/* * Elliptic curves over GF(p): generic functions * * 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 * GECC = Guide to Elliptic Curve Cryptography - Hankerson, Menezes, Vanstone * FIPS 186-3 http://csrc.nist.gov/publications/fips/fips186-3/fips_186-3.pdf * RFC 4492 for the related TLS structures and constants * RFC 7748 for the Curve448 and Curve25519 curve definitions * * [Curve25519] http://cr.yp.to/ecdh/curve25519-20060209.pdf * * [2] CORON, Jean-S'ebastien. Resistance against differential power analysis * for elliptic curve cryptosystems. In : Cryptographic Hardware and * Embedded Systems. Springer Berlin Heidelberg, 1999. p. 292-302. * * * [3] HEDABOU, Mustapha, PINEL, Pierre, et B'EN'ETEAU, Lucien. A comb method to * render ECC resistant against Side Channel Attacks. IACR Cryptology * ePrint Archive, 2004, vol. 2004, p. 342. * */ #if !defined(MBEDTLS_CONFIG_FILE) #include "mbedtls/config.h" #else #include MBEDTLS_CONFIG_FILE #endif #if defined(MBEDTLS_ECP_C) #include "mbedtls/ecp.h" #include "mbedtls/threading.h" #include "mbedtls/platform_util.h" #include #if !defined(MBEDTLS_ECP_ALT) #if defined(MBEDTLS_PLATFORM_C) #include "mbedtls/platform.h" #else #include #include #define mbedtls_printf printf #define mbedtls_calloc calloc #define mbedtls_free free #endif #include "mbedtls/ecp_internal.h" #if ( defined(__ARMCC_VERSION) || defined(_MSC_VER) ) && \ !defined(inline) && !defined(__cplusplus) #define inline __inline #endif #if defined(MBEDTLS_SELF_TEST) /* * Counts of point addition and doubling, and field multiplications. * Used to test resistance of point multiplication to simple timing attacks. */ static unsigned long add_count, dbl_count, mul_count; #endif #if defined(MBEDTLS_ECP_RESTARTABLE) /* * Maximum number of "basic operations" to be done in a row. * * Default value 0 means that ECC operations will not yield. * Note that regardless of the value of ecp_max_ops, always at * least one step is performed before yielding. * * Setting ecp_max_ops=1 can be suitable for testing purposes * as it will interrupt computation at all possible points. */ static unsigned ecp_max_ops = 0; /* * Set ecp_max_ops */ void mbedtls_ecp_set_max_ops( unsigned max_ops ) { ecp_max_ops = max_ops; } /* * Check if restart is enabled */ int mbedtls_ecp_restart_enabled( void ) { return( ecp_max_ops != 0 ); } /* * Restart sub-context for ecp_mul_comb() */ struct mbedtls_ecp_restart_mul { mbedtls_ecp_point R; /* current intermediate result */ size_t i; /* current index in various loops, 0 outside */ mbedtls_ecp_point *T; /* table for precomputed points */ unsigned char T_size; /* number of points in table T */ enum { /* what were we doing last time we returned? */ ecp_rsm_init = 0, /* nothing so far, dummy initial state */ ecp_rsm_pre_dbl, /* precompute 2^n multiples */ ecp_rsm_pre_norm_dbl, /* normalize precomputed 2^n multiples */ ecp_rsm_pre_add, /* precompute remaining points by adding */ ecp_rsm_pre_norm_add, /* normalize all precomputed points */ ecp_rsm_comb_core, /* ecp_mul_comb_core() */ ecp_rsm_final_norm, /* do the final normalization */ } state; }; /* * Init restart_mul sub-context */ static void ecp_restart_rsm_init( mbedtls_ecp_restart_mul_ctx *ctx ) { mbedtls_ecp_point_init( &ctx->R ); ctx->i = 0; ctx->T = NULL; ctx->T_size = 0; ctx->state = ecp_rsm_init; } /* * Free the components of a restart_mul sub-context */ static void ecp_restart_rsm_free( mbedtls_ecp_restart_mul_ctx *ctx ) { unsigned char i; if( ctx == NULL ) return; mbedtls_ecp_point_free( &ctx->R ); if( ctx->T != NULL ) { for( i = 0; i < ctx->T_size; i++ ) mbedtls_ecp_point_free( ctx->T + i ); mbedtls_free( ctx->T ); } ecp_restart_rsm_init( ctx ); } /* * Restart context for ecp_muladd() */ struct mbedtls_ecp_restart_muladd { mbedtls_ecp_point mP; /* mP value */ mbedtls_ecp_point R; /* R intermediate result */ enum { /* what should we do next? */ ecp_rsma_mul1 = 0, /* first multiplication */ ecp_rsma_mul2, /* second multiplication */ ecp_rsma_add, /* addition */ ecp_rsma_norm, /* normalization */ } state; }; /* * Init restart_muladd sub-context */ static void ecp_restart_ma_init( mbedtls_ecp_restart_muladd_ctx *ctx ) { mbedtls_ecp_point_init( &ctx->mP ); mbedtls_ecp_point_init( &ctx->R ); ctx->state = ecp_rsma_mul1; } /* * Free the components of a restart_muladd sub-context */ static void ecp_restart_ma_free( mbedtls_ecp_restart_muladd_ctx *ctx ) { if( ctx == NULL ) return; mbedtls_ecp_point_free( &ctx->mP ); mbedtls_ecp_point_free( &ctx->R ); ecp_restart_ma_init( ctx ); } /* * Initialize a restart context */ void mbedtls_ecp_restart_init( mbedtls_ecp_restart_ctx *ctx ) { ctx->ops_done = 0; ctx->depth = 0; ctx->rsm = NULL; ctx->ma = NULL; } /* * Free the components of a restart context */ void mbedtls_ecp_restart_free( mbedtls_ecp_restart_ctx *ctx ) { if( ctx == NULL ) return; ecp_restart_rsm_free( ctx->rsm ); mbedtls_free( ctx->rsm ); ecp_restart_ma_free( ctx->ma ); mbedtls_free( ctx->ma ); mbedtls_ecp_restart_init( ctx ); } /* * Check if we can do the next step */ int mbedtls_ecp_check_budget( const mbedtls_ecp_group *grp, mbedtls_ecp_restart_ctx *rs_ctx, unsigned ops ) { if( rs_ctx != NULL && ecp_max_ops != 0 ) { /* scale depending on curve size: the chosen reference is 256-bit, * and multiplication is quadratic. Round to the closest integer. */ if( grp->pbits >= 512 ) ops *= 4; else if( grp->pbits >= 384 ) ops *= 2; /* avoid infinite loops: always allow first step */ if( rs_ctx->ops_done != 0 && rs_ctx->ops_done + ops > ecp_max_ops ) return( MBEDTLS_ERR_ECP_IN_PROGRESS ); /* update running count */ rs_ctx->ops_done += ops; } return( 0 ); } /* Call this when entering a function that needs its own sub-context */ #define ECP_RS_ENTER( SUB ) do { \ /* reset ops count for this call if top-level */ \ if( rs_ctx != NULL && rs_ctx->depth++ == 0 ) \ rs_ctx->ops_done = 0; \ \ /* set up our own sub-context if needed */ \ if( mbedtls_ecp_restart_enabled() && \ rs_ctx != NULL && rs_ctx->SUB == NULL ) \ { \ rs_ctx->SUB = mbedtls_calloc( 1, sizeof( *rs_ctx->SUB ) ); \ if( rs_ctx->SUB == NULL ) \ return( MBEDTLS_ERR_ECP_ALLOC_FAILED ); \ \ ecp_restart_## SUB ##_init( rs_ctx->SUB ); \ } \ } while( 0 ) /* Call this when leaving a function that needs its own sub-context */ #define ECP_RS_LEAVE( SUB ) do { \ /* clear our sub-context when not in progress (done or error) */ \ if( rs_ctx != NULL && rs_ctx->SUB != NULL && \ ret != MBEDTLS_ERR_ECP_IN_PROGRESS ) \ { \ ecp_restart_## SUB ##_free( rs_ctx->SUB ); \ mbedtls_free( rs_ctx->SUB ); \ rs_ctx->SUB = NULL; \ } \ \ if( rs_ctx != NULL ) \ rs_ctx->depth--; \ } while( 0 ) #else /* MBEDTLS_ECP_RESTARTABLE */ #define ECP_RS_ENTER( sub ) (void) rs_ctx; #define ECP_RS_LEAVE( sub ) (void) rs_ctx; #endif /* MBEDTLS_ECP_RESTARTABLE */ #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_BP256R1_ENABLED) || \ defined(MBEDTLS_ECP_DP_BP384R1_ENABLED) || \ defined(MBEDTLS_ECP_DP_BP512R1_ENABLED) || \ defined(MBEDTLS_ECP_DP_SECP192K1_ENABLED) || \ defined(MBEDTLS_ECP_DP_SECP224K1_ENABLED) || \ defined(MBEDTLS_ECP_DP_SECP256K1_ENABLED) #define ECP_SHORTWEIERSTRASS #endif #if defined(MBEDTLS_ECP_DP_CURVE25519_ENABLED) || \ defined(MBEDTLS_ECP_DP_CURVE448_ENABLED) #define ECP_MONTGOMERY #endif /* * Curve types: internal for now, might be exposed later */ typedef enum { ECP_TYPE_NONE = 0, ECP_TYPE_SHORT_WEIERSTRASS, /* y^2 = x^3 + a x + b */ ECP_TYPE_MONTGOMERY, /* y^2 = x^3 + a x^2 + x */ } ecp_curve_type; /* * List of supported curves: * - internal ID * - TLS NamedCurve ID (RFC 4492 sec. 5.1.1, RFC 7071 sec. 2) * - size in bits * - readable name * * Curves are listed in order: largest curves first, and for a given size, * fastest curves first. This provides the default order for the SSL module. * * Reminder: update profiles in x509_crt.c when adding a new curves! */ static const mbedtls_ecp_curve_info ecp_supported_curves[] = { #if defined(MBEDTLS_ECP_DP_SECP521R1_ENABLED) { MBEDTLS_ECP_DP_SECP521R1, 25, 521, "secp521r1" }, #endif #if defined(MBEDTLS_ECP_DP_BP512R1_ENABLED) { MBEDTLS_ECP_DP_BP512R1, 28, 512, "brainpoolP512r1" }, #endif #if defined(MBEDTLS_ECP_DP_SECP384R1_ENABLED) { MBEDTLS_ECP_DP_SECP384R1, 24, 384, "secp384r1" }, #endif #if defined(MBEDTLS_ECP_DP_BP384R1_ENABLED) { MBEDTLS_ECP_DP_BP384R1, 27, 384, "brainpoolP384r1" }, #endif #if defined(MBEDTLS_ECP_DP_SECP256R1_ENABLED) { MBEDTLS_ECP_DP_SECP256R1, 23, 256, "secp256r1" }, #endif #if defined(MBEDTLS_ECP_DP_SECP256K1_ENABLED) { MBEDTLS_ECP_DP_SECP256K1, 22, 256, "secp256k1" }, #endif #if defined(MBEDTLS_ECP_DP_BP256R1_ENABLED) { MBEDTLS_ECP_DP_BP256R1, 26, 256, "brainpoolP256r1" }, #endif #if defined(MBEDTLS_ECP_DP_SECP224R1_ENABLED) { MBEDTLS_ECP_DP_SECP224R1, 21, 224, "secp224r1" }, #endif #if defined(MBEDTLS_ECP_DP_SECP224K1_ENABLED) { MBEDTLS_ECP_DP_SECP224K1, 20, 224, "secp224k1" }, #endif #if defined(MBEDTLS_ECP_DP_SECP192R1_ENABLED) { MBEDTLS_ECP_DP_SECP192R1, 19, 192, "secp192r1" }, #endif #if defined(MBEDTLS_ECP_DP_SECP192K1_ENABLED) { MBEDTLS_ECP_DP_SECP192K1, 18, 192, "secp192k1" }, #endif { MBEDTLS_ECP_DP_NONE, 0, 0, NULL }, }; #define ECP_NB_CURVES sizeof( ecp_supported_curves ) / \ sizeof( ecp_supported_curves[0] ) static mbedtls_ecp_group_id ecp_supported_grp_id[ECP_NB_CURVES]; /* * List of supported curves and associated info */ const mbedtls_ecp_curve_info *mbedtls_ecp_curve_list( void ) { return( ecp_supported_curves ); } /* * List of supported curves, group ID only */ const mbedtls_ecp_group_id *mbedtls_ecp_grp_id_list( void ) { static int init_done = 0; if( ! init_done ) { size_t i = 0; const mbedtls_ecp_curve_info *curve_info; for( curve_info = mbedtls_ecp_curve_list(); curve_info->grp_id != MBEDTLS_ECP_DP_NONE; curve_info++ ) { ecp_supported_grp_id[i++] = curve_info->grp_id; } ecp_supported_grp_id[i] = MBEDTLS_ECP_DP_NONE; init_done = 1; } return( ecp_supported_grp_id ); } /* * Get the curve info for the internal identifier */ const mbedtls_ecp_curve_info *mbedtls_ecp_curve_info_from_grp_id( mbedtls_ecp_group_id grp_id ) { const mbedtls_ecp_curve_info *curve_info; for( curve_info = mbedtls_ecp_curve_list(); curve_info->grp_id != MBEDTLS_ECP_DP_NONE; curve_info++ ) { if( curve_info->grp_id == grp_id ) return( curve_info ); } return( NULL ); } /* * Get the curve info from the TLS identifier */ const mbedtls_ecp_curve_info *mbedtls_ecp_curve_info_from_tls_id( uint16_t tls_id ) { const mbedtls_ecp_curve_info *curve_info; for( curve_info = mbedtls_ecp_curve_list(); curve_info->grp_id != MBEDTLS_ECP_DP_NONE; curve_info++ ) { if( curve_info->tls_id == tls_id ) return( curve_info ); } return( NULL ); } /* * Get the curve info from the name */ const mbedtls_ecp_curve_info *mbedtls_ecp_curve_info_from_name( const char *name ) { const mbedtls_ecp_curve_info *curve_info; for( curve_info = mbedtls_ecp_curve_list(); curve_info->grp_id != MBEDTLS_ECP_DP_NONE; curve_info++ ) { if( strcmp( curve_info->name, name ) == 0 ) return( curve_info ); } return( NULL ); } /* * Get the type of a curve */ static inline ecp_curve_type ecp_get_type( const mbedtls_ecp_group *grp ) { if( grp->G.X.p == NULL ) return( ECP_TYPE_NONE ); if( grp->G.Y.p == NULL ) return( ECP_TYPE_MONTGOMERY ); else return( ECP_TYPE_SHORT_WEIERSTRASS ); } /* * Initialize (the components of) a point */ void mbedtls_ecp_point_init( mbedtls_ecp_point *pt ) { if( pt == NULL ) return; mbedtls_mpi_init( &pt->X ); mbedtls_mpi_init( &pt->Y ); mbedtls_mpi_init( &pt->Z ); } /* * Initialize (the components of) a group */ void mbedtls_ecp_group_init( mbedtls_ecp_group *grp ) { if( grp == NULL ) return; grp->id = MBEDTLS_ECP_DP_NONE; mbedtls_mpi_init( &grp->P ); mbedtls_mpi_init( &grp->A ); mbedtls_mpi_init( &grp->B ); mbedtls_ecp_point_init( &grp->G ); mbedtls_mpi_init( &grp->N ); grp->pbits = 0; grp->nbits = 0; grp->h = 0; grp->modp = NULL; grp->t_pre = NULL; grp->t_post = NULL; grp->t_data = NULL; grp->T = NULL; grp->T_size = 0; } /* * Initialize (the components of) a key pair */ void mbedtls_ecp_keypair_init( mbedtls_ecp_keypair *key ) { if( key == NULL ) return; mbedtls_ecp_group_init( &key->grp ); mbedtls_mpi_init( &key->d ); mbedtls_ecp_point_init( &key->Q ); } /* * Unallocate (the components of) a point */ void mbedtls_ecp_point_free( mbedtls_ecp_point *pt ) { if( pt == NULL ) return; mbedtls_mpi_free( &( pt->X ) ); mbedtls_mpi_free( &( pt->Y ) ); mbedtls_mpi_free( &( pt->Z ) ); } /* * Unallocate (the components of) a group */ void mbedtls_ecp_group_free( mbedtls_ecp_group *grp ) { size_t i; if( grp == NULL ) return; if( grp->h != 1 ) { mbedtls_mpi_free( &grp->P ); mbedtls_mpi_free( &grp->A ); mbedtls_mpi_free( &grp->B ); mbedtls_ecp_point_free( &grp->G ); mbedtls_mpi_free( &grp->N ); } if( grp->T != NULL ) { for( i = 0; i < grp->T_size; i++ ) mbedtls_ecp_point_free( &grp->T[i] ); mbedtls_free( grp->T ); } mbedtls_platform_zeroize( grp, sizeof( mbedtls_ecp_group ) ); } /* * Unallocate (the components of) a key pair */ void mbedtls_ecp_keypair_free( mbedtls_ecp_keypair *key ) { if( key == NULL ) return; mbedtls_ecp_group_free( &key->grp ); mbedtls_mpi_free( &key->d ); mbedtls_ecp_point_free( &key->Q ); } /* * Copy the contents of a point */ int mbedtls_ecp_copy( mbedtls_ecp_point *P, const mbedtls_ecp_point *Q ) { int ret; MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &P->X, &Q->X ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &P->Y, &Q->Y ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &P->Z, &Q->Z ) ); cleanup: return( ret ); } /* * Copy the contents of a group object */ int mbedtls_ecp_group_copy( mbedtls_ecp_group *dst, const mbedtls_ecp_group *src ) { return mbedtls_ecp_group_load( dst, src->id ); } /* * Set point to zero */ int mbedtls_ecp_set_zero( mbedtls_ecp_point *pt ) { int ret; MBEDTLS_MPI_CHK( mbedtls_mpi_lset( &pt->X , 1 ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_lset( &pt->Y , 1 ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_lset( &pt->Z , 0 ) ); cleanup: return( ret ); } /* * Tell if a point is zero */ int mbedtls_ecp_is_zero( mbedtls_ecp_point *pt ) { return( mbedtls_mpi_cmp_int( &pt->Z, 0 ) == 0 ); } /* * Compare two points lazyly */ int mbedtls_ecp_point_cmp( const mbedtls_ecp_point *P, const mbedtls_ecp_point *Q ) { if( mbedtls_mpi_cmp_mpi( &P->X, &Q->X ) == 0 && mbedtls_mpi_cmp_mpi( &P->Y, &Q->Y ) == 0 && mbedtls_mpi_cmp_mpi( &P->Z, &Q->Z ) == 0 ) { return( 0 ); } return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA ); } /* * Import a non-zero point from ASCII strings */ int mbedtls_ecp_point_read_string( mbedtls_ecp_point *P, int radix, const char *x, const char *y ) { int ret; MBEDTLS_MPI_CHK( mbedtls_mpi_read_string( &P->X, radix, x ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_read_string( &P->Y, radix, y ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_lset( &P->Z, 1 ) ); cleanup: return( ret ); } /* * Export a point into unsigned binary data (SEC1 2.3.3) */ int mbedtls_ecp_point_write_binary( const mbedtls_ecp_group *grp, const mbedtls_ecp_point *P, int format, size_t *olen, unsigned char *buf, size_t buflen ) { int ret = 0; size_t plen; if( format != MBEDTLS_ECP_PF_UNCOMPRESSED && format != MBEDTLS_ECP_PF_COMPRESSED ) return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA ); /* * Common case: P == 0 */ if( mbedtls_mpi_cmp_int( &P->Z, 0 ) == 0 ) { if( buflen < 1 ) return( MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL ); buf[0] = 0x00; *olen = 1; return( 0 ); } plen = mbedtls_mpi_size( &grp->P ); if( format == MBEDTLS_ECP_PF_UNCOMPRESSED ) { *olen = 2 * plen + 1; if( buflen < *olen ) return( MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL ); buf[0] = 0x04; MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &P->X, buf + 1, plen ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &P->Y, buf + 1 + plen, plen ) ); } else if( format == MBEDTLS_ECP_PF_COMPRESSED ) { *olen = plen + 1; if( buflen < *olen ) return( MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL ); buf[0] = 0x02 + mbedtls_mpi_get_bit( &P->Y, 0 ); MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &P->X, buf + 1, plen ) ); } cleanup: return( ret ); } /* * Import a point from unsigned binary data (SEC1 2.3.4) */ int mbedtls_ecp_point_read_binary( const mbedtls_ecp_group *grp, mbedtls_ecp_point *pt, const unsigned char *buf, size_t ilen ) { int ret; size_t plen; if( ilen < 1 ) return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA ); if( buf[0] == 0x00 ) { if( ilen == 1 ) return( mbedtls_ecp_set_zero( pt ) ); else return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA ); } plen = mbedtls_mpi_size( &grp->P ); if( buf[0] != 0x04 ) return( MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE ); if( ilen != 2 * plen + 1 ) return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA ); MBEDTLS_MPI_CHK( mbedtls_mpi_read_binary( &pt->X, buf + 1, plen ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_read_binary( &pt->Y, buf + 1 + plen, plen ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_lset( &pt->Z, 1 ) ); cleanup: return( ret ); } /* * Import a point from a TLS ECPoint record (RFC 4492) * struct { * opaque point <1..2^8-1>; * } ECPoint; */ int mbedtls_ecp_tls_read_point( const mbedtls_ecp_group *grp, mbedtls_ecp_point *pt, const unsigned char **buf, size_t buf_len ) { unsigned char data_len; const unsigned char *buf_start; /* * We must have at least two bytes (1 for length, at least one for data) */ if( buf_len < 2 ) return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA ); data_len = *(*buf)++; if( data_len < 1 || data_len > buf_len - 1 ) return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA ); /* * Save buffer start for read_binary and update buf */ buf_start = *buf; *buf += data_len; return mbedtls_ecp_point_read_binary( grp, pt, buf_start, data_len ); } /* * Export a point as a TLS ECPoint record (RFC 4492) * struct { * opaque point <1..2^8-1>; * } ECPoint; */ int mbedtls_ecp_tls_write_point( const mbedtls_ecp_group *grp, const mbedtls_ecp_point *pt, int format, size_t *olen, unsigned char *buf, size_t blen ) { int ret; /* * buffer length must be at least one, for our length byte */ if( blen < 1 ) return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA ); if( ( ret = mbedtls_ecp_point_write_binary( grp, pt, format, olen, buf + 1, blen - 1) ) != 0 ) return( ret ); /* * write length to the first byte and update total length */ buf[0] = (unsigned char) *olen; ++*olen; return( 0 ); } /* * Set a group from an ECParameters record (RFC 4492) */ int mbedtls_ecp_tls_read_group( mbedtls_ecp_group *grp, const unsigned char **buf, size_t len ) { uint16_t tls_id; const mbedtls_ecp_curve_info *curve_info; /* * We expect at least three bytes (see below) */ if( len < 3 ) return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA ); /* * First byte is curve_type; only named_curve is handled */ if( *(*buf)++ != MBEDTLS_ECP_TLS_NAMED_CURVE ) return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA ); /* * Next two bytes are the namedcurve value */ tls_id = *(*buf)++; tls_id <<= 8; tls_id |= *(*buf)++; if( ( curve_info = mbedtls_ecp_curve_info_from_tls_id( tls_id ) ) == NULL ) return( MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE ); return mbedtls_ecp_group_load( grp, curve_info->grp_id ); } /* * Write the ECParameters record corresponding to a group (RFC 4492) */ int mbedtls_ecp_tls_write_group( const mbedtls_ecp_group *grp, size_t *olen, unsigned char *buf, size_t blen ) { const mbedtls_ecp_curve_info *curve_info; if( ( curve_info = mbedtls_ecp_curve_info_from_grp_id( grp->id ) ) == NULL ) return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA ); /* * We are going to write 3 bytes (see below) */ *olen = 3; if( blen < *olen ) return( MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL ); /* * First byte is curve_type, always named_curve */ *buf++ = MBEDTLS_ECP_TLS_NAMED_CURVE; /* * Next two bytes are the namedcurve value */ buf[0] = curve_info->tls_id >> 8; buf[1] = curve_info->tls_id & 0xFF; return( 0 ); } /* * Wrapper around fast quasi-modp functions, with fall-back to mbedtls_mpi_mod_mpi. * See the documentation of struct mbedtls_ecp_group. * * This function is in the critial loop for mbedtls_ecp_mul, so pay attention to perf. */ static int ecp_modp( mbedtls_mpi *N, const mbedtls_ecp_group *grp ) { int ret; if( grp->modp == NULL ) return( mbedtls_mpi_mod_mpi( N, N, &grp->P ) ); /* N->s < 0 is a much faster test, which fails only if N is 0 */ if( ( N->s < 0 && mbedtls_mpi_cmp_int( N, 0 ) != 0 ) || mbedtls_mpi_bitlen( N ) > 2 * grp->pbits ) { return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA ); } MBEDTLS_MPI_CHK( grp->modp( N ) ); /* N->s < 0 is a much faster test, which fails only if N is 0 */ while( N->s < 0 && mbedtls_mpi_cmp_int( N, 0 ) != 0 ) MBEDTLS_MPI_CHK( mbedtls_mpi_add_mpi( N, N, &grp->P ) ); while( mbedtls_mpi_cmp_mpi( N, &grp->P ) >= 0 ) /* we known P, N and the result are positive */ MBEDTLS_MPI_CHK( mbedtls_mpi_sub_abs( N, N, &grp->P ) ); cleanup: return( ret ); } /* * Fast mod-p functions expect their argument to be in the 0..p^2 range. * * In order to guarantee that, we need to ensure that operands of * mbedtls_mpi_mul_mpi are in the 0..p range. So, after each operation we will * bring the result back to this range. * * The following macros are shortcuts for doing that. */ /* * Reduce a mbedtls_mpi mod p in-place, general case, to use after mbedtls_mpi_mul_mpi */ #if defined(MBEDTLS_SELF_TEST) #define INC_MUL_COUNT mul_count++; #else #define INC_MUL_COUNT #endif #define MOD_MUL( N ) do { MBEDTLS_MPI_CHK( ecp_modp( &N, grp ) ); INC_MUL_COUNT } \ while( 0 ) /* * Reduce a mbedtls_mpi mod p in-place, to use after mbedtls_mpi_sub_mpi * N->s < 0 is a very fast test, which fails only if N is 0 */ #define MOD_SUB( N ) \ while( N.s < 0 && mbedtls_mpi_cmp_int( &N, 0 ) != 0 ) \ MBEDTLS_MPI_CHK( mbedtls_mpi_add_mpi( &N, &N, &grp->P ) ) /* * Reduce a mbedtls_mpi mod p in-place, to use after mbedtls_mpi_add_mpi and mbedtls_mpi_mul_int. * We known P, N and the result are positive, so sub_abs is correct, and * a bit faster. */ #define MOD_ADD( N ) \ while( mbedtls_mpi_cmp_mpi( &N, &grp->P ) >= 0 ) \ MBEDTLS_MPI_CHK( mbedtls_mpi_sub_abs( &N, &N, &grp->P ) ) #if defined(ECP_SHORTWEIERSTRASS) /* * For curves in short Weierstrass form, we do all the internal operations in * Jacobian coordinates. * * For multiplication, we'll use a comb method with coutermeasueres against * SPA, hence timing attacks. */ /* * Normalize jacobian coordinates so that Z == 0 || Z == 1 (GECC 3.2.1) * Cost: 1N := 1I + 3M + 1S */ static int ecp_normalize_jac( const mbedtls_ecp_group *grp, mbedtls_ecp_point *pt ) { int ret; mbedtls_mpi Zi, ZZi; if( mbedtls_mpi_cmp_int( &pt->Z, 0 ) == 0 ) return( 0 ); #if defined(MBEDTLS_ECP_NORMALIZE_JAC_ALT) if( mbedtls_internal_ecp_grp_capable( grp ) ) return( mbedtls_internal_ecp_normalize_jac( grp, pt ) ); #endif /* MBEDTLS_ECP_NORMALIZE_JAC_ALT */ mbedtls_mpi_init( &Zi ); mbedtls_mpi_init( &ZZi ); /* * X = X / Z^2 mod p */ MBEDTLS_MPI_CHK( mbedtls_mpi_inv_mod( &Zi, &pt->Z, &grp->P ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &ZZi, &Zi, &Zi ) ); MOD_MUL( ZZi ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &pt->X, &pt->X, &ZZi ) ); MOD_MUL( pt->X ); /* * Y = Y / Z^3 mod p */ MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &pt->Y, &pt->Y, &ZZi ) ); MOD_MUL( pt->Y ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &pt->Y, &pt->Y, &Zi ) ); MOD_MUL( pt->Y ); /* * Z = 1 */ MBEDTLS_MPI_CHK( mbedtls_mpi_lset( &pt->Z, 1 ) ); cleanup: mbedtls_mpi_free( &Zi ); mbedtls_mpi_free( &ZZi ); return( ret ); } /* * Normalize jacobian coordinates of an array of (pointers to) points, * using Montgomery's trick to perform only one inversion mod P. * (See for example Cohen's "A Course in Computational Algebraic Number * Theory", Algorithm 10.3.4.) * * Warning: fails (returning an error) if one of the points is zero! * This should never happen, see choice of w in ecp_mul_comb(). * * Cost: 1N(t) := 1I + (6t - 3)M + 1S */ static int ecp_normalize_jac_many( const mbedtls_ecp_group *grp, mbedtls_ecp_point *T[], size_t T_size ) { int ret; size_t i; mbedtls_mpi *c, u, Zi, ZZi; if( T_size < 2 ) return( ecp_normalize_jac( grp, *T ) ); #if defined(MBEDTLS_ECP_NORMALIZE_JAC_MANY_ALT) if( mbedtls_internal_ecp_grp_capable( grp ) ) return( mbedtls_internal_ecp_normalize_jac_many( grp, T, T_size ) ); #endif if( ( c = mbedtls_calloc( T_size, sizeof( mbedtls_mpi ) ) ) == NULL ) return( MBEDTLS_ERR_ECP_ALLOC_FAILED ); for( i = 0; i < T_size; i++ ) mbedtls_mpi_init( &c[i] ); mbedtls_mpi_init( &u ); mbedtls_mpi_init( &Zi ); mbedtls_mpi_init( &ZZi ); /* * c[i] = Z_0 * ... * Z_i */ MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &c[0], &T[0]->Z ) ); for( i = 1; i < T_size; i++ ) { MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &c[i], &c[i-1], &T[i]->Z ) ); MOD_MUL( c[i] ); } /* * u = 1 / (Z_0 * ... * Z_n) mod P */ MBEDTLS_MPI_CHK( mbedtls_mpi_inv_mod( &u, &c[T_size-1], &grp->P ) ); for( i = T_size - 1; ; i-- ) { /* * Zi = 1 / Z_i mod p * u = 1 / (Z_0 * ... * Z_i) mod P */ if( i == 0 ) { MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &Zi, &u ) ); } else { MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &Zi, &u, &c[i-1] ) ); MOD_MUL( Zi ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &u, &u, &T[i]->Z ) ); MOD_MUL( u ); } /* * proceed as in normalize() */ MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &ZZi, &Zi, &Zi ) ); MOD_MUL( ZZi ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &T[i]->X, &T[i]->X, &ZZi ) ); MOD_MUL( T[i]->X ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &T[i]->Y, &T[i]->Y, &ZZi ) ); MOD_MUL( T[i]->Y ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &T[i]->Y, &T[i]->Y, &Zi ) ); MOD_MUL( T[i]->Y ); /* * Post-precessing: reclaim some memory by shrinking coordinates * - not storing Z (always 1) * - shrinking other coordinates, but still keeping the same number of * limbs as P, as otherwise it will too likely be regrown too fast. */ MBEDTLS_MPI_CHK( mbedtls_mpi_shrink( &T[i]->X, grp->P.n ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_shrink( &T[i]->Y, grp->P.n ) ); mbedtls_mpi_free( &T[i]->Z ); if( i == 0 ) break; } cleanup: mbedtls_mpi_free( &u ); mbedtls_mpi_free( &Zi ); mbedtls_mpi_free( &ZZi ); for( i = 0; i < T_size; i++ ) mbedtls_mpi_free( &c[i] ); mbedtls_free( c ); return( ret ); } /* * Conditional point inversion: Q -> -Q = (Q.X, -Q.Y, Q.Z) without leak. * "inv" must be 0 (don't invert) or 1 (invert) or the result will be invalid */ static int ecp_safe_invert_jac( const mbedtls_ecp_group *grp, mbedtls_ecp_point *Q, unsigned char inv ) { int ret; unsigned char nonzero; mbedtls_mpi mQY; mbedtls_mpi_init( &mQY ); /* Use the fact that -Q.Y mod P = P - Q.Y unless Q.Y == 0 */ MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mpi( &mQY, &grp->P, &Q->Y ) ); nonzero = mbedtls_mpi_cmp_int( &Q->Y, 0 ) != 0; MBEDTLS_MPI_CHK( mbedtls_mpi_safe_cond_assign( &Q->Y, &mQY, inv & nonzero ) ); cleanup: mbedtls_mpi_free( &mQY ); return( ret ); } /* * Point doubling R = 2 P, Jacobian coordinates * * Based on http://www.hyperelliptic.org/EFD/g1p/auto-shortw-jacobian.html#doubling-dbl-1998-cmo-2 . * * We follow the variable naming fairly closely. The formula variations that trade a MUL for a SQR * (plus a few ADDs) aren't useful as our bignum implementation doesn't distinguish squaring. * * Standard optimizations are applied when curve parameter A is one of { 0, -3 }. * * Cost: 1D := 3M + 4S (A == 0) * 4M + 4S (A == -3) * 3M + 6S + 1a otherwise */ static int ecp_double_jac( const mbedtls_ecp_group *grp, mbedtls_ecp_point *R, const mbedtls_ecp_point *P ) { int ret; mbedtls_mpi M, S, T, U; #if defined(MBEDTLS_SELF_TEST) dbl_count++; #endif #if defined(MBEDTLS_ECP_DOUBLE_JAC_ALT) if( mbedtls_internal_ecp_grp_capable( grp ) ) return( mbedtls_internal_ecp_double_jac( grp, R, P ) ); #endif /* MBEDTLS_ECP_DOUBLE_JAC_ALT */ mbedtls_mpi_init( &M ); mbedtls_mpi_init( &S ); mbedtls_mpi_init( &T ); mbedtls_mpi_init( &U ); /* Special case for A = -3 */ if( grp->A.p == NULL ) { /* M = 3(X + Z^2)(X - Z^2) */ MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &S, &P->Z, &P->Z ) ); MOD_MUL( S ); MBEDTLS_MPI_CHK( mbedtls_mpi_add_mpi( &T, &P->X, &S ) ); MOD_ADD( T ); MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mpi( &U, &P->X, &S ) ); MOD_SUB( U ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &S, &T, &U ) ); MOD_MUL( S ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_int( &M, &S, 3 ) ); MOD_ADD( M ); } else { /* M = 3.X^2 */ MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &S, &P->X, &P->X ) ); MOD_MUL( S ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_int( &M, &S, 3 ) ); MOD_ADD( M ); /* Optimize away for "koblitz" curves with A = 0 */ if( mbedtls_mpi_cmp_int( &grp->A, 0 ) != 0 ) { /* M += A.Z^4 */ MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &S, &P->Z, &P->Z ) ); MOD_MUL( S ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &T, &S, &S ) ); MOD_MUL( T ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &S, &T, &grp->A ) ); MOD_MUL( S ); MBEDTLS_MPI_CHK( mbedtls_mpi_add_mpi( &M, &M, &S ) ); MOD_ADD( M ); } } /* S = 4.X.Y^2 */ MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &T, &P->Y, &P->Y ) ); MOD_MUL( T ); MBEDTLS_MPI_CHK( mbedtls_mpi_shift_l( &T, 1 ) ); MOD_ADD( T ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &S, &P->X, &T ) ); MOD_MUL( S ); MBEDTLS_MPI_CHK( mbedtls_mpi_shift_l( &S, 1 ) ); MOD_ADD( S ); /* U = 8.Y^4 */ MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &U, &T, &T ) ); MOD_MUL( U ); MBEDTLS_MPI_CHK( mbedtls_mpi_shift_l( &U, 1 ) ); MOD_ADD( U ); /* T = M^2 - 2.S */ MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &T, &M, &M ) ); MOD_MUL( T ); MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mpi( &T, &T, &S ) ); MOD_SUB( T ); MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mpi( &T, &T, &S ) ); MOD_SUB( T ); /* S = M(S - T) - U */ MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mpi( &S, &S, &T ) ); MOD_SUB( S ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &S, &S, &M ) ); MOD_MUL( S ); MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mpi( &S, &S, &U ) ); MOD_SUB( S ); /* U = 2.Y.Z */ MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &U, &P->Y, &P->Z ) ); MOD_MUL( U ); MBEDTLS_MPI_CHK( mbedtls_mpi_shift_l( &U, 1 ) ); MOD_ADD( U ); MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &R->X, &T ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &R->Y, &S ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &R->Z, &U ) ); cleanup: mbedtls_mpi_free( &M ); mbedtls_mpi_free( &S ); mbedtls_mpi_free( &T ); mbedtls_mpi_free( &U ); return( ret ); } /* * Addition: R = P + Q, mixed affine-Jacobian coordinates (GECC 3.22) * * The coordinates of Q must be normalized (= affine), * but those of P don't need to. R is not normalized. * * Special cases: (1) P or Q is zero, (2) R is zero, (3) P == Q. * None of these cases can happen as intermediate step in ecp_mul_comb(): * - at each step, P, Q and R are multiples of the base point, the factor * being less than its order, so none of them is zero; * - Q is an odd multiple of the base point, P an even multiple, * due to the choice of precomputed points in the modified comb method. * So branches for these cases do not leak secret information. * * We accept Q->Z being unset (saving memory in tables) as meaning 1. * * Cost: 1A := 8M + 3S */ static int ecp_add_mixed( const mbedtls_ecp_group *grp, mbedtls_ecp_point *R, const mbedtls_ecp_point *P, const mbedtls_ecp_point *Q ) { int ret; mbedtls_mpi T1, T2, T3, T4, X, Y, Z; #if defined(MBEDTLS_SELF_TEST) add_count++; #endif #if defined(MBEDTLS_ECP_ADD_MIXED_ALT) if( mbedtls_internal_ecp_grp_capable( grp ) ) return( mbedtls_internal_ecp_add_mixed( grp, R, P, Q ) ); #endif /* MBEDTLS_ECP_ADD_MIXED_ALT */ /* * Trivial cases: P == 0 or Q == 0 (case 1) */ if( mbedtls_mpi_cmp_int( &P->Z, 0 ) == 0 ) return( mbedtls_ecp_copy( R, Q ) ); if( Q->Z.p != NULL && mbedtls_mpi_cmp_int( &Q->Z, 0 ) == 0 ) return( mbedtls_ecp_copy( R, P ) ); /* * Make sure Q coordinates are normalized */ if( Q->Z.p != NULL && mbedtls_mpi_cmp_int( &Q->Z, 1 ) != 0 ) return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA ); mbedtls_mpi_init( &T1 ); mbedtls_mpi_init( &T2 ); mbedtls_mpi_init( &T3 ); mbedtls_mpi_init( &T4 ); mbedtls_mpi_init( &X ); mbedtls_mpi_init( &Y ); mbedtls_mpi_init( &Z ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &T1, &P->Z, &P->Z ) ); MOD_MUL( T1 ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &T2, &T1, &P->Z ) ); MOD_MUL( T2 ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &T1, &T1, &Q->X ) ); MOD_MUL( T1 ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &T2, &T2, &Q->Y ) ); MOD_MUL( T2 ); MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mpi( &T1, &T1, &P->X ) ); MOD_SUB( T1 ); MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mpi( &T2, &T2, &P->Y ) ); MOD_SUB( T2 ); /* Special cases (2) and (3) */ if( mbedtls_mpi_cmp_int( &T1, 0 ) == 0 ) { if( mbedtls_mpi_cmp_int( &T2, 0 ) == 0 ) { ret = ecp_double_jac( grp, R, P ); goto cleanup; } else { ret = mbedtls_ecp_set_zero( R ); goto cleanup; } } MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &Z, &P->Z, &T1 ) ); MOD_MUL( Z ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &T3, &T1, &T1 ) ); MOD_MUL( T3 ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &T4, &T3, &T1 ) ); MOD_MUL( T4 ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &T3, &T3, &P->X ) ); MOD_MUL( T3 ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_int( &T1, &T3, 2 ) ); MOD_ADD( T1 ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &X, &T2, &T2 ) ); MOD_MUL( X ); MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mpi( &X, &X, &T1 ) ); MOD_SUB( X ); MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mpi( &X, &X, &T4 ) ); MOD_SUB( X ); MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mpi( &T3, &T3, &X ) ); MOD_SUB( T3 ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &T3, &T3, &T2 ) ); MOD_MUL( T3 ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &T4, &T4, &P->Y ) ); MOD_MUL( T4 ); MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mpi( &Y, &T3, &T4 ) ); MOD_SUB( Y ); MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &R->X, &X ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &R->Y, &Y ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &R->Z, &Z ) ); cleanup: mbedtls_mpi_free( &T1 ); mbedtls_mpi_free( &T2 ); mbedtls_mpi_free( &T3 ); mbedtls_mpi_free( &T4 ); mbedtls_mpi_free( &X ); mbedtls_mpi_free( &Y ); mbedtls_mpi_free( &Z ); return( ret ); } /* * Randomize jacobian coordinates: * (X, Y, Z) -> (l^2 X, l^3 Y, l Z) for random l * This is sort of the reverse operation of ecp_normalize_jac(). * * This countermeasure was first suggested in [2]. */ static int ecp_randomize_jac( const mbedtls_ecp_group *grp, mbedtls_ecp_point *pt, int (*f_rng)(void *, unsigned char *, size_t), void *p_rng ) { int ret; mbedtls_mpi l, ll; size_t p_size; int count = 0; #if defined(MBEDTLS_ECP_RANDOMIZE_JAC_ALT) if( mbedtls_internal_ecp_grp_capable( grp ) ) return( mbedtls_internal_ecp_randomize_jac( grp, pt, f_rng, p_rng ) ); #endif /* MBEDTLS_ECP_RANDOMIZE_JAC_ALT */ p_size = ( grp->pbits + 7 ) / 8; mbedtls_mpi_init( &l ); mbedtls_mpi_init( &ll ); /* Generate l such that 1 < l < p */ do { MBEDTLS_MPI_CHK( mbedtls_mpi_fill_random( &l, p_size, f_rng, p_rng ) ); while( mbedtls_mpi_cmp_mpi( &l, &grp->P ) >= 0 ) MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( &l, 1 ) ); if( count++ > 10 ) return( MBEDTLS_ERR_ECP_RANDOM_FAILED ); } while( mbedtls_mpi_cmp_int( &l, 1 ) <= 0 ); /* Z = l * Z */ MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &pt->Z, &pt->Z, &l ) ); MOD_MUL( pt->Z ); /* X = l^2 * X */ MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &ll, &l, &l ) ); MOD_MUL( ll ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &pt->X, &pt->X, &ll ) ); MOD_MUL( pt->X ); /* Y = l^3 * Y */ MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &ll, &ll, &l ) ); MOD_MUL( ll ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &pt->Y, &pt->Y, &ll ) ); MOD_MUL( pt->Y ); cleanup: mbedtls_mpi_free( &l ); mbedtls_mpi_free( &ll ); return( ret ); } /* * Check and define parameters used by the comb method (see below for details) */ #if MBEDTLS_ECP_WINDOW_SIZE < 2 || MBEDTLS_ECP_WINDOW_SIZE > 7 #error "MBEDTLS_ECP_WINDOW_SIZE out of bounds" #endif /* d = ceil( n / w ) */ #define COMB_MAX_D ( MBEDTLS_ECP_MAX_BITS + 1 ) / 2 /* number of precomputed points */ #define COMB_MAX_PRE ( 1 << ( MBEDTLS_ECP_WINDOW_SIZE - 1 ) ) /* * Compute the representation of m that will be used with our comb method. * * The basic comb method is described in GECC 3.44 for example. We use a * modified version that provides resistance to SPA by avoiding zero * digits in the representation as in [3]. We modify the method further by * requiring that all K_i be odd, which has the small cost that our * representation uses one more K_i, due to carries, but saves on the size of * the precomputed table. * * Summary of the comb method and its modifications: * * - The goal is to compute m*P for some w*d-bit integer m. * * - The basic comb method splits m into the w-bit integers * x[0] .. x[d-1] where x[i] consists of the bits in m whose * index has residue i modulo d, and computes m * P as * S[x[0]] + 2 * S[x[1]] + .. + 2^(d-1) S[x[d-1]], where * S[i_{w-1} .. i_0] := i_{w-1} 2^{(w-1)d} P + ... + i_1 2^d P + i_0 P. * * - If it happens that, say, x[i+1]=0 (=> S[x[i+1]]=0), one can replace the sum by * .. + 2^{i-1} S[x[i-1]] - 2^i S[x[i]] + 2^{i+1} S[x[i]] + 2^{i+2} S[x[i+2]] .., * thereby successively converting it into a form where all summands * are nonzero, at the cost of negative summands. This is the basic idea of [3]. * * - More generally, even if x[i+1] != 0, we can first transform the sum as * .. - 2^i S[x[i]] + 2^{i+1} ( S[x[i]] + S[x[i+1]] ) + 2^{i+2} S[x[i+2]] .., * and then replace S[x[i]] + S[x[i+1]] = S[x[i] ^ x[i+1]] + 2 S[x[i] & x[i+1]]. * Performing and iterating this procedure for those x[i] that are even * (keeping track of carry), we can transform the original sum into one of the form * S[x'[0]] +- 2 S[x'[1]] +- .. +- 2^{d-1} S[x'[d-1]] + 2^d S[x'[d]] * with all x'[i] odd. It is therefore only necessary to know S at odd indices, * which is why we are only computing half of it in the first place in * ecp_precompute_comb