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//
// AutomaticKeyRotationManager.swift
// MullvadVPN
//
// Created by pronebird on 05/05/2020.
// Copyright © 2020 Mullvad VPN AB. All rights reserved.
//
import Combine
import Foundation
import os
/// A private key rotation retry interval on failure (in seconds)
private let kRetryIntervalOnFailure = 300
/// A private key rotation interval (in days)
private let kRotationInterval = 4
class AutomaticKeyRotationManager {
enum Error: Swift.Error {
/// An RPC failure
case rpc(MullvadRpc.Error)
/// A failure to read the tunnel configuration
case readTunnelConfiguration(TunnelConfigurationManager.Error)
/// A failure to update tunnel configuration
case updateTunnelConfiguration(TunnelConfigurationManager.Error)
var localizedDescription: String {
switch self {
case .rpc(let error):
return "Rpc error: \(error.localizedDescription)"
case .readTunnelConfiguration(let error):
return "Read configuration error: \(error.localizedDescription)"
case .updateTunnelConfiguration(let error):
return "Update configuration error: \(error.localizedDescription)"
}
}
}
struct KeyRotationEvent {
var isNew: Bool
var creationDate: Date
var publicKey: WireguardPublicKey
}
private let rpc = MullvadRpc.withEphemeralURLSession()
private let persistentKeychainReference: Data
private var rotateKeySubscriber: AnyCancellable?
/// A dispatch queue used for synchronization
private let dispatchQueue = DispatchQueue(label: "net.mullvad.vpn.key-manager", qos: .background)
/// A timer source used to schedule a delayed key rotation
private var timerSource: DispatchSourceTimer?
/// Internal lock used for access synchronization to public members of this class
private let lock = NSLock()
/// Internal variable indicating that the key rotation has already started
private var isAutomaticRotationEnabled = false
/// A variable backing the `eventHandler` public property
private var _eventHandler: ((KeyRotationEvent) -> Void)?
/// An event handler that's invoked when key rotation occurred
var eventHandler: ((KeyRotationEvent) -> Void)? {
get {
lock.withCriticalBlock {
self._eventHandler
}
}
set {
lock.withCriticalBlock {
self._eventHandler = newValue
}
}
}
init(persistentKeychainReference: Data) {
self.persistentKeychainReference = persistentKeychainReference
}
func startAutomaticRotation() {
dispatchQueue.async {
guard !self.isAutomaticRotationEnabled else { return }
os_log(.default, log: tunnelProviderLog, "Start automatic key rotation")
self.isAutomaticRotationEnabled = true
self.performKeyRotation()
}
}
func stopAutomaticRotation() {
dispatchQueue.async {
guard self.isAutomaticRotationEnabled else { return }
os_log(.default, log: tunnelProviderLog, "Stop automatic key rotation")
self.isAutomaticRotationEnabled = false
self.rotateKeySubscriber?.cancel()
self.timerSource?.cancel()
}
}
private func performKeyRotation() {
rotateKeySubscriber = tryRotatingPrivateKey()
.receive(on: dispatchQueue)
.sink(receiveCompletion: { [weak self] (completion) in
guard let self = self else { return }
switch completion {
case .finished:
break
case .failure(let error):
os_log(.error, log: tunnelProviderLog,
"Failed to rotate the private key: %{public}s. Retry in %d seconds.",
error.localizedDescription,
kRetryIntervalOnFailure)
self.scheduleRetry(wallDeadline: .now() + .seconds(kRetryIntervalOnFailure))
}
}) { [weak self] (keyRotationEvent) in
guard let self = self else { return }
if keyRotationEvent.isNew {
os_log(.default, log: tunnelProviderLog, "Finished private key rotation")
self.eventHandler?(keyRotationEvent)
}
if let rotationDate = Self.nextRotation(creationDate: keyRotationEvent.creationDate) {
let interval = rotationDate.timeIntervalSinceNow
os_log(.default, log: tunnelProviderLog,
"Next private key rotation on %{public}s", "\(rotationDate)")
self.scheduleRetry(wallDeadline: .now() + .seconds(Int(interval)))
} else {
os_log(.error, log: tunnelProviderLog,
"Failed to compute the next private rotation date. Retry in %d seconds.")
self.scheduleRetry(wallDeadline: .now() + .seconds(kRetryIntervalOnFailure))
}
}
}
private func scheduleRetry(wallDeadline: DispatchWallTime) {
let timerSource = DispatchSource.makeTimerSource(queue: dispatchQueue)
timerSource.setEventHandler { [weak self] in
self?.performKeyRotation()
}
timerSource.schedule(wallDeadline: wallDeadline)
timerSource.activate()
self.timerSource = timerSource
}
private func tryRotatingPrivateKey() -> AnyPublisher<KeyRotationEvent, Error> {
return TunnelConfigurationManager
.load(searchTerm: .persistentReference(persistentKeychainReference))
.mapError { .readTunnelConfiguration($0) }
.publisher
.flatMap { (keychainEntry) -> AnyPublisher<KeyRotationEvent, Error> in
let currentPrivateKey = keychainEntry.tunnelConfiguration.interface.privateKey
if Self.shouldRotateKey(creationDate: currentPrivateKey.creationDate) {
return self.replaceWireguardKey(
accountToken: keychainEntry.accountToken,
oldPublicKey: currentPrivateKey.publicKey
).map({ (newTunnelConfiguration) -> KeyRotationEvent in
let newPrivateKey = newTunnelConfiguration.interface.privateKey
return KeyRotationEvent(
isNew: true,
creationDate: newPrivateKey.creationDate,
publicKey: newPrivateKey.publicKey
)
}).eraseToAnyPublisher()
} else {
let result = KeyRotationEvent(
isNew: false,
creationDate: currentPrivateKey.creationDate,
publicKey: currentPrivateKey.publicKey
)
return Result.Publisher(result).eraseToAnyPublisher()
}
}.eraseToAnyPublisher()
}
private func replaceWireguardKey(accountToken: String, oldPublicKey: WireguardPublicKey)
-> AnyPublisher<TunnelConfiguration, Error>
{
let newPrivateKey = WireguardPrivateKey()
return rpc.replaceWireguardKey(
accountToken: accountToken,
oldPublicKey: oldPublicKey.rawRepresentation,
newPublicKey: newPrivateKey.publicKey.rawRepresentation)
.mapError { .rpc($0) }
.flatMap { (addresses) in
TunnelConfigurationManager
.update(searchTerm: .persistentReference(self.persistentKeychainReference))
{ (tunnelConfiguration) in
tunnelConfiguration.interface.privateKey = newPrivateKey
tunnelConfiguration.interface.addresses = [
addresses.ipv4Address,
addresses.ipv6Address
]
}
.mapError { .updateTunnelConfiguration($0) }
.publisher
}.eraseToAnyPublisher()
}
class func nextRotation(creationDate: Date) -> Date? {
return Calendar.current.date(byAdding: .day, value: kRotationInterval, to: creationDate)
}
class func shouldRotateKey(creationDate: Date) -> Bool {
return nextRotation(creationDate: creationDate)
.map { $0 <= Date() } ?? false
}
}
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