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+/* $OpenBSD: kexdh.c,v 1.34 2020/12/04 02:29:25 djm Exp $ */
+/*
+ * Copyright (c) 2019 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"
+
+#ifdef WITH_OPENSSL
+
+#include <sys/types.h>
+
+#include <stdio.h>
+#include <string.h>
+#include <signal.h>
+
+#include "openbsd-compat/openssl-compat.h"
+#include <openssl/dh.h>
+
+#include "sshkey.h"
+#include "kex.h"
+#include "sshbuf.h"
+#include "digest.h"
+#include "ssherr.h"
+#include "dh.h"
+#include "log.h"
+
+int
+kex_dh_keygen(struct kex *kex)
+{
+ switch (kex->kex_type) {
+ case KEX_DH_GRP1_SHA1:
+ kex->dh = dh_new_group1();
+ break;
+ case KEX_DH_GRP14_SHA1:
+ case KEX_DH_GRP14_SHA256:
+ kex->dh = dh_new_group14();
+ break;
+ case KEX_DH_GRP16_SHA512:
+ kex->dh = dh_new_group16();
+ break;
+ case KEX_DH_GRP18_SHA512:
+ kex->dh = dh_new_group18();
+ break;
+ default:
+ return SSH_ERR_INVALID_ARGUMENT;
+ }
+ if (kex->dh == NULL)
+ return SSH_ERR_ALLOC_FAIL;
+ return (dh_gen_key(kex->dh, kex->we_need * 8));
+}
+
+int
+kex_dh_compute_key(struct kex *kex, BIGNUM *dh_pub, struct sshbuf *out)
+{
+ BIGNUM *shared_secret = NULL;
+ u_char *kbuf = NULL;
+ size_t klen = 0;
+ int kout, r;
+
+#ifdef DEBUG_KEXDH
+ fprintf(stderr, "dh_pub= ");
+ BN_print_fp(stderr, dh_pub);
+ fprintf(stderr, "\n");
+ debug("bits %d", BN_num_bits(dh_pub));
+ DHparams_print_fp(stderr, kex->dh);
+ fprintf(stderr, "\n");
+#endif
+
+ if (!dh_pub_is_valid(kex->dh, dh_pub)) {
+ r = SSH_ERR_MESSAGE_INCOMPLETE;
+ goto out;
+ }
+ klen = DH_size(kex->dh);
+ if ((kbuf = malloc(klen)) == NULL ||
+ (shared_secret = BN_new()) == NULL) {
+ r = SSH_ERR_ALLOC_FAIL;
+ goto out;
+ }
+ if ((kout = DH_compute_key(kbuf, dh_pub, kex->dh)) < 0 ||
+ BN_bin2bn(kbuf, kout, shared_secret) == NULL) {
+ r = SSH_ERR_LIBCRYPTO_ERROR;
+ goto out;
+ }
+#ifdef DEBUG_KEXDH
+ dump_digest("shared secret", kbuf, kout);
+#endif
+ r = sshbuf_put_bignum2(out, shared_secret);
+ out:
+ freezero(kbuf, klen);
+ BN_clear_free(shared_secret);
+ return r;
+}
+
+int
+kex_dh_keypair(struct kex *kex)
+{
+ const BIGNUM *pub_key;
+ struct sshbuf *buf = NULL;
+ int r;
+
+ if ((r = kex_dh_keygen(kex)) != 0)
+ return r;
+ DH_get0_key(kex->dh, &pub_key, NULL);
+ if ((buf = sshbuf_new()) == NULL)
+ return SSH_ERR_ALLOC_FAIL;
+ if ((r = sshbuf_put_bignum2(buf, pub_key)) != 0 ||
+ (r = sshbuf_get_u32(buf, NULL)) != 0)
+ goto out;
+#ifdef DEBUG_KEXDH
+ DHparams_print_fp(stderr, kex->dh);
+ fprintf(stderr, "pub= ");
+ BN_print_fp(stderr, pub_key);
+ fprintf(stderr, "\n");
+#endif
+ kex->client_pub = buf;
+ buf = NULL;
+ out:
+ sshbuf_free(buf);
+ return r;
+}
+
+int
+kex_dh_enc(struct kex *kex, const struct sshbuf *client_blob,
+ struct sshbuf **server_blobp, struct sshbuf **shared_secretp)
+{
+ const BIGNUM *pub_key;
+ struct sshbuf *server_blob = NULL;
+ int r;
+
+ *server_blobp = NULL;
+ *shared_secretp = NULL;
+
+ if ((r = kex_dh_keygen(kex)) != 0)
+ goto out;
+ DH_get0_key(kex->dh, &pub_key, NULL);
+ if ((server_blob = sshbuf_new()) == NULL) {
+ r = SSH_ERR_ALLOC_FAIL;
+ goto out;
+ }
+ if ((r = sshbuf_put_bignum2(server_blob, pub_key)) != 0 ||
+ (r = sshbuf_get_u32(server_blob, NULL)) != 0)
+ goto out;
+ if ((r = kex_dh_dec(kex, client_blob, shared_secretp)) != 0)
+ goto out;
+ *server_blobp = server_blob;
+ server_blob = NULL;
+ out:
+ DH_free(kex->dh);
+ kex->dh = NULL;
+ sshbuf_free(server_blob);
+ return r;
+}
+
+int
+kex_dh_dec(struct kex *kex, const struct sshbuf *dh_blob,
+ struct sshbuf **shared_secretp)
+{
+ struct sshbuf *buf = NULL;
+ BIGNUM *dh_pub = NULL;
+ int r;
+
+ *shared_secretp = NULL;
+
+ if ((buf = sshbuf_new()) == NULL) {
+ r = SSH_ERR_ALLOC_FAIL;
+ goto out;
+ }
+ if ((r = sshbuf_put_stringb(buf, dh_blob)) != 0 ||
+ (r = sshbuf_get_bignum2(buf, &dh_pub)) != 0)
+ goto out;
+ sshbuf_reset(buf);
+ if ((r = kex_dh_compute_key(kex, dh_pub, buf)) != 0)
+ goto out;
+ *shared_secretp = buf;
+ buf = NULL;
+ out:
+ BN_free(dh_pub);
+ DH_free(kex->dh);
+ kex->dh = NULL;
+ sshbuf_free(buf);
+ return r;
+}
+#endif /* WITH_OPENSSL */