/*
* Copyright (C) 2012 Michael Brown <mbrown@fensystems.co.uk>.
*
* This program 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 any later version.
*
* This program 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 this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
FILE_LICENCE ( GPL2_OR_LATER );
#include <stdint.h>
#include <string.h>
#include <assert.h>
#include <ipxe/bigint.h>
/** @file
*
* Big integer support
*/
/**
* Perform modular multiplication of big integers
*
* @v multiplicand0 Element 0 of big integer to be multiplied
* @v multiplier0 Element 0 of big integer to be multiplied
* @v modulus0 Element 0 of big integer modulus
* @v result0 Element 0 of big integer to hold result
*/
void bigint_mod_multiply_raw ( const bigint_element_t *multiplicand0,
const bigint_element_t *multiplier0,
const bigint_element_t *modulus0,
bigint_element_t *result0,
unsigned int size ) {
const bigint_t ( size ) __attribute__ (( may_alias )) *multiplicand =
( ( const void * ) multiplicand0 );
const bigint_t ( size ) __attribute__ (( may_alias )) *multiplier =
( ( const void * ) multiplier0 );
const bigint_t ( size ) __attribute__ (( may_alias )) *modulus =
( ( const void * ) modulus0 );
bigint_t ( size ) __attribute__ (( may_alias )) *result =
( ( void * ) result0 );
bigint_t ( size * 2 ) temp_result;
bigint_t ( size * 2 ) temp_modulus;
int rotation;
int i;
/* Perform multiplication */
bigint_multiply ( multiplicand, multiplier, &temp_result );
/* Rescale modulus to match result */
bigint_grow ( modulus, &temp_modulus );
rotation = ( bigint_max_set_bit ( &temp_result ) -
bigint_max_set_bit ( &temp_modulus ) );
for ( i = 0 ; i < rotation ; i++ )
bigint_rol ( &temp_modulus );
/* Subtract multiples of modulus */
for ( i = 0 ; i <= rotation ; i++ ) {
if ( bigint_is_geq ( &temp_result, &temp_modulus ) )
bigint_subtract ( &temp_modulus, &temp_result );
bigint_ror ( &temp_modulus );
}
/* Resize result */
bigint_shrink ( &temp_result, result );
/* Sanity check */
assert ( bigint_is_geq ( modulus, result ) );
}
/**
* Perform modular exponentiation of big integers
*
* @v base0 Element 0 of big integer base
* @v modulus0 Element 0 of big integer modulus
* @v exponent0 Element 0 of big integer exponent
* @v result0 Element 0 of big integer to hold result
* @v size Number of elements in base, modulus, and result
* @v exponent_size Number of elements in exponent
*/
void bigint_mod_exp_raw ( const bigint_element_t *base0,
const bigint_element_t *modulus0,
const bigint_element_t *exponent0,
bigint_element_t *result0,
unsigned int size,
unsigned int exponent_size ) {
const bigint_t ( size ) __attribute__ (( may_alias )) *base =
( ( const void * ) base0 );
const bigint_t ( size ) __attribute__ (( may_alias )) *modulus =
( ( const void * ) modulus0 );
const bigint_t ( exponent_size ) __attribute__ (( may_alias ))
*exponent = ( ( const void * ) exponent0 );
bigint_t ( size ) __attribute__ (( may_alias )) *result =
( ( void * ) result0 );
bigint_t ( size ) temp_base;
bigint_t ( exponent_size ) temp_exponent;
static const uint8_t start[1] = { 0x01 };
memcpy ( &temp_base, base, sizeof ( temp_base ) );
memcpy ( &temp_exponent, exponent, sizeof ( temp_exponent ) );
bigint_init ( result, start, sizeof ( start ) );
while ( ! bigint_is_zero ( &temp_exponent ) ) {
if ( bigint_bit_is_set ( &temp_exponent, 0 ) ) {
bigint_mod_multiply ( result, &temp_base,
modulus, result );
}
bigint_ror ( &temp_exponent );
bigint_mod_multiply ( &temp_base, &temp_base, modulus,
&temp_base );
}
}
