rendcommon.c

关于tor匿名通信的源代码

/* Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
 * Copyright (c) 2007-2008, The Tor Project, Inc. */
/* See LICENSE for licensing information */
/* $Id$ */
const char rendcommon_c_id[] =
  "$Id$";

/**
 * \file rendcommon.c
 * \brief Rendezvous implementation: shared code between
 * introducers, services, clients, and rendezvous points.
 **/

#include "or.h"

/** Return 0 if one and two are the same service ids, else -1 or 1 */
int
rend_cmp_service_ids(const char *one, const char *two)
{
  return strcasecmp(one,two);
}

/** Free the storage held by the service descriptor <b>desc</b>.
 */
void
rend_service_descriptor_free(rend_service_descriptor_t *desc)
{
  if (desc->pk)
    crypto_free_pk_env(desc->pk);
  if (desc->intro_nodes) {
    SMARTLIST_FOREACH(desc->intro_nodes, rend_intro_point_t *, intro,
      rend_intro_point_free(intro););
    smartlist_free(desc->intro_nodes);
  }
  tor_free(desc);
}

/** Length of the descriptor cookie that is used for versioned hidden
 * service descriptors. */
#define REND_DESC_COOKIE_LEN 16

/** Length of the replica number that is used to determine the secret ID
 * part of versioned hidden service descriptors. */
#define REND_REPLICA_LEN 1

/** Compute the descriptor ID for <b>service_id</b> of length
 * <b>REND_SERVICE_ID_LEN</b> and <b>secret_id_part</b> of length
 * <b>DIGEST_LEN</b>, and write it to <b>descriptor_id_out</b> of length
 * <b>DIGEST_LEN</b>. */
void
rend_get_descriptor_id_bytes(char *descriptor_id_out,
                             const char *service_id,
                             const char *secret_id_part)
{
  crypto_digest_env_t *digest = crypto_new_digest_env();
  crypto_digest_add_bytes(digest, service_id, REND_SERVICE_ID_LEN);
  crypto_digest_add_bytes(digest, secret_id_part, DIGEST_LEN);
  crypto_digest_get_digest(digest, descriptor_id_out, DIGEST_LEN);
  crypto_free_digest_env(digest);
}

/** Compute the secret ID part for time_period,
 * a <b>descriptor_cookie</b> of length
 * <b>REND_DESC_COOKIE_LEN</b> which may also be <b>NULL</b> if no
 * descriptor_cookie shall be used, and <b>replica</b>, and write it to
 * <b>secret_id_part</b> of length DIGEST_LEN. */
static void
get_secret_id_part_bytes(char *secret_id_part, uint32_t time_period,
                         const char *descriptor_cookie, uint8_t replica)
{
  crypto_digest_env_t *digest = crypto_new_digest_env();
  time_period = htonl(time_period);
  crypto_digest_add_bytes(digest, (char*)&time_period, sizeof(uint32_t));
  if (descriptor_cookie) {
    crypto_digest_add_bytes(digest, descriptor_cookie,
                            REND_DESC_COOKIE_LEN);
  }
  crypto_digest_add_bytes(digest, (const char *)&replica, REND_REPLICA_LEN);
  crypto_digest_get_digest(digest, secret_id_part, DIGEST_LEN);
  crypto_free_digest_env(digest);
}

/** Return the time period for time <b>now</b> plus a potentially
 * intended <b>deviation</b> of one or more periods, based on the first byte
 * of <b>service_id</b>. */
static uint32_t
get_time_period(time_t now, uint8_t deviation, const char *service_id)
{
  /* The time period is the number of REND_TIME_PERIOD_V2_DESC_VALIDITY
   * intervals that have passed since the epoch, offset slightly so that
   * each service's time periods start and end at a fraction of that
   * period based on their first byte. */
  return (uint32_t)
    (now + ((uint8_t) *service_id) * REND_TIME_PERIOD_V2_DESC_VALIDITY / 256)
    / REND_TIME_PERIOD_V2_DESC_VALIDITY + deviation;
}

/** Compute the time in seconds that a descriptor that is generated
 * <b>now</b> for <b>service_id</b> will be valid. */
static uint32_t
get_seconds_valid(time_t now, const char *service_id)
{
  uint32_t result = REND_TIME_PERIOD_V2_DESC_VALIDITY -
    ((uint32_t)
     (now + ((uint8_t) *service_id) * REND_TIME_PERIOD_V2_DESC_VALIDITY / 256)
     % REND_TIME_PERIOD_V2_DESC_VALIDITY);
  return result;
}

