onion_crypto.c

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/* Copyright (c) 2001 Matej Pfajfar.
 * Copyright (c) 2001-2004, Roger Dingledine.
 * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
 * Copyright (c) 2007-2021, The Tor Project, Inc. */
/* See LICENSE for licensing information */
 
/**
 * \file onion_crypto.c
 * \brief Functions to handle different kinds of circuit extension crypto.
 *
 * In this module, we provide a set of abstractions to create a uniform
 * interface over the three circuit extension handshakes that Tor has used
 * over the years (TAP, CREATE_FAST, and ntor).  These handshakes are
 * implemented in onion_tap.c, onion_fast.c, and onion_ntor.c respectively.
 *
 * All[*] of these handshakes follow a similar pattern: a client, knowing
 * some key from the relay it wants to extend through, generates the
 * first part of a handshake. A relay receives that handshake, and sends
 * a reply.  Once the client handles the reply, it knows that it is
 * talking to the right relay, and it shares some freshly negotiated key
 * material with that relay.
 *
 * We sometimes call the client's part of the handshake an "onionskin".
 * We do this because historically, Onion Routing used a multi-layer
 * structure called an "onion" to construct circuits. Each layer of the
 * onion contained key material chosen by the client, the identity of
 * the next relay in the circuit, and a smaller onion, encrypted with
 * the key of the next relay.  When we changed Tor to use a telescoping
 * circuit extension design, it corresponded to sending each layer of the
 * onion separately -- as a series of onionskins.
 **/
 
#include "core/or/or.h"
#include "core/or/extendinfo.h"
#include "core/crypto/onion_crypto.h"
#include "core/crypto/onion_fast.h"
#include "core/crypto/onion_ntor.h"
#include "core/crypto/onion_tap.h"
#include "feature/relay/router.h"
#include "lib/crypt_ops/crypto_dh.h"
#include "lib/crypt_ops/crypto_util.h"
 
#include "core/or/crypt_path_st.h"
#include "core/or/extend_info_st.h"
 
/** Return a new server_onion_keys_t object with all of the keys
 * and other info we might need to do onion handshakes.  (We make a copy of
 * our keys for each cpuworker to avoid race conditions with the main thread,
 * and to avoid locking) */
server_onion_keys_t *
server_onion_keys_new(void)
{
  server_onion_keys_t *keys = tor_malloc_zero(sizeof(server_onion_keys_t));
  memcpy(keys->my_identity, router_get_my_id_digest(), DIGEST_LEN);
  dup_onion_keys(&keys->onion_key, &keys->last_onion_key);
  keys->curve25519_key_map = construct_ntor_key_map();
  keys->junk_keypair = tor_malloc_zero(sizeof(curve25519_keypair_t));
  curve25519_keypair_generate(keys->junk_keypair, 0);
  return keys;
}
/** Release all storage held in <b>keys</b>. */
void
server_onion_keys_free_(server_onion_keys_t *keys)
{
  if (! keys)
    return;
 
  crypto_pk_free(keys->onion_key);
  crypto_pk_free(keys->last_onion_key);
  ntor_key_map_free(keys->curve25519_key_map);
  tor_free(keys->junk_keypair);
  memwipe(keys, 0, sizeof(server_onion_keys_t));
  tor_free(keys);
}
 
/** Release whatever storage is held in <b>state</b>, depending on its
 * type, and clear its pointer. */
void
onion_handshake_state_release(onion_handshake_state_t *state)
{
  switch (state->tag) {
  case ONION_HANDSHAKE_TYPE_TAP:
    crypto_dh_free(state->u.tap);
    state->u.tap = NULL;
    break;
  case ONION_HANDSHAKE_TYPE_FAST:
    fast_handshake_state_free(state->u.fast);
    state->u.fast = NULL;
    break;
  case ONION_HANDSHAKE_TYPE_NTOR:
    ntor_handshake_state_free(state->u.ntor);
    state->u.ntor = NULL;
    break;
  default:
    /* LCOV_EXCL_START
     * This state should not even exist. */
    log_warn(LD_BUG, "called with unknown handshake state type %d",
             (int)state->tag);
    tor_fragile_assert();
    /* LCOV_EXCL_STOP */
  }
}
 
