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 a SessionManager
final aliceSession = await OmemoSessionManager.generateNewIdentity(
// The bare Jid of Alice as a String
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.
MemoryBTBVTrustManager(),
// Here we specify how many Onetime Prekeys we want to have. XEP-0384 recommends around
// 100 OPKs, so let's generate 100. The parameter defaults to 100.
//opkAmount: 100,
);
// Alice now wants to chat with Bob at his bare Jid "bob@other.server". To make things
// simple, we just generate the identity bundle ourselves. In the real world, we would
// request it using PEP and then convert the device bundle into a OmemoBundle object.
final bobSession = await OmemoSessionManager.generateNewIdentity(
bobJid,
MemoryBTBVTrustManager(),
// Just for illustrative purposes
opkAmount: 1,
);
// 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.
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
''';
// Since Alice has no open session with Bob, we need to tell the session manager to build
// it when sending the message.
final message = await aliceSession.encryptToJid(
// The bare receiver Jid
bobJid,
// The envelope we want to encrypt
envelope,
// Since this is the first time Alice contacts Bob from this device, we need to create
// a new session. Let's also assume that Bob only has one device. We may, however,
// add more bundles to newSessions, if we know of more.
newSessions: [
await bobSession.getDeviceBundle(),
],
);
// Alice now builds the actual message stanza for Bob
final payload = base64.encode(message.ciphertext!);
final aliceDevice = await aliceSession.getDevice();
// ignore: unused_local_variable
final bobDevice = await bobSession.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[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(bobJid, key.rid, key.value, true),
];
// Bob extracts the payload and attempts to decrypt it.
// ignore: unused_local_variable
final bobMessage = await bobSession.decryptMessage(
// base64 decode the payload
base64.decode(payload),
// Specify the Jid of the sender
aliceJid,
// Specify the device identifier of the sender (the "sid" attribute of )
aliceDevice.id,
// The deserialised keys
keys,
);
// 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.
}