Annotation of src/usr.bin/ssh/kexsntrup4591761x25519.c, Revision 1.1
1.1 ! djm 1: /* $OpenBSD: $ */
! 2: /*
! 3: * Copyright (c) 2019 Markus Friedl. All rights reserved.
! 4: *
! 5: * Redistribution and use in source and binary forms, with or without
! 6: * modification, are permitted provided that the following conditions
! 7: * are met:
! 8: * 1. Redistributions of source code must retain the above copyright
! 9: * notice, this list of conditions and the following disclaimer.
! 10: * 2. Redistributions in binary form must reproduce the above copyright
! 11: * notice, this list of conditions and the following disclaimer in the
! 12: * documentation and/or other materials provided with the distribution.
! 13: *
! 14: * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
! 15: * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
! 16: * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
! 17: * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
! 18: * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
! 19: * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
! 20: * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
! 21: * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
! 22: * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
! 23: * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
! 24: */
! 25:
! 26: #include <sys/types.h>
! 27:
! 28: #include <stdio.h>
! 29: #include <string.h>
! 30: #include <signal.h>
! 31:
! 32: #include "sshkey.h"
! 33: #include "kex.h"
! 34: #include "sshbuf.h"
! 35: #include "digest.h"
! 36: #include "ssherr.h"
! 37:
! 38: int
! 39: kex_kem_sntrup4591761x25519_keypair(struct kex *kex)
! 40: {
! 41: struct sshbuf *buf = NULL;
! 42: u_char *cp = NULL;
! 43: size_t need;
! 44: int r;
! 45:
! 46: if ((buf = sshbuf_new()) == NULL)
! 47: return SSH_ERR_ALLOC_FAIL;
! 48: need = crypto_kem_sntrup4591761_PUBLICKEYBYTES + CURVE25519_SIZE;
! 49: if ((r = sshbuf_reserve(buf, need, &cp)) != 0)
! 50: goto out;
! 51: crypto_kem_sntrup4591761_keypair(cp, kex->sntrup4591761_client_key);
! 52: #ifdef DEBUG_KEXECDH
! 53: dump_digest("client public key sntrup4591761:", cp,
! 54: crypto_kem_sntrup4591761_PUBLICKEYBYTES);
! 55: #endif
! 56: cp += crypto_kem_sntrup4591761_PUBLICKEYBYTES;
! 57: kexc25519_keygen(kex->c25519_client_key, cp);
! 58: #ifdef DEBUG_KEXECDH
! 59: dump_digest("client public key c25519:", cp, CURVE25519_SIZE);
! 60: #endif
! 61: kex->kem_client_pub = buf;
! 62: buf = NULL;
! 63: out:
! 64: sshbuf_free(buf);
! 65: return r;
! 66: }
! 67:
! 68: int
! 69: kex_kem_sntrup4591761x25519_enc(struct kex *kex, const u_char *pkblob,
! 70: size_t pklen, struct sshbuf **server_blobp, struct sshbuf **shared_secretp)
! 71: {
! 72: struct sshbuf *server_blob = NULL;
! 73: struct sshbuf *buf = NULL;
! 74: u_char *kem_key, *ciphertext, *server_pub;
! 75: u_char server_key[CURVE25519_SIZE];
! 76: u_char hash[SSH_DIGEST_MAX_LENGTH];
! 77: size_t need;
! 78: int r;
! 79:
! 80: *server_blobp = NULL;
! 81: *shared_secretp = NULL;
! 82:
! 83: /* pkblob contains both KEM and ECDH client pubkeys */
! 84: need = crypto_kem_sntrup4591761_PUBLICKEYBYTES + CURVE25519_SIZE;
! 85: if (pklen != need) {
! 86: r = SSH_ERR_SIGNATURE_INVALID;
! 87: goto out;
! 88: }
! 89: #ifdef DEBUG_KEXECDH
! 90: dump_digest("client public key sntrup4591761:", pkblob,
! 91: crypto_kem_sntrup4591761_PUBLICKEYBYTES);
! 92: dump_digest("client public key 25519:",
! 93: pkblob + crypto_kem_sntrup4591761_PUBLICKEYBYTES, CURVE25519_SIZE);
! 94: #endif
! 95: /* allocate buffer for concatenation of KEM key and ECDH shared key */
! 96: /* the buffer will be hashed and the result is the shared secret */
! 97: if ((buf = sshbuf_new()) == NULL) {
! 98: r = SSH_ERR_ALLOC_FAIL;
! 99: goto out;
! 100: }
! 101: if ((r = sshbuf_reserve(buf, crypto_kem_sntrup4591761_BYTES,
! 102: &kem_key)) != 0)
! 103: goto out;
! 104: /* allocate space for encrypted KEM key and ECDH pub key */
! 105: if ((server_blob = sshbuf_new()) == NULL) {
! 106: r = SSH_ERR_ALLOC_FAIL;
! 107: goto out;
