tor/src/or/rendcommon.c

/* 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);
  }
  if (desc->successful_uploads) {
    SMARTLIST_FOREACH(desc->successful_uploads, char *, c, tor_free(c););
    smartlist_free(desc->successful_uploads);
  }
  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> and write the result to a
 * newly allocated string pointed to by <b>encoded</b>. Return 0 for
 * success, -1 otherwise. */
static int
rend_encode_v2_intro_points(char **encoded, rend_service_descriptor_t *desc)
{
  size_t unenc_len;
  char *unenc = NULL;
  size_t unenc_written = 0;
  int i;
  int r = -1;
  /* Assemble unencrypted list of introduction points. */
  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;
  *encoded = unenc;
  r = 0;
 done:
  if (r<0)
    tor_free(unenc);
  return r;
}

/** Encrypt the encoded introduction points in <b>encoded</b> using
 * authorization type  'basic' with <b>client_cookies</b> and write the
 * result to a newly allocated string pointed to by <b>encrypted_out</b> of
 * length <b>encrypted_len_out</b>. Return 0 for success, -1 otherwise. */
static int
rend_encrypt_v2_intro_points_basic(char **encrypted_out,
                                   size_t *encrypted_len_out,
                                   const char *encoded,
                                   smartlist_t *client_cookies)
{
  int r = -1, i, pos, enclen, client_blocks;
  size_t len, client_entries_len;
  char *enc = NULL, iv[CIPHER_IV_LEN], *client_part = NULL,
       session_key[CIPHER_KEY_LEN];
  smartlist_t *encrypted_session_keys = NULL;
  crypto_digest_env_t *digest;
  crypto_cipher_env_t *cipher;
  tor_assert(encoded);
  tor_assert(client_cookies && smartlist_len(client_cookies) > 0);

  /* Generate session key. */
  if (crypto_rand(session_key, CIPHER_KEY_LEN) < 0) {
    log_warn(LD_REND, "Unable to generate random session key to encrypt "
                      "introduction point string.");
    goto done;
  }

  /* Determine length of encrypted introduction points including session
   * keys. */
  client_blocks = 1 + ((smartlist_len(client_cookies) - 1) /
                       REND_BASIC_AUTH_CLIENT_MULTIPLE);
  client_entries_len = client_blocks * REND_BASIC_AUTH_CLIENT_MULTIPLE *
                       REND_BASIC_AUTH_CLIENT_ENTRY_LEN;
  len = 2 + client_entries_len + CIPHER_IV_LEN + strlen(encoded);
  if (client_blocks >= 256) {
    log_warn(LD_REND, "Too many clients in introduction point string.");
    goto done;
  }
  enc = tor_malloc_zero(len);
  enc[0] = 0x01; /* type of authorization. */
  enc[1] = (uint8_t)client_blocks;

  /* Encrypt with random session key. */
  cipher = crypto_create_init_cipher(session_key, 1);
  enclen = crypto_cipher_encrypt_with_iv(cipher,
      enc + 2 + client_entries_len,
      CIPHER_IV_LEN + strlen(encoded), encoded, strlen(encoded));
  crypto_free_cipher_env(cipher);
  if (enclen < 0) {
    log_warn(LD_REND, "Could not encrypt introduction point string.");
    goto done;
  }
  memcpy(iv, enc + 2 + client_entries_len, CIPHER_IV_LEN);

  /* Encrypt session key for cookies, determine client IDs, and put both
   * in a smartlist. */
  encrypted_session_keys = smartlist_create();
  SMARTLIST_FOREACH_BEGIN(client_cookies, const char *, cookie) {
    client_part = tor_malloc_zero(REND_BASIC_AUTH_CLIENT_ENTRY_LEN);
    /* Encrypt session key. */
    cipher = crypto_create_init_cipher(cookie, 1);
    if (crypto_cipher_encrypt(cipher, client_part +
                                  REND_BASIC_AUTH_CLIENT_ID_LEN,
                              session_key, CIPHER_KEY_LEN) < 0) {
      log_warn(LD_REND, "Could not encrypt session key for client.");
      crypto_free_cipher_env(cipher);
      tor_free(client_part);
      goto done;
    }
    crypto_free_cipher_env(cipher);

    /* Determine client ID. */
    digest = crypto_new_digest_env();
    crypto_digest_add_bytes(digest, cookie, REND_DESC_COOKIE_LEN);
    crypto_digest_add_bytes(digest, iv, CIPHER_IV_LEN);
    crypto_digest_get_digest(digest, client_part,
                             REND_BASIC_AUTH_CLIENT_ID_LEN);
    crypto_free_digest_env(digest);

    /* Put both together. */
    smartlist_add(encrypted_session_keys, client_part);
  } SMARTLIST_FOREACH_END(cookie);

  /* Add some fake client IDs and encrypted session keys. */
  for (i = (smartlist_len(client_cookies) - 1) %
           REND_BASIC_AUTH_CLIENT_MULTIPLE;
       i < REND_BASIC_AUTH_CLIENT_MULTIPLE - 1; i++) {
    client_part = tor_malloc_zero(REND_BASIC_AUTH_CLIENT_ENTRY_LEN);
    if (crypto_rand(client_part, REND_BASIC_AUTH_CLIENT_ENTRY_LEN) < 0) {
      log_warn(LD_REND, "Unable to generate fake client entry.");
      tor_free(client_part);
      goto done;
    }
    smartlist_add(encrypted_session_keys, client_part);
  }
  /* Sort smartlist and put elements in result in order. */
  smartlist_sort_digests(encrypted_session_keys);
  pos = 2;
  SMARTLIST_FOREACH(encrypted_session_keys, const char *, entry, {
    memcpy(enc + pos, entry, REND_BASIC_AUTH_CLIENT_ENTRY_LEN);
    pos += REND_BASIC_AUTH_CLIENT_ENTRY_LEN;
  });
  *encrypted_out = enc;
  *encrypted_len_out = len;
  enc = NULL; /* prevent free. */
  r = 0;
 done:
  tor_free(enc);
  if (encrypted_session_keys) {
    SMARTLIST_FOREACH(encrypted_session_keys, char *, d, tor_free(d););
    smartlist_free(encrypted_session_keys);
  }
  return r;
}

