mbedtls/library/ecdsa.c
2017-08-09 11:44:53 +02:00

573 lines
16 KiB
C

/*
* Elliptic curve DSA
*
* Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
* SPDX-License-Identifier: Apache-2.0
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may
* not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* This file is part of mbed TLS (https://tls.mbed.org)
*/
/*
* References:
*
* SEC1 http://www.secg.org/index.php?action=secg,docs_secg
*/
#if !defined(MBEDTLS_CONFIG_FILE)
#include "mbedtls/config.h"
#else
#include MBEDTLS_CONFIG_FILE
#endif
#if defined(MBEDTLS_ECDSA_C)
#include "mbedtls/ecdsa.h"
#include "mbedtls/asn1write.h"
#include <string.h>
#if defined(MBEDTLS_ECDSA_DETERMINISTIC)
#include "mbedtls/hmac_drbg.h"
#endif
#if defined(MBEDTLS_PLATFORM_C)
#include "mbedtls/platform.h"
#else
#include <stdlib.h>
#define mbedtls_calloc calloc
#define mbedtls_free free
#endif
#if defined(MBEDTLS_ECP_RESTARTABLE)
/*
* Sub-contect for ecdsa_verify()
*/
struct mbedtls_ecdsa_restart_ver
{
int state; /* dummy */
};
/*
* Init verify restart sub-context
*/
static void ecdsa_restart_ver_init( mbedtls_ecdsa_restart_ver_ctx *ctx )
{
memset( ctx, 0, sizeof( *ctx ) );
}
/*
* Free the components of a verify restart sub-context
*/
static void ecdsa_restart_ver_free( mbedtls_ecdsa_restart_ver_ctx *ctx )
{
if( ctx == NULL )
return;
memset( ctx, 0, sizeof( *ctx ) );
}
#define ECDSA_RS_ECP &rs_ctx->ecp
#else /* MBEDTLS_ECP_RESTARTABLE */
#define ECDSA_RS_ECP NULL
#endif /* MBEDTLS_ECP_RESTARTABLE */
/*
* Derive a suitable integer for group grp from a buffer of length len
* SEC1 4.1.3 step 5 aka SEC1 4.1.4 step 3
*/
static int derive_mpi( const mbedtls_ecp_group *grp, mbedtls_mpi *x,
const unsigned char *buf, size_t blen )
{
int ret;
size_t n_size = ( grp->nbits + 7 ) / 8;
size_t use_size = blen > n_size ? n_size : blen;
MBEDTLS_MPI_CHK( mbedtls_mpi_read_binary( x, buf, use_size ) );
if( use_size * 8 > grp->nbits )
MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( x, use_size * 8 - grp->nbits ) );
/* While at it, reduce modulo N */
if( mbedtls_mpi_cmp_mpi( x, &grp->N ) >= 0 )
MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mpi( x, x, &grp->N ) );
cleanup:
return( ret );
}
/*
* Compute ECDSA signature of a hashed message (SEC1 4.1.3)
* Obviously, compared to SEC1 4.1.3, we skip step 4 (hash message)
*/
int mbedtls_ecdsa_sign( mbedtls_ecp_group *grp, mbedtls_mpi *r, mbedtls_mpi *s,
const mbedtls_mpi *d, const unsigned char *buf, size_t blen,
int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
{
int ret, key_tries, sign_tries, blind_tries;
mbedtls_ecp_point R;
mbedtls_mpi k, e, t;
/* Fail cleanly on curves such as Curve25519 that can't be used for ECDSA */
if( grp->N.p == NULL )
return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
mbedtls_ecp_point_init( &R );
mbedtls_mpi_init( &k ); mbedtls_mpi_init( &e ); mbedtls_mpi_init( &t );
sign_tries = 0;
do
{
/*
* Steps 1-3: generate a suitable ephemeral keypair
* and set r = xR mod n
*/
key_tries = 0;
do
{
MBEDTLS_MPI_CHK( mbedtls_ecp_gen_keypair( grp, &k, &R, f_rng, p_rng ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( r, &R.X, &grp->N ) );
if( key_tries++ > 10 )
{
ret = MBEDTLS_ERR_ECP_RANDOM_FAILED;
goto cleanup;
}
}
while( mbedtls_mpi_cmp_int( r, 0 ) == 0 );
/*
* Step 5: derive MPI from hashed message
*/
MBEDTLS_MPI_CHK( derive_mpi( grp, &e, buf, blen ) );
/*
* Generate a random value to blind inv_mod in next step,
* avoiding a potential timing leak.
