1 /* $NetBSD: ssh-ecdsa-sk.c,v 1.2 2020/02/27 00:24:40 christos Exp $ */ 2 /* $OpenBSD: ssh-ecdsa-sk.c,v 1.5 2019/11/26 03:04:27 djm Exp $ */ 3 /* 4 * Copyright (c) 2000 Markus Friedl. All rights reserved. 5 * Copyright (c) 2010 Damien Miller. All rights reserved. 6 * Copyright (c) 2019 Google Inc. All rights reserved. 7 * 8 * Redistribution and use in source and binary forms, with or without 9 * modification, are permitted provided that the following conditions 10 * are met: 11 * 1. Redistributions of source code must retain the above copyright 12 * notice, this list of conditions and the following disclaimer. 13 * 2. Redistributions in binary form must reproduce the above copyright 14 * notice, this list of conditions and the following disclaimer in the 15 * documentation and/or other materials provided with the distribution. 16 * 17 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 18 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 19 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 20 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 21 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 22 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 23 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 24 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 25 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 26 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 27 */ 28 #include "includes.h" 29 __RCSID("$NetBSD: ssh-ecdsa-sk.c,v 1.2 2020/02/27 00:24:40 christos Exp $"); 30 31 /* #define DEBUG_SK 1 */ 32 33 #include <sys/types.h> 34 35 #include <openssl/bn.h> 36 #include <openssl/ec.h> 37 #include <openssl/ecdsa.h> 38 #include <openssl/evp.h> 39 40 #include <string.h> 41 #include <stdio.h> /* needed for DEBUG_SK only */ 42 43 #include "sshbuf.h" 44 #include "ssherr.h" 45 #include "digest.h" 46 #define SSHKEY_INTERNAL 47 #include "sshkey.h" 48 49 /* ARGSUSED */ 50 int 51 ssh_ecdsa_sk_verify(const struct sshkey *key, 52 const u_char *signature, size_t signaturelen, 53 const u_char *data, size_t datalen, u_int compat, 54 struct sshkey_sig_details **detailsp) 55 { 56 ECDSA_SIG *sig = NULL; 57 BIGNUM *sig_r = NULL, *sig_s = NULL; 58 u_char sig_flags; 59 u_char msghash[32], apphash[32], sighash[32]; 60 u_int sig_counter; 61 int ret = SSH_ERR_INTERNAL_ERROR; 62 struct sshbuf *b = NULL, *sigbuf = NULL, *original_signed = NULL; 63 char *ktype = NULL; 64 struct sshkey_sig_details *details = NULL; 65 #ifdef DEBUG_SK 66 char *tmp = NULL; 67 #endif 68 69 if (detailsp != NULL) 70 *detailsp = NULL; 71 if (key == NULL || key->ecdsa == NULL || 72 sshkey_type_plain(key->type) != KEY_ECDSA_SK || 73 signature == NULL || signaturelen == 0) 74 return SSH_ERR_INVALID_ARGUMENT; 75 76 if (key->ecdsa_nid != NID_X9_62_prime256v1) 77 return SSH_ERR_INTERNAL_ERROR; 78 79 /* fetch signature */ 80 if ((b = sshbuf_from(signature, signaturelen)) == NULL) 81 return SSH_ERR_ALLOC_FAIL; 82 if (sshbuf_get_cstring(b, &ktype, NULL) != 0 || 83 sshbuf_froms(b, &sigbuf) != 0 || 84 sshbuf_get_u8(b, &sig_flags) != 0 || 85 sshbuf_get_u32(b, &sig_counter) != 0) { 86 ret = SSH_ERR_INVALID_FORMAT; 87 goto out; 88 } 89 if (strcmp(sshkey_ssh_name_plain(key), ktype) != 0) { 90 ret = SSH_ERR_KEY_TYPE_MISMATCH; 91 goto out; 92 } 93 if (sshbuf_len(b) != 0) { 94 ret = SSH_ERR_UNEXPECTED_TRAILING_DATA; 95 goto out; 96 } 97 98 /* parse signature */ 99 if (sshbuf_get_bignum2(sigbuf, &sig_r) != 0 || 100 sshbuf_get_bignum2(sigbuf, &sig_s) != 0) { 101 ret = SSH_ERR_INVALID_FORMAT; 102 goto out; 103 } 104 if ((sig = ECDSA_SIG_new()) == NULL) { 105 ret = SSH_ERR_ALLOC_FAIL; 106 goto out; 107 } 108 if (!ECDSA_SIG_set0(sig, sig_r, sig_s)) { 109 ret = SSH_ERR_LIBCRYPTO_ERROR; 110 goto out; 111 } 112 #ifdef DEBUG_SK 113 fprintf(stderr, "%s: data: (len %zu)\n", __func__, datalen); 114 /* sshbuf_dump_data(data, datalen, stderr); */ 115 fprintf(stderr, "%s: sig_r: %s\n", __func__, (tmp = BN_bn2hex(sig_r))); 116 free(tmp); 117 fprintf(stderr, "%s: sig_s: %s\n", __func__, (tmp = BN_bn2hex(sig_s))); 118 free(tmp); 119 fprintf(stderr, "%s: sig_flags = 0x%02x, sig_counter = %u\n", 120 __func__, sig_flags, sig_counter); 121 #endif 122 sig_r = sig_s = NULL; /* transferred */ 123 124 if (sshbuf_len(sigbuf) != 0) { 125 ret = SSH_ERR_UNEXPECTED_TRAILING_DATA; 126 goto out; 127 } 128 129 /* Reconstruct data that was supposedly signed */ 130 if ((original_signed = sshbuf_new()) == NULL) { 131 ret = SSH_ERR_ALLOC_FAIL; 132 goto out; 133 } 134 if ((ret = ssh_digest_memory(SSH_DIGEST_SHA256, data, datalen, 135 msghash, sizeof(msghash))) != 0) 136 goto out; 137 /* Application value is hashed before signature */ 138 if ((ret = ssh_digest_memory(SSH_DIGEST_SHA256, key->sk_application, 139 strlen(key->sk_application), apphash, sizeof(apphash))) != 0) 140 goto out; 141 #ifdef DEBUG_SK 142 fprintf(stderr, "%s: hashed application:\n", __func__); 143 sshbuf_dump_data(apphash, sizeof(apphash), stderr); 144 fprintf(stderr, "%s: hashed message:\n", __func__); 145 sshbuf_dump_data(msghash, sizeof(msghash), stderr); 146 #endif 147 if ((ret = sshbuf_put(original_signed, 148 apphash, sizeof(apphash))) != 0 || 149 (ret = sshbuf_put_u8(original_signed, sig_flags)) != 0 || 150 (ret = sshbuf_put_u32(original_signed, sig_counter)) != 0 || 151 (ret = sshbuf_put(original_signed, msghash, sizeof(msghash))) != 0) 152 goto out; 153 /* Signature is over H(original_signed) */ 154 if ((ret = ssh_digest_buffer(SSH_DIGEST_SHA256, original_signed, 155 sighash, sizeof(sighash))) != 0) 156 goto out; 157 if ((details = calloc(1, sizeof(*details))) == NULL) { 158 ret = SSH_ERR_ALLOC_FAIL; 159 goto out; 160 } 161 details->sk_counter = sig_counter; 162 details->sk_flags = sig_flags; 163 #ifdef DEBUG_SK 164 fprintf(stderr, "%s: signed buf:\n", __func__); 165 sshbuf_dump(original_signed, stderr); 166 fprintf(stderr, "%s: signed hash:\n", __func__); 167 sshbuf_dump_data(sighash, sizeof(sighash), stderr); 168 #endif 169 170 /* Verify it */ 171 switch (ECDSA_do_verify(sighash, sizeof(sighash), sig, key->ecdsa)) { 172 case 1: 173 ret = 0; 174 break; 175 case 0: 176 ret = SSH_ERR_SIGNATURE_INVALID; 177 goto out; 178 default: 179 ret = SSH_ERR_LIBCRYPTO_ERROR; 180 goto out; 181 } 182 /* success */ 183 if (detailsp != NULL) { 184 *detailsp = details; 185 details = NULL; 186 } 187 out: 188 explicit_bzero(&sig_flags, sizeof(sig_flags)); 189 explicit_bzero(&sig_counter, sizeof(sig_counter)); 190 explicit_bzero(msghash, sizeof(msghash)); 191 explicit_bzero(sighash, sizeof(msghash)); 192 explicit_bzero(apphash, sizeof(apphash)); 193 sshkey_sig_details_free(details); 194 sshbuf_free(original_signed); 195 sshbuf_free(sigbuf); 196 sshbuf_free(b); 197 ECDSA_SIG_free(sig); 198 BN_clear_free(sig_r); 199 BN_clear_free(sig_s); 200 free(ktype); 201 return ret; 202 } 203