1 /* $OpenBSD: kexc25519.c,v 1.9 2015/03/26 07:00:04 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 "includes.h" 29 30 #include <sys/types.h> 31 32 #include <signal.h> 33 #include <string.h> 34 35 #include <openssl/bn.h> 36 #include <openssl/evp.h> 37 38 #include "sshbuf.h" 39 #include "ssh2.h" 40 #include "sshkey.h" 41 #include "cipher.h" 42 #include "kex.h" 43 #include "log.h" 44 #include "digest.h" 45 #include "ssherr.h" 46 47 extern int crypto_scalarmult_curve25519(u_char a[CURVE25519_SIZE], 48 const u_char b[CURVE25519_SIZE], const u_char c[CURVE25519_SIZE]) 49 __attribute__((__bounded__(__minbytes__, 1, CURVE25519_SIZE))) 50 __attribute__((__bounded__(__minbytes__, 2, CURVE25519_SIZE))) 51 __attribute__((__bounded__(__minbytes__, 3, CURVE25519_SIZE))); 52 53 void 54 kexc25519_keygen(u_char key[CURVE25519_SIZE], u_char pub[CURVE25519_SIZE]) 55 { 56 static const u_char basepoint[CURVE25519_SIZE] = {9}; 57 58 arc4random_buf(key, CURVE25519_SIZE); 59 crypto_scalarmult_curve25519(pub, key, basepoint); 60 } 61 62 int 63 kexc25519_shared_key(const u_char key[CURVE25519_SIZE], 64 const u_char pub[CURVE25519_SIZE], struct sshbuf *out) 65 { 66 u_char shared_key[CURVE25519_SIZE]; 67 int r; 68 69 /* Check for all-zero public key */ 70 explicit_bzero(shared_key, CURVE25519_SIZE); 71 if (timingsafe_bcmp(pub, shared_key, CURVE25519_SIZE) == 0) 72 return SSH_ERR_KEY_INVALID_EC_VALUE; 73 74 crypto_scalarmult_curve25519(shared_key, key, pub); 75 #ifdef DEBUG_KEXECDH 76 dump_digest("shared secret", shared_key, CURVE25519_SIZE); 77 #endif 78 sshbuf_reset(out); 79 r = sshbuf_put_bignum2_bytes(out, shared_key, CURVE25519_SIZE); 80 explicit_bzero(shared_key, CURVE25519_SIZE); 81 return r; 82 } 83 84 int 85 kex_c25519_hash( 86 int hash_alg, 87 const char *client_version_string, 88 const char *server_version_string, 89 const char *ckexinit, size_t ckexinitlen, 90 const char *skexinit, size_t skexinitlen, 91 const u_char *serverhostkeyblob, size_t sbloblen, 92 const u_char client_dh_pub[CURVE25519_SIZE], 93 const u_char server_dh_pub[CURVE25519_SIZE], 94 const u_char *shared_secret, size_t secretlen, 95 u_char *hash, size_t *hashlen) 96 { 97 struct sshbuf *b; 98 int r; 99 100 if (*hashlen < ssh_digest_bytes(hash_alg)) 101 return SSH_ERR_INVALID_ARGUMENT; 102 if ((b = sshbuf_new()) == NULL) 103 return SSH_ERR_ALLOC_FAIL; 104 if ((r = sshbuf_put_cstring(b, client_version_string)) < 0 || 105 (r = sshbuf_put_cstring(b, server_version_string)) < 0 || 106 /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */ 107 (r = sshbuf_put_u32(b, ckexinitlen+1)) < 0 || 108 (r = sshbuf_put_u8(b, SSH2_MSG_KEXINIT)) < 0 || 109 (r = sshbuf_put(b, ckexinit, ckexinitlen)) < 0 || 110 (r = sshbuf_put_u32(b, skexinitlen+1)) < 0 || 111 (r = sshbuf_put_u8(b, SSH2_MSG_KEXINIT)) < 0 || 112 (r = sshbuf_put(b, skexinit, skexinitlen)) < 0 || 113 (r = sshbuf_put_string(b, serverhostkeyblob, sbloblen)) < 0 || 114 (r = sshbuf_put_string(b, client_dh_pub, CURVE25519_SIZE)) < 0 || 115 (r = sshbuf_put_string(b, server_dh_pub, CURVE25519_SIZE)) < 0 || 116 (r = sshbuf_put(b, shared_secret, secretlen)) < 0) { 117 sshbuf_free(b); 118 return r; 119 } 120 #ifdef DEBUG_KEX 121 sshbuf_dump(b, stderr); 122 #endif 123 if (ssh_digest_buffer(hash_alg, b, hash, *hashlen) != 0) { 124 sshbuf_free(b); 125 return SSH_ERR_LIBCRYPTO_ERROR; 126 } 127 sshbuf_free(b); 128 *hashlen = ssh_digest_bytes(hash_alg); 129 #ifdef DEBUG_KEX 130 dump_digest("hash", hash, *hashlen); 131 #endif 132 return 0; 133 } 134