/** Encrypt the encoded introduction points in <b>encoded</b> using
 * authorization type 'stealth' with <b>descriptor_cookie</b> of length
 * REND_DESC_COOKIE_LEN and write the result to a newly allocated string
 * pointed to by <b>encrypted_out</b> of length <b>encrypted_len_out</b>.
 * Return 0 for success, -1 otherwise. */
static int
rend_encrypt_v2_intro_points_stealth(char **encrypted_out,
                                     size_t *encrypted_len_out,
                                     const char *encoded,
                                     const char *descriptor_cookie)
{
  int r = -1, enclen;
  crypto_cipher_env_t *cipher;
  char *enc;
  tor_assert(encoded);
  tor_assert(descriptor_cookie);

  enc = tor_malloc_zero(1 + CIPHER_IV_LEN + strlen(encoded));
  enc[0] = 0x02; /* Auth type */
  cipher = crypto_create_init_cipher(descriptor_cookie, 1);
  enclen = crypto_cipher_encrypt_with_iv(cipher, enc + 1,
                                         CIPHER_IV_LEN+strlen(encoded),
                                         encoded, strlen(encoded));
  crypto_free_cipher_env(cipher);
  if (enclen < 0) {
    log_warn(LD_REND, "Could not encrypt introduction point string.");
    goto done;
  }
  *encrypted_out = enc;
  *encrypted_len_out = enclen;
  enc = NULL; /* prevent free */
  r = 0;
 done:
  tor_free(enc);
  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>service_key</b>, depending on
 * <b>auth_type</b> a <b>descriptor_cookie</b> and a list of
 * <b>client_cookies</b> (which are both <b>NULL</b> if no client
 * authorization is performed), 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,
                           uint8_t period, rend_auth_type_t auth_type,
                           crypto_pk_env_t *client_key,
                           smartlist_t *client_cookies)
{
  char service_id[DIGEST_LEN];
  uint32_t time_period;
  char *ipos_base64 = NULL, *ipos = NULL, *ipos_encrypted = NULL,
       *descriptor_cookie = NULL;
  size_t ipos_len = 0, ipos_encrypted_len = 0;
  int k;
  uint32_t seconds_valid;
  crypto_pk_env_t *service_key = auth_type == REND_STEALTH_AUTH ?
                                 client_key : desc->pk;
  tor_assert(service_key);
  if (auth_type == REND_STEALTH_AUTH) {
    descriptor_cookie = smartlist_get(client_cookies, 0);
    tor_assert(descriptor_cookie);
  }
  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(service_key, 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) {
    if (rend_encode_v2_intro_points(&ipos, desc) < 0) {
      log_warn(LD_REND, "Encoding of introduction points did not succeed.");
      return -1;
    }
    switch (auth_type) {
      case REND_NO_AUTH:
        ipos_len = strlen(ipos);
        break;
      case REND_BASIC_AUTH:
        if (rend_encrypt_v2_intro_points_basic(&ipos_encrypted,
                                               &ipos_encrypted_len, ipos,
                                               client_cookies) < 0) {
          log_warn(LD_REND, "Encrypting of introduction points did not "
                            "succeed.");
          tor_free(ipos);
          return -1;
        }
        tor_free(ipos);
        ipos = ipos_encrypted;
        ipos_len = ipos_encrypted_len;
        break;
      case REND_STEALTH_AUTH:
        if (rend_encrypt_v2_intro_points_stealth(&ipos_encrypted,
                                                 &ipos_encrypted_len, ipos,
                                                 descriptor_cookie) < 0) {
          log_warn(LD_REND, "Encrypting of introduction points did not "
                            "succeed.");
          tor_free(ipos);
          return -1;
        }
        tor_free(ipos);
        ipos = ipos_encrypted;
        ipos_len = ipos_encrypted_len;
        break;
      default:
        log_warn(LD_REND|LD_BUG, "Unrecognized authorization type %d",
                 (int)auth_type);
        tor_free(ipos);
        return -1;
    }
    /* Base64-encode introduction points. */
    ipos_base64 = tor_malloc_zero(ipos_len * 2);
    if (base64_encode(ipos_base64, ipos_len * 2, ipos, ipos_len)<0) {
      log_warn(LD_REND, "Could not encode introduction point string to "
               "base64. length=%d", (int)ipos_len);
      tor_free(ipos_base64);
      tor_free(ipos);
      return -1;
    }
    tor_free(ipos);
  }
  /* 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(service_key, &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;
    }
    written = result;
    /* Add introduction points. */
    if (ipos_base64) {
      result = tor_snprintf(desc_str + written, desc_len - written,
                            "introduction-points\n"
                            "-----BEGIN MESSAGE-----\n%s"
                            "-----END MESSAGE-----\n",
                            ipos_base64);
      if (result < 0) {
        log_warn(LD_BUG, "could not write introduction points.");
        rend_encoded_v2_service_descriptor_free(enc);
        goto err;
      }
      written += result;
    }
    /* Add signature. */
    strlcpy(desc_str + written, "signature\n", desc_len - written);
    written += strlen(desc_str + written);
    if (crypto_digest(desc_digest, desc_str, written) < 0) {
      log_warn(LD_BUG, "could not create digest.");
      rend_encoded_v2_service_descriptor_free(enc);
      goto err;
    }
    if (router_append_dirobj_signature(desc_str + written,
                                       desc_len - written,
                                       desc_digest, service_key) < 0) {
      log_warn(LD_BUG, "Couldn't sign desc.");
      rend_encoded_v2_service_descriptor_free(enc);
      goto err;
    }
    written += strlen(desc_str+written);
    if (written+2 > desc_len) {
        log_warn(LD_BUG, "Could not finish desc.");
        rend_encoded_v2_service_descriptor_free(enc);
        goto err;
    }
    desc_str[written++] = '\n';
    desc_str[written++] = 0;
    /* Check if we can parse our own descriptor. */
    if (!rend_desc_v2_is_parsable(enc)) {
      log_warn(LD_BUG, "Could not parse my own descriptor: %s", desc_str);
      rend_encoded_v2_service_descriptor_free(enc);
      goto err;
    }
    smartlist_add(descs_out, enc);
  }

