Diff: polarssl/ecdsa.c

Revision:

0:137634ff4186

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/polarssl/ecdsa.c	Thu Jun 11 03:27:03 2015 +0000
@@ -0,0 +1,503 @@
+/*
+ *  Elliptic curve DSA
+ *
+ *  Copyright (C) 2006-2014, ARM Limited, All Rights Reserved
+ *
+ *  This file is part of mbed TLS (https://tls.mbed.org)
+ *
+ *  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
+ *  (at your option) 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.,
+ *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+/*
+ * References:
+ *
+ * SEC1 http://www.secg.org/index.php?action=secg,docs_secg
+ */
+
+#if !defined(POLARSSL_CONFIG_FILE)
+#include "polarssl/config.h"
+#else
+#include POLARSSL_CONFIG_FILE
+#endif
+
+#if defined(POLARSSL_ECDSA_C)
+
+#include "polarssl/ecdsa.h"
+#include "polarssl/asn1write.h"
+
+#include <string.h>
+
+#if defined(POLARSSL_ECDSA_DETERMINISTIC)
+#include "polarssl/hmac_drbg.h"
+#endif
+
+#if defined(POLARSSL_ECDSA_DETERMINISTIC)
+/*
+ * This a hopefully temporary compatibility function.
+ *
+ * Since we can't ensure the caller will pass a valid md_alg before the next
+ * interface change, try to pick up a decent md by size.
+ *
+ * Argument is the minimum size in bytes of the MD output.
+ */
+static const md_info_t *md_info_by_size( size_t min_size )
+{
+    const md_info_t *md_cur, *md_picked = NULL;
+    const int *md_alg;
+
+    for( md_alg = md_list(); *md_alg != 0; md_alg++ )
+    {
+        if( ( md_cur = md_info_from_type( (md_type_t) *md_alg ) ) == NULL ||
+            (size_t) md_cur->size < min_size ||
+            ( md_picked != NULL && md_cur->size > md_picked->size ) )
+            continue;
+
+        md_picked = md_cur;
+    }
+
+    return( md_picked );
+}
+#endif /* POLARSSL_ECDSA_DETERMINISTIC */
+
+/*
+ * 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 ecp_group *grp, 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;
+
+    MPI_CHK( mpi_read_binary( x, buf, use_size ) );
+    if( use_size * 8 > grp->nbits )
+        MPI_CHK( mpi_shift_r( x, use_size * 8 - grp->nbits ) );
+
+    /* While at it, reduce modulo N */
+    if( mpi_cmp_mpi( x, &grp->N ) >= 0 )
+        MPI_CHK( 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 ecdsa_sign( ecp_group *grp, mpi *r, mpi *s,
+                const 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;
+    ecp_point R;
+    mpi k, e, t;
+
+    /* Fail cleanly on curves such as Curve25519 that can't be used for ECDSA */
+    if( grp->N.p == NULL )
+        return( POLARSSL_ERR_ECP_BAD_INPUT_DATA );
+
+    ecp_point_init( &R );
+    mpi_init( &k ); mpi_init( &e ); 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
+        {
+            MPI_CHK( ecp_gen_keypair( grp, &k, &R, f_rng, p_rng ) );
+            MPI_CHK( mpi_mod_mpi( r, &R.X, &grp->N ) );
+
+            if( key_tries++ > 10 )
+            {
+                ret = POLARSSL_ERR_ECP_RANDOM_FAILED;
+                goto cleanup;
+            }
+        }
+        while( mpi_cmp_int( r, 0 ) == 0 );
+
+        /*
+         * Step 5: derive MPI from hashed message
+         */
+        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;
+            MPI_CHK( mpi_fill_random( &t, n_size, f_rng, p_rng ) );
+            MPI_CHK( mpi_shift_r( &t, 8 * n_size - grp->nbits ) );
+
+            /* See ecp_gen_keypair() */
+            if( ++blind_tries > 30 )
+                return( POLARSSL_ERR_ECP_RANDOM_FAILED );
+        }
+        while( mpi_cmp_int( &t, 1 ) < 0 ||
+               mpi_cmp_mpi( &t, &grp->N ) >= 0 );
