djm@openbsd.org | dfd5916 | 2019-01-21 10:20:12 +0000 | [diff] [blame^] | 1 | /* $OpenBSD: kexsntrup4591761x25519.c,v 1.1 2019/01/21 10:20:12 djm Exp $ */ |
| 2 | /* |
| 3 | * Copyright (c) 2019 Markus Friedl. All rights reserved. |
| 4 | * |
| 5 | * Redistribution and use in source and binary forms, with or without |
| 6 | * modification, are permitted provided that the following conditions |
| 7 | * are met: |
| 8 | * 1. Redistributions of source code must retain the above copyright |
| 9 | * notice, this list of conditions and the following disclaimer. |
| 10 | * 2. Redistributions in binary form must reproduce the above copyright |
| 11 | * notice, this list of conditions and the following disclaimer in the |
| 12 | * documentation and/or other materials provided with the distribution. |
| 13 | * |
| 14 | * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR |
| 15 | * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES |
| 16 | * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. |
| 17 | * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, |
| 18 | * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT |
| 19 | * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
| 20 | * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
| 21 | * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
| 22 | * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF |
| 23 | * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| 24 | */ |
| 25 | |
| 26 | #include <sys/types.h> |
| 27 | |
| 28 | #include <stdio.h> |
| 29 | #include <string.h> |
| 30 | #include <signal.h> |
| 31 | |
| 32 | #include "sshkey.h" |
| 33 | #include "kex.h" |
| 34 | #include "sshbuf.h" |
| 35 | #include "digest.h" |
| 36 | #include "ssherr.h" |
| 37 | |
| 38 | int |
| 39 | kex_kem_sntrup4591761x25519_keypair(struct kex *kex) |
| 40 | { |
| 41 | struct sshbuf *buf = NULL; |
| 42 | u_char *cp = NULL; |
| 43 | size_t need; |
| 44 | int r; |
| 45 | |
| 46 | if ((buf = sshbuf_new()) == NULL) |
| 47 | return SSH_ERR_ALLOC_FAIL; |
| 48 | need = crypto_kem_sntrup4591761_PUBLICKEYBYTES + CURVE25519_SIZE; |
| 49 | if ((r = sshbuf_reserve(buf, need, &cp)) != 0) |
| 50 | goto out; |
| 51 | crypto_kem_sntrup4591761_keypair(cp, kex->sntrup4591761_client_key); |
| 52 | #ifdef DEBUG_KEXECDH |
| 53 | dump_digest("client public key sntrup4591761:", cp, |
| 54 | crypto_kem_sntrup4591761_PUBLICKEYBYTES); |
| 55 | #endif |
| 56 | cp += crypto_kem_sntrup4591761_PUBLICKEYBYTES; |
| 57 | kexc25519_keygen(kex->c25519_client_key, cp); |
| 58 | #ifdef DEBUG_KEXECDH |
| 59 | dump_digest("client public key c25519:", cp, CURVE25519_SIZE); |
| 60 | #endif |
| 61 | kex->kem_client_pub = buf; |
| 62 | buf = NULL; |
| 63 | out: |
| 64 | sshbuf_free(buf); |
| 65 | return r; |
| 66 | } |
| 67 | |
| 68 | int |
| 69 | kex_kem_sntrup4591761x25519_enc(struct kex *kex, const u_char *pkblob, |
