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* Copyright (c) 2000 Markus Friedl. All rights reserved.
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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RCSID("$OpenBSD: ssh-dss.c,v 1.19 2003/11/10 16:23:41 jakob Exp $");
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#include <openssl/bn.h>
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#include <openssl/evp.h>
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#define INTBLOB_LEN 20
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#define SIGBLOB_LEN (2*INTBLOB_LEN)
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ssh_dss_sign(const Key *key, u_char **sigp, u_int *lenp,
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const u_char *data, u_int datalen)
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const EVP_MD *evp_md = EVP_sha1();
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u_char digest[EVP_MAX_MD_SIZE], sigblob[SIGBLOB_LEN];
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u_int rlen, slen, len, dlen;
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if (key == NULL || key->type != KEY_DSA || key->dsa == NULL) {
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error("ssh_dss_sign: no DSA key");
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EVP_DigestInit(&md, evp_md);
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EVP_DigestUpdate(&md, data, datalen);
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EVP_DigestFinal(&md, digest, &dlen);
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sig = DSA_do_sign(digest, dlen, key->dsa);
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memset(digest, 'd', sizeof(digest));
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error("ssh_dss_sign: sign failed");
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rlen = BN_num_bytes(sig->r);
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slen = BN_num_bytes(sig->s);
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if (rlen > INTBLOB_LEN || slen > INTBLOB_LEN) {
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error("bad sig size %u %u", rlen, slen);
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memset(sigblob, 0, SIGBLOB_LEN);
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BN_bn2bin(sig->r, sigblob+ SIGBLOB_LEN - INTBLOB_LEN - rlen);
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BN_bn2bin(sig->s, sigblob+ SIGBLOB_LEN - slen);
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if (datafellows & SSH_BUG_SIGBLOB) {
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*sigp = xmalloc(SIGBLOB_LEN);
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memcpy(*sigp, sigblob, SIGBLOB_LEN);
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buffer_put_cstring(&b, "ssh-dss");
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buffer_put_string(&b, sigblob, SIGBLOB_LEN);
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memcpy(*sigp, buffer_ptr(&b), len);
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ssh_dss_verify(const Key *key, const u_char *signature, u_int signaturelen,
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const u_char *data, u_int datalen)
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const EVP_MD *evp_md = EVP_sha1();
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u_char digest[EVP_MAX_MD_SIZE], *sigblob;
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if (key == NULL || key->type != KEY_DSA || key->dsa == NULL) {
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error("ssh_dss_verify: no DSA key");
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/* fetch signature */
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if (datafellows & SSH_BUG_SIGBLOB) {
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sigblob = xmalloc(signaturelen);
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memcpy(sigblob, signature, signaturelen);
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buffer_append(&b, signature, signaturelen);
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ktype = buffer_get_string(&b, NULL);
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if (strcmp("ssh-dss", ktype) != 0) {
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error("ssh_dss_verify: cannot handle type %s", ktype);
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sigblob = buffer_get_string(&b, &len);
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rlen = buffer_len(&b);
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error("ssh_dss_verify: "
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"remaining bytes in signature %d", rlen);
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if (len != SIGBLOB_LEN) {
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fatal("bad sigbloblen %u != SIGBLOB_LEN", len);
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/* parse signature */
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if ((sig = DSA_SIG_new()) == NULL)
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fatal("ssh_dss_verify: DSA_SIG_new failed");
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if ((sig->r = BN_new()) == NULL)
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fatal("ssh_dss_verify: BN_new failed");
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if ((sig->s = BN_new()) == NULL)
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fatal("ssh_dss_verify: BN_new failed");
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BN_bin2bn(sigblob, INTBLOB_LEN, sig->r);
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BN_bin2bn(sigblob+ INTBLOB_LEN, INTBLOB_LEN, sig->s);
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memset(sigblob, 0, len);
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EVP_DigestInit(&md, evp_md);
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EVP_DigestUpdate(&md, data, datalen);
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EVP_DigestFinal(&md, digest, &dlen);
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ret = DSA_do_verify(digest, dlen, sig, key->dsa);
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memset(digest, 'd', sizeof(digest));
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debug("ssh_dss_verify: signature %s",
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ret == 1 ? "correct" : ret == 0 ? "incorrect" : "error");