tkey iOS SDK - TSS

Web3Auth uses tKey MPC to manage user wallets in a distributed fashion, leveraging various factors or shares managed by users, including their devices, private inputs, backup locations, and cloud service providers. As long as a user can access 2 out of n (2/n) of these shares, they can access their key.

The companion example application is here.

If you are instead seeking the Android implementation, please see here.

Add the MPC tKey iOS SDK

1. In Xcode, with your app project open, navigate to File > Add Packages.

2. When prompted, add the tKey iOS SDK repository:

   https://github.com/tkey/tkey-ios

   From the Dependency Rule dropdown, select Branch and type alpha as the branch.

3. When finished, Xcode will automatically begin resolving and downloading your dependencies in the background.

Documentation

Follow the full documentation here.

SDK Overview

The design of the SDK is relatively straight forward.

• It makes use of the underlying libtkey.xcframework which contains arm64 and arm64-simulator binaries.
• These binaries are built from a common cross-compilable codebase which is a native port of the original implementation of (tkey)[https://github.com/tkey/tkey].
• All marshalling of types across the foreign function interface as well as memory safety is handled by the SDK.

This SDK can be split into methods which are synchronous and methods which are asynchronous:

• Methods which are synchronous are expected to return immediately with no underlying network operations.
• Methods which are asyncronous are dispatched to a serial execution queue and perform network operations with the Metadata Server. The relevant network implementation is already supplied as part of the SDK.

All classes that are part of the modules namespace are static in nature and can only operate on a ThresholdKey object which has been properly setup.

Currently only the Secp256k1 curve is supported.

Please note that all code examples are minimilistic in nature, this is intentionally done for clarity, since most functions can throw.

ThresholdKey

The instance of tkey, this can be considered the most important object in the SDK.

Creation

To create a ThresholdKey object at minimum a StorageLayer is required, however it is more practical to use a ServiceProvider as well.

    let postbox = try! PrivateKey.generate()
    let storage_layer = try! StorageLayer(enable_logging: true, host_url: "https://metadata.tor.us", server_time_offset: 2)
    let service_provider = try! ServiceProvider(enable_logging: true, postbox_key: postbox.hex)
    let threshold_key = try! ThresholdKey(
        storage_layer: storage_layer,
        service_provider: service_provider,
        enable_logging: true,
        manual_sync: false)

Initiation

Once you have created a ThresholdKey object, it can then be initialized.

A KeyDetails object is returned from the initialization call.

    let key_details = try! await threshold_key.initialize(never_initialize_new_key: false, include_local_metadata_transitions: false)

Additionally the following optional parameters can be supplied to this call

Parameter	Type	Description
import_share	String	Initialise tkey with an existing share. This allows you to directly initialise tKey without using the service provider login.
input	ShareStore	Import an existing ShareStore into tkey.

Reconstructing the Private Key

Once the required number of shares are available to the ThresholdKey object or existing shares have been inserted into it, the private key can then be reconstructed.

This method returns a KeyReconstructionResult.

    let reconstructedKeyResult = try! await threshold_key.reconstruct()

Getting the key details.

    let key_details = try! threshold_key.get_key_details()

This returns a KeyDetails object.

Whenever a method is called which affects the state of the ThresholdKey, this method will need to be called again if updated details of the ThresholdKey is needed.

Generating a new Share

Shares are generated on the same threshold (e.g, 2/3 -> 2/4). A GenerateShareStoreResult object is returned by the function.

   let newShare = try! await threshold_key.generate_new_share()

Deleting a Share

Shares can be deleted by their share index. Note that deleting a share will invaidate any persisted share.

    let shareStore = try! await threshold_key.delete_share(share_index: idx)

Modules for additonal functionality

For more advanced operations on a ThresholdKey object, you can make use of the provided modules.

PrivateKeysModule

This module provides an interface for setting, getting and managing private keys for a ThresholdKey object.

SecurityQuestionModule

This module allows the creation of a security share with a password. This is particularly useful to recover a ThresholdKey

SeedPhraseModule

This module provides functionality for setting, changing, getting, and deleting seed phrases for a ThresholdKey object.

ShareSerializationModule

The ShareSerializationModule allows the serialization and deserialization of shares between mnemonic and hex formats.

ShareTransferModule

The ShareTransferModule is used to transfering an existing share to another device.