*/
blind_tries = 0;
do
{
size_t n_size = ( grp->nbits + 7 ) / 8;
MBEDTLS_MPI_CHK( mbedtls_mpi_fill_random( &t, n_size, f_rng, p_rng ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( &t, 8 * n_size - grp->nbits ) );
/* See mbedtls_ecp_gen_keypair() */
if( ++blind_tries > 30 )
return( MBEDTLS_ERR_ECP_RANDOM_FAILED );
}
while( mbedtls_mpi_cmp_int( &t, 1 ) < 0 ||
mbedtls_mpi_cmp_mpi( &t, &grp->N ) >= 0 );
/*
* Step 6: compute s = (e + r * d) / k = t (e + rd) / (kt) mod n
*/
MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( s, r, d ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_add_mpi( &e, &e, s ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &e, &e, &t ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &k, &k, &t ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_inv_mod( s, &k, &grp->N ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( s, s, &e ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( s, s, &grp->N ) );
if( sign_tries++ > 10 )
{
ret = MBEDTLS_ERR_ECP_RANDOM_FAILED;
goto cleanup;
}
}
while( mbedtls_mpi_cmp_int( s, 0 ) == 0 );
cleanup:
mbedtls_ecp_point_free( &R );
mbedtls_mpi_free( &k ); mbedtls_mpi_free( &e ); mbedtls_mpi_free( &t );
return( ret );
}
#if defined(MBEDTLS_ECDSA_DETERMINISTIC)
/*
* Deterministic signature wrapper
*/
int mbedtls_ecdsa_sign_det( mbedtls_ecp_group *grp, mbedtls_mpi *r, mbedtls_mpi *s,
const mbedtls_mpi *d, const unsigned char *buf, size_t blen,
mbedtls_md_type_t md_alg )
{
int ret;
mbedtls_hmac_drbg_context rng_ctx;
unsigned char data[2 * MBEDTLS_ECP_MAX_BYTES];
size_t grp_len = ( grp->nbits + 7 ) / 8;
const mbedtls_md_info_t *md_info;
mbedtls_mpi h;
if( ( md_info = mbedtls_md_info_from_type( md_alg ) ) == NULL )
return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
mbedtls_mpi_init( &h );
mbedtls_hmac_drbg_init( &rng_ctx );
/* Use private key and message hash (reduced) to initialize HMAC_DRBG */
MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( d, data, grp_len ) );
MBEDTLS_MPI_CHK( derive_mpi( grp, &h, buf, blen ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &h, data + grp_len, grp_len ) );
mbedtls_hmac_drbg_seed_buf( &rng_ctx, md_info, data, 2 * grp_len );
ret = mbedtls_ecdsa_sign( grp, r, s, d, buf, blen,
mbedtls_hmac_drbg_random, &rng_ctx );
cleanup:
mbedtls_hmac_drbg_free( &rng_ctx );
mbedtls_mpi_free( &h );
return( ret );
}
#endif /* MBEDTLS_ECDSA_DETERMINISTIC */
/*
* Verify ECDSA signature of hashed message (SEC1 4.1.4)
* Obviously, compared to SEC1 4.1.3, we skip step 2 (hash message)
*/
static int ecdsa_verify_restartable( mbedtls_ecp_group *grp,
const unsigned char *buf, size_t blen,
const mbedtls_ecp_point *Q,
const mbedtls_mpi *r, const mbedtls_mpi *s,
mbedtls_ecdsa_restart_ctx *rs_ctx )
{
int ret;
mbedtls_mpi e, s_inv, u1, u2;
mbedtls_ecp_point R;
#if !defined(MBEDTLS_ECP_RESTARTABLE)
(void) rs_ctx;
#endif
mbedtls_ecp_point_init( &R );
mbedtls_mpi_init( &e ); mbedtls_mpi_init( &s_inv );
mbedtls_mpi_init( &u1 ); mbedtls_mpi_init( &u2 );
/* Fail cleanly on curves such as Curve25519 that can't be used for ECDSA */
if( grp->N.p == NULL )
return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
#if defined(MBEDTLS_ECP_RESTARTABLE)
/* reset ops count for this call if top-level */
if( rs_ctx != NULL && rs_ctx->ecp.depth++ == 0 )
rs_ctx->ecp.ops_done = 0;
/* set up our own sub-context if needed */
if( mbedtls_ecp_restart_enabled() && rs_ctx != NULL && rs_ctx->ver == NULL )
{
