diff --git a/include/mbedtls/ecdsa.h b/include/mbedtls/ecdsa.h
index ff6efbc3f..a213e91ec 100644
--- a/include/mbedtls/ecdsa.h
+++ b/include/mbedtls/ecdsa.h
@@ -101,6 +101,20 @@ int mbedtls_ecdsa_sign( mbedtls_ecp_group *grp, mbedtls_mpi *r, mbedtls_mpi *s,
* Usage of the Digital Signature Algorithm (DSA) and Elliptic
* Curve Digital Signature Algorithm (ECDSA).
*
+ *
+ * \warning Since the output of the internal RNG is always the same for
+ * the same key and message, this limits the efficiency of
+ * blinding and leaks information through side channels. For
+ * secure behavior use mbedtls_ecdsa_sign_det_ext() instead.
+ *
+ * (Optimally the blinding is a random value that is different
+ * on every execution. In this case the blinding is still
+ * random from the attackers perspective, but is the same on
+ * each execution. This means that this blinding does not
+ * prevent attackers from recovering secrets by combining
+ * several measurement traces, but may prevent some attacks
+ * that exploit relationships between secret data.)
+ *
* \param grp The ECP group.
* \param r The first output integer.
* \param s The second output integer.
@@ -121,9 +135,56 @@ int mbedtls_ecdsa_sign( mbedtls_ecp_group *grp, mbedtls_mpi *r, mbedtls_mpi *s,
*
* \see ecp.h
*/
-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 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 );
+/**
+ * \brief This function computes the ECDSA signature of a
+ * previously-hashed message, deterministic version.
+ *
+ * For more information, see RFC-6979: Deterministic
+ * Usage of the Digital Signature Algorithm (DSA) and Elliptic
+ * Curve Digital Signature Algorithm (ECDSA).
+ *
+ * \note If the bitlength of the message hash is larger than the
+ * bitlength of the group order, then the hash is truncated as
+ * defined in Standards for Efficient Cryptography Group
+ * (SECG): SEC1 Elliptic Curve Cryptography, section
+ * 4.1.3, step 5.
+ *
+ * \see ecp.h
+ *
+ * \param grp The context for the elliptic curve to use.
+ * This must be initialized and have group parameters
+ * set, for example through mbedtls_ecp_group_load().
+ * \param r The MPI context in which to store the first part
+ * the signature. This must be initialized.
+ * \param s The MPI context in which to store the second part
+ * the signature. This must be initialized.
+ * \param d The private signing key. This must be initialized
+ * and setup, for example through mbedtls_ecp_gen_privkey().
+ * \param buf The hashed content to be signed. This must be a readable
+ * buffer of length \p blen Bytes. It may be \c NULL if
+ * \p blen is zero.
+ * \param blen The length of \p buf in Bytes.
+ * \param md_alg The hash algorithm used to hash the original data.
+ * \param f_rng_blind The RNG function used for blinding. This must not be
+ * \c NULL.
+ * \param p_rng_blind The RNG context to be passed to \p f_rng. This may be
+ * \c NULL if \p f_rng doesn't need a context parameter.
+ *
+ * \return \c 0 on success.
+ * \return An \c MBEDTLS_ERR_ECP_XXX or \c MBEDTLS_MPI_XXX
+ * error code on failure.
