459 lines
13 KiB
C
459 lines
13 KiB
C
/*
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* Elliptic curve DSA
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*
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* Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
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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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* This file is part of mbed TLS (https://tls.mbed.org)
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*/
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/*
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* References:
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*
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* SEC1 http://www.secg.org/index.php?action=secg,docs_secg
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*/
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#if !defined(MBEDTLS_CONFIG_FILE)
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#include "mbedtls/config.h"
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#else
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#include MBEDTLS_CONFIG_FILE
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#endif
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#if defined(MBEDTLS_ECDSA_C)
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#include "mbedtls/ecdsa.h"
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#include "mbedtls/asn1write.h"
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#include <string.h>
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#if defined(MBEDTLS_ECDSA_DETERMINISTIC)
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#include "mbedtls/hmac_drbg.h"
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#endif
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/*
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* Derive a suitable integer for group grp from a buffer of length len
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* SEC1 4.1.3 step 5 aka SEC1 4.1.4 step 3
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*/
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static int derive_mpi( const mbedtls_ecp_group *grp, mbedtls_mpi *x,
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const unsigned char *buf, size_t blen )
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{
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int ret;
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size_t n_size = ( grp->nbits + 7 ) / 8;
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size_t use_size = blen > n_size ? n_size : blen;
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MBEDTLS_MPI_CHK( mbedtls_mpi_read_binary( x, buf, use_size ) );
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if( use_size * 8 > grp->nbits )
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MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( x, use_size * 8 - grp->nbits ) );
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/* While at it, reduce modulo N */
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if( mbedtls_mpi_cmp_mpi( x, &grp->N ) >= 0 )
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MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mpi( x, x, &grp->N ) );
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cleanup:
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return( ret );
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}
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#if !defined(MBEDTLS_ECDSA_SIGN_ALT)
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/*
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* Compute ECDSA signature of a hashed message (SEC1 4.1.3)
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* Obviously, compared to SEC1 4.1.3, we skip step 4 (hash message)
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*/
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int mbedtls_ecdsa_sign( mbedtls_ecp_group *grp, mbedtls_mpi *r, mbedtls_mpi *s,
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const mbedtls_mpi *d, const unsigned char *buf, size_t blen,
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int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
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{
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int ret, key_tries, sign_tries, blind_tries;
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mbedtls_ecp_point R;
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mbedtls_mpi k, e, t;
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/* Fail cleanly on curves such as Curve25519 that can't be used for ECDSA */
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if( grp->N.p == NULL )
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return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
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/* Make sure d is in range 1..n-1 */
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if( mbedtls_mpi_cmp_int( d, 1 ) < 0 || mbedtls_mpi_cmp_mpi( d, &grp->N ) >= 0 )
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return( MBEDTLS_ERR_ECP_INVALID_KEY );
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mbedtls_ecp_point_init( &R );
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mbedtls_mpi_init( &k ); mbedtls_mpi_init( &e ); mbedtls_mpi_init( &t );
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sign_tries = 0;
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do
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{
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/*
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* Steps 1-3: generate a suitable ephemeral keypair
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* and set r = xR mod n
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*/
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key_tries = 0;
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do
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{
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MBEDTLS_MPI_CHK( mbedtls_ecp_gen_keypair( grp, &k, &R, f_rng, p_rng ) );
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MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( r, &R.X, &grp->N ) );
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if( key_tries++ > 10 )
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{
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ret = MBEDTLS_ERR_ECP_RANDOM_FAILED;
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goto cleanup;
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}
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}
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while( mbedtls_mpi_cmp_int( r, 0 ) == 0 );
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/*
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* Step 5: derive MPI from hashed message
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*/
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MBEDTLS_MPI_CHK( derive_mpi( grp, &e, buf, blen ) );
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/*
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* Generate a random value to blind inv_mod in next step,
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* avoiding a potential timing leak.
