445 lines
12 KiB
C
445 lines
12 KiB
C
/**
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* Internal bignum functions
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*
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* Copyright The Mbed TLS Contributors
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* SPDX-License-Identifier: Apache-2.0
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*
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* Licensed under the Apache License, Version 2.0 (the "License"); you may
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* not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include "common.h"
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#if defined(MBEDTLS_BIGNUM_C)
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#include <string.h>
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#include "mbedtls/platform_util.h"
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#include "mbedtls/error.h"
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#include "mbedtls/bignum.h"
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#include "bignum_core.h"
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#include "bignum_mod.h"
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#include "bignum_mod_raw.h"
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#define MPI_VALIDATE_RET( cond ) \
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MBEDTLS_INTERNAL_VALIDATE_RET( cond, MBEDTLS_ERR_MPI_BAD_INPUT_DATA )
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#define MPI_VALIDATE( cond ) \
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MBEDTLS_INTERNAL_VALIDATE( cond )
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#define ciL (sizeof(mbedtls_mpi_uint)) /* chars in limb */
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#define biL (ciL << 3) /* bits in limb */
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#define biH (ciL << 2) /* half limb size */
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/*
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* Convert between bits/chars and number of limbs
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* Divide first in order to avoid potential overflows
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*/
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#define BITS_TO_LIMBS(i) ( (i) / biL + ( (i) % biL != 0 ) )
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#define CHARS_TO_LIMBS(i) ( (i) / ciL + ( (i) % ciL != 0 ) )
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/*
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* Count leading zero bits in a given integer
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*/
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static size_t mpi_clz( const mbedtls_mpi_uint x )
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{
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size_t j;
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mbedtls_mpi_uint mask = (mbedtls_mpi_uint) 1 << (biL - 1);
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for( j = 0; j < biL; j++ )
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{
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if( x & mask ) break;
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mask >>= 1;
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}
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return j;
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}
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/*
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* Return the number of bits
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*/
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static size_t mpi_bitlen( const mbedtls_mpi_uint *X, size_t nx )
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{
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size_t i, j;
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if( nx == 0 )
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return( 0 );
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for( i = nx - 1; i > 0; i-- )
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if( X[i] != 0 )
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break;
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j = biL - mpi_clz( X[i] );
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return( ( i * biL ) + j );
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}
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/* Get a specific byte, without range checks. */
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#define GET_BYTE( X, i ) \
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( ( ( X )[( i ) / ciL] >> ( ( ( i ) % ciL ) * 8 ) ) & 0xff )
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void mbedtls_mpi_mod_residue_release( mbedtls_mpi_mod_residue *r )
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{
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if ( r == NULL )
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return;
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r->n = 0;
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r->p = NULL;
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}
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int mbedtls_mpi_mod_residue_setup( mbedtls_mpi_mod_residue *r,
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mbedtls_mpi_mod_modulus *m,
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mbedtls_mpi_uint *X )
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{
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if( X == NULL || m == NULL || r == NULL || X >= m->p)
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return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
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r->n = m->n;
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r->p = X;
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return( 0 );
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}
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void mbedtls_mpi_mod_modulus_init( mbedtls_mpi_mod_modulus *m )
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{
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if ( m == NULL )
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return;
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m->rep.mont = 0;
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}
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void mbedtls_mpi_mod_modulus_free( mbedtls_mpi_mod_modulus *m )
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{
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if ( m == NULL )
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return;
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m->p = NULL;
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m->n = 0;
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m->plen = 0;
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m->ext_rep = 0;
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m->int_rep = 0;
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m->rep.mont = NULL;
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m->rep.ored = NULL;
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}
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int mbedtls_mpi_mod_modulus_setup( mbedtls_mpi_mod_modulus *m,
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mbedtls_mpi_uint *X,
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size_t nx,
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int ext_rep,
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int int_rep )
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{
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if ( X == NULL || m == NULL )
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return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
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m->p = X;
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m->n = nx;
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m->ext_rep = ext_rep;
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m->int_rep = int_rep;
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m->plen = mpi_bitlen( X, nx );
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return( 0 );
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}
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/* Check X to have at least n limbs and set it to 0. */
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static int mpi_core_clear( mbedtls_mpi_uint *X,
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size_t nx,
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size_t limbs )
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{
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if( X == NULL )
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return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
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else if( nx < limbs )
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return( MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL );
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else
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{
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memset( X, 0, nx * ciL );
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return( 0 );
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}
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}
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/* Convert a big-endian byte array aligned to the size of mbedtls_mpi_uint
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* into the storage form used by mbedtls_mpi. */
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static mbedtls_mpi_uint mpi_bigendian_to_host_c( mbedtls_mpi_uint x )
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{
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uint8_t i;
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unsigned char *x_ptr;
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mbedtls_mpi_uint tmp = 0;
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for( i = 0, x_ptr = (unsigned char*) &x; i < ciL; i++, x_ptr++ )
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{
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tmp <<= CHAR_BIT;
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tmp |= (mbedtls_mpi_uint) *x_ptr;
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}
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return( tmp );
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}
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static mbedtls_mpi_uint mpi_bigendian_to_host( mbedtls_mpi_uint x )
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{
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#if defined(__BYTE_ORDER__)
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/* Nothing to do on bigendian systems. */
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#if ( __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__ )
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return( x );
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#endif /* __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__ */
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#if ( __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__ )
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/* For GCC and Clang, have builtins for byte swapping. */
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#if defined(__GNUC__) && defined(__GNUC_PREREQ)
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#if __GNUC_PREREQ(4,3)
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#define have_bswap
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#endif
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#endif
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#if defined(__clang__) && defined(__has_builtin)
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#if __has_builtin(__builtin_bswap32) && \
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__has_builtin(__builtin_bswap64)
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#define have_bswap
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#endif
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#endif
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#if defined(have_bswap)
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/* The compiler is hopefully able to statically evaluate this! */
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switch( sizeof(mbedtls_mpi_uint) )
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{
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case 4:
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return( __builtin_bswap32(x) );
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case 8:
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return( __builtin_bswap64(x) );
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}
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#endif
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#endif /* __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__ */
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#endif /* __BYTE_ORDER__ */
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/* Fall back to C-based reordering if we don't know the byte order
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* or we couldn't use a compiler-specific builtin. */
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return( mpi_bigendian_to_host_c( x ) );
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}
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static void mpi_core_bigendian_to_host( mbedtls_mpi_uint * const X,
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size_t limbs )
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{
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mbedtls_mpi_uint *cur_limb_left;
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mbedtls_mpi_uint *cur_limb_right;
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if( limbs == 0 )
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return;
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/*
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* Traverse limbs and
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* - adapt byte-order in each limb
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* - swap the limbs themselves.
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* For that, simultaneously traverse the limbs from left to right
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* and from right to left, as long as the left index is not bigger
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* than the right index (it's not a problem if limbs is odd and the
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* indices coincide in the last iteration).
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*/
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for( cur_limb_left = X, cur_limb_right = X + ( limbs - 1 );
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cur_limb_left <= cur_limb_right;
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cur_limb_left++, cur_limb_right-- )
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{
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mbedtls_mpi_uint tmp;
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/* Note that if cur_limb_left == cur_limb_right,
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* this code effectively swaps the bytes only once. */
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tmp = mpi_bigendian_to_host( *cur_limb_left );
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*cur_limb_left = mpi_bigendian_to_host( *cur_limb_right );
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*cur_limb_right = tmp;
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}
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}
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/*
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* Import X from unsigned binary data, little endian
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*
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* This function is guaranteed to return an MPI with at least the necessary
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* number of limbs (in particular, it does not skip 0s in the input).
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*/
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int mbedtls_mpi_core_read_le( mbedtls_mpi_uint *X,
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size_t nx,
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const unsigned char *buf,
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size_t buflen )
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{
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int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
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size_t i;
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size_t const limbs = CHARS_TO_LIMBS( buflen );
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/* Ensure that target MPI has at least the necessary number of limbs */
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MBEDTLS_MPI_CHK( mpi_core_clear( X, nx, limbs ) );
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for( i = 0; i < buflen; i++ )
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X[i / ciL] |= ((mbedtls_mpi_uint) buf[i]) << ((i % ciL) << 3);
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cleanup:
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return( ret );
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}
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/*
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* Import X from unsigned binary data, big endian
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*
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* This function is guaranteed to return an MPI with exactly the necessary
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* number of limbs (in particular, it does not skip 0s in the input).