  log_info(LD_REND, "Successfully encoded a v2 descriptor and "
                    "confirmed that it is parsable.");
  goto done;

 err:
  SMARTLIST_FOREACH(descs_out, rend_encoded_v2_service_descriptor_t *, d,
                    rend_encoded_v2_service_descriptor_free(d););
  smartlist_clear(descs_out);
  seconds_valid = -1;

 done:
  tor_free(ipos_base64);
  return seconds_valid;
}

/** Encode a service descriptor for <b>desc</b>, and sign it with
 * <b>key</b>. Store the descriptor in *<b>str_out</b>, and set
 * *<b>len_out</b> to its length.
 */
int
rend_encode_service_descriptor(rend_service_descriptor_t *desc,
                               crypto_pk_env_t *key,
                               char **str_out, size_t *len_out)
{
  char *cp;
  char *end;
  int i, r;
  size_t asn1len;
  size_t buflen =
         PK_BYTES*2*(smartlist_len(desc->intro_nodes)+2);/*Too long, but ok*/
  cp = *str_out = tor_malloc(buflen);
  end = cp + PK_BYTES*2*(smartlist_len(desc->intro_nodes)+1);
  r = crypto_pk_asn1_encode(desc->pk, cp+2, end-(cp+2));
  if (r < 0) {
    tor_free(*str_out);
    return -1;
  }
  asn1len = r;
  set_uint16(cp, htons((uint16_t)asn1len));
  cp += 2+asn1len;
  set_uint32(cp, htonl((uint32_t)desc->timestamp));
  cp += 4;
  set_uint16(cp, htons((uint16_t)smartlist_len(desc->intro_nodes)));
  cp += 2;
  for (i=0; i < smartlist_len(desc->intro_nodes); ++i) {
    rend_intro_point_t *intro = smartlist_get(desc->intro_nodes, i);
    char ipoint[HEX_DIGEST_LEN+2];
    ipoint[0] = '$';
    base16_encode(ipoint+1, HEX_DIGEST_LEN+1,
                  intro->extend_info->identity_digest,
                  DIGEST_LEN);
    tor_assert(buflen + *str_out >= cp); /* XXX021 This assert is a kludge. */
    strlcpy(cp, ipoint, buflen-(cp-*str_out));
    cp += strlen(ipoint)+1;
  }
  note_crypto_pk_op(REND_SERVER);
  r = crypto_pk_private_sign_digest(key, cp, *str_out, cp-*str_out);
  if (r<0) {
    tor_free(*str_out);
    return -1;
  }
  cp += r;
  *len_out = (size_t)(cp-*str_out);
  return 0;
}

/** Parse a service descriptor at <b>str</b> (<b>len</b> bytes).  On
 * success, return a newly alloced service_descriptor_t.  On failure,
 * return NULL.
 */
rend_service_descriptor_t *
rend_parse_service_descriptor(const char *str, size_t len)
{
  rend_service_descriptor_t *result = NULL;
  int i, n_intro_points;
  size_t keylen, asn1len;
  const char *end, *cp, *eos;
  rend_intro_point_t *intro;

  result = tor_malloc_zero(sizeof(rend_service_descriptor_t));
  cp = str;
  end = str+len;
  if (end-cp<2) goto truncated;
  result->version = 0;
  if (end-cp < 2) goto truncated;
  asn1len = ntohs(get_uint16(cp));
  cp += 2;
  if ((size_t)(end-cp) < asn1len) goto truncated;
  result->pk = crypto_pk_asn1_decode(cp, asn1len);
  if (!result->pk) goto truncated;
  cp += asn1len;
  if (end-cp < 4) goto truncated;
  result->timestamp = (time_t) ntohl(get_uint32(cp));
  cp += 4;
  result->protocols = 1<<2; /* always use intro format 2 */
  if (end-cp < 2) goto truncated;
  n_intro_points = ntohs(get_uint16(cp));
  cp += 2;

