source: trunk/third/openssh/ssh-dss.c @ 18759

/*
 * 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"
RCSID("$OpenBSD: ssh-dss.c,v 1.17 2002/07/04 10:41:47 markus Exp $");

#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"
#include "ssh-dss.h"

#define INTBLOB_LEN     20
#define SIGBLOB_LEN     (2*INTBLOB_LEN)

int
ssh_dss_sign(Key *key, u_char **sigp, u_int *lenp,
    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(Key *key, u_char *signature, u_int signaturelen,
    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 = signature;
                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);

        if (!(datafellows & SSH_BUG_SIGBLOB)) {
                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;
}