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*/
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blind_tries = 0;
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do
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{
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size_t n_size = ( grp->nbits + 7 ) / 8;
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MBEDTLS_MPI_CHK( mbedtls_mpi_fill_random( &t, n_size, f_rng, p_rng ) );
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MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( &t, 8 * n_size - grp->nbits ) );
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/* See mbedtls_ecp_gen_keypair() */
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if( ++blind_tries > 30 )
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return( MBEDTLS_ERR_ECP_RANDOM_FAILED );
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}
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while( mbedtls_mpi_cmp_int( &t, 1 ) < 0 ||
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mbedtls_mpi_cmp_mpi( &t, &grp->N ) >= 0 );
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/*
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* Step 6: compute s = (e + r * d) / k = t (e + rd) / (kt) mod n
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*/
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MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( s, r, d ) );
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MBEDTLS_MPI_CHK( mbedtls_mpi_add_mpi( &e, &e, s ) );
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MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &e, &e, &t ) );
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MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &k, &k, &t ) );
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MBEDTLS_MPI_CHK( mbedtls_mpi_inv_mod( s, &k, &grp->N ) );
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MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( s, s, &e ) );
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MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( s, s, &grp->N ) );
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if( sign_tries++ > 10 )
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{
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ret = MBEDTLS_ERR_ECP_RANDOM_FAILED;
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goto cleanup;
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}
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}
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while( mbedtls_mpi_cmp_int( s, 0 ) == 0 );
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cleanup:
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mbedtls_ecp_point_free( &R );
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mbedtls_mpi_free( &k ); mbedtls_mpi_free( &e ); mbedtls_mpi_free( &t );
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return( ret );
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}
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#endif /* MBEDTLS_ECDSA_SIGN_ALT */
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#if defined(MBEDTLS_ECDSA_DETERMINISTIC)
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/*
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* Deterministic signature wrapper
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*/
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int mbedtls_ecdsa_sign_det( mbedtls_ecp_group *grp, mbedtls_mpi *r, mbedtls_mpi *s,
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const mbedtls_mpi *d, const unsigned char *buf, size_t blen,
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mbedtls_md_type_t md_alg )
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{
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int ret;
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mbedtls_hmac_drbg_context rng_ctx;
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unsigned char data[2 * MBEDTLS_ECP_MAX_BYTES];
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size_t grp_len = ( grp->nbits + 7 ) / 8;
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const mbedtls_md_info_t *md_info;
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mbedtls_mpi h;
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if( ( md_info = mbedtls_md_info_from_type( md_alg ) ) == NULL )
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return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
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mbedtls_mpi_init( &h );
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mbedtls_hmac_drbg_init( &rng_ctx );
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/* Use private key and message hash (reduced) to initialize HMAC_DRBG */
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MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( d, data, grp_len ) );
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MBEDTLS_MPI_CHK( derive_mpi( grp, &h, buf, blen ) );
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MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &h, data + grp_len, grp_len ) );
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mbedtls_hmac_drbg_seed_buf( &rng_ctx, md_info, data, 2 * grp_len );
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ret = mbedtls_ecdsa_sign( grp, r, s, d, buf, blen,
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mbedtls_hmac_drbg_random, &rng_ctx );
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cleanup:
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mbedtls_hmac_drbg_free( &rng_ctx );
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mbedtls_mpi_free( &h );
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return( ret );
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}
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#endif /* MBEDTLS_ECDSA_DETERMINISTIC */
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#if !defined(MBEDTLS_ECDSA_VERIFY_ALT)
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/*
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* Verify ECDSA signature of hashed message (SEC1 4.1.4)
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* Obviously, compared to SEC1 4.1.3, we skip step 2 (hash message)
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*/
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int mbedtls_ecdsa_verify( mbedtls_ecp_group *grp,
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const unsigned char *buf, size_t blen,
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const mbedtls_ecp_point *Q, const mbedtls_mpi *r, const mbedtls_mpi *s)
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{
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int ret;
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mbedtls_mpi e, s_inv, u1, u2;
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mbedtls_ecp_point R;
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mbedtls_ecp_point_init( &R );
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mbedtls_mpi_init( &e ); mbedtls_mpi_init( &s_inv ); mbedtls_mpi_init( &u1 ); mbedtls_mpi_init( &u2 );
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/* Fail cleanly on curves such as Curve25519 that can't be used for ECDSA */
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if( grp->N.p == NULL )
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return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
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/*
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* Step 1: make sure r and s are in range 1..n-1
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*/
