<?php

# Copyright (c) 2009-2015 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';

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

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

$myLog = new Log('ykval-sync');
$myLog->addField('ip', $ipaddr);
$myLog->log(LOG_INFO, 'Request: ' . $_SERVER['QUERY_STRING']);
$myLog->log(LOG_DEBUG, "Received request from $ipaddr");

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

// verify request sent by whitelisted address
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);
}

// 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, $_GET);

    if ($value == NULL)
    {
        $myLog->log(LOG_NOTICE, "Received request with parameter[s] ($param) missing value");
        sendResp(S_MISSING_PARAMETER, $myLog);
    }

    $syncParams[$param] = $value;
    $tmp_log .= "$param=$value ";
}
$myLog->log(LOG_INFO, $tmp_log);


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

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

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

// Verify correctness of numeric 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);
}

// Verify correctness of OTP input
if (!is_otp($syncParams['otp'])) {
    $myLog->log(LOG_NOTICE, "Input parameter " . $syncParams['otp'] . " not correct");
    sendResp(S_MISSING_PARAMETER, $myLog);
}

// Verify correctness of pubid input
if (!is_pubid($syncParams['yk_publicname'])) {
    $myLog->log(LOG_NOTICE, "Input parameter " . $syncParams['yk_publicname'] . " not correct");
    sendResp(S_MISSING_PARAMETER, $myLog);
}

// Verify correctness of nonce input
if (!is_nonce($syncParams['nonce'])) {
    $myLog->log(LOG_NOTICE, "Input parameter " . $syncParams['nonce'] . " not correct");
    sendResp(S_MISSING_PARAMETER, $myLog);
}

// get local counter data
$sync->addField('otp', $syncParams['otp']);
$yk_publicname = $syncParams['yk_publicname'];
if (($localParams = $sync->getLocalParams($yk_publicname)) === FALSE)
{
    $myLog->log(LOG_NOTICE, "Invalid Yubikey $yk_publicname");
    sendResp(S_BACKEND_ERROR, $myLog);
}

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

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

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);
}

$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, '', $extra);