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/* $OpenBSD: ssh-dss.c,v 1.21 2006/03/25 13:17:02 djm 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 "includes.h"
#include <openssl/bn.h>
#include <openssl/evp.h>
#include "xmalloc.h"
#include "buffer.h"
#include "bufaux.h"
#include "compat.h"
#include "log.h"
#include "key.h"
#define INTBLOB_LEN 20
#define SIGBLOB_LEN (2*INTBLOB_LEN)
int
ssh_dss_sign(const Key *key, u_char **sigp, u_int *lenp,
const u_char *data, u_int datalen)
{
DSA_SIG *sig;
const EVP_MD *evp_md = EVP_sha1();
EVP_MD_CTX md;
u_char digest[EVP_MAX_MD_SIZE], sigblob[SIGBLOB_LEN];
u_int rlen, slen, len, dlen;
Buffer b;
if (key == NULL || key->type != KEY_DSA || key->dsa == NULL) {
error("ssh_dss_sign: no DSA key");
return -1;
}
EVP_DigestInit(&md, evp_md);
EVP_DigestUpdate(&md, data, datalen);
EVP_DigestFinal(&md, digest, &dlen);
sig = DSA_do_sign(digest, dlen, key->dsa);
memset(digest, 'd', sizeof(digest));
if (sig == NULL) {
error("ssh_dss_sign: sign failed");
return -1;
}
rlen = BN_num_bytes(sig->r);
slen = BN_num_bytes(sig->s);
if (rlen > INTBLOB_LEN || slen > INTBLOB_LEN) {
error("bad sig size %u %u", rlen, slen);
DSA_SIG_free(sig);
return -1;
}
memset(sigblob, 0, SIGBLOB_LEN);
BN_bn2bin(sig->r, sigblob+ SIGBLOB_LEN - INTBLOB_LEN - rlen);
BN_bn2bin(sig->s, sigblob+ SIGBLOB_LEN - slen);
DSA_SIG_free(sig);
if (datafellows & SSH_BUG_SIGBLOB) {
if (lenp != NULL)
*lenp = SIGBLOB_LEN;
if (sigp != NULL) {
*sigp = xmalloc(SIGBLOB_LEN);
memcpy(*sigp, sigblob, SIGBLOB_LEN);
}
} else {
/* ietf-drafts */
buffer_init(&b);
buffer_put_cstring(&b, "ssh-dss");
buffer_put_string(&b, sigblob, SIGBLOB_LEN);
len = buffer_len(&b);
if (lenp != NULL)
*lenp = len;
if (sigp != NULL) {
*sigp = xmalloc(len);
memcpy(*sigp, buffer_ptr(&b), len);
}
buffer_free(&b);
}
return 0;
}
int
ssh_dss_verify(const Key *key, const u_char *signature, u_int signaturelen,
const u_char *data, u_int datalen)
{
DSA_SIG *sig;
const EVP_MD *evp_md = EVP_sha1();
EVP_MD_CTX md;
u_char digest[EVP_MAX_MD_SIZE], *sigblob;
u_int len, dlen;
int rlen, ret;
Buffer b;
if (key == NULL || key->type != KEY_DSA || key->dsa == NULL) {
error("ssh_dss_verify: no DSA key");
return -1;
}
/* fetch signature */
if (datafellows & SSH_BUG_SIGBLOB) {
sigblob = xmalloc(signaturelen);
memcpy(sigblob, signature, signaturelen);
len = signaturelen;
} else {
/* ietf-drafts */
char *ktype;
buffer_init(&b);
buffer_append(&b, signature, signaturelen);
ktype = buffer_get_string(&b, NULL);
if (strcmp("ssh-dss", ktype) != 0) {
error("ssh_dss_verify: cannot handle type %s", ktype);
buffer_free(&b);
xfree(ktype);
return -1;
}
xfree(ktype);
sigblob = buffer_get_string(&b, &len);
rlen = buffer_len(&b);
buffer_free(&b);
if (rlen != 0) {
error("ssh_dss_verify: "
"remaining bytes in signature %d", rlen);
xfree(sigblob);
return -1;
}
}
if (len != SIGBLOB_LEN) {
fatal("bad sigbloblen %u != SIGBLOB_LEN", len);
}
/* parse signature */
if ((sig = DSA_SIG_new()) == NULL)
fatal("ssh_dss_verify: DSA_SIG_new failed");
if ((sig->r = BN_new()) == NULL)
fatal("ssh_dss_verify: BN_new failed");
if ((sig->s = BN_new()) == NULL)
fatal("ssh_dss_verify: BN_new failed");
BN_bin2bn(sigblob, INTBLOB_LEN, sig->r);
BN_bin2bn(sigblob+ INTBLOB_LEN, INTBLOB_LEN, sig->s);
/* clean up */
memset(sigblob, 0, len);
xfree(sigblob);
/* sha1 the data */
EVP_DigestInit(&md, evp_md);
EVP_DigestUpdate(&md, data, datalen);
EVP_DigestFinal(&md, digest, &dlen);
ret = DSA_do_verify(digest, dlen, sig, key->dsa);
memset(digest, 'd', sizeof(digest));
DSA_SIG_free(sig);
debug("ssh_dss_verify: signature %s",
ret == 1 ? "correct" : ret == 0 ? "incorrect" : "error");
return ret;
}
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