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/* $OpenBSD: ssh-ecdsa-sk.c,v 1.5 2019/11/26 03:04:27 djm Exp $ */
/*
* Copyright (c) 2000 Markus Friedl. All rights reserved.
* Copyright (c) 2010 Damien Miller. All rights reserved.
* Copyright (c) 2019 Google Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
/* #define DEBUG_SK 1 */
#include "includes.h"
#ifdef ENABLE_SK
#include <sys/types.h>
#include <openssl/bn.h>
#include <openssl/ec.h>
#include <openssl/ecdsa.h>
#include <openssl/evp.h>
#include <string.h>
#include <stdio.h> /* needed for DEBUG_SK only */
#include "openbsd-compat/openssl-compat.h"
#include "sshbuf.h"
#include "ssherr.h"
#include "digest.h"
#define SSHKEY_INTERNAL
#include "sshkey.h"
/* ARGSUSED */
int
ssh_ecdsa_sk_verify(const struct sshkey *key,
const u_char *signature, size_t signaturelen,
const u_char *data, size_t datalen, u_int compat,
struct sshkey_sig_details **detailsp)
{
ECDSA_SIG *sig = NULL;
BIGNUM *sig_r = NULL, *sig_s = NULL;
u_char sig_flags;
u_char msghash[32], apphash[32], sighash[32];
u_int sig_counter;
int ret = SSH_ERR_INTERNAL_ERROR;
struct sshbuf *b = NULL, *sigbuf = NULL, *original_signed = NULL;
char *ktype = NULL;
struct sshkey_sig_details *details = NULL;
#ifdef DEBUG_SK
char *tmp = NULL;
#endif
if (detailsp != NULL)
*detailsp = NULL;
if (key == NULL || key->ecdsa == NULL ||
sshkey_type_plain(key->type) != KEY_ECDSA_SK ||
signature == NULL || signaturelen == 0)
return SSH_ERR_INVALID_ARGUMENT;
if (key->ecdsa_nid != NID_X9_62_prime256v1)
return SSH_ERR_INTERNAL_ERROR;
/* fetch signature */
if ((b = sshbuf_from(signature, signaturelen)) == NULL)
return SSH_ERR_ALLOC_FAIL;
if (sshbuf_get_cstring(b, &ktype, NULL) != 0 ||
sshbuf_froms(b, &sigbuf) != 0 ||
sshbuf_get_u8(b, &sig_flags) != 0 ||
sshbuf_get_u32(b, &sig_counter) != 0) {
ret = SSH_ERR_INVALID_FORMAT;
goto out;
}
if (strcmp(sshkey_ssh_name_plain(key), ktype) != 0) {
ret = SSH_ERR_KEY_TYPE_MISMATCH;
goto out;
}
if (sshbuf_len(b) != 0) {
ret = SSH_ERR_UNEXPECTED_TRAILING_DATA;
goto out;
}
/* parse signature */
if (sshbuf_get_bignum2(sigbuf, &sig_r) != 0 ||
sshbuf_get_bignum2(sigbuf, &sig_s) != 0) {
ret = SSH_ERR_INVALID_FORMAT;
goto out;
}
if ((sig = ECDSA_SIG_new()) == NULL) {
ret = SSH_ERR_ALLOC_FAIL;
goto out;
}
if (!ECDSA_SIG_set0(sig, sig_r, sig_s)) {
ret = SSH_ERR_LIBCRYPTO_ERROR;
goto out;
}
#ifdef DEBUG_SK
fprintf(stderr, "%s: data: (len %zu)\n", __func__, datalen);
/* sshbuf_dump_data(data, datalen, stderr); */
fprintf(stderr, "%s: sig_r: %s\n", __func__, (tmp = BN_bn2hex(sig_r)));
free(tmp);
fprintf(stderr, "%s: sig_s: %s\n", __func__, (tmp = BN_bn2hex(sig_s)));
free(tmp);
fprintf(stderr, "%s: sig_flags = 0x%02x, sig_counter = %u\n",
__func__, sig_flags, sig_counter);
#endif
sig_r = sig_s = NULL; /* transferred */
if (sshbuf_len(sigbuf) != 0) {
ret = SSH_ERR_UNEXPECTED_TRAILING_DATA;
goto out;
}
/* Reconstruct data that was supposedly signed */
if ((original_signed = sshbuf_new()) == NULL) {
ret = SSH_ERR_ALLOC_FAIL;
goto out;
}
if ((ret = ssh_digest_memory(SSH_DIGEST_SHA256, data, datalen,
msghash, sizeof(msghash))) != 0)
goto out;
/* Application value is hashed before signature */
if ((ret = ssh_digest_memory(SSH_DIGEST_SHA256, key->sk_application,
strlen(key->sk_application), apphash, sizeof(apphash))) != 0)
goto out;
#ifdef DEBUG_SK
fprintf(stderr, "%s: hashed application:\n", __func__);
sshbuf_dump_data(apphash, sizeof(apphash), stderr);
fprintf(stderr, "%s: hashed message:\n", __func__);
sshbuf_dump_data(msghash, sizeof(msghash), stderr);
#endif
if ((ret = sshbuf_put(original_signed,
apphash, sizeof(apphash))) != 0 ||
(ret = sshbuf_put_u8(original_signed, sig_flags)) != 0 ||
(ret = sshbuf_put_u32(original_signed, sig_counter)) != 0 ||
(ret = sshbuf_put(original_signed, msghash, sizeof(msghash))) != 0)
goto out;
/* Signature is over H(original_signed) */
if ((ret = ssh_digest_buffer(SSH_DIGEST_SHA256, original_signed,
sighash, sizeof(sighash))) != 0)
goto out;
if ((details = calloc(1, sizeof(*details))) == NULL) {
ret = SSH_ERR_ALLOC_FAIL;
goto out;
}
details->sk_counter = sig_counter;
details->sk_flags = sig_flags;
#ifdef DEBUG_SK
fprintf(stderr, "%s: signed buf:\n", __func__);
sshbuf_dump(original_signed, stderr);
fprintf(stderr, "%s: signed hash:\n", __func__);
sshbuf_dump_data(sighash, sizeof(sighash), stderr);
#endif
/* Verify it */
switch (ECDSA_do_verify(sighash, sizeof(sighash), sig, key->ecdsa)) {
case 1:
ret = 0;
break;
case 0:
ret = SSH_ERR_SIGNATURE_INVALID;
goto out;
default:
ret = SSH_ERR_LIBCRYPTO_ERROR;
goto out;
}
/* success */
if (detailsp != NULL) {
*detailsp = details;
details = NULL;
}
out:
explicit_bzero(&sig_flags, sizeof(sig_flags));
explicit_bzero(&sig_counter, sizeof(sig_counter));
explicit_bzero(msghash, sizeof(msghash));
explicit_bzero(sighash, sizeof(msghash));
explicit_bzero(apphash, sizeof(apphash));
sshkey_sig_details_free(details);
sshbuf_free(original_signed);
sshbuf_free(sigbuf);
sshbuf_free(b);
ECDSA_SIG_free(sig);
BN_clear_free(sig_r);
BN_clear_free(sig_s);
free(ktype);
return ret;
}
#endif /* ENABLE_SK */
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