/* $OpenBSD: ssh-dss.c,v 1.50 2024/01/11 01:45:36 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"

#if defined(WITH_OPENSSL) && defined(WITH_DSA)

#include <sys/types.h>

#include <openssl/bn.h>
#include <openssl/dsa.h>
#include <openssl/evp.h>

#include <stdarg.h>
#include <string.h>

#include "sshbuf.h"
#include "ssherr.h"
#include "digest.h"
#define SSHKEY_INTERNAL
#include "sshkey.h"

#include "openbsd-compat/openssl-compat.h"

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

static u_int
ssh_dss_size(const struct sshkey *key)
{
        const BIGNUM *dsa_p;

        if (key->dsa == NULL)
                return 0;
        DSA_get0_pqg(key->dsa, &dsa_p, NULL, NULL);
        return BN_num_bits(dsa_p);
}

static int
ssh_dss_alloc(struct sshkey *k)
{
        if ((k->dsa = DSA_new()) == NULL)
                return SSH_ERR_ALLOC_FAIL;
        return 0;
}

static void
ssh_dss_cleanup(struct sshkey *k)
{
        DSA_free(k->dsa);
        k->dsa = NULL;
}

static int
ssh_dss_equal(const struct sshkey *a, const struct sshkey *b)
{
        const BIGNUM *dsa_p_a, *dsa_q_a, *dsa_g_a, *dsa_pub_key_a;
        const BIGNUM *dsa_p_b, *dsa_q_b, *dsa_g_b, *dsa_pub_key_b;

        if (a->dsa == NULL || b->dsa == NULL)
                return 0;
        DSA_get0_pqg(a->dsa, &dsa_p_a, &dsa_q_a, &dsa_g_a);
        DSA_get0_pqg(b->dsa, &dsa_p_b, &dsa_q_b, &dsa_g_b);
        DSA_get0_key(a->dsa, &dsa_pub_key_a, NULL);
        DSA_get0_key(b->dsa, &dsa_pub_key_b, NULL);
        if (dsa_p_a == NULL || dsa_p_b == NULL ||
            dsa_q_a == NULL || dsa_q_b == NULL ||
            dsa_g_a == NULL || dsa_g_b == NULL ||
            dsa_pub_key_a == NULL || dsa_pub_key_b == NULL)
                return 0;
        if (BN_cmp(dsa_p_a, dsa_p_b) != 0)
                return 0;
        if (BN_cmp(dsa_q_a, dsa_q_b) != 0)
                return 0;
        if (BN_cmp(dsa_g_a, dsa_g_b) != 0)
                return 0;
        if (BN_cmp(dsa_pub_key_a, dsa_pub_key_b) != 0)
                return 0;
        return 1;
}

static int
ssh_dss_serialize_public(const struct sshkey *key, struct sshbuf *b,
    enum sshkey_serialize_rep opts)
{
        int r;
        const BIGNUM *dsa_p, *dsa_q, *dsa_g, *dsa_pub_key;

        if (key->dsa == NULL)
                return SSH_ERR_INVALID_ARGUMENT;
        DSA_get0_pqg(key->dsa, &dsa_p, &dsa_q, &dsa_g);
        DSA_get0_key(key->dsa, &dsa_pub_key, NULL);
        if (dsa_p == NULL || dsa_q == NULL ||
            dsa_g == NULL || dsa_pub_key == NULL)
                return SSH_ERR_INTERNAL_ERROR;
        if ((r = sshbuf_put_bignum2(b, dsa_p)) != 0 ||
            (r = sshbuf_put_bignum2(b, dsa_q)) != 0 ||
            (r = sshbuf_put_bignum2(b, dsa_g)) != 0 ||
            (r = sshbuf_put_bignum2(b, dsa_pub_key)) != 0)
                return r;

        return 0;
}

static int
ssh_dss_serialize_private(const struct sshkey *key, struct sshbuf *b,
    enum sshkey_serialize_rep opts)
{
        int r;
        const BIGNUM *dsa_priv_key;

