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/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
#include <boost/optional.hpp>
#include <string>
#include "mongo/crypto/mechanism_scram.h"
#include "mongo/platform/mutex.h"
#include "mongo/stdx/unordered_map.h"
#include "mongo/util/net/hostandport.h"
namespace mongo {
/**
* A cache for the intermediate steps of the SCRAM-SHA-1 computation.
*
* Clients wishing to authenticate to a server using SCRAM-SHA-1
* must produce a set of credential objects from their password,
* a salt, and an iteration count. The computation to generate these
* is very expensive, proportional to the iteration count. The high
* cost of this computation prevents brute force attacks on
* intercepted SCRAM authentication data, or a stolen password
* database. The inputs to the function are unlikely to frequently
* change. Caching the relationship between the inputs and the
* resulting output should make repeated authentication attempts
* to a single server much faster.
*
* This is explicitly permitted by RFC5802, section 5.1:
*
* "Note that a client implementation MAY cache
* ClientKey&ServerKey (or just SaltedPassword) for later
* reauthentication to the same service, as it is likely that the
* server is going to advertise the same salt value upon
* reauthentication. This might be useful for mobile clients where
* CPU usage is a concern."
*/
template <typename HashBlock>
class SCRAMClientCache {
private:
using HostToSecretsPair = std::pair<scram::Presecrets<HashBlock>, scram::Secrets<HashBlock>>;
using HostToSecretsMap = stdx::unordered_map<HostAndPort, HostToSecretsPair>;
public:
struct Stats {
// Count of cache entries
int64_t count{0};
// Number of cache hits
int64_t hits{0};
// Number of cache misses
int64_t misses{0};
};
/**
* Returns precomputed SCRAMSecrets, if one has already been
* stored for the specified hostname and the provided presecrets
* match those recorded for the hostname. Otherwise, no secrets
* are returned.
*/
scram::Secrets<HashBlock> getCachedSecrets(
const HostAndPort& target, const scram::Presecrets<HashBlock>& presecrets) const {
const stdx::lock_guard<Latch> lock(_hostToSecretsMutex);
// Search the cache for a record associated with the host we're trying to connect to.
auto foundSecret = _hostToSecrets.find(target);
if (foundSecret == _hostToSecrets.end()) {
++_stats.misses;
return {};
}
// Presecrets contain parameters provided by the server, which may change. If the
// cached presecrets don't match the presecrets we have on hand, we must not return the
// stale cached secrets. We'll need to rerun the SCRAM computation.
const auto& foundPresecrets = foundSecret->second.first;
if (foundPresecrets == presecrets) {
++_stats.hits;
return foundSecret->second.second;
} else {
++_stats.misses;
return {};
}
}
/**
* Records a set of precomputed SCRAMSecrets for the specified
* host, along with the presecrets used to generate them.
*/
void setCachedSecrets(HostAndPort target,
scram::Presecrets<HashBlock> presecrets,
scram::Secrets<HashBlock> secrets) {
const stdx::lock_guard<Latch> lock(_hostToSecretsMutex);
typename HostToSecretsMap::iterator it;
bool insertionSuccessful;
auto cacheRecord = std::make_pair(std::move(presecrets), std::move(secrets));
// Insert the presecrets, and the secrets we computed for them into the cache
std::tie(it, insertionSuccessful) = _hostToSecrets.emplace(std::move(target), cacheRecord);
// If there was already a cache entry for the target HostAndPort, we should overwrite it.
// We have fresher presecrets and secrets.
if (!insertionSuccessful) {
it->second = std::move(cacheRecord);
}
}
/**
* Return metrics about the cache
*/
Stats getStats() const {
const stdx::lock_guard<Latch> lock(_hostToSecretsMutex);
Stats stats = _stats;
stats.count = _hostToSecrets.size();
return stats;
}
private:
mutable Mutex _hostToSecretsMutex = MONGO_MAKE_LATCH("SCRAMClientCache::_hostToSecretsMutex");
HostToSecretsMap _hostToSecrets;
mutable Stats _stats;
};
} // namespace mongo
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