/** Compute the binary <b>desc_id_out</b> (DIGEST_LEN bytes long) for a given
 * base32-encoded <b>service_id</b> and optional unencoded
 * <b>descriptor_cookie</b> of length REND_DESC_COOKIE_LEN,
 * at time <b>now</b> for replica number
 * <b>replica</b>. <b>desc_id</b> needs to have <b>DIGEST_LEN</b> bytes
 * free. Return 0 for success, -1 otherwise. */
int
rend_compute_v2_desc_id(char *desc_id_out, const char *service_id,
                        const char *descriptor_cookie, time_t now,
                        uint8_t replica)
{
  char service_id_binary[REND_SERVICE_ID_LEN];
  char secret_id_part[DIGEST_LEN];
  uint32_t time_period;
  if (!service_id ||
      strlen(service_id) != REND_SERVICE_ID_LEN_BASE32) {
    log_warn(LD_REND, "Could not compute v2 descriptor ID: "
                      "Illegal service ID: %s", safe_str(service_id));
    return -1;
  }
  if (replica >= REND_NUMBER_OF_NON_CONSECUTIVE_REPLICAS) {
    log_warn(LD_REND, "Could not compute v2 descriptor ID: "
                      "Replica number out of range: %d", replica);
    return -1;
  }
  /* Convert service ID to binary. */
  if (base32_decode(service_id_binary, REND_SERVICE_ID_LEN,
                    service_id, REND_SERVICE_ID_LEN_BASE32) < 0) {
    log_warn(LD_REND, "Could not compute v2 descriptor ID: "
                      "Illegal characters in service ID: %s",
             safe_str(service_id));
    return -1;
  }
  /* Calculate current time-period. */
  time_period = get_time_period(now, 0, service_id_binary);
  /* Calculate secret-id-part = h(time-period + replica). */
  get_secret_id_part_bytes(secret_id_part, time_period, descriptor_cookie,
                           replica);
  /* Calculate descriptor ID. */
  rend_get_descriptor_id_bytes(desc_id_out, service_id_binary, secret_id_part);
  return 0;
}