+
+        /*
+         * Step 6: compute s = (e + r * d) / k = t (e + rd) / (kt) mod n
+         */
+        MPI_CHK( mpi_mul_mpi( s, r, d ) );
+        MPI_CHK( mpi_add_mpi( &e, &e, s ) );
+        MPI_CHK( mpi_mul_mpi( &e, &e, &t ) );
+        MPI_CHK( mpi_mul_mpi( &k, &k, &t ) );
+        MPI_CHK( mpi_inv_mod( s, &k, &grp->N ) );
+        MPI_CHK( mpi_mul_mpi( s, s, &e ) );
+        MPI_CHK( mpi_mod_mpi( s, s, &grp->N ) );
+
+        if( sign_tries++ > 10 )
+        {
+            ret = POLARSSL_ERR_ECP_RANDOM_FAILED;
+            goto cleanup;
+        }
+    }
+    while( mpi_cmp_int( s, 0 ) == 0 );
+
+cleanup:
+    ecp_point_free( &R );
+    mpi_free( &k ); mpi_free( &e ); mpi_free( &t );
+
+    return( ret );
+}
+
+#if defined(POLARSSL_ECDSA_DETERMINISTIC)
+/*
+ * Deterministic signature wrapper
+ */
+int ecdsa_sign_det( ecp_group *grp, mpi *r, mpi *s,
+                    const mpi *d, const unsigned char *buf, size_t blen,
+                    md_type_t md_alg )
+{
+    int ret;
+    hmac_drbg_context rng_ctx;
+    unsigned char data[2 * POLARSSL_ECP_MAX_BYTES];
+    size_t grp_len = ( grp->nbits + 7 ) / 8;
+    const md_info_t *md_info;
+    mpi h;
+
+    /* Temporary fallback */
+    if( md_alg == POLARSSL_MD_NONE )
+        md_info = md_info_by_size( blen );
+    else
+        md_info = md_info_from_type( md_alg );
+
+    if( md_info == NULL )
+        return( POLARSSL_ERR_ECP_BAD_INPUT_DATA );
+
+    mpi_init( &h );
+    memset( &rng_ctx, 0, sizeof( hmac_drbg_context ) );
+
+    /* Use private key and message hash (reduced) to initialize HMAC_DRBG */
+    MPI_CHK( mpi_write_binary( d, data, grp_len ) );
+    MPI_CHK( derive_mpi( grp, &h, buf, blen ) );
+    MPI_CHK( mpi_write_binary( &h, data + grp_len, grp_len ) );
+    hmac_drbg_init_buf( &rng_ctx, md_info, data, 2 * grp_len );
+
+    ret = ecdsa_sign( grp, r, s, d, buf, blen,
+                      hmac_drbg_random, &rng_ctx );
+
+cleanup:
+    hmac_drbg_free( &rng_ctx );
+    mpi_free( &h );
+
+    return( ret );
+}
+#endif /* POLARSSL_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 ecdsa_verify( ecp_group *grp,
+                  const unsigned char *buf, size_t blen,
+                  const ecp_point *Q, const mpi *r, const mpi *s)
+{
+    int ret;
+    mpi e, s_inv, u1, u2;
+    ecp_point R, P;
+
+    ecp_point_init( &R ); ecp_point_init( &P );
+    mpi_init( &e ); mpi_init( &s_inv ); mpi_init( &u1 ); mpi_init( &u2 );
+
+    /* Fail cleanly on curves such as Curve25519 that can't be used for ECDSA */
+    if( grp->N.p == NULL )
+        return( POLARSSL_ERR_ECP_BAD_INPUT_DATA );
+
+    /*
+     * Step 1: make sure r and s are in range 1..n-1
+     */
+    if( mpi_cmp_int( r, 1 ) < 0 || mpi_cmp_mpi( r, &grp->N ) >= 0 ||
+        mpi_cmp_int( s, 1 ) < 0 || mpi_cmp_mpi( s, &grp->N ) >= 0 )
+    {
+        ret = POLARSSL_ERR_ECP_VERIFY_FAILED;
+        goto cleanup;
+    }
+
+    /*
+     * Additional precaution: make sure Q is valid
+     */
+    MPI_CHK( ecp_check_pubkey( grp, Q ) );
+
+    /*
+     * Step 3: derive MPI from hashed message
+     */
+    MPI_CHK( derive_mpi( grp, &e, buf, blen ) );
+
+    /*
+     * Step 4: u1 = e / s mod n, u2 = r / s mod n
+     */
+    MPI_CHK( mpi_inv_mod( &s_inv, s, &grp->N ) );
+
+    MPI_CHK( mpi_mul_mpi( &u1, &e, &s_inv ) );
+    MPI_CHK( mpi_mod_mpi( &u1, &u1, &grp->N ) );
+
+    MPI_CHK( mpi_mul_mpi( &u2, r, &s_inv ) );
+    MPI_CHK( 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
+     * ecp_mul() for countermesures.
