8_t i = 0; i < size; ++i)
            y[i] ^= d[i];
        state.posn += size;
        len -= size;
        d += size;
        if (state.posn == 16) {
            GF128::mul(state.Y, state.H);
            state.posn = 0;
        }
    }
}
 
void GHASH::finalize(void *token, size_t len)
{
    // Pad with zeroes to a multiple of 16 bytes.
    pad();
 
    // The token is the current value of Y.
    if (len > 16)
        len = 16;
    memcpy(token, state.Y, len);
}
 
void GHASH::pad()
{
    if (state.posn != 0) {
        // Padding involves XOR'ing the rest of state.Y with zeroes,
        // which does nothing.  Immediately process the next chunk.
        GF128::mul(state.Y, state.H);
        state.posn = 0;
    }
}
 
void GHASH::clear()
{
    clean(state);
}