From 9b99a8942f4afd63e5653482d20a2be1330c8c6a Mon Sep 17 00:00:00 2001 From: Gilles Peskine Date: Fri, 14 Sep 2018 18:32:19 +0200 Subject: [PATCH] mbedtls_ecp_muladd is only for short Weierstrass curves Document that mbedtls_ecp_muladd and mbedtls_ecp_muladd_restartable are only implemented on short Weierstrass curves. Exclude these functions at build time if no short Weierstrass curve is included in the build. Before, these functions failed to compile in such a configuration. Signed-off-by: Gilles Peskine --- include/mbedtls/ecp.h | 34 ++++++++++++++++++++++++++++++++++ library/ecp.c | 2 ++ 2 files changed, 36 insertions(+) diff --git a/include/mbedtls/ecp.h b/include/mbedtls/ecp.h index 450e354926..8185224a9f 100644 --- a/include/mbedtls/ecp.h +++ b/include/mbedtls/ecp.h @@ -61,6 +61,26 @@ #define MBEDTLS_ERR_ECP_IN_PROGRESS -0x4B00 /**< Operation in progress, call again with the same parameters to continue. */ +/* Flags indicating whether to include code that is specific to certain + * types of curves. These flags are for internal library use only. */ +#if defined(MBEDTLS_ECP_DP_SECP192R1_ENABLED) || \ + defined(MBEDTLS_ECP_DP_SECP224R1_ENABLED) || \ + defined(MBEDTLS_ECP_DP_SECP256R1_ENABLED) || \ + defined(MBEDTLS_ECP_DP_SECP384R1_ENABLED) || \ + defined(MBEDTLS_ECP_DP_SECP521R1_ENABLED) || \ + defined(MBEDTLS_ECP_DP_SECP192K1_ENABLED) || \ + defined(MBEDTLS_ECP_DP_SECP224K1_ENABLED) || \ + defined(MBEDTLS_ECP_DP_SECP256K1_ENABLED) || \ + defined(MBEDTLS_ECP_DP_BP256R1_ENABLED) || \ + defined(MBEDTLS_ECP_DP_BP384R1_ENABLED) || \ + defined(MBEDTLS_ECP_DP_BP512R1_ENABLED) +#define MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED +#endif +#if defined(MBEDTLS_ECP_DP_CURVE25519_ENABLED) || \ + defined(MBEDTLS_ECP_DP_CURVE448_ENABLED) +#define MBEDTLS_ECP_MONTGOMERY_ENABLED +#endif + #ifdef __cplusplus extern "C" { #endif @@ -906,6 +926,7 @@ int mbedtls_ecp_mul_restartable( mbedtls_ecp_group *grp, mbedtls_ecp_point *R, int (*f_rng)(void *, unsigned char *, size_t), void *p_rng, mbedtls_ecp_restart_ctx *rs_ctx ); +#if defined(MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED) /** * \brief This function performs multiplication and addition of two * points by integers: \p R = \p m * \p P + \p n * \p Q @@ -915,6 +936,10 @@ int mbedtls_ecp_mul_restartable( mbedtls_ecp_group *grp, mbedtls_ecp_point *R, * \note In contrast to mbedtls_ecp_mul(), this function does not * guarantee a constant execution flow and timing. * + * \note This function is only defined for short Weierstrass curves. + * It may not be included in builds without any short + * Weierstrass curve. + * * \param grp The ECP group to use. * This must be initialized and have group parameters * set, for example through mbedtls_ecp_group_load(). @@ -933,6 +958,8 @@ int mbedtls_ecp_mul_restartable( mbedtls_ecp_group *grp, mbedtls_ecp_point *R, * valid private keys, or \p P or \p Q are not valid public * keys. * \return #MBEDTLS_ERR_MPI_ALLOC_FAILED on memory-allocation failure. + * \return #MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE if \p grp does not + * designate a short Weierstrass curve. * \return Another negative error code on other kinds of failure. */ int mbedtls_ecp_muladd( mbedtls_ecp_group *grp, mbedtls_ecp_point *R, @@ -950,6 +977,10 @@ int mbedtls_ecp_muladd( mbedtls_ecp_group *grp, mbedtls_ecp_point *R, * but it can return early and restart according to the limit * set with \c mbedtls_ecp_set_max_ops() to reduce blocking. * + * \note This function is only defined for short Weierstrass curves. + * It may not be included in builds without any short + * Weierstrass curve. + * * \param grp The ECP group to use. * This must be initialized and have group parameters * set, for example through mbedtls_ecp_group_load(). @@ -969,6 +1000,8 @@ int mbedtls_ecp_muladd( mbedtls_ecp_group *grp, mbedtls_ecp_point *R, * valid private keys, or \p P or \p Q are not valid public * keys. * \return #MBEDTLS_ERR_MPI_ALLOC_FAILED on memory-allocation failure. + * \return #MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE if \p grp does not + * designate a short Weierstrass curve. * \return #MBEDTLS_ERR_ECP_IN_PROGRESS if maximum number of * operations was reached: see \c mbedtls_ecp_set_max_ops(). * \return Another negative error code on other kinds of failure. @@ -978,6 +1011,7 @@ int mbedtls_ecp_muladd_restartable( const mbedtls_mpi *m, const mbedtls_ecp_point *P, const mbedtls_mpi *n, const mbedtls_ecp_point *Q, mbedtls_ecp_restart_ctx *rs_ctx ); +#endif /* MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED */ /** * \brief This function checks that a point is a valid public key diff --git a/library/ecp.c b/library/ecp.c index 2f69d68692..1b289f67a6 100644 --- a/library/ecp.c +++ b/library/ecp.c @@ -2781,6 +2781,7 @@ cleanup: } #endif /* ECP_SHORTWEIERSTRASS */ +#if defined(MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED) /* * R = m * P with shortcuts for m == 1 and m == -1 * NOT constant-time - ONLY for short Weierstrass! @@ -2926,6 +2927,7 @@ int mbedtls_ecp_muladd( mbedtls_ecp_group *grp, mbedtls_ecp_point *R, ECP_VALIDATE_RET( Q != NULL ); return( mbedtls_ecp_muladd_restartable( grp, R, m, P, n, Q, NULL ) ); } +#endif /* MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED */ #if defined(ECP_MONTGOMERY) /*