  result->intro_nodes = smartlist_create();
  for (i=0;i<n_intro_points;++i) {
    if (end-cp < 2) goto truncated;
    eos = (const char *)memchr(cp,'\0',end-cp);
    if (!eos) goto truncated;
    /* Write nickname to extend info, but postpone the lookup whether
     * we know that router. It's not part of the parsing process. */
    intro = tor_malloc_zero(sizeof(rend_intro_point_t));
    intro->extend_info = tor_malloc_zero(sizeof(extend_info_t));
    strlcpy(intro->extend_info->nickname, cp,
            sizeof(intro->extend_info->nickname));
    smartlist_add(result->intro_nodes, intro);
    cp = eos+1;
  }
  keylen = crypto_pk_keysize(result->pk);
  tor_assert(end-cp >= 0);
  if ((size_t)(end-cp) < keylen) goto truncated;
  if ((size_t)(end-cp) > keylen) {
    log_warn(LD_PROTOCOL,
             "Signature is %d bytes too long on service descriptor.",
             (int)((size_t)(end-cp) - keylen));
    goto error;
  }
  note_crypto_pk_op(REND_CLIENT);
  if (crypto_pk_public_checksig_digest(result->pk,
                                       (char*)str,cp-str, /* data */
                                       (char*)cp,end-cp  /* signature*/
                                       )<0) {
    log_warn(LD_PROTOCOL, "Bad signature on service descriptor.");
    goto error;
  }

  return result;
 truncated:
  log_warn(LD_PROTOCOL, "Truncated service descriptor.");
 error:
  rend_service_descriptor_free(result);
  return NULL;
}

/** Sets <b>out</b> to the first 10 bytes of the digest of <b>pk</b>,
 * base32 encoded.  NUL-terminates out.  (We use this string to
 * identify services in directory requests and .onion URLs.)
 */
int
rend_get_service_id(crypto_pk_env_t *pk, char *out)
{
  char buf[DIGEST_LEN];
  tor_assert(pk);
  if (crypto_pk_get_digest(pk, buf) < 0)
    return -1;
  base32_encode(out, REND_SERVICE_ID_LEN_BASE32+1, buf, REND_SERVICE_ID_LEN);
  return 0;
}

/* ==== Rendezvous service descriptor cache. */

/** How old do we let hidden service descriptors get before discarding
 * them as too old? */
#define REND_CACHE_MAX_AGE (2*24*60*60)
/** How wrong do we assume our clock may be when checking whether hidden
 * services are too old or too new? */
#define REND_CACHE_MAX_SKEW (24*60*60)

/** Map from service id (as generated by rend_get_service_id) to
 * rend_cache_entry_t. */
static strmap_t *rend_cache = NULL;

/** Map from descriptor id to rend_cache_entry_t; only for hidden service
 * directories. */
static digestmap_t *rend_cache_v2_dir = NULL;

/** Initializes the service descriptor cache.
 */
void
rend_cache_init(void)
{
  rend_cache = strmap_new();
  rend_cache_v2_dir = digestmap_new();
}

/** Helper: free storage held by a single service descriptor cache entry. */
static void
_rend_cache_entry_free(void *p)
{
  rend_cache_entry_t *e = p;
  rend_service_descriptor_free(e->parsed);
  tor_free(e->desc);
  tor_free(e);
}

/** Free all storage held by the service descriptor cache. */
void
rend_cache_free_all(void)
{
  if (rend_cache)
    strmap_free(rend_cache, _rend_cache_entry_free);
  if (rend_cache_v2_dir)
    digestmap_free(rend_cache_v2_dir, _rend_cache_entry_free);
  rend_cache = NULL;
  rend_cache_v2_dir = NULL;
}

/** Removes all old entries from the service descriptor cache.
 */
void
rend_cache_clean(void)
{
  strmap_iter_t *iter;
  const char *key;
  void *val;
  rend_cache_entry_t *ent;
  time_t cutoff;
  cutoff = time(NULL) - REND_CACHE_MAX_AGE - REND_CACHE_MAX_SKEW;
  for (iter = strmap_iter_init(rend_cache); !strmap_iter_done(iter); ) {
    strmap_iter_get(iter, &key, &val);
    ent = (rend_cache_entry_t*)val;
    if (ent->parsed->timestamp < cutoff) {
      iter = strmap_iter_next_rmv(rend_cache, iter);
      _rend_cache_entry_free(ent);
    } else {
      iter = strmap_iter_next(rend_cache, iter);
    }
  }
}

/** Remove all old v2 descriptors and those for which this hidden service
 * directory is not responsible for any more. */
void
rend_cache_clean_v2_descs_as_dir(void)
{
  digestmap_iter_t *iter;
  time_t cutoff = time(NULL) - REND_CACHE_MAX_AGE - REND_CACHE_MAX_SKEW;
  for (iter = digestmap_iter_init(rend_cache_v2_dir);
       !digestmap_iter_done(iter); ) {
    const char *key;
    void *val;
    rend_cache_entry_t *ent;
    digestmap_iter_get(iter, &key, &val);
    ent = val;
    if (ent->parsed->timestamp < cutoff ||
        !hid_serv_responsible_for_desc_id(key)) {
      char key_base32[REND_DESC_ID_V2_LEN_BASE32 + 1];
      base32_encode(key_base32, sizeof(key_base32), key, DIGEST_LEN);
      log_info(LD_REND, "Removing descriptor with ID '%s' from cache",
               safe_str(key_base32));
      iter = digestmap_iter_next_rmv(rend_cache_v2_dir, iter);
      _rend_cache_entry_free(ent);
    } else {
      iter = digestmap_iter_next(rend_cache_v2_dir, iter);
    }
  }
}

/** Determines whether <b>a</b> is in the interval of <b>b</b> (excluded) and
 * <b>c</b> (included) in a circular digest ring; returns 1 if this is the
 * case, and 0 otherwise.
 */
int
rend_id_is_in_interval(const char *a, const char *b, const char *c)
{
  int a_b, b_c, c_a;
  tor_assert(a);
  tor_assert(b);
  tor_assert(c);