/** Perform the first step of a circuit-creation handshake of type <b>type</b>
 * (one of ONION_HANDSHAKE_TYPE_*): generate the initial "onion skin" in
 * <b>onion_skin_out</b>, and store any state information in <b>state_out</b>.
 * Return -1 on failure, and the length of the onionskin on acceptance.
 */
int
onion_skin_create(int type,
                  const extend_info_t *node,
                  onion_handshake_state_t *state_out,
                  uint8_t *onion_skin_out)
{
  int r = -1;
 
  switch (type) {
  case ONION_HANDSHAKE_TYPE_TAP:
    if (!node->onion_key)
      return -1;
 
    if (onion_skin_TAP_create(node->onion_key,
                              &state_out->u.tap,
                              (char*)onion_skin_out) < 0)
      return -1;
 
    r = TAP_ONIONSKIN_CHALLENGE_LEN;
    break;
  case ONION_HANDSHAKE_TYPE_FAST:
    if (fast_onionskin_create(&state_out->u.fast, onion_skin_out) < 0)
      return -1;
 
    r = CREATE_FAST_LEN;
    break;
  case ONION_HANDSHAKE_TYPE_NTOR:
    if (!extend_info_supports_ntor(node))
      return -1;
    if (onion_skin_ntor_create((const uint8_t*)node->identity_digest,
                               &node->curve25519_onion_key,
                               &state_out->u.ntor,
                               onion_skin_out) < 0)
      return -1;
 
    r = NTOR_ONIONSKIN_LEN;
    break;
  default:
    /* LCOV_EXCL_START
     * We should never try to create an impossible handshake type. */
    log_warn(LD_BUG, "called with unknown handshake state type %d", type);
    tor_fragile_assert();
    r = -1;
    /* LCOV_EXCL_STOP */
  }
 
  if (r > 0)
    state_out->tag = (uint16_t) type;
 
  return r;
}
 
/* This is the maximum value for keys_out_len passed to
 * onion_skin_server_handshake, plus 16. We can make it bigger if needed:
 * It just defines how many bytes to stack-allocate. */
#define MAX_KEYS_TMP_LEN 128
 
/** Perform the second (server-side) step of a circuit-creation handshake of
 * type <b>type</b>, responding to the client request in <b>onion_skin</b>
 * using the keys in <b>keys</b>.  On success, write our response into
 * <b>reply_out</b>, generate <b>keys_out_len</b> bytes worth of key material
 * in <b>keys_out_len</b>, a hidden service nonce to <b>rend_nonce_out</b>,
 * and return the length of the reply. On failure, return -1.
 */
int
onion_skin_server_handshake(int type,
                      const uint8_t *onion_skin, size_t onionskin_len,
                      const server_onion_keys_t *keys,
                      uint8_t *reply_out,
                      uint8_t *keys_out, size_t keys_out_len,
                      uint8_t *rend_nonce_out)
{
  int r = -1;
 
  switch (type) {
  case ONION_HANDSHAKE_TYPE_TAP:
    if (onionskin_len != TAP_ONIONSKIN_CHALLENGE_LEN)
      return -1;
    if (onion_skin_TAP_server_handshake((const char*)onion_skin,
                                        keys->onion_key, keys->last_onion_key,
                                        (char*)reply_out,
                                        (char*)keys_out, keys_out_len)<0)
      return -1;
    r = TAP_ONIONSKIN_REPLY_LEN;
    memcpy(rend_nonce_out, reply_out+DH1024_KEY_LEN, DIGEST_LEN);
    break;
  case ONION_HANDSHAKE_TYPE_FAST:
    if (onionskin_len != CREATE_FAST_LEN)
      return -1;
    if (fast_server_handshake(onion_skin, reply_out, keys_out, keys_out_len)<0)
      return -1;
    r = CREATED_FAST_LEN;
    memcpy(rend_nonce_out, reply_out+DIGEST_LEN, DIGEST_LEN);
    break;
  case ONION_HANDSHAKE_TYPE_NTOR:
    if (onionskin_len < NTOR_ONIONSKIN_LEN)
      return -1;
    {
      size_t keys_tmp_len = keys_out_len + DIGEST_LEN;
      tor_assert(keys_tmp_len <= MAX_KEYS_TMP_LEN);
      uint8_t keys_tmp[MAX_KEYS_TMP_LEN];
 
