1 /* $OpenBSD: ssh-ecdsa-sk.c,v 1.5 2019/11/26 03:04:27 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 <sys/types.h> 31 32 #include <openssl/bn.h> 33 #include <openssl/ec.h> 34 #include <openssl/ecdsa.h> 35 #include <openssl/evp.h> 36 37 #include <string.h> 38 #include <stdio.h> /* needed for DEBUG_SK only */ 39 40 #include "sshbuf.h" 41 #include "ssherr.h" 42 #include "digest.h" 43 #define SSHKEY_INTERNAL 44 #include "sshkey.h" 45 46 /* ARGSUSED */ 47 int 48 ssh_ecdsa_sk_verify(const struct sshkey *key, 49 const u_char *signature, size_t signaturelen, 50 const u_char *data, size_t datalen, u_int compat, 51 struct sshkey_sig_details **detailsp) 52 { 53 ECDSA_SIG *sig = NULL; 54 BIGNUM *sig_r = NULL, *sig_s = NULL; 55 u_char sig_flags; 56 u_char msghash[32], apphash[32], sighash[32]; 57 u_int sig_counter; 58 int ret = SSH_ERR_INTERNAL_ERROR; 59 struct sshbuf *b = NULL, *sigbuf = NULL, *original_signed = NULL; 60 char *ktype = NULL; 61 struct sshkey_sig_details *details = NULL; 62 #ifdef DEBUG_SK 63 char *tmp = NULL; 64 #endif 65 66 if (detailsp != NULL) 67 *detailsp = NULL; 68 if (key == NULL || key->ecdsa == NULL || 69 sshkey_type_plain(key->type) != KEY_ECDSA_SK || 70 signature == NULL || signaturelen == 0) 71 return SSH_ERR_INVALID_ARGUMENT; 72 73 if (key->ecdsa_nid != NID_X9_62_prime256v1) 74 return SSH_ERR_INTERNAL_ERROR; 75 76 /* fetch signature */ 77 if ((b = sshbuf_from(signature, signaturelen)) == NULL) 78 return SSH_ERR_ALLOC_FAIL; 79 if (sshbuf_get_cstring(b, &ktype, NULL) != 0 || 80 sshbuf_froms(b, &sigbuf) != 0 || 81 sshbuf_get_u8(b, &sig_flags) != 0 || 82 sshbuf_get_u32(b, &sig_counter) != 0) { 83 ret = SSH_ERR_INVALID_FORMAT; 84 goto out; 85 } 86 if (strcmp(sshkey_ssh_name_plain(key), ktype) != 0) { 87 ret = SSH_ERR_KEY_TYPE_MISMATCH; 88 goto out; 89 } 90 if (sshbuf_len(b) != 0) { 91 ret = SSH_ERR_UNEXPECTED_TRAILING_DATA; 92 goto out; 93 } 94 95 /* parse signature */ 96 if (sshbuf_get_bignum2(sigbuf, &sig_r) != 0 || 97 sshbuf_get_bignum2(sigbuf, &sig_s) != 0) { 98 ret = SSH_ERR_INVALID_FORMAT; 99 goto out; 100 } 101 if ((sig = ECDSA_SIG_new()) == NULL) { 102 ret = SSH_ERR_ALLOC_FAIL; 103 goto out; 104 } 105 if (!ECDSA_SIG_set0(sig, sig_r, sig_s)) { 106 ret = SSH_ERR_LIBCRYPTO_ERROR; 107 goto out; 108 } 109 #ifdef DEBUG_SK 110 fprintf(stderr, "%s: data: (len %zu)\n", __func__, datalen); 111 /* sshbuf_dump_data(data, datalen, stderr); */ 112 fprintf(stderr, "%s: sig_r: %s\n", __func__, (tmp = BN_bn2hex(sig_r))); 113 free(tmp); 114 fprintf(stderr, "%s: sig_s: %s\n", __func__, (tmp = BN_bn2hex(sig_s))); 115 free(tmp); 116 fprintf(stderr, "%s: sig_flags = 0x%02x, sig_counter = %u\n", 117 __func__, sig_flags, sig_counter); 118 #endif 119 sig_r = sig_s = NULL; /* transferred */ 120 121 if (sshbuf_len(sigbuf) != 0) { 122 ret = SSH_ERR_UNEXPECTED_TRAILING_DATA; 123 goto out; 124 } 125 126 /* Reconstruct data that was supposedly signed */ 127 if ((original_signed = sshbuf_new()) == NULL) { 128 ret = SSH_ERR_ALLOC_FAIL; 129 goto out; 130 } 131 if ((ret = ssh_digest_memory(SSH_DIGEST_SHA256, data, datalen, 132 msghash, sizeof(msghash))) != 0) 133 goto out; 134 /* Application value is hashed before signature */ 135 if ((ret = ssh_digest_memory(SSH_DIGEST_SHA256, key->sk_application, 136 strlen(key->sk_application), apphash, sizeof(apphash))) != 0) 137 goto out; 138 #ifdef DEBUG_SK 139 fprintf(stderr, "%s: hashed application:\n", __func__); 140 sshbuf_dump_data(apphash, sizeof(apphash), stderr); 141 fprintf(stderr, "%s: hashed message:\n", __func__); 142 sshbuf_dump_data(msghash, sizeof(msghash), stderr); 143 #endif 144 if ((ret = sshbuf_put(original_signed, 145 apphash, sizeof(apphash))) != 0 || 146 (ret = sshbuf_put_u8(original_signed, sig_flags)) != 0 || 147 (ret = sshbuf_put_u32(original_signed, sig_counter)) != 0 || 148 (ret = sshbuf_put(original_signed, msghash, sizeof(msghash))) != 0) 149 goto out; 150 /* Signature is over H(original_signed) */ 151 if ((ret = ssh_digest_buffer(SSH_DIGEST_SHA256, original_signed, 152 sighash, sizeof(sighash))) != 0) 153 goto out; 154 if ((details = calloc(1, sizeof(*details))) == NULL) { 155 ret = SSH_ERR_ALLOC_FAIL; 156 goto out; 157 } 158 details->sk_counter = sig_counter; 159 details->sk_flags = sig_flags; 160 #ifdef DEBUG_SK 161 fprintf(stderr, "%s: signed buf:\n", __func__); 162 sshbuf_dump(original_signed, stderr); 163 fprintf(stderr, "%s: signed hash:\n", __func__); 164 sshbuf_dump_data(sighash, sizeof(sighash), stderr); 165 #endif 166 167 /* Verify it */ 168 switch (ECDSA_do_verify(sighash, sizeof(sighash), sig, key->ecdsa)) { 169 case 1: 170 ret = 0; 171 break; 172 case 0: 173 ret = SSH_ERR_SIGNATURE_INVALID; 174 goto out; 175 default: 176 ret = SSH_ERR_LIBCRYPTO_ERROR; 177 goto out; 178 } 179 /* success */ 180 if (detailsp != NULL) { 181 *detailsp = details; 182 details = NULL; 183 } 184 out: 185 explicit_bzero(&sig_flags, sizeof(sig_flags)); 186 explicit_bzero(&sig_counter, sizeof(sig_counter)); 187 explicit_bzero(msghash, sizeof(msghash)); 188 explicit_bzero(sighash, sizeof(msghash)); 189 explicit_bzero(apphash, sizeof(apphash)); 190 sshkey_sig_details_free(details); 191 sshbuf_free(original_signed); 192 sshbuf_free(sigbuf); 193 sshbuf_free(b); 194 ECDSA_SIG_free(sig); 195 BN_clear_free(sig_r); 196 BN_clear_free(sig_s); 197 free(ktype); 198 return ret; 199 } 200