  /* There are five cases in which a is outside the interval ]b,c]: */
  a_b = memcmp(a,b,DIGEST_LEN);
  if (a_b == 0)
    return 0; /* 1. a == b (b is excluded) */
  b_c = memcmp(b,c,DIGEST_LEN);
  if (b_c == 0)
    return 0; /* 2. b == c (interval is empty) */
  else if (a_b <= 0 && b_c < 0)
    return 0; /* 3. a b c */
  c_a = memcmp(c,a,DIGEST_LEN);
  if (c_a < 0 && a_b <= 0)
    return 0; /* 4. c a b */
  else if (b_c < 0 && c_a < 0)
    return 0; /* 5. b c a */

  /* In the other cases (a c b; b a c; c b a), a is inside the interval. */
  return 1;
}

/** Return true iff <b>query</b> is a syntactically valid service ID (as
 * generated by rend_get_service_id).  */
int
rend_valid_service_id(const char *query)
{
  if (strlen(query) != REND_SERVICE_ID_LEN_BASE32)
    return 0;

  if (strspn(query, BASE32_CHARS) != REND_SERVICE_ID_LEN_BASE32)
    return 0;

  return 1;
}

/** If we have a cached rend_cache_entry_t for the service ID <b>query</b>
 * with <b>version</b>, set *<b>e</b> to that entry and return 1.
 * Else return 0. If <b>version</b> is nonnegative, only return an entry
 * in that descriptor format version. Otherwise (if <b>version</b> is
 * negative), return the most recent format we have.
 */
int
rend_cache_lookup_entry(const char *query, int version, rend_cache_entry_t **e)
{
  char key[REND_SERVICE_ID_LEN_BASE32+2]; /* <version><query>\0 */
  tor_assert(rend_cache);
  if (!rend_valid_service_id(query))
    return -1;
  *e = NULL;
  if (version != 0) {
    tor_snprintf(key, sizeof(key), "2%s", query);
    *e = strmap_get_lc(rend_cache, key);
  }
  if (!*e && version != 2) {
    tor_snprintf(key, sizeof(key), "0%s", query);
    *e = strmap_get_lc(rend_cache, key);
  }
  if (!*e)
    return 0;
  return 1;
}

/** <b>query</b> is a base-32'ed service id. If it's malformed, return -1.
 * Else look it up.
 *   - If it is found, point *desc to it, and write its length into
 *     *desc_len, and return 1.
 *   - If it is not found, return 0.
 * Note: calls to rend_cache_clean or rend_cache_store may invalidate
 * *desc.
 */
int
rend_cache_lookup_desc(const char *query, int version, const char **desc,
                       size_t *desc_len)
{
  rend_cache_entry_t *e;
  int r;
  r = rend_cache_lookup_entry(query,version,&e);
  if (r <= 0) return r;
  *desc = e->desc;
  *desc_len = e->len;
  return 1;
}

/** Lookup the v2 service descriptor with base32-encoded <b>desc_id</b> and
 * copy the pointer to it to *<b>desc</b>.  Return 1 on success, 0 on
 * well-formed-but-not-found, and -1 on failure.
 */
int
rend_cache_lookup_v2_desc_as_dir(const char *desc_id, const char **desc)
{
  rend_cache_entry_t *e;
  char desc_id_digest[DIGEST_LEN];
  tor_assert(rend_cache_v2_dir);
  if (base32_decode(desc_id_digest, DIGEST_LEN,
                    desc_id, REND_DESC_ID_V2_LEN_BASE32) < 0) {
    log_warn(LD_REND, "Descriptor ID contains illegal characters: %s",
             safe_str(desc_id));
    return -1;
  }
  /* Determine if we are responsible. */
  if (hid_serv_responsible_for_desc_id(desc_id_digest) < 0) {
    log_info(LD_REND, "Could not answer fetch request for v2 descriptor; "
                      "either we are no hidden service directory, or we are "
                      "not responsible for the requested ID.");
    return -1;
  }
  /* Lookup descriptor and return. */
  e = digestmap_get(rend_cache_v2_dir, desc_id_digest);
  if (e) {
    *desc = e->desc;
    return 1;
  }
  return 0;
}