+     */
+    MPI_CHK( ecp_mul( grp, &R, &u1, &grp->G, NULL, NULL ) );
+    MPI_CHK( ecp_mul( grp, &P, &u2, Q, NULL, NULL ) );
+    MPI_CHK( ecp_add( grp, &R, &R, &P ) );
+
+    if( ecp_is_zero( &R ) )
+    {
+        ret = POLARSSL_ERR_ECP_VERIFY_FAILED;
+        goto cleanup;
+    }
+
+    /*
+     * Step 6: convert xR to an integer (no-op)
+     * Step 7: reduce xR mod n (gives v)
+     */
+    MPI_CHK( mpi_mod_mpi( &R.X, &R.X, &grp->N ) );
+
+    /*
+     * Step 8: check if v (that is, R.X) is equal to r
+     */
+    if( mpi_cmp_mpi( &R.X, r ) != 0 )
+    {
+        ret = POLARSSL_ERR_ECP_VERIFY_FAILED;
+        goto cleanup;
+    }
+
+cleanup:
+    ecp_point_free( &R ); ecp_point_free( &P );
+    mpi_free( &e ); mpi_free( &s_inv ); mpi_free( &u1 ); mpi_free( &u2 );
+
+    return( ret );
+}
+
+/*
+ * RFC 4492 page 20:
+ *
+ *     Ecdsa-Sig-Value ::= SEQUENCE {
+ *         r       INTEGER,
+ *         s       INTEGER
+ *     }
+ *
+ * Size is at most
+ *    1 (tag) + 1 (len) + 1 (initial 0) + ECP_MAX_BYTES for each of r and s,
+ *    twice that + 1 (tag) + 2 (len) for the sequence
+ * (assuming ECP_MAX_BYTES is less than 126 for r and s,
+ * and less than 124 (total len <= 255) for the sequence)
+ */
+#if POLARSSL_ECP_MAX_BYTES > 124
+#error "POLARSSL_ECP_MAX_BYTES bigger than expected, please fix MAX_SIG_LEN"
+#endif
+#define MAX_SIG_LEN ( 3 + 2 * ( 3 + POLARSSL_ECP_MAX_BYTES ) )
+
+/*
+ * Convert a signature (given by context) to ASN.1
+ */
+static int ecdsa_signature_to_asn1( ecdsa_context *ctx,
+                                    unsigned char *sig, size_t *slen )
+{
+    int ret;
+    unsigned char buf[MAX_SIG_LEN];
+    unsigned char *p = buf + sizeof( buf );
+    size_t len = 0;
+
+    ASN1_CHK_ADD( len, asn1_write_mpi( &p, buf, &ctx->s ) );
+    ASN1_CHK_ADD( len, asn1_write_mpi( &p, buf, &ctx->r ) );
+
+    ASN1_CHK_ADD( len, asn1_write_len( &p, buf, len ) );
+    ASN1_CHK_ADD( len, asn1_write_tag( &p, buf,
+                                       ASN1_CONSTRUCTED | ASN1_SEQUENCE ) );
+
+    memcpy( sig, p, len );
+    *slen = len;
+
+    return( 0 );
+}
+
+/*
+ * Compute and write signature
+ */
+int ecdsa_write_signature( ecdsa_context *ctx,
+                           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;
+
+    if( ( ret = ecdsa_sign( &ctx->grp, &ctx->r, &ctx->s, &ctx->d,
+                            hash, hlen, f_rng, p_rng ) ) != 0 )
+    {
+        return( ret );
+    }
+
+    return( ecdsa_signature_to_asn1( ctx, sig, slen ) );
+}
+
+#if defined(POLARSSL_ECDSA_DETERMINISTIC)
+/*
+ * Compute and write signature deterministically
+ */
+int ecdsa_write_signature_det( ecdsa_context *ctx,