and accessing it with index abs(i) / 2 in ecp_select_comb. * * - For the sake of compactness, only the seven low-order bits of x[i] * are used to represent its absolute value (K_i in the paper), and the msb * of x[i] encodes the the sign (s_i in the paper): it is set if and only if * if s_i == -1; * * Calling conventions: * - x is an array of size d + 1 * - w is the size, ie number of teeth, of the comb, and must be between * 2 and 7 (in practice, between 2 and MBEDTLS_ECP_WINDOW_SIZE) * - m is the MPI, expected to be odd and such that bitlength(m) <= w * d * (the result will be incorrect if these assumptions are not satisfied) */ static void ecp_comb_recode_core( unsigned char x[], size_t d, unsigned char w, const mbedtls_mpi *m ) { size_t i, j; unsigned char c, cc, adjust; memset( x, 0, d+1 ); /* First get the classical comb values (except for x_d = 0) */ for( i = 0; i < d; i++ ) for( j = 0; j < w; j++ ) x[i] |= mbedtls_mpi_get_bit( m, i + d * j ) << j; /* Now make sure x_1 .. x_d are odd */ c = 0; for( i = 1; i <= d; i++ ) { /* Add carry and update it */ cc = x[i] & c; x[i] = x[i] ^ c; c = cc; /* Adjust if needed, avoiding branches */ adjust = 1 - ( x[i] & 0x01 ); c |= x[i] & ( x[i-1] * adjust ); x[i] = x[i] ^ ( x[i-1] * adjust ); x[i-1] |= adjust << 7; } } /* * Precompute points for the adapted comb method * * Assumption: T must be able to hold 2^{w - 1} elements. * * Operation: If i = i_{w-1} ... i_1 is the binary representation of i, * sets T[i] = i_{w-1} 2^{(w-1)d} P + ... + i_1 2^d P + P. * * Cost: d(w-1) D + (2^{w-1} - 1) A + 1 N(w-1) + 1 N(2^{w-1} - 1) * * Note: Even comb values (those where P would be omitted from the * sum defining T[i] above) are not needed in our adaption * the the comb method. See ecp_comb_recode_core(). * * This function currently works in four steps: * (1) [dbl] Computation of intermediate T[i] for 2-powers values of i * (2) [norm_dbl] Normalization of coordinates of these T[i] * (3) [add] Computation of all T[i] * (4) [norm_add] Normalization of all T[i] * * Step 1 can be interrupted but not the others; together with the final * coordinate normalization they are the largest steps done at once, depending * on the window size. Here are operation counts for P-256: * * step (2) (3) (4) * w = 5 142 165 208 * w = 4 136 77 160 * w = 3 130 33 136 * w = 2 124 11 124 * * So if ECC operations are blocking for too long even with a low max_ops * value, it's useful to set MBEDTLS_ECP_WINDOW_SIZE to a lower value in order * to minimize maximum blocking time. */ static int ecp_precompute_comb( const mbedtls_ecp_group *grp, mbedtls_ecp_point T[], const mbedtls_ecp_point *P, unsigned char w, size_t d, mbedtls_ecp_restart_ctx *rs_ctx ) { int ret; unsigned char i; size_t j = 0; const unsigned char T_size = 1U << ( w - 1 ); mbedtls_ecp_point *cur, *TT[COMB_MAX_PRE - 1]; #if !defined(MBEDTLS_ECP_RESTARTABLE) (void) rs_ctx; #endif #if defined(MBEDTLS_ECP_RESTARTABLE) if( rs_ctx != NULL && rs_ctx->rsm != NULL ) { if( rs_ctx->rsm->state == ecp_rsm_pre_dbl ) goto dbl; if( rs_ctx->rsm->state == ecp_rsm_pre_norm_dbl ) goto norm_dbl; if( rs_ctx->rsm->state == ecp_rsm_pre_add ) goto add; if( rs_ctx->rsm->state == ecp_rsm_pre_norm_add ) goto norm_add; } #endif /* * Set T[0] = P and * T[2^{l-1}] = 2^{dl} P for l = 1 .. w-1 (this is not the final value) */ #if defined(MBEDTLS_ECP_RESTARTABLE) if( rs_ctx != NULL && rs_ctx->rsm != NULL ) { rs_ctx->rsm->state = ecp_rsm_pre_dbl; /* initial state for the loop */ rs_ctx->rsm->i = 0; } dbl: #endif MBEDTLS_MPI_CHK( mbedtls_ecp_copy( &T[0], P ) ); #if defined(MBEDTLS_ECP_RESTARTABLE) if( rs_ctx != NULL && rs_ctx->rsm != NULL && rs_ctx->rsm->i != 0 ) j = rs_ctx->rsm->i; else #endif j = 0; for( ; j < d * ( w - 1 ); j++ ) { MBEDTLS_ECP_BUDGET( MBEDTLS_ECP_OPS_DBL ); i = 1U << ( j / d ); cur = T + i; if( j % d == 0 ) MBEDTLS_MPI_CHK( mbedtls_ecp_copy( cur, T + ( i >> 1 ) ) ); MBEDTLS_MPI_CHK( ecp_double_jac( grp, cur, cur ) ); } /* * Normalize current elements in T. As T has holes, * use an auxiliary array of pointers to elements in T. */ #if defined(MBEDTLS_ECP_RESTARTABLE) if( rs_ctx != NULL && rs_ctx->rsm != NULL ) rs_ctx->rsm->state = ecp_rsm_pre_norm_dbl; norm_dbl: #endif j = 0; for( i = 1; i < T_size; i <<= 1 ) TT[j++] = T + i; MBEDTLS_ECP_BUDGET( MBEDTLS_ECP_OPS_INV + 6 * j - 2 ); MBEDTLS_MPI_CHK( ecp_normalize_jac_many( grp, TT, j ) ); /* * Compute the remaining ones using the minimal number of additions * Be careful to update T[2^l] only after using it! */ #if defined(MBEDTLS_ECP_RESTARTABLE) if( rs_ctx != NULL && rs_ctx->rsm != NULL ) rs_ctx->rsm->state = ecp_rsm_pre_add; add: #endif MBEDTLS_ECP_BUDGET( ( T_size - 1 ) * MBEDTLS_ECP_OPS_ADD ); for( i = 1; i < T_size; i <<= 1 ) { j = i; while( j-- ) MBEDTLS_MPI_CHK( ecp_add_mixed( grp, &T[i + j], &T[j], &T[i] ) ); } /* * Normalize final elements in T. Even though there are no holes now, * we still need the auxiliary array for homogeneity with last time. * Also, skip T[0] which is already normalised, being a copy of P. */ #if defined(MBEDTLS_ECP_RESTARTABLE) if( rs_ctx != NULL && rs_ctx->rsm != NULL ) rs_ctx->rsm->state = ecp_rsm_pre_norm_add; norm_add: #endif for( j = 0; j + 1 < T_size; j++ ) TT[j] = T + j + 1; MBEDTLS_ECP_BUDGET( MBEDTLS_ECP_OPS_INV + 6 * j - 2 ); MBEDTLS_MPI_CHK( ecp_normalize_jac_many( grp, TT, j ) ); cleanup: #if defined(MBEDTLS_ECP_RESTARTABLE) if( rs_ctx != NULL && rs_ctx->rsm != NULL && ret == MBEDTLS_ERR_ECP_IN_PROGRESS ) { if( rs_ctx->rsm->state == ecp_rsm_pre_dbl ) rs_ctx->rsm->i = j; } #endif return( ret ); } /* * Select precomputed point: R = sign(i) * T[ abs(i) / 2 ] * * See ecp_comb_recode_core() for background */ static int ecp_select_comb( const mbedtls_ecp_group *grp, mbedtls_ecp_point *R, const mbedtls_ecp_point T[], unsigned char T_size, unsigned char i ) { int ret; unsigned char ii, j; /* Ignore the "sign" bit and scale down */ ii = ( i & 0x7Fu ) >> 1; /* Read the whole table to thwart cache-based timing attacks */ for( j = 0; j < T_size; j++ ) { MBEDTLS_MPI_CHK( mbedtls_mpi_safe_cond_assign( &R->X, &T[j].X, j == ii ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_safe_cond_assign( &R->Y, &T[j].Y, j == ii ) ); } /* Safely invert result if i is "negative" */ MBEDTLS_MPI_CHK( ecp_safe_invert_jac( grp, R, i >> 7 ) ); cleanup: return( ret ); } /* * Core multiplication algorithm for the (modified) comb method. * This part is actually common with the basic comb method (GECC 3.44) * * Cost: d A + d D + 1 R */ static int ecp_mul_comb_core( const mbedtls_ecp_group *grp, mbedtls_ecp_point *R, const mbedtls_ecp_point T[], unsigned char T_size, const unsigned char x[], size_t d, int (*f_rng)(void *, unsigned char *, size_t), void *p_rng, mbedtls_ecp_restart_ctx *rs_ctx ) { int ret; mbedtls_ecp_point Txi; size_t i; mbedtls_ecp_point_init( &Txi ); #if !defined(MBEDTLS_ECP_RESTARTABLE) (void) rs_ctx; #endif #if defined(MBEDTLS_ECP_RESTARTABLE) if( rs_ctx != NULL && rs_ctx->rsm != NULL && rs_ctx->rsm->state != ecp_rsm_comb_core ) { rs_ctx->rsm->i = 0; rs_ctx->rsm->state = ecp_rsm_comb_core; } /* new 'if' instead of nested for the sake of the 'else' branch */ if( rs_ctx != NULL && rs_ctx->rsm != NULL && rs_ctx->rsm->i != 0 ) { /* restore current index (R already pointing to rs_ctx->rsm->R) */ i = rs_ctx->rsm->i; } else #endif { /* Start with a non-zero point and randomize its coordinates */ i = d; MBEDTLS_MPI_CHK( ecp_select_comb( grp, R, T, T_size, x[i] ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_lset( &R->Z, 1 ) ); if( f_rng != 0 ) MBEDTLS_MPI_CHK( ecp_randomize_jac( grp, R, f_rng, p_rng ) ); } while( i-- != 0 ) { MBEDTLS_ECP_BUDGET( MBEDTLS_ECP_OPS_DBL + MBEDTLS_ECP_OPS_ADD ); MBEDTLS_MPI_CHK( ecp_double_jac( grp, R, R ) ); MBEDTLS_MPI_CHK( ecp_select_comb( grp, &Txi, T, T_size, x[i] ) ); MBEDTLS_MPI_CHK( ecp_add_mixed( grp, R, R, &Txi ) ); } cleanup: mbedtls_ecp_point_free( &Txi ); #if defined(MBEDTLS_ECP_RESTARTABLE) if( rs_ctx != NULL && rs_ctx->rsm != NULL && ret == MBEDTLS_ERR_ECP_IN_PROGRESS ) { /* was decreased before actually doing it */ rs_ctx->rsm->i = i + 1; /* no need to save R, already pointing to rs_ctx->rsm->R */ } #endif return( ret ); } /* * Recode the scalar to get constant-time comb multiplication * * As the actual scalar recoding needs an odd scalar as a starting point, * this wrapper ensures that by replacing m by N - m if necessary, and * informs the caller that the result of multiplication will be negated. * * This works because we only support large prime order for Short Weierstrass * curves, so N is always odd hence either m or N - m is. * * See ecp_comb_recode_core() for background. */ static int ecp_comb_recode_scalar( const mbedtls_ecp_group *grp, const mbedtls_mpi *m, unsigned char k[COMB_MAX_D + 1], size_t d, unsigned char w, unsigned char *parity_trick ) { int ret; mbedtls_mpi M, mm; mbedtls_mpi_init( &M ); mbedtls_mpi_init( &mm ); /* N is always odd (see above), just make extra sure */ if( mbedtls_mpi_get_bit( &grp->N, 0 ) != 1 ) return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA ); /* do we need the parity trick? */ *parity_trick = ( mbedtls_mpi_get_bit( m, 0 ) == 0 ); /* execute parity fix in constant time */ MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &M, m ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mpi( &mm, &grp->N, m ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_safe_cond_assign( &M, &mm, *parity_trick ) ); /* actual scalar recoding */ ecp_comb_recode_core( k, d, w, &M ); cleanup: mbedtls_mpi_free( &mm ); mbedtls_mpi_free( &M ); return( ret ); } /* * Perform comb multiplication (for short