/** Parse *desc, calculate its service id, and store it in the cache.
 * If we have a newer v0 descriptor with the same ID, ignore this one.
 * If we have an older descriptor with the same ID, replace it.
 * If we are acting as client due to the published flag and have any v2
 * descriptor with the same ID, reject this one in order to not get
 * confused with having both versions for the same service.
 *
 * Return -2 if it's malformed or otherwise rejected; return -1 if we
 * already have a v2 descriptor here; return 0 if it's the same or older
 * than one we've already got; return 1 if it's novel.
 *
 * The published flag tells us if we store the descriptor
 * in our role as directory (1) or if we cache it as client (0).
 */
int
rend_cache_store(const char *desc, size_t desc_len, int published)
{
  rend_cache_entry_t *e;
  rend_service_descriptor_t *parsed;
  char query[REND_SERVICE_ID_LEN_BASE32+1];
  char key[REND_SERVICE_ID_LEN_BASE32+2]; /* 0<query>\0 */
  time_t now;
  or_options_t *options = get_options();
  tor_assert(rend_cache);
  parsed = rend_parse_service_descriptor(desc,desc_len);
  if (!parsed) {
    log_warn(LD_PROTOCOL,"Couldn't parse service descriptor.");
    return -2;
  }
  if (rend_get_service_id(parsed->pk, query)<0) {
    log_warn(LD_BUG,"Couldn't compute service ID.");
    rend_service_descriptor_free(parsed);
    return -2;
  }
  now = time(NULL);
  if (parsed->timestamp < now-REND_CACHE_MAX_AGE-REND_CACHE_MAX_SKEW) {
    log_fn(LOG_PROTOCOL_WARN, LD_REND,
           "Service descriptor %s is too old.", safe_str(query));
    rend_service_descriptor_free(parsed);
    return -2;
  }
  if (parsed->timestamp > now+REND_CACHE_MAX_SKEW) {
    log_fn(LOG_PROTOCOL_WARN, LD_REND,
           "Service descriptor %s is too far in the future.", safe_str(query));
    rend_service_descriptor_free(parsed);
    return -2;
  }
  /* Do we have a v2 descriptor and fetched this descriptor as a client? */
  tor_snprintf(key, sizeof(key), "2%s", query);
  if (!published && strmap_get_lc(rend_cache, key)) {
    log_info(LD_REND, "We already have a v2 descriptor for service %s.",
             safe_str(query));
    rend_service_descriptor_free(parsed);
    return -1;
  }
  /* report novel publication to statistics */
  if (published && options->HSAuthorityRecordStats) {
    hs_usage_note_publish_total(query, now);
  }
  tor_snprintf(key, sizeof(key), "0%s", query);
  e = (rend_cache_entry_t*) strmap_get_lc(rend_cache, key);
  if (e && e->parsed->timestamp > parsed->timestamp) {
    log_info(LD_REND,"We already have a newer service descriptor %s with the "
             "same ID and version.", safe_str(query));
    rend_service_descriptor_free(parsed);
    return 0;
  }
  if (e && e->len == desc_len && !memcmp(desc,e->desc,desc_len)) {
    log_info(LD_REND,"We already have this service descriptor %s.",
             safe_str(query));
    e->received = time(NULL);
    rend_service_descriptor_free(parsed);
    return 0;
  }
  if (!e) {
    e = tor_malloc_zero(sizeof(rend_cache_entry_t));
    strmap_set_lc(rend_cache, key, e);
    /* report novel publication to statistics */
    if (published && options->HSAuthorityRecordStats) {
      hs_usage_note_publish_novel(query, now);
    }
  } else {
    rend_service_descriptor_free(e->parsed);
    tor_free(e->desc);
  }
  e->received = time(NULL);
  e->parsed = parsed;
  e->len = desc_len;
  e->desc = tor_malloc(desc_len);
  memcpy(e->desc, desc, desc_len);

  log_debug(LD_REND,"Successfully stored rend desc '%s', len %d.",
            safe_str(query), (int)desc_len);
  return 1;
}

/** Parse the v2 service descriptor(s) in <b>desc</b> and store it/them to the
 * local rend cache. Don't attempt to decrypt the included list of introduction
 * points (as we don't have a descriptor cookie for it).
 *
 * If we have a newer descriptor with the same ID, ignore this one.
 * If we have an older descriptor with the same ID, replace it.
 * Return -2 if we are not acting as hidden service directory;
 * return -1 if the descriptor(s) were not parsable; return 0 if all
 * descriptors are the same or older than those we've already got;
 * return a positive number for the number of novel stored descriptors.
 */
int
rend_cache_store_v2_desc_as_dir(const char *desc)
{
  rend_service_descriptor_t *parsed;
  char desc_id[DIGEST_LEN];
  char *intro_content;
  size_t intro_size;
  size_t encoded_size;
  char desc_id_base32[REND_DESC_ID_V2_LEN_BASE32 + 1];
  int number_parsed = 0, number_stored = 0;
  const char *current_desc = desc;
  const char *next_desc;
  rend_cache_entry_t *e;
  time_t now = time(NULL);
  tor_assert(rend_cache_v2_dir);
  tor_assert(desc);
  if (!hid_serv_acting_as_directory()) {
    /* Cannot store descs, because we are (currently) not acting as
     * hidden service directory. */
    log_info(LD_REND, "Cannot store descs: Not acting as hs dir");
    return -2;
  }
  while (rend_parse_v2_service_descriptor(&parsed, desc_id, &intro_content,
                                          &intro_size, &encoded_size,
                                          &next_desc, current_desc) >= 0) {
    number_parsed++;
    /* We don't care about the introduction points. */
    tor_free(intro_content);
    /* For pretty log statements. */
    base32_encode(desc_id_base32, sizeof(desc_id_base32),
                  desc_id, DIGEST_LEN);
    /* Is desc ID in the range that we are (directly or indirectly) responsible
     * for? */
    if (!hid_serv_responsible_for_desc_id(desc_id)) {
      log_info(LD_REND, "Service descriptor with desc ID %s is not in "
                        "interval that we are responsible for.",
               safe_str(desc_id_base32));
      goto skip;
    }
    /* Is descriptor too old? */
    if (parsed->timestamp < now - REND_CACHE_MAX_AGE-REND_CACHE_MAX_SKEW) {
      log_info(LD_REND, "Service descriptor with desc ID %s is too old.",
               safe_str(desc_id_base32));
      goto skip;
    }
    /* Is descriptor too far in the future? */
    if (parsed->timestamp > now + REND_CACHE_MAX_SKEW) {
      log_info(LD_REND, "Service descriptor with desc ID %s is too far in the "
                        "future.",
               safe_str(desc_id_base32));
      goto skip;
    }
    /* Do we already have a newer descriptor? */
    e = digestmap_get(rend_cache_v2_dir, desc_id);
    if (e && e->parsed->timestamp > parsed->timestamp) {
      log_info(LD_REND, "We already have a newer service descriptor with the "
                        "same desc ID %s and version.",
               safe_str(desc_id_base32));
      goto skip;
    }
    /* Do we already have this descriptor? */
    if (e && !strcmp(desc, e->desc)) {
      log_info(LD_REND, "We already have this service descriptor with desc "
                        "ID %s.", safe_str(desc_id_base32));
      e->received = time(NULL);
      goto skip;
    }
    /* Store received descriptor. */
    if (!e) {
      e = tor_malloc_zero(sizeof(rend_cache_entry_t));
      digestmap_set(rend_cache_v2_dir, desc_id, e);
    } else {
      rend_service_descriptor_free(e->parsed);
      tor_free(e->desc);
    }
    e->received = time(NULL);
    e->parsed = parsed;
    e->desc = tor_strndup(current_desc, encoded_size);
    e->len = encoded_size;
    log_info(LD_REND, "Successfully stored service descriptor with desc ID "
                      "'%s' and len %d.",
             safe_str(desc_id_base32), (int)encoded_size);
    number_stored++;
    goto advance;
  skip:
    rend_service_descriptor_free(parsed);
  advance:
    /* advance to next descriptor, if available. */
    current_desc = next_desc;
    /* check if there is a next descriptor. */
    if (!current_desc ||
        strcmpstart(current_desc, "rendezvous-service-descriptor "))
      break;
  }
  if (!number_parsed) {
    log_info(LD_REND, "Could not parse any descriptor.");
    return -1;
  }
  log_info(LD_REND, "Parsed %d and added %d descriptor%s.",
           number_parsed, number_stored, number_stored != 1 ? "s" : "");
  return number_stored;
}

