220 lines
7.0 KiB
C
220 lines
7.0 KiB
C
/* $OpenBSD: kexsntrup761x25519.c,v 1.1 2020/12/29 00:59:15 djm Exp $ */
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/*
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* Copyright (c) 2019 Markus Friedl. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#include "includes.h"
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#include <sys/types.h>
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#include <stdio.h>
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#include <string.h>
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#include <signal.h>
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#include "sshkey.h"
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#include "kex.h"
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#include "sshbuf.h"
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#include "digest.h"
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#include "ssherr.h"
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int
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kex_kem_sntrup761x25519_keypair(struct kex *kex)
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{
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struct sshbuf *buf = NULL;
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u_char *cp = NULL;
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size_t need;
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int r;
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if ((buf = sshbuf_new()) == NULL)
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return SSH_ERR_ALLOC_FAIL;
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need = crypto_kem_sntrup761_PUBLICKEYBYTES + CURVE25519_SIZE;
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if ((r = sshbuf_reserve(buf, need, &cp)) != 0)
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goto out;
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crypto_kem_sntrup761_keypair(cp, kex->sntrup761_client_key);
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#ifdef DEBUG_KEXECDH
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dump_digest("client public key sntrup761:", cp,
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crypto_kem_sntrup761_PUBLICKEYBYTES);
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#endif
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cp += crypto_kem_sntrup761_PUBLICKEYBYTES;
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kexc25519_keygen(kex->c25519_client_key, cp);
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#ifdef DEBUG_KEXECDH
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dump_digest("client public key c25519:", cp, CURVE25519_SIZE);
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#endif
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kex->client_pub = buf;
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buf = NULL;
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out:
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sshbuf_free(buf);
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return r;
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}
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int
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kex_kem_sntrup761x25519_enc(struct kex *kex,
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const struct sshbuf *client_blob, struct sshbuf **server_blobp,
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struct sshbuf **shared_secretp)
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{
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struct sshbuf *server_blob = NULL;
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struct sshbuf *buf = NULL;
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const u_char *client_pub;
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u_char *kem_key, *ciphertext, *server_pub;
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u_char server_key[CURVE25519_SIZE];
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u_char hash[SSH_DIGEST_MAX_LENGTH];
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size_t need;
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int r;
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*server_blobp = NULL;
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*shared_secretp = NULL;
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/* client_blob contains both KEM and ECDH client pubkeys */
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need = crypto_kem_sntrup761_PUBLICKEYBYTES + CURVE25519_SIZE;
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if (sshbuf_len(client_blob) != need) {
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r = SSH_ERR_SIGNATURE_INVALID;
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goto out;
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}
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client_pub = sshbuf_ptr(client_blob);
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#ifdef DEBUG_KEXECDH
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dump_digest("client public key sntrup761:", client_pub,
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crypto_kem_sntrup761_PUBLICKEYBYTES);
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dump_digest("client public key 25519:",
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client_pub + crypto_kem_sntrup761_PUBLICKEYBYTES,
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CURVE25519_SIZE);
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#endif
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/* allocate buffer for concatenation of KEM key and ECDH shared key */
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/* the buffer will be hashed and the result is the shared secret */
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if ((buf = sshbuf_new()) == NULL) {
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r = SSH_ERR_ALLOC_FAIL;
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goto out;
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}
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if ((r = sshbuf_reserve(buf, crypto_kem_sntrup761_BYTES,
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&kem_key)) != 0)
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goto out;
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/* allocate space for encrypted KEM key and ECDH pub key */
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if ((server_blob = sshbuf_new()) == NULL) {
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r = SSH_ERR_ALLOC_FAIL;
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goto out;
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}
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need = crypto_kem_sntrup761_CIPHERTEXTBYTES + CURVE25519_SIZE;
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if ((r = sshbuf_reserve(server_blob, need, &ciphertext)) != 0)
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goto out;
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/* generate and encrypt KEM key with client key */
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crypto_kem_sntrup761_enc(ciphertext, kem_key, client_pub);
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/* generate ECDH key pair, store server pubkey after ciphertext */
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server_pub = ciphertext + crypto_kem_sntrup761_CIPHERTEXTBYTES;
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kexc25519_keygen(server_key, server_pub);
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/* append ECDH shared key */