Weierstrass curves) * once the auxiliary table has been pre-computed. * * Scalar recoding may use a parity trick that makes us compute -m * P, * if that is the case we'll need to recover m * P at the end. */ static int ecp_mul_comb_after_precomp( const mbedtls_ecp_group *grp, mbedtls_ecp_point *R, const mbedtls_mpi *m, const mbedtls_ecp_point *T, unsigned char T_size, unsigned char w, size_t d, int (*f_rng)(void *, unsigned char *, size_t), void *p_rng, mbedtls_ecp_restart_ctx *rs_ctx ) { int ret; unsigned char parity_trick; unsigned char k[COMB_MAX_D + 1]; mbedtls_ecp_point *RR = R; #if defined(MBEDTLS_ECP_RESTARTABLE) if( rs_ctx != NULL && rs_ctx->rsm != NULL ) { RR = &rs_ctx->rsm->R; if( rs_ctx->rsm->state == ecp_rsm_final_norm ) goto final_norm; } #endif MBEDTLS_MPI_CHK( ecp_comb_recode_scalar( grp, m, k, d, w, &parity_trick ) ); MBEDTLS_MPI_CHK( ecp_mul_comb_core( grp, RR, T, T_size, k, d, f_rng, p_rng, rs_ctx ) ); MBEDTLS_MPI_CHK( ecp_safe_invert_jac( grp, RR, parity_trick ) ); #if defined(MBEDTLS_ECP_RESTARTABLE) if( rs_ctx != NULL && rs_ctx->rsm != NULL ) rs_ctx->rsm->state = ecp_rsm_final_norm; final_norm: #endif MBEDTLS_ECP_BUDGET( MBEDTLS_ECP_OPS_INV ); MBEDTLS_MPI_CHK( ecp_normalize_jac( grp, RR ) ); #if defined(MBEDTLS_ECP_RESTARTABLE) if( rs_ctx != NULL && rs_ctx->rsm != NULL ) MBEDTLS_MPI_CHK( mbedtls_ecp_copy( R, RR ) ); #endif cleanup: return( ret ); } /* * Pick window size based on curve size and whether we optimize for base point */ static unsigned char ecp_pick_window_size( const mbedtls_ecp_group *grp, unsigned char p_eq_g ) { unsigned char w; /* * Minimize the number of multiplications, that is minimize * 10 * d * w + 18 * 2^(w-1) + 11 * d + 7 * w, with d = ceil( nbits / w ) * (see costs of the various parts, with 1S = 1M) */ w = grp->nbits >= 384 ? 5 : 4; /* * If P == G, pre-compute a bit more, since this may be re-used later. * Just adding one avoids upping the cost of the first mul too much, * and the memory cost too. */ if( p_eq_g ) w++; /* * Make sure w is within bounds. * (The last test is useful only for very small curves in the test suite.) */ if( w > MBEDTLS_ECP_WINDOW_SIZE ) w = MBEDTLS_ECP_WINDOW_SIZE; if( w >= grp->nbits ) w = 2; return( w ); } /* * Multiplication using the comb method - for curves in short Weierstrass form * * This function is mainly responsible for administrative work: * - managing the restart context if enabled * - managing the table of precomputed points (passed between the below two * functions): allocation, computation, ownership tranfer, freeing. * * It delegates the actual arithmetic work to: * ecp_precompute_comb() and ecp_mul_comb_with_precomp() * * See comments on ecp_comb_recode_core() regarding the computation strategy. */ static int ecp_mul_comb( mbedtls_ecp_group *grp, mbedtls_ecp_point *R, const mbedtls_mpi *m, const mbedtls_ecp_point *P, int (*f_rng)(void *, unsigned char *, size_t), void *p_rng, mbedtls_ecp_restart_ctx *rs_ctx ) { int ret; unsigned char w, p_eq_g, i; size_t d; unsigned char T_size, T_ok; mbedtls_ecp_point *T; ECP_RS_ENTER( rsm ); /* Is P the base point ? */ #if MBEDTLS_ECP_FIXED_POINT_OPTIM == 1 p_eq_g = ( mbedtls_mpi_cmp_mpi( &P->Y, &grp->G.Y ) == 0 && mbedtls_mpi_cmp_mpi( &P->X, &grp->G.X ) == 0 ); #else p_eq_g = 0; #endif /* Pick window size and deduce related sizes */ w = ecp_pick_window_size( grp, p_eq_g ); T_size = 1U << ( w - 1 ); d = ( grp->nbits + w - 1 ) / w; /* Pre-computed table: do we have it already for the base point? */ if( p_eq_g && grp->T != NULL ) { /* second pointer to the same table, will be deleted on exit */ T = grp->T; T_ok = 1; } else #if defined(MBEDTLS_ECP_RESTARTABLE) /* Pre-computed table: do we have one in progress? complete? */ if( rs_ctx != NULL && rs_ctx->rsm != NULL && rs_ctx->rsm->T != NULL ) { /* transfer ownership of T from rsm to local function */ T = rs_ctx->rsm->T; rs_ctx->rsm->T = NULL; rs_ctx->rsm->T_size = 0; T_ok = rs_ctx->rsm->state >= ecp_rsm_comb_core; } else #endif /* Allocate table if we didn't have any */ { T = mbedtls_calloc( T_size, sizeof( mbedtls_ecp_point ) ); if( T == NULL ) { ret = MBEDTLS_ERR_ECP_ALLOC_FAILED; goto cleanup; } for( i = 0; i < T_size; i++ ) mbedtls_ecp_point_init( &T[i] ); T_ok = 0; } /* Compute table (or finish computing it) if not done already */ if( !T_ok ) { MBEDTLS_MPI_CHK( ecp_precompute_comb( grp, T, P, w, d, rs_ctx ) ); if( p_eq_g ) { /* almost transfer ownership of T to the group, but keep a copy of * the pointer to use for caling the next function more easily */ grp->T = T; grp->T_size = T_size; } } /* Actual comb multiplication using precomputed points */ MBEDTLS_MPI_CHK( ecp_mul_comb_after_precomp( grp, R, m, T, T_size, w, d, f_rng, p_rng, rs_ctx ) ); cleanup: /* does T belong to the group? */ if( T == grp->T ) T = NULL; /* does T belong to the restart context? */ #if defined(MBEDTLS_ECP_RESTARTABLE) if( rs_ctx != NULL && rs_ctx->rsm != NULL && ret == MBEDTLS_ERR_ECP_IN_PROGRESS && T != NULL ) { /* transfer ownership of T from local function to rsm */ rs_ctx->rsm->T_size = T_size; rs_ctx->rsm->T = T; T = NULL; } #endif /* did T belong to us? then let's destroy it! */ if( T != NULL ) { for( i = 0; i < T_size; i++ ) mbedtls_ecp_point_free( &T[i] ); mbedtls_free( T ); } /* don't free R while in progress in case R == P */ #if defined(MBEDTLS_ECP_RESTARTABLE) if( ret != MBEDTLS_ERR_ECP_IN_PROGRESS ) #endif /* prevent caller from using invalid value */ if( ret != 0 ) mbedtls_ecp_point_free( R ); ECP_RS_LEAVE( rsm ); return( ret ); } #endif /* ECP_SHORTWEIERSTRASS */ #if defined(ECP_MONTGOMERY) /* * For Montgomery curves, we do all the internal arithmetic in projective * coordinates. Import/export of points uses only the x coordinates, which is * internaly represented as X / Z. * * For scalar multiplication, we'll use a Montgomery ladder. */ /* * Normalize Montgomery x/z coordinates: X = X/Z, Z = 1 * Cost: 1M + 1I */ static int ecp_normalize_mxz( const mbedtls_ecp_group *grp, mbedtls_ecp_point *P ) { int ret; #if defined(MBEDTLS_ECP_NORMALIZE_MXZ_ALT) if( mbedtls_internal_ecp_grp_capable( grp ) ) return( mbedtls_internal_ecp_normalize_mxz( grp, P ) ); #endif /* MBEDTLS_ECP_NORMALIZE_MXZ_ALT */ MBEDTLS_MPI_CHK( mbedtls_mpi_inv_mod( &P->Z, &P->Z, &grp->P ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &P->X, &P->X, &P->Z ) ); MOD_MUL( P->X ); MBEDTLS_MPI_CHK( mbedtls_mpi_lset( &P->Z, 1 ) ); cleanup: return( ret ); } /* * Randomize projective x/z coordinates: * (X, Z) -> (l X, l Z) for random l * This is sort of the reverse operation of ecp_normalize_mxz(). * * This countermeasure was first suggested in [2]. * Cost: 2M */ static int ecp_randomize_mxz( const mbedtls_ecp_group *grp, mbedtls_ecp_point *P, int (*f_rng)(void *, unsigned char *, size_t), void *p_rng ) { int ret; mbedtls_mpi l; size_t p_size; int count = 0; #if defined(MBEDTLS_ECP_RANDOMIZE_MXZ_ALT) if( mbedtls_internal_ecp_grp_capable( grp ) ) return( mbedtls_internal_ecp_randomize_mxz( grp, P, f_rng, p_rng ); #endif /* MBEDTLS_ECP_RANDOMIZE_MXZ_ALT */ p_size = ( grp->pbits + 7 ) / 8; mbedtls_mpi_init( &l ); /* Generate l such that 1 < l < p */ do { MBEDTLS_MPI_CHK( mbedtls_mpi_fill_random( &l, p_size, f_rng, p_rng ) ); while( mbedtls_mpi_cmp_mpi( &l, &grp->P ) >= 0 ) MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( &l, 1 ) ); if( count++ > 10 ) return( MBEDTLS_ERR_ECP_RANDOM_FAILED ); } while( mbedtls_mpi_cmp_int( &l, 1 ) <= 0 ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &P->X, &P->X, &l ) ); MOD_MUL( P->X ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &P->Z, &P->Z, &l ) ); MOD_MUL( P->Z ); cleanup: mbedtls_mpi_free( &l ); return( ret ); } /* * Double-and-add: R = 2P, S = P + Q, with d = X(P - Q), * for Montgomery curves in x/z coordinates. * * http://www.hyperelliptic.org/EFD/g1p/auto-code/montgom/xz/ladder/mladd-1987-m.op3 * with * d = X1 * P = (X2, Z2) * Q = (X3, Z3) * R = (X4, Z4) * S = (X5, Z5) * and eliminating temporary variables tO, ..., t4. * * Cost: 5M + 4S */ static int ecp_double_add_mxz( const mbedtls_ecp_group *grp, mbedtls_ecp_point *R, mbedtls_ecp_point *S, const mbedtls_ecp_point *P, const mbedtls_ecp_point *Q, const mbedtls_mpi *d ) { int ret; mbedtls_mpi A, AA, B, BB, E, C, D, DA, CB; #if defined(MBEDTLS_ECP_DOUBLE_ADD_MXZ_ALT) if( mbedtls_internal_ecp_grp_capable( grp ) ) return( mbedtls_internal_ecp_double_add_mxz( grp, R, S, P, Q, d ) ); #endif /* MBEDTLS_ECP_DOUBLE_ADD_MXZ_ALT */ mbedtls_mpi_init( &A ); mbedtls_mpi_init( &AA ); mbedtls_mpi_init( &B ); mbedtls_mpi_init( &BB ); mbedtls_mpi_init( &E ); mbedtls_mpi_init( &C ); mbedtls_mpi_init( &D ); mbedtls_mpi_init( &DA ); mbedtls_mpi_init( &CB ); MBEDTLS_MPI_CHK( mbedtls_mpi_add_mpi( &A, &P->X, &P->Z ) ); MOD_ADD( A ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &AA, &A, &A ) ); MOD_MUL( AA ); MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mpi( &B, &P->X, &P->Z ) ); MOD_SUB( B ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &BB, &B, &B ) ); MOD_MUL( BB ); MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mpi( &E, &AA, &BB ) ); MOD_SUB( E ); MBEDTLS_MPI_CHK( mbedtls_mpi_add_mpi( &C, &Q->X, &Q->Z ) ); MOD_ADD( C ); MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mpi( &D, &Q->X, &Q->Z ) ); MOD_SUB( D ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &DA, &D, &A ) ); MOD_MUL( DA ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &CB, &C, &B ) ); MOD_MUL( CB ); MBEDTLS_MPI_CHK( mbedtls_mpi_add_mpi( &S->X, &DA, &CB ) ); MOD_MUL( S->X ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &S->X, &S->X, &S->X ) ); MOD_MUL( S->X ); MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mpi( &S->Z, &DA, &CB ) ); MOD_SUB( S->Z ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &S->Z, &S->Z, &S->Z ) ); MOD_MUL( S->Z ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &S->Z, d, &S->Z ) ); MOD_MUL( S->Z ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &R->X, &AA, &BB ) ); MOD_MUL( R->X ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &R->Z, &grp->A, &E ) ); MOD_MUL( R->Z ); MBEDTLS_MPI_CHK( mbedtls_mpi_add_mpi( &R->Z, &BB, &R->Z ) ); MOD_ADD( R->Z ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &R->Z, &E, &R->Z ) ); MOD_MUL( R->Z ); cleanup: mbedtls_mpi_free( &A ); mbedtls_mpi_free( &AA ); mbedtls_mpi_free( &B ); mbedtls_mpi_free( &BB ); mbedtls_mpi_free( &E ); mbedtls_mpi_free( &C ); mbedtls_mpi_free( &D ); mbedtls_mpi_free( &DA ); mbedtls_mpi_free( &CB ); return( ret ); } /* * Multiplication with Montgomery ladder in x/z coordinates, * for curves in Montgomery form */ static int ecp_mul_mxz( mbedtls_ecp_group *grp, mbedtls_ecp_point *R, const mbedtls_mpi *m, const mbedtls_ecp_point *P, int (*f_rng)(void *, unsigned char *, size_t), void *p_rng ) { int ret; size_t i; unsigned char b; mbedtls_ecp_point RP; mbedtls_mpi PX; mbedtls_ecp_point_init( &RP ); mbedtls_mpi_init( &PX ); /* Save PX and read from P before writing to R, in case P == R */ MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &PX, &P->X ) ); MBEDTLS_MPI_CHK( mbedtls_ecp_copy( &RP, P ) ); /* Set R to zero in modified x/z coordinates */ MBEDTLS_MPI_CHK( mbedtls_mpi_lset( &R->X, 1 ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_lset( &R->Z, 0 ) ); mbedtls_mpi_free( &R->Y ); /* RP.X might be sligtly larger than P, so reduce it */ MOD_ADD( RP.X ); /* Randomize coordinates of the starting point */ if( f_rng != NULL ) MBEDTLS_MPI_CHK( ecp_randomize_mxz( grp, &RP, f_rng, p_rng ) ); /* Loop invariant: R = result so far, RP = R + P */ i = mbedtls_mpi_bitlen( m ); /* one past the (zero-based) most significant bit */ while( i-- > 0 ) { b = mbedtls_mpi_get_bit( m, i ); /* * if (b) R = 2R + P else R = 2R, * which is: * if (b) double_add( RP, R, RP, R ) * else double_add( R, RP, R, RP ) * but using safe conditional swaps to avoid leaks */ MBEDTLS_MPI_CHK( mbedtls_mpi_safe_cond_swap( &R->X, &RP.X, b ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_safe_cond_swap( &R->Z, &RP.Z, b ) ); MBEDTLS_MPI_CHK( ecp_double_add_mxz( grp, R, &RP, R, &RP, &PX ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_safe_cond_swap( &R->X, &RP.X, b ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_safe_cond_swap( &R->Z, &RP.Z, b ) ); } MBEDTLS_MPI_CHK( ecp_normalize_mxz( grp, R ) ); cleanup: mbedtls_ecp_point_free( &RP ); mbedtls_mpi_free( &PX ); return( ret ); } #endif /* ECP_MONTGOMERY */ /* * Restartable multiplication R = m * P */ int mbedtls_ecp_mul_restartable( mbedtls_ecp_group *grp, mbedtls_ecp_point *R, const mbedtls_mpi *m, const mbedtls_ecp_point *P, int (*f_rng)(void *, unsigned char *, size_t), void *p_rng, mbedtls_ecp_restart_ctx *rs_ctx ) { int ret = MBEDTLS_ERR_ECP_BAD_INPUT_DATA; #if defined(MBEDTLS_ECP_INTERNAL_ALT) char is_grp_capable = 0; #endif #if defined(MBEDTLS_ECP_RESTARTABLE) /* reset ops count for this call if top-level */ if( rs_ctx != NULL && rs_ctx->depth++ == 0 ) rs_ctx->ops_done = 0; #endif #if defined(MBEDTLS_ECP_INTERNAL_ALT) if( ( is_grp_capable = mbedtls_internal_ecp_grp_capable( grp ) ) ) MBEDTLS_MPI_CHK( mbedtls_internal_ecp_init( grp ) ); #endif /* MBEDTLS_ECP_INTERNAL_ALT */ #if defined(MBEDTLS_ECP_RESTARTABLE) /* skip argument check when restarting */ if( rs_ctx == NULL || rs_ctx->rsm == NULL ) #endif { /* check_privkey is free */ MBEDTLS_ECP_BUDGET( MBEDTLS_ECP_OPS_CHK ); /* Common sanity checks */ MBEDTLS_MPI_CHK( mbedtls_ecp_check_privkey( grp, m ) ); MBEDTLS_MPI_CHK( mbedtls_ecp_check_pubkey( grp, P ) ); } ret = MBEDTLS_ERR_ECP_BAD_INPUT_DATA; #if defined(ECP_MONTGOMERY) if( ecp_get_type( grp ) == ECP_TYPE_MONTGOMERY ) MBEDTLS_MPI_CHK( ecp_mul_mxz( grp, R, m, P, f_rng, p_rng ) ); #endif #if defined(ECP_SHORTWEIERSTRASS) if( ecp_get_type( grp ) == ECP_TYPE_SHORT_WEIERSTRASS ) MBEDTLS_MPI_CHK( ecp_mul_comb( grp, R, m, P, f_rng, p_rng, rs_ctx ) ); #endif cleanup: #if defined(MBEDTLS_ECP_INTERNAL_ALT) if( is_grp_capable ) mbedtls_internal_ecp_free( grp ); #endif /* MBEDTLS_ECP_INTERNAL_ALT */ #if defined(MBEDTLS_ECP_RESTARTABLE) if( rs_ctx != NULL ) rs_ctx->depth--; #endif return( ret ); } /* * Multiplication R = m * P */ int mbedtls_ecp_mul( mbedtls_ecp_group *grp, mbedtls_ecp_point *R, const mbedtls_mpi *m, const mbedtls_ecp_point *P, int (*f_rng)(void *, unsigned char *, size_t), void *p_rng ) { return( mbedtls_ecp_mul_restartable( grp, R, m, P, f_rng, p_rng, NULL ) ); } #if defined(ECP_SHORTWEIERSTRASS) /* * Check that an affine point is valid as a public key, * short weierstrass curves (SEC1 3.2.3.1) */ static int ecp_check_pubkey_sw( const mbedtls_ecp_group *grp, const mbedtls_ecp_point *pt ) { int ret; mbedtls_mpi YY, RHS; /* pt coordinates must be normalized for our checks */ if( mbedtls_mpi_cmp_int( &pt->X, 0 ) < 0 || mbedtls_mpi_cmp_int( &pt->Y, 0 ) < 0 || mbedtls_mpi_cmp_mpi( &pt->X, &grp->P ) >= 0 || mbedtls_mpi_cmp_mpi( &pt->Y, &grp->P ) >= 0 ) return( MBEDTLS_ERR_ECP_INVALID_KEY ); mbedtls_mpi_init( &YY ); mbedtls_mpi_init( &RHS ); /* * YY = Y^2 * RHS = X (X^2 + A) + B = X^3 + A X + B */ MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &YY, &pt->Y, &pt->Y ) ); MOD_MUL( YY ); MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &RHS, &pt->X, &pt->X ) ); MOD_MUL( RHS ); /* Special case for A = -3 */ if( grp->A.p == NULL ) { MBEDTLS_MPI_CHK( mbedtls_mpi_sub_int( &RHS, &RHS, 3 ) ); MOD_SUB( RHS ); } else { MBEDTLS_MPI_CHK( mbedtls_mpi_add_mpi( &RHS, &RHS, &grp->A ) ); MOD_ADD( RHS ); } MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &RHS, &RHS, &pt->X ) ); MOD_MUL( RHS ); MBEDTLS_MPI_CHK( mbedtls_mpi_add_mpi( &RHS, &RHS, &grp->B ) ); MOD_ADD( RHS ); if( mbedtls_mpi_cmp_mpi( &YY, &RHS ) != 0 ) ret = MBEDTLS_ERR_ECP_INVALID_KEY; cleanup: mbedtls_mpi_free( &YY ); mbedtls_mpi_free( &RHS ); return( ret ); } #endif /* ECP_SHORTWEIERSTRASS */ /* * R = m * P with shortcuts for m == 1 and m == -1 * NOT constant-time - ONLY for short Weierstrass! */ static int mbedtls_ecp_mul_shortcuts( mbedtls_ecp_group *grp, mbedtls_ecp_point *R, const mbedtls_mpi *m, const mbedtls_ecp_point *P, mbedtls_ecp_restart_ctx *rs_ctx ) { int ret; if( mbedtls_mpi_cmp_int( m, 1 ) == 0 ) { MBEDTLS_MPI_CHK( mbedtls_ecp_copy( R, P ) ); } else if( mbedtls_mpi_cmp_int( m, -1 ) == 0 ) { MBEDTLS_MPI_CHK( mbedtls_ecp_copy( R, P ) ); if( mbedtls_mpi_cmp_int( &R->Y, 0 ) != 0 ) MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mpi( &R->Y, &grp->P, &R->Y ) ); } else { MBEDTLS_MPI_CHK( mbedtls_ecp_mul_restartable( grp, R, m, P, NULL, NULL, rs_ctx ) ); } cleanup: return( ret ); } /* * Restartable linear combination * NOT constant-time */ int mbedtls_ecp_muladd_restartable( mbedtls_ecp_group *grp, mbedtls_ecp_point *R, const mbedtls_mpi *m, const mbedtls_ecp_point *P, const mbedtls_mpi *n, const mbedtls_ecp_point *Q, mbedtls_ecp_restart_ctx *rs_ctx ) { int ret; mbedtls_ecp_point mP; mbedtls_ecp_point *pmP = &mP; mbedtls_ecp_point *pR = R; #if defined(MBEDTLS_ECP_INTERNAL_ALT) char is_grp_capable = 0; #endif if( ecp_get_type( grp ) != ECP_TYPE_SHORT_WEIERSTRASS ) return( MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE ); mbedtls_ecp_point_init( &mP ); #if defined(MBEDTLS_ECP_INTERNAL_ALT) if( ( is_grp_capable = mbedtls_internal_ecp_grp_capable( grp ) ) ) MBEDTLS_MPI_CHK( mbedtls_internal_ecp_init( grp ) ); #endif /* MBEDTLS_ECP_INTERNAL_ALT */ ECP_RS_ENTER( ma ); #if defined(MBEDTLS_ECP_RESTARTABLE) if( rs_ctx != NULL && rs_ctx->ma != NULL ) { /* redirect intermediate results to restart context */ pmP = &rs_ctx->ma->mP; pR = &rs_ctx->ma->R; /* jump to next operation */ if( rs_ctx->ma->state == ecp_rsma_mul2 ) goto mul2; if( rs_ctx->ma->state == ecp_rsma_add ) goto add; if( rs_ctx->ma->state == ecp_rsma_norm ) goto norm; } #endif /* MBEDTLS_ECP_RESTARTABLE */ MBEDTLS_MPI_CHK( mbedtls_ecp_mul_shortcuts( grp, pmP, m, P, rs_ctx ) ); #if defined(MBEDTLS_ECP_RESTARTABLE) if( rs_ctx != NULL && rs_ctx->ma != NULL ) rs_ctx->ma->state = ecp_rsma_mul2; mul2: #endif MBEDTLS_MPI_CHK( mbedtls_ecp_mul_shortcuts( grp, pR, n, Q, rs_ctx ) ); #if defined(MBEDTLS_ECP_RESTARTABLE) if( rs_ctx != NULL && rs_ctx->ma != NULL ) rs_ctx->ma->state = ecp_rsma_add; add: #endif MBEDTLS_ECP_BUDGET( MBEDTLS_ECP_OPS_ADD ); MBEDTLS_MPI_CHK( ecp_add_mixed( grp, pR, pmP, pR ) ); #if defined(MBEDTLS_ECP_RESTARTABLE) if( rs_ctx != NULL && rs_ctx->ma != NULL ) rs_ctx->ma->state = ecp_rsma_norm; norm: #endif MBEDTLS_ECP_BUDGET( MBEDTLS_ECP_OPS_INV ); MBEDTLS_MPI_CHK( ecp_normalize_jac( grp, pR ) ); #if defined(MBEDTLS_ECP_RESTARTABLE) if( rs_ctx != NULL && rs_ctx->ma != NULL ) MBEDTLS_MPI_CHK( mbedtls_ecp_copy( R, pR ) ); #endif cleanup: #if defined(MBEDTLS_ECP_INTERNAL_ALT) if( is_grp_capable ) mbedtls_internal_ecp_free( grp ); #endif /* MBEDTLS_ECP_INTERNAL_ALT */ mbedtls_ecp_point_free( &mP ); ECP_RS_LEAVE( ma ); return( ret ); } /* * Linear combination * NOT constant-time */ int mbedtls_ecp_muladd( mbedtls_ecp_group *grp, mbedtls_ecp_point *R, const mbedtls_mpi *m, const mbedtls_ecp_point *P, const mbedtls_mpi *n, const mbedtls_ecp_point *Q ) { return( mbedtls_ecp_muladd_restartable( grp, R, m, P, n, Q, NULL ) ); } #if defined(ECP_MONTGOMERY) /* * Check validity of a public key for Montgomery curves with x-only schemes */ static int ecp_check_pubkey_mx( const mbedtls_ecp_group *grp, const mbedtls_ecp_point *pt ) { /* [Curve25519 