/** Parse the v2 service descriptor in <b>desc</b>, decrypt the included list
 * of introduction points with <b>descriptor_cookie</b> (which may also be
 * <b>NULL</b> if decryption is not necessary), and store the descriptor to
 * the local cache under its version and service id.
 *
 * If we have a newer v2 descriptor with the same ID, ignore this one.
 * If we have an older descriptor with the same ID, replace it.
 * If we have any v0 descriptor with the same ID, reject this one in order
 * to not get confused with having both versions for the same service.
 * Return -2 if it's malformed or otherwise rejected; return -1 if we
 * already have a v0 descriptor here; return 0 if it's the same or older
 * than one we've already got; return 1 if it's novel.
 */
int
rend_cache_store_v2_desc_as_client(const char *desc,
                                   const rend_data_t *rend_query)
{
  /*XXXX this seems to have a bit of duplicate code with
   * rend_cache_store_v2_desc_as_dir().  Fix that. */
  /* Though having similar elements, both functions were separated on
   * purpose:
   * - dirs don't care about encoded/encrypted introduction points, clients
   *   do.
   * - dirs store descriptors in a separate cache by descriptor ID, whereas
   *   clients store them by service ID; both caches are different data
   *   structures and have different access methods.
   * - dirs store a descriptor only if they are responsible for its ID,
   *   clients do so in every way (because they have requested it before).
   * - dirs can process multiple concatenated descriptors which is required
   *   for replication, whereas clients only accept a single descriptor.
   * Thus, combining both methods would result in a lot of if statements
   * which probably would not improve, but worsen code readability. -KL */
  rend_service_descriptor_t *parsed = NULL;
  char desc_id[DIGEST_LEN];
  char *intro_content = NULL;
  size_t intro_size;
  size_t encoded_size;
  const char *next_desc;
  time_t now = time(NULL);
  char key[REND_SERVICE_ID_LEN_BASE32+2];
  char service_id[REND_SERVICE_ID_LEN_BASE32+1];
  rend_cache_entry_t *e;
  tor_assert(rend_cache);
  tor_assert(desc);
  /* Parse the descriptor. */
  if (rend_parse_v2_service_descriptor(&parsed, desc_id, &intro_content,
                                       &intro_size, &encoded_size,
                                       &next_desc, desc) < 0) {
    if (parsed) rend_service_descriptor_free(parsed);
    tor_free(intro_content);
    log_warn(LD_REND, "Could not parse descriptor.");
    return -2;
  }
  /* Compute service ID from public key. */
  if (rend_get_service_id(parsed->pk, service_id)<0) {
    log_warn(LD_REND, "Couldn't compute service ID.");
    rend_service_descriptor_free(parsed);
    tor_free(intro_content);
    return -2;
  }
  /* Decode/decrypt introduction points. */
  if (intro_content) {
    if (rend_query->auth_type != REND_NO_AUTH &&
        rend_query->descriptor_cookie) {
      char *ipos_decrypted;
      size_t ipos_decrypted_size;
      if (rend_decrypt_introduction_points(&ipos_decrypted,
                                           &ipos_decrypted_size,
                                           rend_query->descriptor_cookie,
                                           intro_content,
                                           intro_size) < 0) {
        log_warn(LD_REND, "Failed to decrypt introduction points. We are "
                 "probably unable to parse the encoded introduction points.");
      } else {
        /* Replace encrypted with decrypted introduction points. */
        log_info(LD_REND, "Successfully decrypted introduction points.");
        tor_free(intro_content);
        intro_content = ipos_decrypted;
        intro_size = ipos_decrypted_size;
      }
    }
    if (rend_parse_introduction_points(parsed, intro_content,
                                       intro_size) <= 0) {
      log_warn(LD_REND, "Failed to parse introduction points. Either the "
               "service has published a corrupt descriptor or you have "
               "provided invalid authorization data.");
      if (parsed)
        rend_service_descriptor_free(parsed);
      tor_free(intro_content);
      return -2;
    }
  } else {
    log_info(LD_REND, "Descriptor does not contain any introduction points.");
    parsed->intro_nodes = smartlist_create();
  }
  /* We don't need the encoded/encrypted introduction points any longer. */
  tor_free(intro_content);
  /* Is descriptor too old? */
  if (parsed->timestamp < now - REND_CACHE_MAX_AGE-REND_CACHE_MAX_SKEW) {
    log_warn(LD_REND, "Service descriptor with service ID %s is too old.",
             safe_str(service_id));
    rend_service_descriptor_free(parsed);
    return -2;
  }
  /* Is descriptor too far in the future? */
  if (parsed->timestamp > now + REND_CACHE_MAX_SKEW) {
    log_warn(LD_REND, "Service descriptor with service ID %s is too far in "
                      "the future.", safe_str(service_id));
    rend_service_descriptor_free(parsed);
    return -2;
  }
  /* Do we have a v0 descriptor? */
  tor_snprintf(key, sizeof(key), "0%s", service_id);
  if (strmap_get_lc(rend_cache, key)) {
    log_info(LD_REND, "We already have a v0 descriptor for service ID %s.",
             safe_str(service_id));
    return -1;
  }
  /* Do we already have a newer descriptor? */
  tor_snprintf(key, sizeof(key), "2%s", service_id);
  e = (rend_cache_entry_t*) strmap_get_lc(rend_cache, key);
  if (e && e->parsed->timestamp > parsed->timestamp) {
    log_info(LD_REND, "We already have a newer service descriptor for "
                      "service ID %s with the same desc ID and version.",
             safe_str(service_id));
    rend_service_descriptor_free(parsed);
    return 0;
  }
  /* Do we already have this descriptor? */
  if (e && !strcmp(desc, e->desc)) {
    log_info(LD_REND,"We already have this service descriptor %s.",
             safe_str(service_id));
    e->received = time(NULL);
    rend_service_descriptor_free(parsed);
    return 0;
  }
  if (!e) {
    e = tor_malloc_zero(sizeof(rend_cache_entry_t));
    strmap_set_lc(rend_cache, key, e);
  } else {
    rend_service_descriptor_free(e->parsed);
    tor_free(e->desc);
  }
  e->received = time(NULL);
  e->parsed = parsed;
  e->desc = tor_malloc_zero(encoded_size + 1);
  strlcpy(e->desc, desc, encoded_size + 1);
  e->len = encoded_size;
  log_debug(LD_REND,"Successfully stored rend desc '%s', len %d.",
            safe_str(service_id), (int)encoded_size);
  return 1;
}

