import 'dart:convert';
import 'package:omemo_dart/omemo_dart.dart';
/// This example aims to demonstrate how omemo_dart is used. Since omemo_dart is not
/// dependent on any XMPP library, you need to convert stanzas to the appropriate
/// intermediary format and back.
void main() async {
const aliceJid = 'alice@some.server';
const bobJid = 'bob@other.serve';
// You are Alice and want to begin using OMEMO, so you first create an OmemoManager.
final aliceManager = OmemoManager(
// Generate Alice's OMEMO device bundle. We can specify how many One-time Prekeys we want, but
// per default, omemo_dart generates 100 (recommended by XEP-0384).
await OmemoDevice.generateNewDevice(aliceJid),
// The trust manager we want to use. In this case, we use the provided one that
// implements "Blind Trust Before Verification". To make things simpler, we keep
// no persistent data and can thus use the MemoryBTBVTrustManager. If we wanted to keep
// the state, we would have to override BlindTrustBeforeVerificationTrustManager.
BlindTrustBeforeVerificationTrustManager(),
// This function is called whenever we need to send an OMEMO heartbeat to [recipient].
// [result] is the encryted data to include. This needs to be wired into your XMPP library's
// OMEMO implementation.
// For simplicity, we use an empty function and imagine it works.
(result, recipient) async => {},
// This function is called whenever we need to fetch the device list for [jid].
// This needs to be wired into your XMPP library's OMEMO implementation.
// For simplicity, we use an empty function and imagine it works.
(jid) async => [],
// This function is called whenever we need to fetch the device bundle with id [id] from [jid].
// This needs to be wired into your XMPP library's OMEMO implementation.
// For simplicity, we use an empty function and imagine it works.
(jid, id) async => null,
// This function is called whenever we need to subscribe to [jid]'s device list PubSub node.
// This needs to be wired into your XMPP library's OMEMO implementation.
// For simplicity, we use an empty function and imagine it works.
(jid) async {},
// This function is called whenever our own device bundle has to be republished to our PEP node.
// This needs to be wired into your XMPP library's OMEMO implementation.
// For simplicity, we use an empty function and imagine it works.
(device) async {},
);
// Bob, on his side, also creates an [OmemoManager] similar to Alice.
final bobManager = OmemoManager(
await OmemoDevice.generateNewDevice(bobJid),
BlindTrustBeforeVerificationTrustManager(),
(result, recipient) async => {},
(jid) async => [],
(jid, id) async => null,
(jid) async {},
(device) async {},
);
// Alice prepares to send the message to Bob, so she builds the message stanza and
// collects all the children of the stanza that should be encrypted into a string.
// Note that this leaves out the wrapping stanza, i.e. if we want to send a
// we only include the 's children.
const aliceMessageStanzaBody = '''
Hello Bob, it's me, Alice!
''';
// Since OMEMO 0.8.3 mandates usage of XEP-0420: Stanza Content Encryption, we have to
// wrap our acual payload - aliceMessageStanzaBody - into an SCE envelope. Note that
// the rpad element must contain a random string. See XEP-0420 for recommendations.
// OMEMO makes the element optional, but let's use for this example.
const envelope = '''
$aliceMessageStanzaBody
s0m3-r4nd0m-b9t3s
''';
// Next, we encrypt the envelope element using Alice's [OmemoManager]. It will
// automatically attempt to fetch the device bundles of Bob.
final message = await aliceManager.onOutgoingStanza(
const OmemoOutgoingStanza(
// The bare receiver Jid
[bobJid],
// The payload we want to encrypt, i.e. the envelope.
envelope,
),
);
// In a proper implementation, we would also do some error checking here.
// Alice now builds the actual message stanza for Bob
final payload = base64.encode(message.ciphertext!);
final aliceDevice = await aliceManager.getDevice();
// Since we know we have just one key for Bob, we take a shortcut. However, in the real
// world, we have to serialise every EncryptedKey to a element and group them
// per Jid.
final key = message.encryptedKeys[bobJid]![0];
// Note that the key's "kex" attribute refers to key.kex. It just means that the
// encrypted key also contains the required data for Bob to build a session with Alice.
// ignore: unused_local_variable
final aliceStanza = '''
${key.value}
$payload
''';
// Alice can now send this message to Bob using our preferred XMPP library.
// ...
// Bob now receives an OMEMO encrypted message from Alice and wants to decrypt it.
// Since we have just one key, let's just deserialise the one key by hand.
final keys = [
EncryptedKey(key.rid, key.value, true),
];
// Bob extracts the payload and attempts to decrypt it.
// ignore: unused_local_variable
final bobMessage = await bobManager.onIncomingStanza(
OmemoIncomingStanza(
// The bare sender JID of the message. In this case, it's Alice's.
aliceJid,
// The 'sid' attribute of the element. Here, we know that Alice only has one device.
aliceDevice.id,
/// The decoded elements. from the header. Note that we only include the ones
/// relevant for Bob, so all children of .
keys,
/// The text of the element, if it exists. If not, then the message might be
/// a hearbeat, where no payload is sent. In that case, use null.
payload,
/// Since we did not receive this message due to a catch-up mechanism, like MAM, we
/// set this to false. If we, however, did use a catch-up mechanism, we must set this
/// to true to prevent the OPKs from being replaced.
false,
),
);
// All Bob has to do now is replace the OMEMO wrapper element
// ) with the content of the element
// of the envelope we just decrypted.
// Bob now has a session with Alice and can send encrypted message to her.
// Since they both used the BlindTrustBeforeVerificationTrustManager, they currently
// use blind trust, meaning that both Alice and Bob accept new devices without any
// hesitation. If Alice, however, decides to verify one of Bob's devices and sets
// it as verified using
// ```
// await aliceSession.trustManager.setDeviceTrust(bobJid, bobDevice.id, BTBVTrustState.verified)
// ```
// then Alice's OmemoSessionManager won't encrypt to new devices unless they are also
// verified. To prevent user confusion, you should check if every device is trusted
// before sending the message and ask the user for a trust decision.
// If you want to make the BlindTrustBeforeVerificationTrustManager persistent, then
// you need to subclass it and override the `Future commitState()` and
// `Future loadState()` functions. commitState is called everytime the internal
// state gets changed. loadState never gets automatically called but is more of a
// function for the user to restore the trust manager. In those functions you have
// access to `ratchetMap`, which maps a `RatchetMapKey` - essentially a tuple consisting
// of a bare Jid and the device identifier - to the trust state, and `devices` which
// maps a bare Jid to its device identifiers.
// To make the entire OmemoSessionManager persistent, you have two options:
// - use the provided `toJson()` and `fromJson()` functions. They, however, serialise
// and deserialise *ALL* known sessions, so it might be slow.
// - subscribe to the session manager's `eventStream`. There, events get triggered
// everytime a ratchet changes, our own device changes or the internal ratchet map
// gets changed. This give finer control over the the serialisation. The session
// manager can then be restored using its constructor. For a list of events, see
// lib/src/omemo/events.dart.
}