1 /* 2 * Elliptic curve Diffie-Hellman 3 * 4 * Copyright (C) 2006-2015, ARM Limited, All Rights Reserved 5 * SPDX-License-Identifier: GPL-2.0 6 * 7 * This program is free software; you can redistribute it and/or modify 8 * it under the terms of the GNU General Public License as published by 9 * the Free Software Foundation; either version 2 of the License, or 10 * (at your option) any later version. 11 * 12 * This program is distributed in the hope that it will be useful, 13 * but WITHOUT ANY WARRANTY; without even the implied warranty of 14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 15 * GNU General Public License for more details. 16 * 17 * You should have received a copy of the GNU General Public License along 18 * with this program; if not, write to the Free Software Foundation, Inc., 19 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * This file is part of mbed TLS (https://tls.mbed.org) 22 */ 23 24 /* 25 * References: 26 * 27 * SEC1 http://www.secg.org/index.php?action=secg,docs_secg 28 * RFC 4492 29 */ 30 31 #if !defined(MBEDTLS_CONFIG_FILE) 32 #include "mbedtls/config.h" 33 #else 34 #include MBEDTLS_CONFIG_FILE 35 #endif 36 37 #if defined(MBEDTLS_ECDH_C) 38 39 #include "mbedtls/ecdh.h" 40 41 #include <string.h> 42 43 #if !defined(MBEDTLS_ECDH_GEN_PUBLIC_ALT) 44 /* 45 * Generate public key: simple wrapper around mbedtls_ecp_gen_keypair 46 */ 47 int mbedtls_ecdh_gen_public( mbedtls_ecp_group *grp, mbedtls_mpi *d, mbedtls_ecp_point *Q, 48 int (*f_rng)(void *, unsigned char *, size_t), 49 void *p_rng ) 50 { 51 return mbedtls_ecp_gen_keypair( grp, d, Q, f_rng, p_rng ); 52 } 53 #endif /* MBEDTLS_ECDH_GEN_PUBLIC_ALT */ 54 55 #if !defined(MBEDTLS_ECDH_COMPUTE_SHARED_ALT) 56 /* 57 * Compute shared secret (SEC1 3.3.1) 58 */ 59 int mbedtls_ecdh_compute_shared( mbedtls_ecp_group *grp, mbedtls_mpi *z, 60 const mbedtls_ecp_point *Q, const mbedtls_mpi *d, 61 int (*f_rng)(void *, unsigned char *, size_t), 62 void *p_rng ) 63 { 64 int ret; 65 mbedtls_ecp_point P; 66 67 mbedtls_ecp_point_init( &P ); 68 69 /* 70 * Make sure Q is a valid pubkey before using it 71 */ 72 MBEDTLS_MPI_CHK( mbedtls_ecp_check_pubkey( grp, Q ) ); 73 74 MBEDTLS_MPI_CHK( mbedtls_ecp_mul( grp, &P, d, Q, f_rng, p_rng ) ); 75 76 if( mbedtls_ecp_is_zero( &P ) ) 77 { 78 ret = MBEDTLS_ERR_ECP_BAD_INPUT_DATA; 79 goto cleanup; 80 } 81 82 MBEDTLS_MPI_CHK( mbedtls_mpi_copy( z, &P.X ) ); 83 84 cleanup: 85 mbedtls_ecp_point_free( &P ); 86 87 return( ret ); 88 } 89 #endif /* MBEDTLS_ECDH_COMPUTE_SHARED_ALT */ 90 91 /* 92 * Initialize context 93 */ 94 void mbedtls_ecdh_init( mbedtls_ecdh_context *ctx ) 95 { 96 memset( ctx, 0, sizeof( mbedtls_ecdh_context ) ); 97 } 98 99 /* 100 * Free context 101 */ 102 void mbedtls_ecdh_free( mbedtls_ecdh_context *ctx ) 103 { 104 if( ctx == NULL ) 105 return; 106 107 mbedtls_ecp_group_free( &ctx->grp ); 108 mbedtls_ecp_point_free( &ctx->Q ); 109 mbedtls_ecp_point_free( &ctx->Qp ); 110 mbedtls_ecp_point_free( &ctx->Vi ); 111 mbedtls_ecp_point_free( &ctx->Vf ); 112 mbedtls_mpi_free( &ctx->d ); 113 mbedtls_mpi_free( &ctx->z ); 114 mbedtls_mpi_free( &ctx->_d ); 115 } 116 117 /* 118 * Setup and write the ServerKeyExhange parameters (RFC 4492) 119 * struct { 120 * ECParameters curve_params; 121 * ECPoint public; 122 * } ServerECDHParams; 123 */ 124 int mbedtls_ecdh_make_params( mbedtls_ecdh_context *ctx, size_t *olen, 125 unsigned char *buf, size_t blen, 126 int (*f_rng)(void *, unsigned char *, size_t), 127 void *p_rng ) 128 { 129 int ret; 130 size_t grp_len, pt_len; 131 132 if( ctx == NULL || ctx->grp.pbits == 0 ) 133 return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA ); 134 135 if( ( ret = mbedtls_ecdh_gen_public( &ctx->grp, &ctx->d, &ctx->Q, f_rng, p_rng ) ) 136 != 0 ) 137 return( ret ); 138 139 if( ( ret = mbedtls_ecp_tls_write_group( &ctx->grp, &grp_len, buf, blen ) ) 140 != 0 ) 141 return( ret ); 142 143 buf += grp_len; 144 blen -= grp_len; 145 146 if( ( ret = mbedtls_ecp_tls_write_point( &ctx->grp, &ctx->Q, ctx->point_format, 147 &pt_len, buf, blen ) ) != 0 ) 148 return( ret ); 149 150 *olen = grp_len + pt_len; 151 return( 0 ); 152 } 153 154 /* 155 * Read the ServerKeyExhange parameters (RFC 4492) 156 * struct { 157 * ECParameters curve_params; 158 * ECPoint public; 159 * } ServerECDHParams; 160 */ 161 int mbedtls_ecdh_read_params( mbedtls_ecdh_context *ctx, 162 const unsigned char **buf, const unsigned char *end ) 163 { 164 int ret; 165 166 if( ( ret = mbedtls_ecp_tls_read_group( &ctx->grp, buf, end - *buf ) ) != 0 ) 167 return( ret ); 168 169 if( ( ret = mbedtls_ecp_tls_read_point( &ctx->grp, &ctx->Qp, buf, end - *buf ) ) 170 != 0 ) 171 return( ret ); 172 173 return( 0 ); 174 } 175 176 /* 177 * Get parameters from a keypair 178 */ 179 int mbedtls_ecdh_get_params( mbedtls_ecdh_context *ctx, const mbedtls_ecp_keypair *key, 180 mbedtls_ecdh_side side ) 181 { 182 int ret; 183 184 if( ( ret = mbedtls_ecp_group_copy( &ctx->grp, &key->grp ) ) != 0 ) 185 return( ret ); 186 187 /* If it's not our key, just import the public part as Qp */ 188 if( side == MBEDTLS_ECDH_THEIRS ) 189 return( mbedtls_ecp_copy( &ctx->Qp, &key->Q ) ); 190 191 /* Our key: import public (as Q) and private parts */ 192 if( side != MBEDTLS_ECDH_OURS ) 193 return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA ); 194 195 if( ( ret = mbedtls_ecp_copy( &ctx->Q, &key->Q ) ) != 0 || 196 ( ret = mbedtls_mpi_copy( &ctx->d, &key->d ) ) != 0 ) 197 return( ret ); 198 199 return( 0 ); 200 } 201 202 /* 203 * Setup and export the client public value 204 */ 205 int mbedtls_ecdh_make_public( mbedtls_ecdh_context *ctx, size_t *olen, 206 unsigned char *buf, size_t blen, 207 int (*f_rng)(void *, unsigned char *, size_t), 208 void *p_rng ) 209 { 210 int ret; 211 212 if( ctx == NULL || ctx->grp.pbits == 0 ) 213 return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA ); 214 215 if( ( ret = mbedtls_ecdh_gen_public( &ctx->grp, &ctx->d, &ctx->Q, f_rng, p_rng ) ) 216 != 0 ) 217 return( ret ); 218 219 return mbedtls_ecp_tls_write_point( &ctx->grp, &ctx->Q, ctx->point_format, 220 olen, buf, blen ); 221 } 222 223 /* 224 * Parse and import the client's public value 225 */ 226 int mbedtls_ecdh_read_public( mbedtls_ecdh_context *ctx, 227 const unsigned char *buf, size_t blen ) 228 { 229 int ret; 230 const unsigned char *p = buf; 231 232 if( ctx == NULL ) 233 return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA ); 234 235 if( ( ret = mbedtls_ecp_tls_read_point( &ctx->grp, &ctx->Qp, &p, blen ) ) != 0 ) 236 return( ret ); 237 238 if( (size_t)( p - buf ) != blen ) 239 return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA ); 240 241 return( 0 ); 242 } 243 244 /* 245 * Derive and export the shared secret 246 */ 247 int mbedtls_ecdh_calc_secret( mbedtls_ecdh_context *ctx, size_t *olen, 248 unsigned char *buf, size_t blen, 249 int (*f_rng)(void *, unsigned char *, size_t), 250 void *p_rng ) 251 { 252 int ret; 253 254 if( ctx == NULL ) 255 return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA ); 256 257 if( ( ret = mbedtls_ecdh_compute_shared( &ctx->grp, &ctx->z, &ctx->Qp, &ctx->d, 258 f_rng, p_rng ) ) != 0 ) 259 { 260 return( ret ); 261 } 262 263 if( mbedtls_mpi_size( &ctx->z ) > blen ) 264 return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA ); 265 266 *olen = ctx->grp.pbits / 8 + ( ( ctx->grp.pbits % 8 ) != 0 ); 267 return mbedtls_mpi_write_binary( &ctx->z, buf, *olen ); 268 } 269 270 #endif /* MBEDTLS_ECDH_C */ 271