| 70 | size_t pklen, struct sshbuf **server_blobp, struct sshbuf **shared_secretp) |
| 71 | { |
| 72 | struct sshbuf *server_blob = NULL; |
| 73 | struct sshbuf *buf = NULL; |
| 74 | u_char *kem_key, *ciphertext, *server_pub; |
| 75 | u_char server_key[CURVE25519_SIZE]; |
| 76 | u_char hash[SSH_DIGEST_MAX_LENGTH]; |
| 77 | size_t need; |
| 78 | int r; |
| 79 | |
| 80 | *server_blobp = NULL; |
| 81 | *shared_secretp = NULL; |
| 82 | |
| 83 | /* pkblob contains both KEM and ECDH client pubkeys */ |
| 84 | need = crypto_kem_sntrup4591761_PUBLICKEYBYTES + CURVE25519_SIZE; |
| 85 | if (pklen != need) { |
| 86 | r = SSH_ERR_SIGNATURE_INVALID; |
| 87 | goto out; |
| 88 | } |
| 89 | #ifdef DEBUG_KEXECDH |
| 90 | dump_digest("client public key sntrup4591761:", pkblob, |
| 91 | crypto_kem_sntrup4591761_PUBLICKEYBYTES); |
| 92 | dump_digest("client public key 25519:", |
| 93 | pkblob + crypto_kem_sntrup4591761_PUBLICKEYBYTES, CURVE25519_SIZE); |
| 94 | #endif |
| 95 | /* allocate buffer for concatenation of KEM key and ECDH shared key */ |
| 96 | /* the buffer will be hashed and the result is the shared secret */ |
| 97 | if ((buf = sshbuf_new()) == NULL) { |
| 98 | r = SSH_ERR_ALLOC_FAIL; |
| 99 | goto out; |
| 100 | } |
| 101 | if ((r = sshbuf_reserve(buf, crypto_kem_sntrup4591761_BYTES, |
| 102 | &kem_key)) != 0) |
| 103 | goto out; |
| 104 | /* allocate space for encrypted KEM key and ECDH pub key */ |
| 105 | if ((server_blob = sshbuf_new()) == NULL) { |
| 106 | r = SSH_ERR_ALLOC_FAIL; |
| 107 | goto out; |
| 108 | } |
| 109 | need = crypto_kem_sntrup4591761_CIPHERTEXTBYTES + CURVE25519_SIZE; |
| 110 | if ((r = sshbuf_reserve(server_blob, need, &ciphertext)) != 0) |
| 111 | goto out; |
| 112 | /* generate and encrypt KEM key with client key */ |
| 113 | crypto_kem_sntrup4591761_enc(ciphertext, kem_key, pkblob); |
| 114 | /* generate ECDH key pair, store server pubkey after ciphertext */ |
| 115 | server_pub = ciphertext + crypto_kem_sntrup4591761_CIPHERTEXTBYTES; |
| 116 | kexc25519_keygen(server_key, server_pub); |
| 117 | /* append ECDH shared key */ |
| 118 | if ((r = kexc25519_shared_key_ext(server_key, |
| 119 | pkblob + crypto_kem_sntrup4591761_PUBLICKEYBYTES, buf, 1)) < 0) |
| 120 | goto out; |
| 121 | if ((r = ssh_digest_buffer(kex->hash_alg, buf, hash, sizeof(hash))) != 0) |
| 122 | goto out; |
| 123 | #ifdef DEBUG_KEXECDH |
| 124 | dump_digest("server public key 25519:", server_pub, CURVE25519_SIZE); |
| 125 | dump_digest("server cipher text:", ciphertext, |
| 126 | crypto_kem_sntrup4591761_CIPHERTEXTBYTES); |
| 127 | dump_digest("server kem key:", kem_key, sizeof(kem_key)); |
| 128 | dump_digest("concatenation of KEM key and ECDH shared key:", |
| 129 | sshbuf_ptr(buf), sshbuf_len(buf)); |
| 130 | #endif |
| 131 | /* string-encoded hash is resulting shared secret */ |
| 132 | sshbuf_reset(buf); |
| 133 | if ((r = sshbuf_put_string(buf, hash, |
| 134 | ssh_digest_bytes(kex->hash_alg))) != 0) |
