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/* $OpenBSD: kexsntrup761x25519.c,v 1.3 2024/09/15 02:20:51 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"
volatile crypto_int16 crypto_int16_optblocker = 0;
volatile crypto_int32 crypto_int32_optblocker = 0;
volatile crypto_int64 crypto_int64_optblocker = 0;
int
kex_kem_sntrup761x25519_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_sntrup761_PUBLICKEYBYTES + CURVE25519_SIZE;
if ((r = sshbuf_reserve(buf, need, &cp)) != 0)
goto out;
crypto_kem_sntrup761_keypair(cp, kex->sntrup761_client_key);
#ifdef DEBUG_KEXECDH
dump_digest("client public key sntrup761:", cp,
crypto_kem_sntrup761_PUBLICKEYBYTES);
#endif
cp += crypto_kem_sntrup761_PUBLICKEYBYTES;
kexc25519_keygen(kex->c25519_client_key, cp);
#ifdef DEBUG_KEXECDH
dump_digest("client public key c25519:", cp, CURVE25519_SIZE);
#endif
kex->client_pub = buf;
buf = NULL;
out:
sshbuf_free(buf);
return r;
}
int
kex_kem_sntrup761x25519_enc(struct kex *kex,
const struct sshbuf *client_blob, struct sshbuf **server_blobp,
struct sshbuf **shared_secretp)
{
struct sshbuf *server_blob = NULL;
struct sshbuf *buf = NULL;
const u_char *client_pub;
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;
/* client_blob contains both KEM and ECDH client pubkeys */
need = crypto_kem_sntrup761_PUBLICKEYBYTES + CURVE25519_SIZE;
if (sshbuf_len(client_blob) != need) {
r = SSH_ERR_SIGNATURE_INVALID;
goto out;
}
client_pub = sshbuf_ptr(client_blob);
#ifdef DEBUG_KEXECDH
dump_digest("client public key sntrup761:", client_pub,
crypto_kem_sntrup761_PUBLICKEYBYTES);
dump_digest("client public key 25519:",
client_pub + crypto_kem_sntrup761_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_sntrup761_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_sntrup761_CIPHERTEXTBYTES + CURVE25519_SIZE;
if ((r = sshbuf_reserve(server_blob, need, &ciphertext)) != 0)
goto out;
/* generate and encrypt KEM key with client key */
crypto_kem_sntrup761_enc(ciphertext, kem_key, client_pub);
/* generate ECDH key pair, store server pubkey after ciphertext */
server_pub = ciphertext + crypto_kem_sntrup761_CIPHERTEXTBYTES;
kexc25519_keygen(server_key, server_pub);
/* append ECDH shared key */
client_pub += crypto_kem_sntrup761_PUBLICKEYBYTES;
if ((r = kexc25519_shared_key_ext(server_key, client_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("server public key 25519:", server_pub, CURVE25519_SIZE);
dump_digest("server cipher text:", ciphertext,
crypto_kem_sntrup761_CIPHERTEXTBYTES);
dump_digest("server kem key:", kem_key, crypto_kem_sntrup761_BYTES);
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_sntrup761x25519_dec(struct kex *kex,
const struct sshbuf *server_blob, 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_sntrup761_CIPHERTEXTBYTES + CURVE25519_SIZE;
if (sshbuf_len(server_blob) != need) {
r = SSH_ERR_SIGNATURE_INVALID;
goto out;
}
ciphertext = sshbuf_ptr(server_blob);
server_pub = ciphertext + crypto_kem_sntrup761_CIPHERTEXTBYTES;
#ifdef DEBUG_KEXECDH
dump_digest("server cipher text:", ciphertext,
crypto_kem_sntrup761_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_sntrup761_BYTES,
&kem_key)) != 0)
goto out;
decoded = crypto_kem_sntrup761_dec(kem_key, ciphertext,
kex->sntrup761_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, crypto_kem_sntrup761_BYTES);
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;
}
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