/* Encode the introduction points in <b>desc</b>, optionally encrypt them with
 * an optional <b>descriptor_cookie</b> of length REND_DESC_COOKIE_LEN,
 * encode it in base64, and write it to a newly allocated string, and write a
 * pointer to it to *<b>ipos_base64</b>. Return 0 for success, -1
 * otherwise. */
static int
rend_encode_v2_intro_points(char **ipos_base64,
                            rend_service_descriptor_t *desc,
                            const char *descriptor_cookie)
{
  size_t unenc_len;
  char *unenc = NULL;
  size_t unenc_written = 0;
  int i;
  int r = -1;
  /* Assemble unencrypted list of introduction points. */
  *ipos_base64 = NULL;
  unenc_len = smartlist_len(desc->intro_nodes) * 1000; /* too long, but ok. */
  unenc = tor_malloc_zero(unenc_len);
  for (i = 0; i < smartlist_len(desc->intro_nodes); i++) {
    char id_base32[REND_INTRO_POINT_ID_LEN_BASE32 + 1];
    char *onion_key = NULL;
    size_t onion_key_len;
    crypto_pk_env_t *intro_key;
    char *service_key = NULL;
    char *address = NULL;
    size_t service_key_len;
    int res;
    rend_intro_point_t *intro = smartlist_get(desc->intro_nodes, i);
    /* Obtain extend info with introduction point details. */
    extend_info_t *info = intro->extend_info;
    /* Encode introduction point ID. */
    base32_encode(id_base32, sizeof(id_base32),
                  info->identity_digest, DIGEST_LEN);
    /* Encode onion key. */
    if (crypto_pk_write_public_key_to_string(info->onion_key, &onion_key,
                                             &onion_key_len) < 0) {
      log_warn(LD_REND, "Could not write onion key.");
      goto done;
    }
    /* Encode intro key. */
    intro_key = intro->intro_key;
    if (!intro_key ||
      crypto_pk_write_public_key_to_string(intro_key, &service_key,
                                           &service_key_len) < 0) {
      log_warn(LD_REND, "Could not write intro key.");
      tor_free(onion_key);
      goto done;
    }
    /* Assemble everything for this introduction point. */
    address = tor_dup_addr(info->addr);
    res = tor_snprintf(unenc + unenc_written, unenc_len - unenc_written,
                         "introduction-point %s\n"
                         "ip-address %s\n"
                         "onion-port %d\n"
                         "onion-key\n%s"
                         "service-key\n%s",
                       id_base32,
                       address,
                       info->port,
                       onion_key,
                       service_key);
    tor_free(address);
    tor_free(onion_key);
    tor_free(service_key);
    if (res < 0) {
      log_warn(LD_REND, "Not enough space for writing introduction point "
                        "string.");
      goto done;
    }
    /* Update total number of written bytes for unencrypted intro points. */
    unenc_written += res;
  }
  /* Finalize unencrypted introduction points. */
  if (unenc_len < unenc_written + 2) {
    log_warn(LD_REND, "Not enough space for finalizing introduction point "
                      "string.");
    goto done;
  }
  unenc[unenc_written++] = '\n';
  unenc[unenc_written++] = 0;
  /* If a descriptor cookie is passed, encrypt introduction points. */
  if (descriptor_cookie) {
    char *enc = tor_malloc_zero(unenc_written + CIPHER_IV_LEN);
    crypto_cipher_env_t *cipher =
      crypto_create_init_cipher(descriptor_cookie, 1);
    int enclen = crypto_cipher_encrypt_with_iv(cipher, enc,
                                               unenc_written + CIPHER_IV_LEN,
                                               unenc, unenc_written);
    crypto_free_cipher_env(cipher);
    if (enclen < 0) {
      log_warn(LD_REND, "Could not encrypt introduction point string.");
      tor_free(enc);
      goto done;
    }
    /* Replace original string with the encrypted one. */
    tor_free(unenc);
    unenc = enc;
    unenc_written = enclen;
  }
  /* Base64-encode introduction points. */
  *ipos_base64 = tor_malloc_zero(unenc_written * 2);
  if (base64_encode(*ipos_base64, unenc_written * 2, unenc, unenc_written)<0) {
    log_warn(LD_REND, "Could not encode introduction point string to "
             "base64.");
    goto done;
  }
  r = 0;
 done:
  if (r<0)
    tor_free(*ipos_base64);
  tor_free(unenc);
  return r;
}

/** Attempt to parse the given <b>desc_str</b> and return true if this
 * succeeds, false otherwise. */
static int
rend_desc_v2_is_parsable(rend_encoded_v2_service_descriptor_t *desc)
{
  rend_service_descriptor_t *test_parsed = NULL;
  char test_desc_id[DIGEST_LEN];
  char *test_intro_content = NULL;
  size_t test_intro_size;
  size_t test_encoded_size;
  const char *test_next;
  int res = rend_parse_v2_service_descriptor(&test_parsed, test_desc_id,
                                         &test_intro_content,
                                         &test_intro_size,
                                         &test_encoded_size,
                                         &test_next, desc->desc_str);
  if (test_parsed)
    rend_service_descriptor_free(test_parsed);
  tor_free(test_intro_content);
  return (res >= 0);
}

/** Free the storage held by an encoded v2 service descriptor. */
void
rend_encoded_v2_service_descriptor_free(
  rend_encoded_v2_service_descriptor_t *desc)
{
  tor_free(desc->desc_str);
  tor_free(desc);
}

/** Free the storage held by an introduction point info. */
void
rend_intro_point_free(rend_intro_point_t *intro)
{
  if (intro->extend_info)
    extend_info_free(intro->extend_info);
  if (intro->intro_key)
    crypto_free_pk_env(intro->intro_key);
  tor_free(intro);
}