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if( mbedtls_mpi_cmp_int( r, 1 ) < 0 || mbedtls_mpi_cmp_mpi( r, &grp->N ) >= 0 ||
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mbedtls_mpi_cmp_int( s, 1 ) < 0 || mbedtls_mpi_cmp_mpi( s, &grp->N ) >= 0 )
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{
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ret = MBEDTLS_ERR_ECP_VERIFY_FAILED;
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goto cleanup;
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}
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/*
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* Additional precaution: make sure Q is valid
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*/
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MBEDTLS_MPI_CHK( mbedtls_ecp_check_pubkey( grp, Q ) );
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/*
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* Step 3: derive MPI from hashed message
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*/
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MBEDTLS_MPI_CHK( derive_mpi( grp, &e, buf, blen ) );
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/*
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* Step 4: u1 = e / s mod n, u2 = r / s mod n
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*/
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MBEDTLS_MPI_CHK( mbedtls_mpi_inv_mod( &s_inv, s, &grp->N ) );
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MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &u1, &e, &s_inv ) );
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MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( &u1, &u1, &grp->N ) );
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MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &u2, r, &s_inv ) );
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MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( &u2, &u2, &grp->N ) );
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/*
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* Step 5: R = u1 G + u2 Q
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*
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* Since we're not using any secret data, no need to pass a RNG to
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* mbedtls_ecp_mul() for countermesures.
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*/
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MBEDTLS_MPI_CHK( mbedtls_ecp_muladd( grp, &R, &u1, &grp->G, &u2, Q ) );
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if( mbedtls_ecp_is_zero( &R ) )
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{
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ret = MBEDTLS_ERR_ECP_VERIFY_FAILED;
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goto cleanup;
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}
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/*
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* Step 6: convert xR to an integer (no-op)
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* Step 7: reduce xR mod n (gives v)
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*/
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MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( &R.X, &R.X, &grp->N ) );
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/*
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* Step 8: check if v (that is, R.X) is equal to r
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*/
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if( mbedtls_mpi_cmp_mpi( &R.X, r ) != 0 )
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{
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ret = MBEDTLS_ERR_ECP_VERIFY_FAILED;
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goto cleanup;
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}
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cleanup:
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mbedtls_ecp_point_free( &R );
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mbedtls_mpi_free( &e ); mbedtls_mpi_free( &s_inv ); mbedtls_mpi_free( &u1 ); mbedtls_mpi_free( &u2 );
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return( ret );
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}
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#endif /* MBEDTLS_ECDSA_VERIFY_ALT */
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/*
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* Convert a signature (given by context) to ASN.1
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*/
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static int ecdsa_signature_to_asn1( const mbedtls_mpi *r, const mbedtls_mpi *s,
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unsigned char *sig, size_t *slen )
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{
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int ret;
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unsigned char buf[MBEDTLS_ECDSA_MAX_LEN];
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unsigned char *p = buf + sizeof( buf );
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size_t len = 0;
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_mpi( &p, buf, s ) );
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_mpi( &p, buf, r ) );
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &p, buf, len ) );
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MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &p, buf,
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MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) );
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memcpy( sig, p, len );
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*slen = len;
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return( 0 );
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}
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/*
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* Compute and write signature
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*/
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int mbedtls_ecdsa_write_signature( mbedtls_ecdsa_context *ctx, mbedtls_md_type_t md_alg,
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const unsigned char *hash, size_t hlen,
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unsigned char *sig, size_t *slen,
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int (*f_rng)(void *, unsigned char *, size_t),
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void *p_rng )
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{
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int ret;
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mbedtls_mpi r, s;
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mbedtls_mpi_init( &r );
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mbedtls_mpi_init( &s );
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#if defined(MBEDTLS_ECDSA_DETERMINISTIC)
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(void) f_rng;
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(void) p_rng;
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MBEDTLS_MPI_CHK( mbedtls_ecdsa_sign_det( &ctx->grp, &r, &s, &ctx->d,
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hash, hlen, md_alg ) );
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#else
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(void) md_alg;
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MBEDTLS_MPI_CHK( mbedtls_ecdsa_sign( &ctx->grp, &r, &s, &ctx->d,
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hash, hlen, f_rng, p_rng ) );
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#endif