+                               const unsigned char *hash, size_t hlen,
+                               unsigned char *sig, size_t *slen,
+                               md_type_t md_alg )
+{
+    int ret;
+
+    if( ( ret = ecdsa_sign_det( &ctx->grp, &ctx->r, &ctx->s, &ctx->d,
+                                hash, hlen, md_alg ) ) != 0 )
+    {
+        return( ret );
+    }
+
+    return( ecdsa_signature_to_asn1( ctx, sig, slen ) );
+}
+#endif /* POLARSSL_ECDSA_DETERMINISTIC */
+
+/*
+ * Read and check signature
+ */
+int ecdsa_read_signature( 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;
+
+    if( ( ret = asn1_get_tag( &p, end, &len,
+                    ASN1_CONSTRUCTED | ASN1_SEQUENCE ) ) != 0 )
+    {
+        return( POLARSSL_ERR_ECP_BAD_INPUT_DATA + ret );
+    }
+
+    if( p + len != end )
+        return( POLARSSL_ERR_ECP_BAD_INPUT_DATA +
+                POLARSSL_ERR_ASN1_LENGTH_MISMATCH );
+
+    if( ( ret = asn1_get_mpi( &p, end, &ctx->r ) ) != 0 ||
+        ( ret = asn1_get_mpi( &p, end, &ctx->s ) ) != 0 )
+        return( POLARSSL_ERR_ECP_BAD_INPUT_DATA + ret );
+
+    if( ( ret = ecdsa_verify( &ctx->grp, hash, hlen,
+                              &ctx->Q, &ctx->r, &ctx->s ) ) != 0 )
+        return( ret );
+
+    if( p != end )
+        return( POLARSSL_ERR_ECP_SIG_LEN_MISMATCH );
+
+    return( 0 );
+}
+
+/*
+ * Generate key pair
+ */
+int ecdsa_genkey( ecdsa_context *ctx, ecp_group_id gid,
+                  int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
+{
+    return( ecp_use_known_dp( &ctx->grp, gid ) ||
+            ecp_gen_keypair( &ctx->grp, &ctx->d, &ctx->Q, f_rng, p_rng ) );
+}
+
+/*
+ * Set context from an ecp_keypair
+ */
+int ecdsa_from_keypair( ecdsa_context *ctx, const ecp_keypair *key )
+{
+    int ret;
+
+    if( ( ret = ecp_group_copy( &ctx->grp, &key->grp ) ) != 0 ||
+        ( ret = mpi_copy( &ctx->d, &key->d ) ) != 0 ||
+        ( ret = ecp_copy( &ctx->Q, &key->Q ) ) != 0 )
+    {
+        ecdsa_free( ctx );
+    }
+
+    return( ret );
+}
+
+/*
+ * Initialize context
+ */
+void ecdsa_init( ecdsa_context *ctx )
+{
+    ecp_group_init( &ctx->grp );
+    mpi_init( &ctx->d );
+    ecp_point_init( &ctx->Q );
+    mpi_init( &ctx->r );
+    mpi_init( &ctx->s );
+}
+
+/*
+ * Free context
+ */
+void ecdsa_free( ecdsa_context *ctx )
+{
+    ecp_group_free( &ctx->grp );
+    mpi_free( &ctx->d );
+    ecp_point_free( &ctx->Q );
+    mpi_free( &ctx->r );
+    mpi_free( &ctx->s );
+}
+
+#if defined(POLARSSL_SELF_TEST)
+
+/*
+ * Checkup routine
+ */
+int ecdsa_self_test( int verbose )
+{
+    ((void) verbose );
+    return( 0 );
+}
+
+#endif /* POLARSSL_SELF_TEST */
+
+#endif /* POLARSSL_ECDSA_C */
+