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Diffstat (limited to '')
| -rw-r--r-- | kexsntrup761x25519.c | 251 |
1 files changed, 251 insertions, 0 deletions
diff --git a/kexsntrup761x25519.c b/kexsntrup761x25519.c new file mode 100644 index 0000000..6afb1ba --- /dev/null +++ b/kexsntrup761x25519.c @@ -0,0 +1,251 @@ +/* $OpenBSD: kexsntrup761x25519.c,v 1.2 2021/12/05 12:28:27 jsg 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 USE_SNTRUP761X25519 + +#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_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; +} + +#else + +#include "ssherr.h" + +struct kex; +struct sshbuf; +struct sshkey; + +int +kex_kem_sntrup761x25519_keypair(struct kex *kex) +{ + return SSH_ERR_SIGN_ALG_UNSUPPORTED; +} + +int +kex_kem_sntrup761x25519_enc(struct kex *kex, + const struct sshbuf *client_blob, struct sshbuf **server_blobp, + struct sshbuf **shared_secretp) +{ + return SSH_ERR_SIGN_ALG_UNSUPPORTED; +} + +int +kex_kem_sntrup761x25519_dec(struct kex *kex, + const struct sshbuf *server_blob, struct sshbuf **shared_secretp) +{ + return SSH_ERR_SIGN_ALG_UNSUPPORTED; +} +#endif /* USE_SNTRUP761X25519 */ |