! 108: }
! 109: need = crypto_kem_sntrup4591761_CIPHERTEXTBYTES + CURVE25519_SIZE;
! 110: if ((r = sshbuf_reserve(server_blob, need, &ciphertext)) != 0)
! 111: goto out;
! 112: /* generate and encrypt KEM key with client key */
! 113: crypto_kem_sntrup4591761_enc(ciphertext, kem_key, pkblob);
! 114: /* generate ECDH key pair, store server pubkey after ciphertext */
! 115: server_pub = ciphertext + crypto_kem_sntrup4591761_CIPHERTEXTBYTES;
! 116: kexc25519_keygen(server_key, server_pub);
! 117: /* append ECDH shared key */
! 118: if ((r = kexc25519_shared_key_ext(server_key,
! 119: pkblob + crypto_kem_sntrup4591761_PUBLICKEYBYTES, buf, 1)) < 0)
! 120: goto out;
! 121: if ((r = ssh_digest_buffer(kex->hash_alg, buf, hash, sizeof(hash))) != 0)
! 122: goto out;
! 123: #ifdef DEBUG_KEXECDH
! 124: dump_digest("server public key 25519:", server_pub, CURVE25519_SIZE);
! 125: dump_digest("server cipher text:", ciphertext,
! 126: crypto_kem_sntrup4591761_CIPHERTEXTBYTES);
! 127: dump_digest("server kem key:", kem_key, sizeof(kem_key));
! 128: dump_digest("concatenation of KEM key and ECDH shared key:",
! 129: sshbuf_ptr(buf), sshbuf_len(buf));
! 130: #endif
! 131: /* string-encoded hash is resulting shared secret */
! 132: sshbuf_reset(buf);
! 133: if ((r = sshbuf_put_string(buf, hash,
! 134: ssh_digest_bytes(kex->hash_alg))) != 0)
! 135: goto out;
! 136: #ifdef DEBUG_KEXECDH
! 137: dump_digest("encoded shared secret:", sshbuf_ptr(buf), sshbuf_len(buf));
! 138: #endif
! 139: *server_blobp = server_blob;
! 140: *shared_secretp = buf;
! 141: server_blob = NULL;
! 142: buf = NULL;
! 143: out:
! 144: explicit_bzero(hash, sizeof(hash));
! 145: explicit_bzero(server_key, sizeof(server_key));
! 146: sshbuf_free(server_blob);
! 147: sshbuf_free(buf);
! 148: return r;
! 149: }
! 150:
! 151: int
! 152: kex_kem_sntrup4591761x25519_dec(struct kex *kex, const u_char *pkblob,
! 153: size_t pklen, struct sshbuf **shared_secretp)
! 154: {
! 155: struct sshbuf *buf = NULL;
! 156: u_char *kem_key = NULL;
! 157: const u_char *ciphertext, *server_pub;
! 158: u_char hash[SSH_DIGEST_MAX_LENGTH];
! 159: size_t need;
! 160: int r, decoded;
! 161:
! 162: *shared_secretp = NULL;
! 163:
! 164: need = crypto_kem_sntrup4591761_CIPHERTEXTBYTES + CURVE25519_SIZE;
! 165: if (pklen != need) {
! 166: r = SSH_ERR_SIGNATURE_INVALID;
! 167: goto out;
! 168: }
! 169: ciphertext = pkblob;
! 170: server_pub = pkblob + crypto_kem_sntrup4591761_CIPHERTEXTBYTES;
! 171: #ifdef DEBUG_KEXECDH
! 172: dump_digest("server cipher text:", ciphertext,
! 173: crypto_kem_sntrup4591761_CIPHERTEXTBYTES);
! 174: dump_digest("server public key c25519:", server_pub, CURVE25519_SIZE);
! 175: #endif
! 176: /* hash concatenation of KEM key and ECDH shared key */
! 177: if ((buf = sshbuf_new()) == NULL) {
! 178: r = SSH_ERR_ALLOC_FAIL;
! 179: goto out;
! 180: }
! 181: if ((r = sshbuf_reserve(buf, crypto_kem_sntrup4591761_BYTES,
! 182: &kem_key)) != 0)
! 183: goto out;
! 184: decoded = crypto_kem_sntrup4591761_dec(kem_key, ciphertext,
! 185: kex->sntrup4591761_client_key);
! 186: if ((r = kexc25519_shared_key_ext(kex->c25519_client_key, server_pub,
! 187: buf, 1)) < 0)
! 188: goto out;
! 189: if ((r = ssh_digest_buffer(kex->hash_alg, buf, hash, sizeof(hash))) != 0)
! 190: goto out;
! 191: #ifdef DEBUG_KEXECDH
! 192: dump_digest("client kem key:", kem_key, sizeof(kem_key));
! 193: dump_digest("concatenation of KEM key and ECDH shared key:",
! 194: sshbuf_ptr(buf), sshbuf_len(buf));
! 195: #endif
! 196: sshbuf_reset(buf);
! 197: if ((r = sshbuf_put_string(buf, hash,
! 198: ssh_digest_bytes(kex->hash_alg))) != 0)
! 199: goto out;
! 200: #ifdef DEBUG_KEXECDH
! 201: dump_digest("encoded shared secret:", sshbuf_ptr(buf), sshbuf_len(buf));
! 202: #endif
! 203: if (decoded != 0) {
! 204: r = SSH_ERR_SIGNATURE_INVALID;
! 205: goto out;
! 206: }
! 207: *shared_secretp = buf;
! 208: buf = NULL;
! 209: out:
! 210: explicit_bzero(hash, sizeof(hash));
! 211: sshbuf_free(buf);
! 212: return r;
! 213: }
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