      if (onion_skin_ntor_server_handshake(
                                   onion_skin, keys->curve25519_key_map,
                                   keys->junk_keypair,
                                   keys->my_identity,
                                   reply_out, keys_tmp, keys_tmp_len)<0) {
        /* no need to memwipe here, since the output will never be used */
        return -1;
      }
 
      memcpy(keys_out, keys_tmp, keys_out_len);
      memcpy(rend_nonce_out, keys_tmp+keys_out_len, DIGEST_LEN);
      memwipe(keys_tmp, 0, sizeof(keys_tmp));
      r = NTOR_REPLY_LEN;
    }
    break;
  default:
    /* LCOV_EXCL_START
     * We should have rejected this far before this point */
    log_warn(LD_BUG, "called with unknown handshake state type %d", type);
    tor_fragile_assert();
    return -1;
    /* LCOV_EXCL_STOP */
  }
 
  return r;
}
 
/** Perform the final (client-side) step of a circuit-creation handshake of
 * type <b>type</b>, using our state in <b>handshake_state</b> and the
 * server's response in <b>reply</b>. On success, generate <b>keys_out_len</b>
 * bytes worth of key material in <b>keys_out_len</b>, set
 * <b>rend_authenticator_out</b> to the "KH" field that can be used to
 * establish introduction points at this hop, and return 0. On failure,
 * return -1, and set *msg_out to an error message if this is worth
 * complaining to the user about. */
int
onion_skin_client_handshake(int type,
                      const onion_handshake_state_t *handshake_state,
                      const uint8_t *reply, size_t reply_len,
                      uint8_t *keys_out, size_t keys_out_len,
                      uint8_t *rend_authenticator_out,
                      const char **msg_out)
{
  if (handshake_state->tag != type)
    return -1;
 
  switch (type) {
  case ONION_HANDSHAKE_TYPE_TAP:
    if (reply_len != TAP_ONIONSKIN_REPLY_LEN) {
      if (msg_out)
        *msg_out = "TAP reply was not of the correct length.";
      return -1;
    }
    if (onion_skin_TAP_client_handshake(handshake_state->u.tap,
                                        (const char*)reply,
                                        (char *)keys_out, keys_out_len,
                                        msg_out) < 0)
      return -1;
 
    memcpy(rend_authenticator_out, reply+DH1024_KEY_LEN, DIGEST_LEN);
 
    return 0;
  case ONION_HANDSHAKE_TYPE_FAST:
    if (reply_len != CREATED_FAST_LEN) {
      if (msg_out)
        *msg_out = "TAP reply was not of the correct length.";
      return -1;
    }
    if (fast_client_handshake(handshake_state->u.fast, reply,
                              keys_out, keys_out_len, msg_out) < 0)
      return -1;
 
    memcpy(rend_authenticator_out, reply+DIGEST_LEN, DIGEST_LEN);
    return 0;
  case ONION_HANDSHAKE_TYPE_NTOR:
    if (reply_len < NTOR_REPLY_LEN) {
      if (msg_out)
        *msg_out = "ntor reply was not of the correct length.";
      return -1;
    }
    {
      size_t keys_tmp_len = keys_out_len + DIGEST_LEN;
      uint8_t *keys_tmp = tor_malloc(keys_tmp_len);
      if (onion_skin_ntor_client_handshake(handshake_state->u.ntor,
                                        reply,
                                        keys_tmp, keys_tmp_len, msg_out) < 0) {
        tor_free(keys_tmp);
        return -1;
      }
      memcpy(keys_out, keys_tmp, keys_out_len);
      memcpy(rend_authenticator_out, keys_tmp + keys_out_len, DIGEST_LEN);
      memwipe(keys_tmp, 0, keys_tmp_len);
      tor_free(keys_tmp);
    }
    return 0;
  default:
    log_warn(LD_BUG, "called with unknown handshake state type %d", type);
    tor_fragile_assert();
    return -1;
  }
}