1 /* $OpenBSD: ssh-ecdsa-sk.c,v 1.6 2020/06/22 05:56:23 djm Exp $ */ 2 /* 3 * Copyright (c) 2000 Markus Friedl. All rights reserved. 4 * Copyright (c) 2010 Damien Miller. All rights reserved. 5 * Copyright (c) 2019 Google Inc. 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 /* #define DEBUG_SK 1 */ 29 30 #include "includes.h" 31 32 #include <sys/types.h> 33 34 #ifdef WITH_OPENSSL 35 #include <openssl/bn.h> 36 #include <openssl/ec.h> 37 #include <openssl/ecdsa.h> 38 #include <openssl/evp.h> 39 #endif 40 41 #include <string.h> 42 #include <stdio.h> /* needed for DEBUG_SK only */ 43 44 #include "openbsd-compat/openssl-compat.h" 45 46 #include "sshbuf.h" 47 #include "ssherr.h" 48 #include "digest.h" 49 #define SSHKEY_INTERNAL 50 #include "sshkey.h" 51 52 /* ARGSUSED */ 53 int 54 ssh_ecdsa_sk_verify(const struct sshkey *key, 55 const u_char *signature, size_t signaturelen, 56 const u_char *data, size_t datalen, u_int compat, 57 struct sshkey_sig_details **detailsp) 58 { 59 #ifdef OPENSSL_HAS_ECC 60 ECDSA_SIG *sig = NULL; 61 BIGNUM *sig_r = NULL, *sig_s = NULL; 62 u_char sig_flags; 63 u_char msghash[32], apphash[32], sighash[32]; 64 u_int sig_counter; 65 int ret = SSH_ERR_INTERNAL_ERROR; 66 struct sshbuf *b = NULL, *sigbuf = NULL, *original_signed = NULL; 67 char *ktype = NULL; 68 struct sshkey_sig_details *details = NULL; 69 #ifdef DEBUG_SK 70 char *tmp = NULL; 71 #endif 72 73 if (detailsp != NULL) 74 *detailsp = NULL; 75 if (key == NULL || key->ecdsa == NULL || 76 sshkey_type_plain(key->type) != KEY_ECDSA_SK || 77 signature == NULL || signaturelen == 0) 78 return SSH_ERR_INVALID_ARGUMENT; 79 80 if (key->ecdsa_nid != NID_X9_62_prime256v1) 81 return SSH_ERR_INTERNAL_ERROR; 82 83 /* fetch signature */ 84 if ((b = sshbuf_from(signature, signaturelen)) == NULL) 85 return SSH_ERR_ALLOC_FAIL; 86 if ((details = calloc(1, sizeof(*details))) == NULL) { 87 ret = SSH_ERR_ALLOC_FAIL; 88 goto out; 89 } 90 if (sshbuf_get_cstring(b, &ktype, NULL) != 0) { 91 ret = SSH_ERR_INVALID_FORMAT; 92 goto out; 93 } 94 if (strcmp(ktype, "sk-ecdsa-sha2-nistp256@openssh.com") != 0) { 95 ret = SSH_ERR_INVALID_FORMAT; 96 goto out; 97 } 98 if (sshbuf_froms(b, &sigbuf) != 0 || 99 sshbuf_get_u8(b, &sig_flags) != 0 || 100 sshbuf_get_u32(b, &sig_counter) != 0) { 101 ret = SSH_ERR_INVALID_FORMAT; 102 goto out; 103 } 104 if (sshbuf_len(b) != 0) { 105 ret = SSH_ERR_UNEXPECTED_TRAILING_DATA; 106 goto out; 107 } 108 109 /* parse signature */ 110 if (sshbuf_get_bignum2(sigbuf, &sig_r) != 0 || 111 sshbuf_get_bignum2(sigbuf, &sig_s) != 0) { 112 ret = SSH_ERR_INVALID_FORMAT; 113 goto out; 114 } 115 if (sshbuf_len(sigbuf) != 0) { 116 ret = SSH_ERR_UNEXPECTED_TRAILING_DATA; 117 goto out; 118 } 119 #ifdef DEBUG_SK 120 fprintf(stderr, "%s: data: (len %zu)\n", __func__, datalen); 121 /* sshbuf_dump_data(data, datalen, stderr); */ 122 fprintf(stderr, "%s: sig_r: %s\n", __func__, (tmp = BN_bn2hex(sig_r))); 123 free(tmp); 124 fprintf(stderr, "%s: sig_s: %s\n", __func__, (tmp = BN_bn2hex(sig_s))); 125 free(tmp); 126 fprintf(stderr, "%s: sig_flags = 0x%02x, sig_counter = %u\n", 127 __func__, sig_flags, sig_counter); 128 #endif 129 if ((sig = ECDSA_SIG_new()) == NULL) { 130 ret = SSH_ERR_ALLOC_FAIL; 131 goto out; 132 } 133 if (!ECDSA_SIG_set0(sig, sig_r, sig_s)) { 134 ret = SSH_ERR_LIBCRYPTO_ERROR; 135 goto out; 136 } 137 sig_r = sig_s = NULL; /* transferred */ 138 139 /* Reconstruct data that was supposedly signed */ 140 if ((original_signed = sshbuf_new()) == NULL) { 141 ret = SSH_ERR_ALLOC_FAIL; 142 goto out; 143 } 144 if ((ret = ssh_digest_memory(SSH_DIGEST_SHA256, data, datalen, 145 msghash, sizeof(msghash))) != 0) 146 goto out; 147 /* Application value is hashed before signature */ 148 if ((ret = ssh_digest_memory(SSH_DIGEST_SHA256, key->sk_application, 149 strlen(key->sk_application), apphash, sizeof(apphash))) != 0) 150 goto out; 151 #ifdef DEBUG_SK 152 fprintf(stderr, "%s: hashed application:\n", __func__); 153 sshbuf_dump_data(apphash, sizeof(apphash), stderr); 154 fprintf(stderr, "%s: hashed message:\n", __func__); 155 sshbuf_dump_data(msghash, sizeof(msghash), stderr); 156 #endif 157 if ((ret = sshbuf_put(original_signed, 158 apphash, sizeof(apphash))) != 0 || 159 (ret = sshbuf_put_u8(original_signed, sig_flags)) != 0 || 160 (ret = sshbuf_put_u32(original_signed, sig_counter)) != 0 || 161 (ret = sshbuf_put(original_signed, msghash, sizeof(msghash))) != 0) 162 goto out; 163 /* Signature is over H(original_signed) */ 164 if ((ret = ssh_digest_buffer(SSH_DIGEST_SHA256, original_signed, 165 sighash, sizeof(sighash))) != 0) 166 goto out; 167 details->sk_counter = sig_counter; 168 details->sk_flags = sig_flags; 169 #ifdef DEBUG_SK 170 fprintf(stderr, "%s: signed buf:\n", __func__); 171 sshbuf_dump(original_signed, stderr); 172 fprintf(stderr, "%s: signed hash:\n", __func__); 173 sshbuf_dump_data(sighash, sizeof(sighash), stderr); 174 #endif 175 176 /* Verify it */ 177 switch (ECDSA_do_verify(sighash, sizeof(sighash), sig, key->ecdsa)) { 178 case 1: 179 ret = 0; 180 break; 181 case 0: 182 ret = SSH_ERR_SIGNATURE_INVALID; 183 goto out; 184 default: 185 ret = SSH_ERR_LIBCRYPTO_ERROR; 186 goto out; 187 } 188 /* success */ 189 if (detailsp != NULL) { 190 *detailsp = details; 191 details = NULL; 192 } 193 out: 194 explicit_bzero(&sig_flags, sizeof(sig_flags)); 195 explicit_bzero(&sig_counter, sizeof(sig_counter)); 196 explicit_bzero(msghash, sizeof(msghash)); 197 explicit_bzero(sighash, sizeof(msghash)); 198 explicit_bzero(apphash, sizeof(apphash)); 199 sshkey_sig_details_free(details); 200 sshbuf_free(original_signed); 201 sshbuf_free(sigbuf); 202 sshbuf_free(b); 203 ECDSA_SIG_free(sig); 204 BN_clear_free(sig_r); 205 BN_clear_free(sig_s); 206 free(ktype); 207 return ret; 208 #else 209 return SSH_ERR_INTERNAL_ERROR; 210 #endif 211 } 212