/** Called when we get a rendezvous-related relay cell on circuit
 * <b>circ</b>.  Dispatch on rendezvous relay command. */
void
rend_process_relay_cell(circuit_t *circ, const crypt_path_t *layer_hint,
                        int command, size_t length,
                        const char *payload)
{
  or_circuit_t *or_circ = NULL;
  origin_circuit_t *origin_circ = NULL;
  int r = -2;
  if (CIRCUIT_IS_ORIGIN(circ)) {
    origin_circ = TO_ORIGIN_CIRCUIT(circ);
    if (!layer_hint || layer_hint != origin_circ->cpath->prev) {
      log_fn(LOG_PROTOCOL_WARN, LD_APP,
             "Relay cell (rend purpose %d) from wrong hop on origin circ",
             command);
      origin_circ = NULL;
    }
  } else {
    or_circ = TO_OR_CIRCUIT(circ);
  }

  switch (command) {
    case RELAY_COMMAND_ESTABLISH_INTRO:
      if (or_circ)
        r = rend_mid_establish_intro(or_circ,payload,length);
      break;
    case RELAY_COMMAND_ESTABLISH_RENDEZVOUS:
      if (or_circ)
        r = rend_mid_establish_rendezvous(or_circ,payload,length);
      break;
    case RELAY_COMMAND_INTRODUCE1:
      if (or_circ)
        r = rend_mid_introduce(or_circ,payload,length);
      break;
    case RELAY_COMMAND_INTRODUCE2:
      if (origin_circ)
        r = rend_service_introduce(origin_circ,payload,length);
      break;
    case RELAY_COMMAND_INTRODUCE_ACK:
      if (origin_circ)
        r = rend_client_introduction_acked(origin_circ,payload,length);
      break;
    case RELAY_COMMAND_RENDEZVOUS1:
      if (or_circ)
        r = rend_mid_rendezvous(or_circ,payload,length);
      break;
    case RELAY_COMMAND_RENDEZVOUS2:
      if (origin_circ)
        r = rend_client_receive_rendezvous(origin_circ,payload,length);
      break;
    case RELAY_COMMAND_INTRO_ESTABLISHED:
      if (origin_circ)
        r = rend_service_intro_established(origin_circ,payload,length);
      break;
    case RELAY_COMMAND_RENDEZVOUS_ESTABLISHED:
      if (origin_circ)
        r = rend_client_rendezvous_acked(origin_circ,payload,length);
      break;
    default:
      tor_fragile_assert();
  }

  if (r == -2)
    log_info(LD_PROTOCOL, "Dropping cell (type %d) for wrong circuit type.",
             command);
}

/** Return the number of entries in our rendezvous descriptor cache. */
int
rend_cache_size(void)
{
  return strmap_size(rend_cache);
}

/** Allocate and return a new rend_data_t with the same
 * contents as <b>query</b>. */
rend_data_t *
rend_data_dup(const rend_data_t *data)
{
  tor_assert(data);
  return tor_memdup(data, sizeof(rend_data_t));
}