<?php

# Copyright (c) 2009-2014 Yubico AB
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are
# met:
#
#   * Redistributions of source code must retain the above copyright
#     notice, this list of conditions and the following disclaimer.
#
#   * 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 COPYRIGHT HOLDERS AND CONTRIBUTORS
# "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 COPYRIGHT
# OWNER OR CONTRIBUTORS 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.

require_once 'ykval-common.php';
require_once 'ykval-config.php';
require_once 'ykval-synclib.php';

$apiKey = '';
$ipaddr = $_SERVER['REMOTE_ADDR'];
$allowed = $baseParams['__YKVAL_ALLOWED_SYNC_POOL__'];

header('content-type: text/plain');


$myLog = new Log('ykval-sync');
$myLog->addField('ip', $ipaddr);

if (empty($_SERVER['QUERY_STRING'])) {
  sendResp(S_MISSING_PARAMETER, $myLog, $apiKey);
}

$myLog->log(LOG_INFO, 'Request: ' . $_SERVER['QUERY_STRING']);

$sync = new SyncLib('ykval-sync:synclib');
$sync->addField('ip', $ipaddr);

if (! $sync->isConnected()) {
  sendResp(S_BACKEND_ERROR, $myLog, $apiKey);
}

#
# Verify that request comes from valid server
#
$myLog->log(LOG_DEBUG, 'Received request from ' . $ipaddr);

if (in_array($ipaddr, $allowed, TRUE) === FALSE) {
  $myLog->log(LOG_NOTICE, 'Operation not allowed from IP ' . $ipaddr);
  $myLog->log(LOG_DEBUG, 'Remote IP ' . $ipaddr . ' not listed in allowed sync pool : ' . implode(', ', $allowed));
  sendResp(S_OPERATION_NOT_ALLOWED, $myLog, $apiKey);
}

#
# Define requirements on protocol
#
$syncParams = array(
  'modified' => NULL,
  'otp' => NULL,
  'nonce' => NULL,
  'yk_publicname' => NULL,
  'yk_counter' => NULL,
  'yk_use' => NULL,
  'yk_high' => NULL,
  'yk_low' => NULL
);

#
# Extract values from HTTP request
#
$tmp_log = "Received ";
foreach ($syncParams as $param=>$value) {
  $value = getHttpVal($param, NULL);
  if ($value==NULL) {
    $myLog->log(LOG_NOTICE, "Received request with parameter[s] (" . $param . ") missing value");
    sendResp(S_MISSING_PARAMETER, $myLog, $apiKey);
  }
  $syncParams[$param]=$value;
  $tmp_log .= "$param=$value ";
}
$myLog->log(LOG_INFO, $tmp_log);

#
# At this point we should have the otp so let's add it to the logging module
#
$myLog->addField('otp', $syncParams['otp']);
$sync->addField('otp', $syncParams['otp']);

#
# Verify correctness of input parameters
#
foreach (array('modified','yk_counter', 'yk_use', 'yk_high', 'yk_low') as $param)
{
  // -1 is valid except for modified
  if ($param !== 'modified' && $syncParams[$param] === '-1')
    continue;

  // [0-9]+
  if ($syncParams[$param] !== '' && ctype_digit($syncParams[$param]))
    continue;

  $myLog->log(LOG_NOTICE, 'Input parameters ' . $param . ' not correct');
  sendResp(S_MISSING_PARAMETER, $myLog, $apiKey);
}

#
# Get local counter data
#
$yk_publicname = $syncParams['yk_publicname'];
$localParams = $sync->getLocalParams($yk_publicname);
if (!$localParams) {
  $myLog->log(LOG_NOTICE, 'Invalid Yubikey ' . $yk_publicname);
  sendResp(S_BACKEND_ERROR, $myLog, $apiKey);
}

/* Conditional update local database */
$sync->updateDbCounters($syncParams);

$myLog->log(LOG_DEBUG, 'Local params ', $localParams);
$myLog->log(LOG_DEBUG, 'Sync request params ', $syncParams);

/**
 * Compare sync and local counters and generate warnings according to
 *	https://developers.yubico.com/yubikey-val/doc/ServerReplicationProtocol.html
 */

if ($sync->countersHigherThan($localParams, $syncParams)) {
  $myLog->log(LOG_WARNING, 'Remote server out of sync.');
}

if ($sync->countersEqual($localParams, $syncParams)) {

  if ($syncParams['modified']==$localParams['modified'] &&
      $syncParams['nonce']==$localParams['nonce']) {
    /* This is not an error. When the remote server received an OTP to verify, it would
     * have sent out sync requests immediately. When the required number of responses had
     * been received, the current implementation discards all additional responses (to
     * return the result to the client as soon as possible). If our response sent last
     * time was discarded, we will end up here when the background ykval-queue processes
     * the sync request again.
     */
    $myLog->log(LOG_INFO, 'Sync request unnecessarily sent');
  }

  if ($syncParams['modified']!=$localParams['modified'] &&
      $syncParams['nonce']==$localParams['nonce']) {
    $deltaModified = $syncParams['modified'] - $localParams['modified'];
    if($deltaModified < -1 || $deltaModified > 1) {
      $myLog->log(LOG_WARNING, 'We might have a replay. 2 events at different times have generated the same counters. The time difference is ' . $deltaModified . ' seconds');
    }
  }

  if ($syncParams['nonce']!=$localParams['nonce']) {
    $myLog->log(LOG_WARNING, 'Remote server has received a request to validate an already validated OTP ');
  }
}

if ($localParams['active'] != 1) {
  /* The remote server has accepted an OTP from a YubiKey which we would not.
   * We still needed to update our counters with the counters from the OTP though.
   */
  $myLog->log(LOG_WARNING, 'Received sync-request for de-activated Yubikey ' . $yk_publicname . ' - check database synchronization!!!');
  sendResp(S_BAD_OTP, $myLog, $apiKey);
}

$extra = array(
  'modified' => $localParams['modified'],
  'nonce' => $localParams['nonce'],
  'yk_publicname' => $yk_publicname,
  'yk_counter' => $localParams['yk_counter'],
  'yk_use' => $localParams['yk_use'],
  'yk_high' => $localParams['yk_high'],
  'yk_low' => $localParams['yk_low']
);

sendResp(S_OK, $myLog, $apiKey, $extra);