rs_ctx->ver = mbedtls_calloc( 1, sizeof( mbedtls_ecdsa_restart_ver_ctx ) );
if( rs_ctx->ver == NULL )
return( MBEDTLS_ERR_ECP_ALLOC_FAILED );
ecdsa_restart_ver_init( rs_ctx->ver );
}
#endif /* MBEDTLS_ECP_RESTARTABLE */
/*
* Step 1: make sure r and s are in range 1..n-1
*/
if( mbedtls_mpi_cmp_int( r, 1 ) < 0 || mbedtls_mpi_cmp_mpi( r, &grp->N ) >= 0 ||
mbedtls_mpi_cmp_int( s, 1 ) < 0 || mbedtls_mpi_cmp_mpi( s, &grp->N ) >= 0 )
{
ret = MBEDTLS_ERR_ECP_VERIFY_FAILED;
goto cleanup;
}
/*
* Additional precaution: make sure Q is valid
*/
MBEDTLS_MPI_CHK( mbedtls_ecp_check_pubkey( grp, Q ) );
/*
* Step 3: derive MPI from hashed message
*/
MBEDTLS_MPI_CHK( derive_mpi( grp, &e, buf, blen ) );
/*
* Step 4: u1 = e / s mod n, u2 = r / s mod n
*/
MBEDTLS_MPI_CHK( mbedtls_mpi_inv_mod( &s_inv, s, &grp->N ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &u1, &e, &s_inv ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( &u1, &u1, &grp->N ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &u2, r, &s_inv ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( &u2, &u2, &grp->N ) );
/*
* Step 5: R = u1 G + u2 Q
*/
MBEDTLS_MPI_CHK( mbedtls_ecp_muladd_restartable( grp,
&R, &u1, &grp->G, &u2, Q, ECDSA_RS_ECP ) );
if( mbedtls_ecp_is_zero( &R ) )
{
ret = MBEDTLS_ERR_ECP_VERIFY_FAILED;
goto cleanup;
}
/*
* Step 6: convert xR to an integer (no-op)
* Step 7: reduce xR mod n (gives v)
*/
MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( &R.X, &R.X, &grp->N ) );
/*
* Step 8: check if v (that is, R.X) is equal to r
*/
if( mbedtls_mpi_cmp_mpi( &R.X, r ) != 0 )
{
ret = MBEDTLS_ERR_ECP_VERIFY_FAILED;
goto cleanup;
}
cleanup:
mbedtls_ecp_point_free( &R );
mbedtls_mpi_free( &e ); mbedtls_mpi_free( &s_inv );
mbedtls_mpi_free( &u1 ); mbedtls_mpi_free( &u2 );
#if defined(MBEDTLS_ECP_RESTARTABLE)
/* clear our sub-context when not in progress (done or error) */
if( rs_ctx != NULL && ret != MBEDTLS_ERR_ECP_IN_PROGRESS ) {
ecdsa_restart_ver_free( rs_ctx->ver );
mbedtls_free( rs_ctx->ver );
rs_ctx->ver = NULL;
}
if( rs_ctx != NULL )
rs_ctx->ecp.depth--;
#endif /* MBEDTLS_ECP_RESTARTABLE */
return( ret );
}
/*
* Verify ECDSA signature of hashed message
*/
int mbedtls_ecdsa_verify( mbedtls_ecp_group *grp,
const unsigned char *buf, size_t blen,
const mbedtls_ecp_point *Q, const mbedtls_mpi *r, const mbedtls_mpi *s)
{
return( ecdsa_verify_restartable( grp, buf, blen, Q, r, s, NULL ) );
}
/*
* Convert a signature (given by context) to ASN.1
*/
static int ecdsa_signature_to_asn1( const mbedtls_mpi *r, const mbedtls_mpi *s,
unsigned char *sig, size_t *slen )
{
int ret;
unsigned char buf[MBEDTLS_ECDSA_MAX_LEN];
unsigned char *p = buf + sizeof( buf );
size_t len = 0;
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_mpi( &p, buf, s ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_mpi( &p, buf, r ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &p, buf, len ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &p, buf,
MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) );
memcpy( sig, p, len );
*slen = len;
return( 0 );
}
/*
* Compute and write signature
*/
int mbedtls_ecdsa_write_signature( mbedtls_ecdsa_context *ctx, mbedtls_md_type_t md_alg,
const unsigned char *hash, size_t hlen,
unsigned char *sig, size_t *slen,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng )
{
int ret;
mbedtls_mpi r, s;
mbedtls_mpi_init( &r );
mbedtls_mpi_init( &s );
#if defined(MBEDTLS_ECDSA_DETERMINISTIC)
(void) f_rng;
(void) p_rng;
MBEDTLS_MPI_CHK( mbedtls_ecdsa_sign_det( &ctx->grp, &r, &s, &ctx->d,