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MBEDTLS_MPI_CHK( ecdsa_signature_to_asn1( &r, &s, sig, slen ) );
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cleanup:
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mbedtls_mpi_free( &r );
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mbedtls_mpi_free( &s );
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return( ret );
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}
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#if ! defined(MBEDTLS_DEPRECATED_REMOVED) && \
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defined(MBEDTLS_ECDSA_DETERMINISTIC)
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int mbedtls_ecdsa_write_signature_det( mbedtls_ecdsa_context *ctx,
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const unsigned char *hash, size_t hlen,
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unsigned char *sig, size_t *slen,
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mbedtls_md_type_t md_alg )
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{
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return( mbedtls_ecdsa_write_signature( ctx, md_alg, hash, hlen, sig, slen,
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NULL, NULL ) );
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}
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#endif
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/*
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* Read and check signature
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*/
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int mbedtls_ecdsa_read_signature( mbedtls_ecdsa_context *ctx,
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const unsigned char *hash, size_t hlen,
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const unsigned char *sig, size_t slen )
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{
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int ret;
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unsigned char *p = (unsigned char *) sig;
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const unsigned char *end = sig + slen;
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size_t len;
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mbedtls_mpi r, s;
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mbedtls_mpi_init( &r );
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mbedtls_mpi_init( &s );
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if( ( ret = mbedtls_asn1_get_tag( &p, end, &len,
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MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) ) != 0 )
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{
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ret += MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
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goto cleanup;
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}
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if( p + len != end )
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{
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ret = MBEDTLS_ERR_ECP_BAD_INPUT_DATA +
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MBEDTLS_ERR_ASN1_LENGTH_MISMATCH;
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goto cleanup;
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}
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if( ( ret = mbedtls_asn1_get_mpi( &p, end, &r ) ) != 0 ||
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( ret = mbedtls_asn1_get_mpi( &p, end, &s ) ) != 0 )
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{
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ret += MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
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goto cleanup;
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}
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if( ( ret = mbedtls_ecdsa_verify( &ctx->grp, hash, hlen,
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&ctx->Q, &r, &s ) ) != 0 )
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goto cleanup;
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if( p != end )
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ret = MBEDTLS_ERR_ECP_SIG_LEN_MISMATCH;
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cleanup:
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mbedtls_mpi_free( &r );
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mbedtls_mpi_free( &s );
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return( ret );
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}
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#if !defined(MBEDTLS_ECDSA_GENKEY_ALT)
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/*
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* Generate key pair
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*/
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int mbedtls_ecdsa_genkey( mbedtls_ecdsa_context *ctx, mbedtls_ecp_group_id gid,
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int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
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{
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return( mbedtls_ecp_group_load( &ctx->grp, gid ) ||
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mbedtls_ecp_gen_keypair( &ctx->grp, &ctx->d, &ctx->Q, f_rng, p_rng ) );
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}
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#endif /* MBEDTLS_ECDSA_GENKEY_ALT */
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/*
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* Set context from an mbedtls_ecp_keypair
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*/
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int mbedtls_ecdsa_from_keypair( mbedtls_ecdsa_context *ctx, const mbedtls_ecp_keypair *key )
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{
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int ret;
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if( ( ret = mbedtls_ecp_group_copy( &ctx->grp, &key->grp ) ) != 0 ||
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( ret = mbedtls_mpi_copy( &ctx->d, &key->d ) ) != 0 ||
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( ret = mbedtls_ecp_copy( &ctx->Q, &key->Q ) ) != 0 )
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{
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mbedtls_ecdsa_free( ctx );
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}
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return( ret );
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}
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/*
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* Initialize context
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*/
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void mbedtls_ecdsa_init( mbedtls_ecdsa_context *ctx )
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{
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mbedtls_ecp_keypair_init( ctx );
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}
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/*
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* Free context
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*/
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void mbedtls_ecdsa_free( mbedtls_ecdsa_context *ctx )
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{
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mbedtls_ecp_keypair_free( ctx );
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}
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#endif /* MBEDTLS_ECDSA_C */
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