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client_pub += crypto_kem_sntrup761_PUBLICKEYBYTES;
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if ((r = kexc25519_shared_key_ext(server_key, client_pub, buf, 1)) < 0)
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goto out;
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if ((r = ssh_digest_buffer(kex->hash_alg, buf, hash, sizeof(hash))) != 0)
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goto out;
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#ifdef DEBUG_KEXECDH
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dump_digest("server public key 25519:", server_pub, CURVE25519_SIZE);
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dump_digest("server cipher text:", ciphertext,
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crypto_kem_sntrup761_CIPHERTEXTBYTES);
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dump_digest("server kem key:", kem_key, sizeof(kem_key));
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dump_digest("concatenation of KEM key and ECDH shared key:",
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sshbuf_ptr(buf), sshbuf_len(buf));
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#endif
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/* string-encoded hash is resulting shared secret */
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sshbuf_reset(buf);
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if ((r = sshbuf_put_string(buf, hash,
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ssh_digest_bytes(kex->hash_alg))) != 0)
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goto out;
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#ifdef DEBUG_KEXECDH
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dump_digest("encoded shared secret:", sshbuf_ptr(buf), sshbuf_len(buf));
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#endif
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*server_blobp = server_blob;
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*shared_secretp = buf;
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server_blob = NULL;
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buf = NULL;
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out:
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explicit_bzero(hash, sizeof(hash));
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explicit_bzero(server_key, sizeof(server_key));
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sshbuf_free(server_blob);
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sshbuf_free(buf);
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return r;
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}
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int
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kex_kem_sntrup761x25519_dec(struct kex *kex,
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const struct sshbuf *server_blob, struct sshbuf **shared_secretp)
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{
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struct sshbuf *buf = NULL;
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u_char *kem_key = NULL;
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const u_char *ciphertext, *server_pub;
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u_char hash[SSH_DIGEST_MAX_LENGTH];
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size_t need;
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int r, decoded;
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*shared_secretp = NULL;
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need = crypto_kem_sntrup761_CIPHERTEXTBYTES + CURVE25519_SIZE;
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if (sshbuf_len(server_blob) != need) {
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r = SSH_ERR_SIGNATURE_INVALID;
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goto out;
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}
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ciphertext = sshbuf_ptr(server_blob);
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server_pub = ciphertext + crypto_kem_sntrup761_CIPHERTEXTBYTES;
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#ifdef DEBUG_KEXECDH
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dump_digest("server cipher text:", ciphertext,
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crypto_kem_sntrup761_CIPHERTEXTBYTES);
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dump_digest("server public key c25519:", server_pub, CURVE25519_SIZE);
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#endif
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/* hash concatenation of KEM key and ECDH shared key */
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if ((buf = sshbuf_new()) == NULL) {
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r = SSH_ERR_ALLOC_FAIL;
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goto out;
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}
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if ((r = sshbuf_reserve(buf, crypto_kem_sntrup761_BYTES,
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&kem_key)) != 0)
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goto out;
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decoded = crypto_kem_sntrup761_dec(kem_key, ciphertext,
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kex->sntrup761_client_key);
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if ((r = kexc25519_shared_key_ext(kex->c25519_client_key, server_pub,
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buf, 1)) < 0)
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goto out;
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if ((r = ssh_digest_buffer(kex->hash_alg, buf, hash, sizeof(hash))) != 0)
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goto out;
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#ifdef DEBUG_KEXECDH
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dump_digest("client kem key:", kem_key, crypto_kem_sntrup761_BYTES);
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dump_digest("concatenation of KEM key and ECDH shared key:",
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sshbuf_ptr(buf), sshbuf_len(buf));
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#endif
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sshbuf_reset(buf);
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if ((r = sshbuf_put_string(buf, hash,
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ssh_digest_bytes(kex->hash_alg))) != 0)
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goto out;
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#ifdef DEBUG_KEXECDH
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dump_digest("encoded shared secret:", sshbuf_ptr(buf), sshbuf_len(buf));
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#endif
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if (decoded != 0) {
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r = SSH_ERR_SIGNATURE_INVALID;
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goto out;
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}
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*shared_secretp = buf;
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buf = NULL;
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out:
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explicit_bzero(hash, sizeof(hash));
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sshbuf_free(buf);
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return r;
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}
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