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/* $OpenBSD: ssh-dss.c,v 1.39 2020/02/26 13:40:09 jsg Exp $ */
/*
* Copyright (c) 2000 Markus Friedl. 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.
*/
#include <sys/types.h>
#include <openssl/bn.h>
#include <openssl/evp.h>
#include <string.h>
#include "sshbuf.h"
#include "compat.h"
#include "ssherr.h"
#include "digest.h"
#define SSHKEY_INTERNAL
#include "sshkey.h"
#define INTBLOB_LEN 20
#define SIGBLOB_LEN (2*INTBLOB_LEN)
int
ssh_dss_sign(const struct sshkey *key, u_char **sigp, size_t *lenp,
const u_char *data, size_t datalen, u_int compat)
{
DSA_SIG *sig = NULL;
const BIGNUM *sig_r, *sig_s;
u_char digest[SSH_DIGEST_MAX_LENGTH], sigblob[SIGBLOB_LEN];
size_t rlen, slen, len, dlen = ssh_digest_bytes(SSH_DIGEST_SHA1);
struct sshbuf *b = NULL;
int ret = SSH_ERR_INVALID_ARGUMENT;
if (lenp != NULL)
*lenp = 0;
if (sigp != NULL)
*sigp = NULL;
if (key == NULL || key->dsa == NULL ||
sshkey_type_plain(key->type) != KEY_DSA)
return SSH_ERR_INVALID_ARGUMENT;
if (dlen == 0)
return SSH_ERR_INTERNAL_ERROR;
if ((ret = ssh_digest_memory(SSH_DIGEST_SHA1, data, datalen,
digest, sizeof(digest))) != 0)
goto out;
if ((sig = DSA_do_sign(digest, dlen, key->dsa)) == NULL) {
ret = SSH_ERR_LIBCRYPTO_ERROR;
goto out;
}
DSA_SIG_get0(sig, &sig_r, &sig_s);
rlen = BN_num_bytes(sig_r);
slen = BN_num_bytes(sig_s);
if (rlen > INTBLOB_LEN || slen > INTBLOB_LEN) {
ret = SSH_ERR_INTERNAL_ERROR;
goto out;
}
explicit_bzero(sigblob, SIGBLOB_LEN);
BN_bn2bin(sig_r, sigblob + SIGBLOB_LEN - INTBLOB_LEN - rlen);
BN_bn2bin(sig_s, sigblob + SIGBLOB_LEN - slen);
if ((b = sshbuf_new()) == NULL) {
ret = SSH_ERR_ALLOC_FAIL;
goto out;
}
if ((ret = sshbuf_put_cstring(b, "ssh-dss")) != 0 ||
(ret = sshbuf_put_string(b, sigblob, SIGBLOB_LEN)) != 0)
goto out;
len = sshbuf_len(b);
if (sigp != NULL) {
if ((*sigp = malloc(len)) == NULL) {
ret = SSH_ERR_ALLOC_FAIL;
goto out;
}
memcpy(*sigp, sshbuf_ptr(b), len);
}
if (lenp != NULL)
*lenp = len;
ret = 0;
out:
explicit_bzero(digest, sizeof(digest));
DSA_SIG_free(sig);
sshbuf_free(b);
return ret;
}
int
ssh_dss_verify(const struct sshkey *key,
const u_char *signature, size_t signaturelen,
const u_char *data, size_t datalen, u_int compat)
{
DSA_SIG *sig = NULL;
BIGNUM *sig_r = NULL, *sig_s = NULL;
u_char digest[SSH_DIGEST_MAX_LENGTH], *sigblob = NULL;
size_t len, dlen = ssh_digest_bytes(SSH_DIGEST_SHA1);
int ret = SSH_ERR_INTERNAL_ERROR;
struct sshbuf *b = NULL;
char *ktype = NULL;
if (key == NULL || key->dsa == NULL ||
sshkey_type_plain(key->type) != KEY_DSA ||
signature == NULL || signaturelen == 0)
return SSH_ERR_INVALID_ARGUMENT;
if (dlen == 0)
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_get_string(b, &sigblob, &len) != 0) {
ret = SSH_ERR_INVALID_FORMAT;
goto out;
}
if (strcmp("ssh-dss", ktype) != 0) {
ret = SSH_ERR_KEY_TYPE_MISMATCH;
goto out;
}
if (sshbuf_len(b) != 0) {
ret = SSH_ERR_UNEXPECTED_TRAILING_DATA;
goto out;
}
if (len != SIGBLOB_LEN) {
ret = SSH_ERR_INVALID_FORMAT;
goto out;
}
/* parse signature */
if ((sig = DSA_SIG_new()) == NULL ||
(sig_r = BN_new()) == NULL ||
(sig_s = BN_new()) == NULL) {
ret = SSH_ERR_ALLOC_FAIL;
goto out;
}
if ((BN_bin2bn(sigblob, INTBLOB_LEN, sig_r) == NULL) ||
(BN_bin2bn(sigblob + INTBLOB_LEN, INTBLOB_LEN, sig_s) == NULL)) {
ret = SSH_ERR_LIBCRYPTO_ERROR;
goto out;
}
if (!DSA_SIG_set0(sig, sig_r, sig_s)) {
ret = SSH_ERR_LIBCRYPTO_ERROR;
goto out;
}
sig_r = sig_s = NULL; /* transferred */
/* sha1 the data */
if ((ret = ssh_digest_memory(SSH_DIGEST_SHA1, data, datalen,
digest, sizeof(digest))) != 0)
goto out;
switch (DSA_do_verify(digest, dlen, sig, key->dsa)) {
case 1:
ret = 0;
break;
case 0:
ret = SSH_ERR_SIGNATURE_INVALID;
goto out;
default:
ret = SSH_ERR_LIBCRYPTO_ERROR;
goto out;
}
out:
explicit_bzero(digest, sizeof(digest));
DSA_SIG_free(sig);
BN_clear_free(sig_r);
BN_clear_free(sig_s);
sshbuf_free(b);
free(ktype);
if (sigblob != NULL)
freezero(sigblob, len);
return ret;
}
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