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-rw-r--r--kexsntrup4591761x25519.c213
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diff --git a/kexsntrup4591761x25519.c b/kexsntrup4591761x25519.c
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+/* $OpenBSD: kexsntrup4591761x25519.c,v 1.1 2019/01/21 10:20:12 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 <sys/types.h>
+
+#include <stdio.h>
+#include <string.h>
+#include <signal.h>
+
+#include "sshkey.h"
+#include "kex.h"
+#include "sshbuf.h"
+#include "digest.h"
+#include "ssherr.h"
+
+int
+kex_kem_sntrup4591761x25519_keypair(struct kex *kex)
+{
+ struct sshbuf *buf = NULL;
+ u_char *cp = NULL;
+ size_t need;
+ int r;
+
+ if ((buf = sshbuf_new()) == NULL)
+ return SSH_ERR_ALLOC_FAIL;
+ need = crypto_kem_sntrup4591761_PUBLICKEYBYTES + CURVE25519_SIZE;
+ if ((r = sshbuf_reserve(buf, need, &cp)) != 0)
+ goto out;
+ crypto_kem_sntrup4591761_keypair(cp, kex->sntrup4591761_client_key);
+#ifdef DEBUG_KEXECDH
+ dump_digest("client public key sntrup4591761:", cp,
+ crypto_kem_sntrup4591761_PUBLICKEYBYTES);
+#endif
+ cp += crypto_kem_sntrup4591761_PUBLICKEYBYTES;
+ kexc25519_keygen(kex->c25519_client_key, cp);
+#ifdef DEBUG_KEXECDH
+ dump_digest("client public key c25519:", cp, CURVE25519_SIZE);
+#endif
+ kex->kem_client_pub = buf;
+ buf = NULL;
+ out:
+ sshbuf_free(buf);
+ return r;
+}
+
+int
+kex_kem_sntrup4591761x25519_enc(struct kex *kex, const u_char *pkblob,
+ size_t pklen, struct sshbuf **server_blobp, struct sshbuf **shared_secretp)
+{
+ struct sshbuf *server_blob = NULL;
+ struct sshbuf *buf = NULL;
+ u_char *kem_key, *ciphertext, *server_pub;
+ u_char server_key[CURVE25519_SIZE];
+ u_char hash[SSH_DIGEST_MAX_LENGTH];
+ size_t need;
+ int r;
+
+ *server_blobp = NULL;
+ *shared_secretp = NULL;
+
+ /* pkblob contains both KEM and ECDH client pubkeys */
+ need = crypto_kem_sntrup4591761_PUBLICKEYBYTES + CURVE25519_SIZE;
+ if (pklen != need) {
+ r = SSH_ERR_SIGNATURE_INVALID;
+ goto out;
+ }
+#ifdef DEBUG_KEXECDH
+ dump_digest("client public key sntrup4591761:", pkblob,
+ crypto_kem_sntrup4591761_PUBLICKEYBYTES);
+ dump_digest("client public key 25519:",
+ pkblob + crypto_kem_sntrup4591761_PUBLICKEYBYTES, CURVE25519_SIZE);
+#endif
+ /* allocate buffer for concatenation of KEM key and ECDH shared key */
+ /* the buffer will be hashed and the result is the shared secret */
+ if ((buf = sshbuf_new()) == NULL) {
+ r = SSH_ERR_ALLOC_FAIL;
+ goto out;
+ }
+ if ((r = sshbuf_reserve(buf, crypto_kem_sntrup4591761_BYTES,
+ &kem_key)) != 0)
+ goto out;
+ /* allocate space for encrypted KEM key and ECDH pub key */
+ if ((server_blob = sshbuf_new()) == NULL) {
+ r = SSH_ERR_ALLOC_FAIL;
+ goto out;
+ }
+ need = crypto_kem_sntrup4591761_CIPHERTEXTBYTES + CURVE25519_SIZE;
+ if ((r = sshbuf_reserve(server_blob, need, &ciphertext)) != 0)
+ goto out;
+ /* generate and encrypt KEM key with client key */
+ crypto_kem_sntrup4591761_enc(ciphertext, kem_key, pkblob);
+ /* generate ECDH key pair, store server pubkey after ciphertext */
+ server_pub = ciphertext + crypto_kem_sntrup4591761_CIPHERTEXTBYTES;