        DSA_get0_key(key->dsa, NULL, &dsa_priv_key);
        if (!sshkey_is_cert(key)) {
                if ((r = ssh_dss_serialize_public(key, b, opts)) != 0)
                        return r;
        }
        if ((r = sshbuf_put_bignum2(b, dsa_priv_key)) != 0)
                return r;

        return 0;
}

static int
ssh_dss_generate(struct sshkey *k, int bits)
{
        DSA *private;

        if (bits != 1024)
                return SSH_ERR_KEY_LENGTH;
        if ((private = DSA_new()) == NULL)
                return SSH_ERR_ALLOC_FAIL;
        if (!DSA_generate_parameters_ex(private, bits, NULL, 0, NULL,
            NULL, NULL) || !DSA_generate_key(private)) {
                DSA_free(private);
                return SSH_ERR_LIBCRYPTO_ERROR;
        }
        k->dsa = private;
        return 0;
}

static int
ssh_dss_copy_public(const struct sshkey *from, struct sshkey *to)
{
        const BIGNUM *dsa_p, *dsa_q, *dsa_g, *dsa_pub_key;
        BIGNUM *dsa_p_dup = NULL, *dsa_q_dup = NULL, *dsa_g_dup = NULL;
        BIGNUM *dsa_pub_key_dup = NULL;
        int r = SSH_ERR_INTERNAL_ERROR;

        DSA_get0_pqg(from->dsa, &dsa_p, &dsa_q, &dsa_g);
        DSA_get0_key(from->dsa, &dsa_pub_key, NULL);
        if ((dsa_p_dup = BN_dup(dsa_p)) == NULL ||
            (dsa_q_dup = BN_dup(dsa_q)) == NULL ||
            (dsa_g_dup = BN_dup(dsa_g)) == NULL ||
            (dsa_pub_key_dup = BN_dup(dsa_pub_key)) == NULL) {
                r = SSH_ERR_ALLOC_FAIL;
                goto out;
        }
        if (!DSA_set0_pqg(to->dsa, dsa_p_dup, dsa_q_dup, dsa_g_dup)) {
                r = SSH_ERR_LIBCRYPTO_ERROR;
                goto out;
        }
        dsa_p_dup = dsa_q_dup = dsa_g_dup = NULL; /* transferred */
        if (!DSA_set0_key(to->dsa, dsa_pub_key_dup, NULL)) {
                r = SSH_ERR_LIBCRYPTO_ERROR;
                goto out;
        }
        dsa_pub_key_dup = NULL; /* transferred */
        /* success */
        r = 0;
 out:
        BN_clear_free(dsa_p_dup);
        BN_clear_free(dsa_q_dup);
        BN_clear_free(dsa_g_dup);
        BN_clear_free(dsa_pub_key_dup);
        return r;
}

static int
ssh_dss_deserialize_public(const char *ktype, struct sshbuf *b,
    struct sshkey *key)
{
        int ret = SSH_ERR_INTERNAL_ERROR;
        BIGNUM *dsa_p = NULL, *dsa_q = NULL, *dsa_g = NULL, *dsa_pub_key = NULL;

        if (sshbuf_get_bignum2(b, &dsa_p) != 0 ||
            sshbuf_get_bignum2(b, &dsa_q) != 0 ||
            sshbuf_get_bignum2(b, &dsa_g) != 0 ||
            sshbuf_get_bignum2(b, &dsa_pub_key) != 0) {
                ret = SSH_ERR_INVALID_FORMAT;
                goto out;
        }
        if (!DSA_set0_pqg(key->dsa, dsa_p, dsa_q, dsa_g)) {
                ret = SSH_ERR_LIBCRYPTO_ERROR;
                goto out;
        }
        dsa_p = dsa_q = dsa_g = NULL; /* transferred */
        if (!DSA_set0_key(key->dsa, dsa_pub_key, NULL)) {
                ret = SSH_ERR_LIBCRYPTO_ERROR;
                goto out;
        }
        dsa_pub_key = NULL; /* transferred */
#ifdef DEBUG_PK
        DSA_print_fp(stderr, key->dsa, 8);
#endif
        /* success */
        ret = 0;
 out:
        BN_clear_free(dsa_p);
        BN_clear_free(dsa_q);
        BN_clear_free(dsa_g);
        BN_clear_free(dsa_pub_key);
        return ret;
}