hash, hlen, md_alg ) );
#else
(void) md_alg;
MBEDTLS_MPI_CHK( mbedtls_ecdsa_sign( &ctx->grp, &r, &s, &ctx->d,
hash, hlen, f_rng, p_rng ) );
#endif
MBEDTLS_MPI_CHK( ecdsa_signature_to_asn1( &r, &s, sig, slen ) );
cleanup:
mbedtls_mpi_free( &r );
mbedtls_mpi_free( &s );
return( ret );
}
#if ! defined(MBEDTLS_DEPRECATED_REMOVED) && \
defined(MBEDTLS_ECDSA_DETERMINISTIC)
int mbedtls_ecdsa_write_signature_det( mbedtls_ecdsa_context *ctx,
const unsigned char *hash, size_t hlen,
unsigned char *sig, size_t *slen,
mbedtls_md_type_t md_alg )
{
return( mbedtls_ecdsa_write_signature( ctx, md_alg, hash, hlen, sig, slen,
NULL, NULL ) );
}
#endif
/*
* Read and check signature
*/
int mbedtls_ecdsa_read_signature( mbedtls_ecdsa_context *ctx,
const unsigned char *hash, size_t hlen,
const unsigned char *sig, size_t slen )
{
return( mbedtls_ecdsa_read_signature_restartable(
ctx, hash, hlen, sig, slen, NULL ) );
}
/*
* Restartable read and check signature
*/
int mbedtls_ecdsa_read_signature_restartable( mbedtls_ecdsa_context *ctx,
const unsigned char *hash, size_t hlen,
const unsigned char *sig, size_t slen,
mbedtls_ecdsa_restart_ctx *rs_ctx )
{
int ret;
unsigned char *p = (unsigned char *) sig;
const unsigned char *end = sig + slen;
size_t len;
mbedtls_mpi r, s;
mbedtls_mpi_init( &r );
mbedtls_mpi_init( &s );
if( ( ret = mbedtls_asn1_get_tag( &p, end, &len,
MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) ) != 0 )
{
ret += MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
goto cleanup;
}
if( p + len != end )
{
ret = MBEDTLS_ERR_ECP_BAD_INPUT_DATA +
MBEDTLS_ERR_ASN1_LENGTH_MISMATCH;
goto cleanup;
}
if( ( ret = mbedtls_asn1_get_mpi( &p, end, &r ) ) != 0 ||
( ret = mbedtls_asn1_get_mpi( &p, end, &s ) ) != 0 )
{
ret += MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
goto cleanup;
}
if( ( ret = ecdsa_verify_restartable( &ctx->grp, hash, hlen,
&ctx->Q, &r, &s, rs_ctx ) ) != 0 )
goto cleanup;
if( p != end )
ret = MBEDTLS_ERR_ECP_SIG_LEN_MISMATCH;
cleanup:
mbedtls_mpi_free( &r );
mbedtls_mpi_free( &s );
return( ret );
}
/*
* Generate key pair
*/
int mbedtls_ecdsa_genkey( mbedtls_ecdsa_context *ctx, mbedtls_ecp_group_id gid,
int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
{
return( mbedtls_ecp_group_load( &ctx->grp, gid ) ||
mbedtls_ecp_gen_keypair( &ctx->grp, &ctx->d, &ctx->Q, f_rng, p_rng ) );
}
/*
* Set context from an mbedtls_ecp_keypair
*/
int mbedtls_ecdsa_from_keypair( mbedtls_ecdsa_context *ctx, const mbedtls_ecp_keypair *key )
{
int ret;
if( ( ret = mbedtls_ecp_group_copy( &ctx->grp, &key->grp ) ) != 0 ||
( ret = mbedtls_mpi_copy( &ctx->d, &key->d ) ) != 0 ||
( ret = mbedtls_ecp_copy( &ctx->Q, &key->Q ) ) != 0 )
{
mbedtls_ecdsa_free( ctx );
}
return( ret );
}
/*
* Initialize context
*/
void mbedtls_ecdsa_init( mbedtls_ecdsa_context *ctx )
{
mbedtls_ecp_keypair_init( ctx );
}
/*
* Free context
*/
void mbedtls_ecdsa_free( mbedtls_ecdsa_context *ctx )
{
mbedtls_ecp_keypair_free( ctx );
}
#if defined(MBEDTLS_ECP_RESTARTABLE)
/*
* Initialize a restart context
*/
void mbedtls_ecdsa_restart_init( mbedtls_ecdsa_restart_ctx *ctx )
{
mbedtls_ecp_restart_init( &ctx->ecp );
ctx->ver = NULL;
}
/*
* Free the components of a restart context
*/
void mbedtls_ecdsa_restart_free( mbedtls_ecdsa_restart_ctx *ctx )
{
mbedtls_ecp_restart_free( &ctx->ecp );
ecdsa_restart_ver_free( ctx->ver );
mbedtls_free( ctx->ver );
ctx->ver = NULL;
}
#endif /* MBEDTLS_ECP_RESTARTABLE */
#endif /* MBEDTLS_ECDSA_C */