/** Encode a set of rend_encoded_v2_service_descriptor_t's for <b>desc</b>
 * at time <b>now</b> using <b>descriptor_cookie</b> (may be <b>NULL</b> if
 * introduction points shall not be encrypted) and <b>period</b> (e.g. 0
 * for the current period, 1 for the next period, etc.) and add them to
 * the existing list <b>descs_out</b>; return the number of seconds that
 * the descriptors will be found by clients, or -1 if the encoding was not
 * successful. */
int
rend_encode_v2_descriptors(smartlist_t *descs_out,
                           rend_service_descriptor_t *desc, time_t now,
                           const char *descriptor_cookie, uint8_t period)
{
  char service_id[DIGEST_LEN];
  uint32_t time_period;
  char *ipos_base64 = NULL;
  int k;
  uint32_t seconds_valid;
  if (!desc) {
    log_warn(LD_REND, "Could not encode v2 descriptor: No desc given.");
    return -1;
  }
  /* Obtain service_id from public key. */
  crypto_pk_get_digest(desc->pk, service_id);
  /* Calculate current time-period. */
  time_period = get_time_period(now, period, service_id);
  /* Determine how many seconds the descriptor will be valid. */
  seconds_valid = period * REND_TIME_PERIOD_V2_DESC_VALIDITY +
                  get_seconds_valid(now, service_id);
  /* Assemble, possibly encrypt, and encode introduction points. */
  if (smartlist_len(desc->intro_nodes) > 0 &&
      rend_encode_v2_intro_points(&ipos_base64, desc, descriptor_cookie) < 0) {
    log_warn(LD_REND, "Encoding of introduction points did not succeed.");
    return -1;
  }
  /* Encode REND_NUMBER_OF_NON_CONSECUTIVE_REPLICAS descriptors. */
  for (k = 0; k < REND_NUMBER_OF_NON_CONSECUTIVE_REPLICAS; k++) {
    char secret_id_part[DIGEST_LEN];
    char secret_id_part_base32[REND_SECRET_ID_PART_LEN_BASE32 + 1];
    char desc_id_base32[REND_DESC_ID_V2_LEN_BASE32 + 1];
    char *permanent_key = NULL;
    size_t permanent_key_len;
    char published[ISO_TIME_LEN+1];
    int i;
    char protocol_versions_string[16]; /* max len: "0,1,2,3,4,5,6,7\0" */
    size_t protocol_versions_written;
    size_t desc_len;
    char *desc_str = NULL;
    int result = 0;
    size_t written = 0;
    char desc_digest[DIGEST_LEN];
    rend_encoded_v2_service_descriptor_t *enc =
      tor_malloc_zero(sizeof(rend_encoded_v2_service_descriptor_t));
    /* Calculate secret-id-part = h(time-period + cookie + replica). */
    get_secret_id_part_bytes(secret_id_part, time_period, descriptor_cookie,
                             k);
    base32_encode(secret_id_part_base32, sizeof(secret_id_part_base32),
                  secret_id_part, DIGEST_LEN);
    /* Calculate descriptor ID. */
    rend_get_descriptor_id_bytes(enc->desc_id, service_id, secret_id_part);
    base32_encode(desc_id_base32, sizeof(desc_id_base32),
                  enc->desc_id, DIGEST_LEN);
    /* PEM-encode the public key */
    if (crypto_pk_write_public_key_to_string(desc->pk, &permanent_key,
                                             &permanent_key_len) < 0) {
      log_warn(LD_BUG, "Could not write public key to string.");
      rend_encoded_v2_service_descriptor_free(enc);
      goto err;
    }
    /* Encode timestamp. */
    format_iso_time(published, desc->timestamp);
    /* Write protocol-versions bitmask to comma-separated value string. */
    protocol_versions_written = 0;
    for (i = 0; i < 8; i++) {
      if (desc->protocols & 1 << i) {
        tor_snprintf(protocol_versions_string + protocol_versions_written,
                     16 - protocol_versions_written, "%d,", i);
        protocol_versions_written += 2;
      }
    }
    if (protocol_versions_written)
      protocol_versions_string[protocol_versions_written - 1] = '\0';
    else
      protocol_versions_string[0]= '\0';
    /* Assemble complete descriptor. */
    desc_len = 2000 + smartlist_len(desc->intro_nodes) * 1000; /* far too long,
                                                                  but okay.*/
    enc->desc_str = desc_str = tor_malloc_zero(desc_len);
    result = tor_snprintf(desc_str, desc_len,
             "rendezvous-service-descriptor %s\n"
             "version 2\n"
             "permanent-key\n%s"
             "secret-id-part %s\n"
             "publication-time %s\n"
             "protocol-versions %s\n",
        desc_id_base32,
        permanent_key,
        secret_id_part_base32,
        published,
        protocol_versions_string);
    tor_free(permanent_key);
    if (result < 0) {
      log_warn(LD_BUG, "Descriptor ran out of room.");
      rend_encoded_v2_service_descriptor_free(enc);
      goto err;
    }