p. 5] Just check X is the correct number of bytes */ /* Allow any public value, if it's too big then we'll just reduce it mod p * (RFC 7748 sec. 5 para. 3). */ if( mbedtls_mpi_size( &pt->X ) > ( grp->nbits + 7 ) / 8 ) return( MBEDTLS_ERR_ECP_INVALID_KEY ); return( 0 ); } #endif /* ECP_MONTGOMERY */ /* * Check that a point is valid as a public key */ int mbedtls_ecp_check_pubkey( const mbedtls_ecp_group *grp, const mbedtls_ecp_point *pt ) { /* Must use affine coordinates */ if( mbedtls_mpi_cmp_int( &pt->Z, 1 ) != 0 ) return( MBEDTLS_ERR_ECP_INVALID_KEY ); #if defined(ECP_MONTGOMERY) if( ecp_get_type( grp ) == ECP_TYPE_MONTGOMERY ) return( ecp_check_pubkey_mx( grp, pt ) ); #endif #if defined(ECP_SHORTWEIERSTRASS) if( ecp_get_type( grp ) == ECP_TYPE_SHORT_WEIERSTRASS ) return( ecp_check_pubkey_sw( grp, pt ) ); #endif return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA ); } /* * Check that an mbedtls_mpi is valid as a private key */ int mbedtls_ecp_check_privkey( const mbedtls_ecp_group *grp, const mbedtls_mpi *d ) { #if defined(ECP_MONTGOMERY) if( ecp_get_type( grp ) == ECP_TYPE_MONTGOMERY ) { /* see RFC 7748 sec. 5 para. 5 */ if( mbedtls_mpi_get_bit( d, 0 ) != 0 || mbedtls_mpi_get_bit( d, 1 ) != 0 || mbedtls_mpi_bitlen( d ) - 1 != grp->nbits ) /* mbedtls_mpi_bitlen is one-based! */ return( MBEDTLS_ERR_ECP_INVALID_KEY ); /* see [Curve25519] page 5 */ if( grp->nbits == 254 && mbedtls_mpi_get_bit( d, 2 ) != 0 ) return( MBEDTLS_ERR_ECP_INVALID_KEY ); return( 0 ); } #endif /* ECP_MONTGOMERY */ #if defined(ECP_SHORTWEIERSTRASS) if( ecp_get_type( grp ) == ECP_TYPE_SHORT_WEIERSTRASS ) { /* see SEC1 3.2 */ if( mbedtls_mpi_cmp_int( d, 1 ) < 0 || mbedtls_mpi_cmp_mpi( d, &grp->N ) >= 0 ) return( MBEDTLS_ERR_ECP_INVALID_KEY ); else return( 0 ); } #endif /* ECP_SHORTWEIERSTRASS */ return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA ); } /* * Generate a private key */ int mbedtls_ecp_gen_privkey( const mbedtls_ecp_group *grp, mbedtls_mpi *d, int (*f_rng)(void *, unsigned char *, size_t), void *p_rng ) { int ret = MBEDTLS_ERR_ECP_BAD_INPUT_DATA; size_t n_size = ( grp->nbits + 7 ) / 8; #if defined(ECP_MONTGOMERY) if( ecp_get_type( grp ) == ECP_TYPE_MONTGOMERY ) { /* [M225] page 5 */ size_t b; do { MBEDTLS_MPI_CHK( mbedtls_mpi_fill_random( d, n_size, f_rng, p_rng ) ); } while( mbedtls_mpi_bitlen( d ) == 0); /* Make sure the most significant bit is nbits */ b = mbedtls_mpi_bitlen( d ) - 1; /* mbedtls_mpi_bitlen is one-based */ if( b > grp->nbits ) MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( d, b - grp->nbits ) ); else MBEDTLS_MPI_CHK( mbedtls_mpi_set_bit( d, grp->nbits, 1 ) ); /* Make sure the last two bits are unset for Curve448, three bits for Curve25519 */ MBEDTLS_MPI_CHK( mbedtls_mpi_set_bit( d, 0, 0 ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_set_bit( d, 1, 0 ) ); if( grp->nbits == 254 ) { MBEDTLS_MPI_CHK( mbedtls_mpi_set_bit( d, 2, 0 ) ); } } #endif /* ECP_MONTGOMERY */ #if defined(ECP_SHORTWEIERSTRASS) if( ecp_get_type( grp ) == ECP_TYPE_SHORT_WEIERSTRASS ) { /* SEC1 3.2.1: Generate d such that 1 <= n < N */ int count = 0; /* * Match the procedure given in RFC 6979 (deterministic ECDSA): * - use the same byte ordering; * - keep the leftmost nbits bits of the generated octet string; * - try until result is in the desired range. * This also avoids any biais, which is especially important for ECDSA. */ do { MBEDTLS_MPI_CHK( mbedtls_mpi_fill_random( d, n_size, f_rng, p_rng ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( d, 8 * n_size - grp->nbits ) ); /* * Each try has at worst a probability 1/2 of failing (the msb has * a probability 1/2 of being 0, and then the result will be < N), * so after 30 tries failure probability is a most 2**(-30). * * For most curves, 1 try is enough with overwhelming probability, * since N starts with a lot of 1s in binary, but some curves * such as secp224k1 are actually very close to the worst case. */ if( ++count > 30 ) return( MBEDTLS_ERR_ECP_RANDOM_FAILED ); } while( mbedtls_mpi_cmp_int( d, 1 ) < 0 || mbedtls_mpi_cmp_mpi( d, &grp->N ) >= 0 ); } #endif /* ECP_SHORTWEIERSTRASS */ cleanup: return( ret ); } /* * Generate a keypair with configurable base point */ int mbedtls_ecp_gen_keypair_base( mbedtls_ecp_group *grp, const mbedtls_ecp_point *G, mbedtls_mpi *d, mbedtls_ecp_point *Q, int (*f_rng)(void *, unsigned char *, size_t), void *p_rng ) { int ret; MBEDTLS_MPI_CHK( mbedtls_ecp_gen_privkey( grp, d, f_rng, p_rng ) ); MBEDTLS_MPI_CHK( mbedtls_ecp_mul( grp, Q, d, G, f_rng, p_rng ) ); cleanup: return( ret ); } /* * Generate key pair, wrapper for conventional base point */ int mbedtls_ecp_gen_keypair( mbedtls_ecp_group *grp, mbedtls_mpi *d, mbedtls_ecp_point *Q, int (*f_rng)(void *, unsigned char *, size_t), void *p_rng ) { return( mbedtls_ecp_gen_keypair_base( grp, &grp->G, d, Q, f_rng, p_rng ) ); } /* * Generate a keypair, prettier wrapper */ int mbedtls_ecp_gen_key( mbedtls_ecp_group_id grp_id, mbedtls_ecp_keypair *key, int (*f_rng)(void *, unsigned char *, size_t), void *p_rng ) { int ret; if( ( ret = mbedtls_ecp_group_load( &key->grp, grp_id ) ) != 0 ) return( ret ); return( mbedtls_ecp_gen_keypair( &key->grp, &key->d, &key->Q, f_rng, p_rng ) ); } /* * Check a public-private key pair */ int mbedtls_ecp_check_pub_priv( const mbedtls_ecp_keypair *pub, const mbedtls_ecp_keypair *prv ) { int ret; mbedtls_ecp_point Q; mbedtls_ecp_group grp; if( pub->grp.id == MBEDTLS_ECP_DP_NONE || pub->grp.id != prv->grp.id || mbedtls_mpi_cmp_mpi( &pub->Q.X, &prv->Q.X ) || mbedtls_mpi_cmp_mpi( &pub->Q.Y, &prv->Q.Y ) || mbedtls_mpi_cmp_mpi( &pub->Q.Z, &prv->Q.Z ) ) { return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA ); } mbedtls_ecp_point_init( &Q ); mbedtls_ecp_group_init( &grp ); /* mbedtls_ecp_mul() needs a non-const group... */ mbedtls_ecp_group_copy( &grp, &prv->grp ); /* Also checks d is valid */ MBEDTLS_MPI_CHK( mbedtls_ecp_mul( &grp, &Q, &prv->d, &prv->grp.G, NULL, NULL ) ); if( mbedtls_mpi_cmp_mpi( &Q.X, &prv->Q.X ) || mbedtls_mpi_cmp_mpi( &Q.Y, &prv->Q.Y ) || mbedtls_mpi_cmp_mpi( &Q.Z, &prv->Q.Z ) ) { ret = MBEDTLS_ERR_ECP_BAD_INPUT_DATA; goto cleanup; } cleanup: mbedtls_ecp_point_free( &Q ); mbedtls_ecp_group_free( &grp ); return( ret ); } #if defined(MBEDTLS_SELF_TEST) /* * Checkup routine */ int mbedtls_ecp_self_test( int verbose ) { int ret; size_t i; mbedtls_ecp_group grp; mbedtls_ecp_point R, P; mbedtls_mpi m; unsigned long add_c_prev, dbl_c_prev, mul_c_prev; /* exponents especially adapted for secp192r1 */ const char *exponents[] = { "000000000000000000000000000000000000000000000001", /* one */ "FFFFFFFFFFFFFFFFFFFFFFFF99DEF836146BC9B1B4D22830", /* N - 1 */ "5EA6F389A38B8BC81E767753B15AA5569E1782E30ABE7D25", /* random */ "400000000000000000000000000000000000000000000000", /* one and zeros */ "7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF", /* all ones */ "555555555555555555555555555555555555555555555555", /* 101010... */ }; mbedtls_ecp_group_init( &grp ); mbedtls_ecp_point_init( &R ); mbedtls_ecp_point_init( &P ); mbedtls_mpi_init( &m ); /* Use secp192r1 if available, or any available curve */ #if defined(MBEDTLS_ECP_DP_SECP192R1_ENABLED) MBEDTLS_MPI_CHK( mbedtls_ecp_group_load( &grp, MBEDTLS_ECP_DP_SECP192R1 ) ); #else MBEDTLS_MPI_CHK( mbedtls_ecp_group_load( &grp, mbedtls_ecp_curve_list()->grp_id ) ); #endif if( verbose != 0 ) mbedtls_printf( " ECP test #1 (constant op_count, base point G): " ); /* Do a dummy multiplication first to trigger precomputation */ MBEDTLS_MPI_CHK( mbedtls_mpi_lset( &m, 2 ) ); MBEDTLS_MPI_CHK( mbedtls_ecp_mul( &grp, &P, &m, &grp.G, NULL, NULL ) ); add_count = 0; dbl_count = 0; mul_count = 0; MBEDTLS_MPI_CHK( mbedtls_mpi_read_string( &m, 16, exponents[0] ) ); MBEDTLS_MPI_CHK( mbedtls_ecp_mul( &grp, &R, &m, &grp.G, NULL, NULL ) ); for( i = 1; i < sizeof( exponents ) / sizeof( exponents[0] ); i++ ) { add_c_prev = add_count; dbl_c_prev = dbl_count; mul_c_prev = mul_count; add_count = 0; dbl_count = 0; mul_count = 0; MBEDTLS_MPI_CHK( mbedtls_mpi_read_string( &m, 16, exponents[i] ) ); MBEDTLS_MPI_CHK( mbedtls_ecp_mul( &grp, &R, &m, &grp.G, NULL, NULL ) ); if( add_count != add_c_prev || dbl_count != dbl_c_prev || mul_count != mul_c_prev ) { if( verbose != 0 ) mbedtls_printf( "failed (%u)\n", (unsigned int) i ); ret = 1; goto cleanup; } } if( verbose != 0 ) mbedtls_printf( "passed\n" ); if( verbose != 0 ) mbedtls_printf( " ECP test #2 (constant op_count, other point): " ); /* We computed P = 2G last time, use it */ add_count = 0; dbl_count = 0; mul_count = 0; MBEDTLS_MPI_CHK( mbedtls_mpi_read_string( &m, 16, exponents[0] ) ); MBEDTLS_MPI_CHK( mbedtls_ecp_mul( &grp, &R, &m, &P, NULL, NULL ) ); for( i = 1; i < sizeof( exponents ) / sizeof( exponents[0] ); i++ ) { add_c_prev = add_count; dbl_c_prev = dbl_count; mul_c_prev = mul_count; add_count = 0; dbl_count = 0; mul_count = 0; MBEDTLS_MPI_CHK( mbedtls_mpi_read_string( &m, 16, exponents[i] ) ); MBEDTLS_MPI_CHK( mbedtls_ecp_mul( &grp, &R, &m, &P, NULL, NULL ) ); if( add_count != add_c_prev || dbl_count != dbl_c_prev || mul_count != mul_c_prev ) { if( verbose != 0 ) mbedtls_printf( "failed (%u)\n", (unsigned int) i ); ret = 1; goto cleanup; } } if( verbose != 0 ) mbedtls_printf( "passed\n" ); cleanup: if( ret < 0 && verbose != 0 ) mbedtls_printf( "Unexpected error, return code = %08X\n", ret ); mbedtls_ecp_group_free( &grp ); mbedtls_ecp_point_free( &R ); mbedtls_ecp_point_free( &P ); mbedtls_mpi_free( &m ); if( verbose != 0 ) mbedtls_printf( "\n" ); return( ret ); } #endif /* MBEDTLS_SELF_TEST */ #endif /* !MBEDTLS_ECP_ALT */ #endif /* MBEDTLS_ECP_C */