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*/
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int mbedtls_mpi_core_read_be( mbedtls_mpi_uint *X,
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size_t nx,
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const unsigned char *buf,
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size_t buflen )
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{
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int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
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size_t const limbs = CHARS_TO_LIMBS( buflen );
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size_t const overhead = ( limbs * ciL ) - buflen;
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unsigned char *Xp;
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MPI_VALIDATE_RET( X != NULL );
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MPI_VALIDATE_RET( buflen == 0 || buf != NULL );
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/* Ensure that target MPI has at least the necessary number of limbs */
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MBEDTLS_MPI_CHK( mpi_core_clear( X, nx, limbs ) );
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/* Avoid calling `memcpy` with NULL source or destination argument,
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* even if buflen is 0. */
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if( buflen != 0 )
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{
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Xp = (unsigned char*) X;
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memcpy( Xp + overhead, buf, buflen );
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mpi_core_bigendian_to_host( X, nx );
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}
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cleanup:
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return( ret );
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}
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/*
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* Export X into unsigned binary data, little endian
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*/
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int mbedtls_mpi_core_write_le( const mbedtls_mpi_uint *X,
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size_t nx,
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unsigned char *buf,
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size_t buflen )
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{
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size_t stored_bytes = nx * ciL;
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size_t bytes_to_copy;
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size_t i;
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if( stored_bytes < buflen )
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{
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bytes_to_copy = stored_bytes;
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}
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else
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{
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bytes_to_copy = buflen;
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/* The output buffer is smaller than the allocated size of X.
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* However X may fit if its leading bytes are zero. */
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for( i = bytes_to_copy; i < stored_bytes; i++ )
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{
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if( GET_BYTE( X, i ) != 0 )
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return( MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL );
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}
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}
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for( i = 0; i < bytes_to_copy; i++ )
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buf[i] = GET_BYTE( X, i );
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if( stored_bytes < buflen )
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{
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/* Write trailing 0 bytes */
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memset( buf + stored_bytes, 0, buflen - stored_bytes );
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}
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return( 0 );
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}
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/*
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* Export X into unsigned binary data, big endian
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*/
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int mbedtls_mpi_core_write_be( const mbedtls_mpi_uint *X,
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size_t nx,
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unsigned char *buf,
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size_t buflen )
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{
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size_t stored_bytes;
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size_t bytes_to_copy;
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unsigned char *p;
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size_t i;
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MPI_VALIDATE_RET( X != NULL );
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MPI_VALIDATE_RET( buflen == 0 || buf != NULL );
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stored_bytes = nx * ciL;
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if( stored_bytes < buflen )
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{
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/* There is enough space in the output buffer. Write initial
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* null bytes and record the position at which to start
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* writing the significant bytes. In this case, the execution
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* trace of this function does not depend on the value of the
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* number. */
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bytes_to_copy = stored_bytes;
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p = buf + buflen - stored_bytes;
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memset( buf, 0, buflen - stored_bytes );
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}
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else
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{
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/* The output buffer is smaller than the allocated size of X.
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* However X may fit if its leading bytes are zero. */
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bytes_to_copy = buflen;
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p = buf;
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for( i = bytes_to_copy; i < stored_bytes; i++ )
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{
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if( GET_BYTE( X, i ) != 0 )
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return( MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL );
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}
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}
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for( i = 0; i < bytes_to_copy; i++ )
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p[bytes_to_copy - i - 1] = GET_BYTE( X, i );
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return( 0 );
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}
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int mbedtls_mpi_mod_raw_read( mbedtls_mpi_uint *X,
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mbedtls_mpi_mod_modulus *m,
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unsigned char *buf,
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size_t buflen )
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{
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if( m->ext_rep & MBEDTLS_MPI_MOD_EXT_REP_LE )
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return mbedtls_mpi_core_read_le( X, m->n, buf, buflen );
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else if( m->ext_rep & MBEDTLS_MPI_MOD_EXT_REP_BE )
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return mbedtls_mpi_core_read_be( X, m->n, buf, buflen );
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else
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return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
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return( 0 );
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}
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int mbedtls_mpi_mod_raw_write( mbedtls_mpi_uint *X,
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mbedtls_mpi_mod_modulus *m,
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unsigned char *buf,
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size_t buflen )
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{
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if( m->ext_rep & MBEDTLS_MPI_MOD_EXT_REP_LE )
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return mbedtls_mpi_core_write_le( X, m->n, buf, buflen );
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else if( m->ext_rep & MBEDTLS_MPI_MOD_EXT_REP_BE )
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return mbedtls_mpi_core_write_be( X, m->n, buf, buflen );
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else
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return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
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return( 0 );
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}
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#endif /* MBEDTLS_BIGNUM_C */
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