Diff: mbedtls/source/ecdsa.c

Revision:

12:0071cb144c7a

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mbedtls/source/ecdsa.c	Tue Nov 01 14:22:56 2016 +0000
@@ -0,0 +1,448 @@
+/*
+ *  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
+
+/*
+ * 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)
+ */
+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)
+{
+    int ret;
+    mbedtls_mpi e, s_inv, u1, u2;
+    mbedtls_ecp_point R;
+
+    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 );
+
+    /*
+     * 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
+     *
+     * Since we're not using any secret data, no need to pass a RNG to
+     * mbedtls_ecp_mul() for countermesures.
+     */
+    MBEDTLS_MPI_CHK( mbedtls_ecp_muladd( grp, &R, &u1, &grp->G, &u2, Q ) );
+
+    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 );
+
+    return( ret );
+}
+
+/*
+ * 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 )
+{
+    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 = mbedtls_ecdsa_verify( &ctx->grp, hash, hlen,
+                              &ctx->Q, &r, &s ) ) != 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 );
+}
+
+#endif /* MBEDTLS_ECDSA_C */