| 135 | goto out; |
| 136 | #ifdef DEBUG_KEXECDH |
| 137 | dump_digest("encoded shared secret:", sshbuf_ptr(buf), sshbuf_len(buf)); |
| 138 | #endif |
| 139 | *server_blobp = server_blob; |
| 140 | *shared_secretp = buf; |
| 141 | server_blob = NULL; |
| 142 | buf = NULL; |
| 143 | out: |
| 144 | explicit_bzero(hash, sizeof(hash)); |
| 145 | explicit_bzero(server_key, sizeof(server_key)); |
| 146 | sshbuf_free(server_blob); |
| 147 | sshbuf_free(buf); |
| 148 | return r; |
| 149 | } |
| 150 | |
| 151 | int |
| 152 | kex_kem_sntrup4591761x25519_dec(struct kex *kex, const u_char *pkblob, |
| 153 | size_t pklen, struct sshbuf **shared_secretp) |
| 154 | { |
| 155 | struct sshbuf *buf = NULL; |
| 156 | u_char *kem_key = NULL; |
| 157 | const u_char *ciphertext, *server_pub; |
| 158 | u_char hash[SSH_DIGEST_MAX_LENGTH]; |
| 159 | size_t need; |
| 160 | int r, decoded; |
| 161 | |
| 162 | *shared_secretp = NULL; |
| 163 | |
| 164 | need = crypto_kem_sntrup4591761_CIPHERTEXTBYTES + CURVE25519_SIZE; |
| 165 | if (pklen != need) { |
| 166 | r = SSH_ERR_SIGNATURE_INVALID; |
| 167 | goto out; |
| 168 | } |
| 169 | ciphertext = pkblob; |
| 170 | server_pub = pkblob + crypto_kem_sntrup4591761_CIPHERTEXTBYTES; |
| 171 | #ifdef DEBUG_KEXECDH |
| 172 | dump_digest("server cipher text:", ciphertext, |
| 173 | crypto_kem_sntrup4591761_CIPHERTEXTBYTES); |
| 174 | dump_digest("server public key c25519:", server_pub, CURVE25519_SIZE); |
| 175 | #endif |
| 176 | /* hash concatenation of KEM key and ECDH shared key */ |
| 177 | if ((buf = sshbuf_new()) == NULL) { |
| 178 | r = SSH_ERR_ALLOC_FAIL; |
| 179 | goto out; |
| 180 | } |
| 181 | if ((r = sshbuf_reserve(buf, crypto_kem_sntrup4591761_BYTES, |
| 182 | &kem_key)) != 0) |
| 183 | goto out; |
| 184 | decoded = crypto_kem_sntrup4591761_dec(kem_key, ciphertext, |
| 185 | kex->sntrup4591761_client_key); |
| 186 | if ((r = kexc25519_shared_key_ext(kex->c25519_client_key, server_pub, |
| 187 | buf, 1)) < 0) |
| 188 | goto out; |
| 189 | if ((r = ssh_digest_buffer(kex->hash_alg, buf, hash, sizeof(hash))) != 0) |
| 190 | goto out; |
| 191 | #ifdef DEBUG_KEXECDH |
| 192 | dump_digest("client kem key:", kem_key, sizeof(kem_key)); |
| 193 | dump_digest("concatenation of KEM key and ECDH shared key:", |
| 194 | sshbuf_ptr(buf), sshbuf_len(buf)); |
| 195 | #endif |
| 196 | sshbuf_reset(buf); |
| 197 | if ((r = sshbuf_put_string(buf, hash, |
| 198 | ssh_digest_bytes(kex->hash_alg))) != 0) |
| 199 | goto out; |
| 200 | #ifdef DEBUG_KEXECDH |
| 201 | dump_digest("encoded shared secret:", sshbuf_ptr(buf), sshbuf_len(buf)); |
| 202 | #endif |
| 203 | if (decoded != 0) { |
| 204 | r = SSH_ERR_SIGNATURE_INVALID; |
| 205 | goto out; |
| 206 | } |
| 207 | *shared_secretp = buf; |
| 208 | buf = NULL; |
| 209 | out: |
| 210 | explicit_bzero(hash, sizeof(hash)); |
| 211 | sshbuf_free(buf); |
| 212 | return r; |
| 213 | } |