static int
ssh_dss_deserialize_private(const char *ktype, struct sshbuf *b,
    struct sshkey *key)
{
        int r;
        BIGNUM *dsa_priv_key = NULL;

        if (!sshkey_is_cert(key)) {
                if ((r = ssh_dss_deserialize_public(ktype, b, key)) != 0)
                        return r;
        }

        if ((r = sshbuf_get_bignum2(b, &dsa_priv_key)) != 0)
                return r;
        if (!DSA_set0_key(key->dsa, NULL, dsa_priv_key)) {
                BN_clear_free(dsa_priv_key);
                return SSH_ERR_LIBCRYPTO_ERROR;
        }
        return 0;
}

static int
ssh_dss_sign(struct sshkey *key,
    u_char **sigp, size_t *lenp,
    const u_char *data, size_t datalen,
    const char *alg, const char *sk_provider, const char *sk_pin, 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;
}

static int
ssh_dss_verify(const struct sshkey *key,
    const u_char *sig, size_t siglen,
    const u_char *data, size_t dlen, const char *alg, u_int compat,
    struct sshkey_sig_details **detailsp)
{
        DSA_SIG *dsig = NULL;
        BIGNUM *sig_r = NULL, *sig_s = NULL;
        u_char digest[SSH_DIGEST_MAX_LENGTH], *sigblob = NULL;
        size_t len, hlen = 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 ||
            sig == NULL || siglen == 0)
                return SSH_ERR_INVALID_ARGUMENT;
        if (hlen == 0)
                return SSH_ERR_INTERNAL_ERROR;

        /* fetch signature */
        if ((b = sshbuf_from(sig, siglen)) == 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 ((dsig = 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(dsig, 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, dlen,
            digest, sizeof(digest))) != 0)
                goto out;

        switch (DSA_do_verify(digest, hlen, dsig, 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(dsig);
        BN_clear_free(sig_r);
        BN_clear_free(sig_s);
        sshbuf_free(b);
        free(ktype);
        if (sigblob != NULL)
                freezero(sigblob, len);
        return ret;
}

static const struct sshkey_impl_funcs sshkey_dss_funcs = {
        /* .size = */           ssh_dss_size,
        /* .alloc = */          ssh_dss_alloc,
        /* .cleanup = */        ssh_dss_cleanup,
        /* .equal = */          ssh_dss_equal,
        /* .ssh_serialize_public = */ ssh_dss_serialize_public,
        /* .ssh_deserialize_public = */ ssh_dss_deserialize_public,
        /* .ssh_serialize_private = */ ssh_dss_serialize_private,
        /* .ssh_deserialize_private = */ ssh_dss_deserialize_private,
        /* .generate = */       ssh_dss_generate,
        /* .copy_public = */    ssh_dss_copy_public,
        /* .sign = */           ssh_dss_sign,
        /* .verify = */         ssh_dss_verify,
};

const struct sshkey_impl sshkey_dss_impl = {
        /* .name = */           "ssh-dss",
        /* .shortname = */      "DSA",
        /* .sigalg = */         NULL,
        /* .type = */           KEY_DSA,
        /* .nid = */            0,
        /* .cert = */           0,
        /* .sigonly = */        0,
        /* .keybits = */        0,
        /* .funcs = */          &sshkey_dss_funcs,
};

const struct sshkey_impl sshkey_dsa_cert_impl = {
        /* .name = */           "ssh-dss-cert-v01@openssh.com",
        /* .shortname = */      "DSA-CERT",
        /* .sigalg = */         NULL,
        /* .type = */           KEY_DSA_CERT,
        /* .nid = */            0,
        /* .cert = */           1,
        /* .sigonly = */        0,
        /* .keybits = */        0,
        /* .funcs = */          &sshkey_dss_funcs,
};

#endif /* WITH_OPENSSL && WITH_DSA */