+ kexc25519_keygen(server_key, server_pub);
+ /* append ECDH shared key */
+ if ((r = kexc25519_shared_key_ext(server_key,
+ pkblob + crypto_kem_sntrup4591761_PUBLICKEYBYTES, buf, 1)) < 0)
+ goto out;
+ if ((r = ssh_digest_buffer(kex->hash_alg, buf, hash, sizeof(hash))) != 0)
+ goto out;
+#ifdef DEBUG_KEXECDH
+ dump_digest("server public key 25519:", server_pub, CURVE25519_SIZE);
+ dump_digest("server cipher text:", ciphertext,
+ crypto_kem_sntrup4591761_CIPHERTEXTBYTES);
+ dump_digest("server kem key:", kem_key, sizeof(kem_key));
+ dump_digest("concatenation of KEM key and ECDH shared key:",
+ sshbuf_ptr(buf), sshbuf_len(buf));
+#endif
+ /* string-encoded hash is resulting shared secret */
+ sshbuf_reset(buf);
+ if ((r = sshbuf_put_string(buf, hash,
+ ssh_digest_bytes(kex->hash_alg))) != 0)
+ goto out;
+#ifdef DEBUG_KEXECDH
+ dump_digest("encoded shared secret:", sshbuf_ptr(buf), sshbuf_len(buf));
+#endif
+ *server_blobp = server_blob;
+ *shared_secretp = buf;
+ server_blob = NULL;
+ buf = NULL;
+ out:
+ explicit_bzero(hash, sizeof(hash));
+ explicit_bzero(server_key, sizeof(server_key));
+ sshbuf_free(server_blob);
+ sshbuf_free(buf);
+ return r;
+}
+
+int
+kex_kem_sntrup4591761x25519_dec(struct kex *kex, const u_char *pkblob,
+ size_t pklen, struct sshbuf **shared_secretp)
+{
+ struct sshbuf *buf = NULL;
+ u_char *kem_key = NULL;
+ const u_char *ciphertext, *server_pub;
+ u_char hash[SSH_DIGEST_MAX_LENGTH];
+ size_t need;
+ int r, decoded;
+
+ *shared_secretp = NULL;
+
+ need = crypto_kem_sntrup4591761_CIPHERTEXTBYTES + CURVE25519_SIZE;
+ if (pklen != need) {
+ r = SSH_ERR_SIGNATURE_INVALID;
+ goto out;
+ }
+ ciphertext = pkblob;
+ server_pub = pkblob + crypto_kem_sntrup4591761_CIPHERTEXTBYTES;
+#ifdef DEBUG_KEXECDH
+ dump_digest("server cipher text:", ciphertext,
+ crypto_kem_sntrup4591761_CIPHERTEXTBYTES);
+ dump_digest("server public key c25519:", server_pub, CURVE25519_SIZE);
+#endif
+ /* hash concatenation of KEM key and ECDH shared key */
+ if ((buf = sshbuf_new()) == NULL) {
+ r = SSH_ERR_ALLOC_FAIL;
+ goto out;
+ }
+ if ((r = sshbuf_reserve(buf, crypto_kem_sntrup4591761_BYTES,
+ &kem_key)) != 0)
+ goto out;
+ decoded = crypto_kem_sntrup4591761_dec(kem_key, ciphertext,
+ kex->sntrup4591761_client_key);
+ if ((r = kexc25519_shared_key_ext(kex->c25519_client_key, server_pub,
+ buf, 1)) < 0)
+ goto out;
+ if ((r = ssh_digest_buffer(kex->hash_alg, buf, hash, sizeof(hash))) != 0)
+ goto out;
+#ifdef DEBUG_KEXECDH
+ dump_digest("client kem key:", kem_key, sizeof(kem_key));
+ dump_digest("concatenation of KEM key and ECDH shared key:",
+ sshbuf_ptr(buf), sshbuf_len(buf));
+#endif
+ sshbuf_reset(buf);
+ if ((r = sshbuf_put_string(buf, hash,
+ ssh_digest_bytes(kex->hash_alg))) != 0)
+ goto out;
+#ifdef DEBUG_KEXECDH
+ dump_digest("encoded shared secret:", sshbuf_ptr(buf), sshbuf_len(buf));
+#endif
+ if (decoded != 0) {
+ r = SSH_ERR_SIGNATURE_INVALID;
+ goto out;
+ }
+ *shared_secretp = buf;
+ buf = NULL;
+ out:
+ explicit_bzero(hash, sizeof(hash));
+ sshbuf_free(buf);
+ return r;
+}