1/* $OpenBSD: kexc25519.c,v 1.17 2019/01/21 10:40:11 djm Exp $ */ 2/* 3 * Copyright (c) 2019 Markus Friedl. All rights reserved. 4 * Copyright (c) 2010 Damien Miller. All rights reserved. 5 * Copyright (c) 2013 Aris Adamantiadis. All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 17 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 18 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 19 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 21 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 22 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 23 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 25 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 26 */ 27 28#include "includes.h" 29 30#include <sys/types.h> 31 32#include <stdio.h> 33#include <string.h> 34#include <signal.h> 35 36#include "sshkey.h" 37#include "kex.h" 38#include "sshbuf.h" 39#include "digest.h" 40#include "ssherr.h" 41#include "ssh2.h" 42 43extern int crypto_scalarmult_curve25519(u_char a[CURVE25519_SIZE], 44 const u_char b[CURVE25519_SIZE], const u_char c[CURVE25519_SIZE]) 45 __attribute__((__bounded__(__minbytes__, 1, CURVE25519_SIZE))) 46 __attribute__((__bounded__(__minbytes__, 2, CURVE25519_SIZE))) 47 __attribute__((__bounded__(__minbytes__, 3, CURVE25519_SIZE))); 48 49void 50kexc25519_keygen(u_char key[CURVE25519_SIZE], u_char pub[CURVE25519_SIZE]) 51{ 52 static const u_char basepoint[CURVE25519_SIZE] = {9}; 53 54 arc4random_buf(key, CURVE25519_SIZE); 55 crypto_scalarmult_curve25519(pub, key, basepoint); 56} 57 58int 59kexc25519_shared_key_ext(const u_char key[CURVE25519_SIZE], 60 const u_char pub[CURVE25519_SIZE], struct sshbuf *out, int raw) 61{ 62 u_char shared_key[CURVE25519_SIZE]; 63 u_char zero[CURVE25519_SIZE]; 64 int r; 65 66 crypto_scalarmult_curve25519(shared_key, key, pub); 67 68 /* Check for all-zero shared secret */ 69 explicit_bzero(zero, CURVE25519_SIZE); 70 if (timingsafe_bcmp(zero, shared_key, CURVE25519_SIZE) == 0) 71 return SSH_ERR_KEY_INVALID_EC_VALUE; 72 73#ifdef DEBUG_KEXECDH 74 dump_digest("shared secret", shared_key, CURVE25519_SIZE); 75#endif 76 if (raw) 77 r = sshbuf_put(out, shared_key, CURVE25519_SIZE); 78 else 79 r = sshbuf_put_bignum2_bytes(out, shared_key, CURVE25519_SIZE); 80 explicit_bzero(shared_key, CURVE25519_SIZE); 81 return r; 82} 83 84int 85kexc25519_shared_key(const u_char key[CURVE25519_SIZE], 86 const u_char pub[CURVE25519_SIZE], struct sshbuf *out) 87{ 88 return kexc25519_shared_key_ext(key, pub, out, 0); 89} 90 91int 92kex_c25519_keypair(struct kex *kex) 93{ 94 struct sshbuf *buf = NULL; 95 u_char *cp = NULL; 96 int r; 97 98 if ((buf = sshbuf_new()) == NULL) 99 return SSH_ERR_ALLOC_FAIL; 100 if ((r = sshbuf_reserve(buf, CURVE25519_SIZE, &cp)) != 0) 101 goto out; 102 kexc25519_keygen(kex->c25519_client_key, cp); 103#ifdef DEBUG_KEXECDH 104 dump_digest("client public key c25519:", cp, CURVE25519_SIZE); 105#endif 106 kex->client_pub = buf; 107 buf = NULL; 108 out: 109 sshbuf_free(buf); 110 return r; 111} 112 113int 114kex_c25519_enc(struct kex *kex, const struct sshbuf *client_blob, 115 struct sshbuf **server_blobp, struct sshbuf **shared_secretp) 116{ 117 struct sshbuf *server_blob = NULL; 118 struct sshbuf *buf = NULL; 119 const u_char *client_pub; 120 u_char *server_pub; 121 u_char server_key[CURVE25519_SIZE]; 122 int r; 123 124 *server_blobp = NULL; 125 *shared_secretp = NULL; 126 127 if (sshbuf_len(client_blob) != CURVE25519_SIZE) { 128 r = SSH_ERR_SIGNATURE_INVALID; 129 goto out; 130 } 131 client_pub = sshbuf_ptr(client_blob); 132#ifdef DEBUG_KEXECDH 133 dump_digest("client public key 25519:", client_pub, CURVE25519_SIZE); 134#endif 135 /* allocate space for encrypted KEM key and ECDH pub key */ 136 if ((server_blob = sshbuf_new()) == NULL) { 137 r = SSH_ERR_ALLOC_FAIL; 138 goto out; 139 } 140 if ((r = sshbuf_reserve(server_blob, CURVE25519_SIZE, &server_pub)) != 0) 141 goto out; 142 kexc25519_keygen(server_key, server_pub); 143 /* allocate shared secret */ 144 if ((buf = sshbuf_new()) == NULL) { 145 r = SSH_ERR_ALLOC_FAIL; 146 goto out; 147 } 148 if ((r = kexc25519_shared_key_ext(server_key, client_pub, buf, 0)) < 0) 149 goto out; 150#ifdef DEBUG_KEXECDH 151 dump_digest("server public key 25519:", server_pub, CURVE25519_SIZE); 152 dump_digest("encoded shared secret:", sshbuf_ptr(buf), sshbuf_len(buf)); 153#endif 154 *server_blobp = server_blob; 155 *shared_secretp = buf; 156 server_blob = NULL; 157 buf = NULL; 158 out: 159 explicit_bzero(server_key, sizeof(server_key)); 160 sshbuf_free(server_blob); 161 sshbuf_free(buf); 162 return r; 163} 164 165int 166kex_c25519_dec(struct kex *kex, const struct sshbuf *server_blob, 167 struct sshbuf **shared_secretp) 168{ 169 struct sshbuf *buf = NULL; 170 const u_char *server_pub; 171 int r; 172 173 *shared_secretp = NULL; 174 175 if (sshbuf_len(server_blob) != CURVE25519_SIZE) { 176 r = SSH_ERR_SIGNATURE_INVALID; 177 goto out; 178 } 179 server_pub = sshbuf_ptr(server_blob); 180#ifdef DEBUG_KEXECDH 181 dump_digest("server public key c25519:", server_pub, CURVE25519_SIZE); 182#endif 183 /* shared secret */ 184 if ((buf = sshbuf_new()) == NULL) { 185 r = SSH_ERR_ALLOC_FAIL; 186 goto out; 187 } 188 if ((r = kexc25519_shared_key_ext(kex->c25519_client_key, server_pub, 189 buf, 0)) < 0) 190 goto out; 191#ifdef DEBUG_KEXECDH 192 dump_digest("encoded shared secret:", sshbuf_ptr(buf), sshbuf_len(buf)); 193#endif 194 *shared_secretp = buf; 195 buf = NULL; 196 out: 197 sshbuf_free(buf); 198 return r; 199} 200