+ */
+int mbedtls_ecdsa_sign_det_ext( 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 (*f_rng_blind)(void *, unsigned char *,
+ size_t),
+ void *p_rng_blind );
#endif /* MBEDTLS_ECDSA_DETERMINISTIC */
/**
diff --git a/library/ecdsa.c b/library/ecdsa.c
index 17a88bdd2..b3e516179 100644
--- a/library/ecdsa.c
+++ b/library/ecdsa.c
@@ -70,9 +70,14 @@ cleanup:
* 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 )
+static int ecdsa_sign_internal( 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 (*f_rng_blind)(void *, unsigned char *,
+ size_t),
+ void *p_rng_blind )
{
int ret, key_tries, sign_tries, blind_tries;
mbedtls_ecp_point R;
@@ -99,7 +104,10 @@ int mbedtls_ecdsa_sign( mbedtls_ecp_group *grp, mbedtls_mpi *r, mbedtls_mpi *s,
key_tries = 0;
do
{
- MBEDTLS_MPI_CHK( mbedtls_ecp_gen_keypair( grp, &k, &R, f_rng, p_rng ) );
+ MBEDTLS_MPI_CHK( mbedtls_ecp_gen_privkey( grp, &k, f_rng, p_rng ) );
+
+ MBEDTLS_MPI_CHK( mbedtls_ecp_mul( grp, &R, &k, &grp->G,
+ f_rng_blind, p_rng_blind ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( r, &R.X, &grp->N ) );
if( key_tries++ > 10 )
@@ -123,7 +131,8 @@ int mbedtls_ecdsa_sign( mbedtls_ecp_group *grp, mbedtls_mpi *r, mbedtls_mpi *s,
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_fill_random( &t, n_size, f_rng_blind,
+ p_rng_blind ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( &t, 8 * n_size - grp->nbits ) );
/* See mbedtls_ecp_gen_keypair() */
@@ -158,15 +167,27 @@ cleanup:
return( ret );
}
+
+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 )
+{
+ /* Use the same RNG for both blinding and ephemeral key generation */
+ return( ecdsa_sign_internal( grp, r, s, d, buf, blen, f_rng, p_rng,
+ f_rng, p_rng ) );
+}
#endif /* MBEDTLS_ECDSA_SIGN_ALT */
#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 )
+static int ecdsa_sign_det_internal( 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 (*f_rng_blind)(void *, unsigned char *,
+ size_t),
+ void *p_rng_blind )
{
int ret;
mbedtls_hmac_drbg_context rng_ctx;
@@ -187,8 +208,20 @@ int mbedtls_ecdsa_sign_det( mbedtls_ecp_group *grp, mbedtls_mpi *r, mbedtls_mpi
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 );
+ if( f_rng_blind != NULL )
+ ret = ecdsa_sign_internal( grp, r, s, d, buf, blen,
+ mbedtls_hmac_drbg_random, &rng_ctx,
+ f_rng_blind, p_rng_blind );
+ else
+ /*
+ * Use the same RNG for both blinding and ephemeral key generation.
+ * Since the RNG output is always the same for the same key and message,
+ * this limits the efficiency of blinding and leaks information through
+ * side channels.
+ */
+ ret = ecdsa_sign_internal( grp, r, s, d, buf, blen,
+ mbedtls_hmac_drbg_random, &rng_ctx,
+ mbedtls_hmac_drbg_random, &rng_ctx );
cleanup:
mbedtls_hmac_drbg_free( &rng_ctx );
@@ -196,6 +229,30 @@ cleanup:
return( ret );
}
+
+/*
+ * Deterministic signature wrappers
+ */
+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 )
+{
+ return( ecdsa_sign_det_internal( grp, r, s, d, buf, blen, md_alg,
+ NULL, NULL ) );
+}
+
+int mbedtls_ecdsa_sign_det_ext( 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 (*f_rng_blind)(void *, unsigned char *,
+ size_t),
+ void *p_rng_blind )
+{
+ return( ecdsa_sign_det_internal( grp, r, s, d, buf, blen, md_alg,
+ f_rng_blind, p_rng_blind ) );
+}
#endif /* MBEDTLS_ECDSA_DETERMINISTIC */
#if !defined(MBEDTLS_ECDSA_VERIFY_ALT)
@@ -326,17 +383,15 @@ int mbedtls_ecdsa_write_signature( mbedtls_ecdsa_context *ctx, mbedtls_md_type_t
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 ) );
+ MBEDTLS_MPI_CHK( ecdsa_sign_det_internal( &ctx->grp, &r, &s, &ctx->d,
+ hash, hlen, md_alg,
+ f_rng, p_rng ) );
#else
(void) md_alg;
MBEDTLS_MPI_CHK( mbedtls_ecdsa_sign( &ctx->grp, &r, &s, &ctx->d,
hash, hlen, f_rng, p_rng ) );
-#endif
+#endif /* MBEDTLS_ECDSA_DETERMINISTIC */
MBEDTLS_MPI_CHK( ecdsa_signature_to_asn1( &r, &s, sig, slen ) );