1 /* $OpenBSD: kexc25519.c,v 1.10 2016/05/02 08:49:03 djm Exp $ */ 2 /* 3 * Copyright (c) 2001, 2013 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 <sys/types.h> 29 30 #include <signal.h> 31 #include <string.h> 32 33 #include <openssl/bn.h> 34 #include <openssl/evp.h> 35 36 #include "sshbuf.h" 37 #include "ssh2.h" 38 #include "sshkey.h" 39 #include "cipher.h" 40 #include "kex.h" 41 #include "log.h" 42 #include "digest.h" 43 #include "ssherr.h" 44 45 extern int crypto_scalarmult_curve25519(u_char a[CURVE25519_SIZE], 46 const u_char b[CURVE25519_SIZE], const u_char c[CURVE25519_SIZE]) 47 __attribute__((__bounded__(__minbytes__, 1, CURVE25519_SIZE))) 48 __attribute__((__bounded__(__minbytes__, 2, CURVE25519_SIZE))) 49 __attribute__((__bounded__(__minbytes__, 3, CURVE25519_SIZE))); 50 51 void 52 kexc25519_keygen(u_char key[CURVE25519_SIZE], u_char pub[CURVE25519_SIZE]) 53 { 54 static const u_char basepoint[CURVE25519_SIZE] = {9}; 55 56 arc4random_buf(key, CURVE25519_SIZE); 57 crypto_scalarmult_curve25519(pub, key, basepoint); 58 } 59 60 int 61 kexc25519_shared_key(const u_char key[CURVE25519_SIZE], 62 const u_char pub[CURVE25519_SIZE], struct sshbuf *out) 63 { 64 u_char shared_key[CURVE25519_SIZE]; 65 int r; 66 67 /* Check for all-zero public key */ 68 explicit_bzero(shared_key, CURVE25519_SIZE); 69 if (timingsafe_bcmp(pub, shared_key, CURVE25519_SIZE) == 0) 70 return SSH_ERR_KEY_INVALID_EC_VALUE; 71 72 crypto_scalarmult_curve25519(shared_key, key, pub); 73 #ifdef DEBUG_KEXECDH 74 dump_digest("shared secret", shared_key, CURVE25519_SIZE); 75 #endif 76 sshbuf_reset(out); 77 r = sshbuf_put_bignum2_bytes(out, shared_key, CURVE25519_SIZE); 78 explicit_bzero(shared_key, CURVE25519_SIZE); 79 return r; 80 } 81 82 int 83 kex_c25519_hash( 84 int hash_alg, 85 const char *client_version_string, 86 const char *server_version_string, 87 const u_char *ckexinit, size_t ckexinitlen, 88 const u_char *skexinit, size_t skexinitlen, 89 const u_char *serverhostkeyblob, size_t sbloblen, 90 const u_char client_dh_pub[CURVE25519_SIZE], 91 const u_char server_dh_pub[CURVE25519_SIZE], 92 const u_char *shared_secret, size_t secretlen, 93 u_char *hash, size_t *hashlen) 94 { 95 struct sshbuf *b; 96 int r; 97 98 if (*hashlen < ssh_digest_bytes(hash_alg)) 99 return SSH_ERR_INVALID_ARGUMENT; 100 if ((b = sshbuf_new()) == NULL) 101 return SSH_ERR_ALLOC_FAIL; 102 if ((r = sshbuf_put_cstring(b, client_version_string)) < 0 || 103 (r = sshbuf_put_cstring(b, server_version_string)) < 0 || 104 /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */ 105 (r = sshbuf_put_u32(b, ckexinitlen+1)) < 0 || 106 (r = sshbuf_put_u8(b, SSH2_MSG_KEXINIT)) < 0 || 107 (r = sshbuf_put(b, ckexinit, ckexinitlen)) < 0 || 108 (r = sshbuf_put_u32(b, skexinitlen+1)) < 0 || 109 (r = sshbuf_put_u8(b, SSH2_MSG_KEXINIT)) < 0 || 110 (r = sshbuf_put(b, skexinit, skexinitlen)) < 0 || 111 (r = sshbuf_put_string(b, serverhostkeyblob, sbloblen)) < 0 || 112 (r = sshbuf_put_string(b, client_dh_pub, CURVE25519_SIZE)) < 0 || 113 (r = sshbuf_put_string(b, server_dh_pub, CURVE25519_SIZE)) < 0 || 114 (r = sshbuf_put(b, shared_secret, secretlen)) < 0) { 115 sshbuf_free(b); 116 return r; 117 } 118 #ifdef DEBUG_KEX 119 sshbuf_dump(b, stderr); 120 #endif 121 if (ssh_digest_buffer(hash_alg, b, hash, *hashlen) != 0) { 122 sshbuf_free(b); 123 return SSH_ERR_LIBCRYPTO_ERROR; 124 } 125 sshbuf_free(b); 126 *hashlen = ssh_digest_bytes(hash_alg); 127 #ifdef DEBUG_KEX 128 dump_digest("hash", hash, *hashlen); 129 #endif 130 return 0; 131 } 132