Dynacred - the OmniLedger Wallet

This library implements a wallet in TypeScript that can be used to hold the private keys and to communicate with the instances in OmniLedger. You can find a short summary of what OmniLedger can do here: https://c4dt.org/article/omniledger Dynacred uses different smart contracts in OmniLedger to implement a simple user account system that can do the following:

• delegate operation on the account to other devices (browser, mobile phones, mobile app)
• keep ids of other accounts
• define Decentralized Access Rights Control DARC, which can be used to
  • define recovery options
  • authenticate using CAS, compatible with WordPress, Matrix, Apache
  • protect Calypso encrypted data
• encrypt and decrypt data using Calypso

One of the next steps we'd like to do is to add access to the ByzCoin EVM, so that the wallet can be used to interact with the BEVM.

For more information about dynacred and byzcoin, see DYNACRED.

What the wallet stores

The wallet itself is stored on the OmniLedger blockchain. To access your wallet and modify it, you need to sign transactions with a private key to authenticate. Dynacred stores your private key in the browser-DB. As such you need to run your scripts always from the same host, else the library will not find the private key.

Start with Dynacred

The easiest way to start with dynacred is to ask [email protected] for an account. You'll receive a link that can be opened in a browser and that will store the private key in your browser. Once your set up you can start using the dynacred library in your own projects. An example project is the WebApp, which uses nearly all of dynacred's functionalities.

Library structure

This dynacred version makes extended use of rxjs observables to implement a reactive dynacred. The library only needs to have the credID and the privateKey of the user. All the rest is kept up-to-date by looking it up on the blockchain.

Every user has its own instance of the User class. It needs access to a db (from the browser or mobile app) and to a ByzCoinRPC instance. The User class is mostly an object with references to instances for all the user can do.

Global State, Transactions, Blocks, Contracts, and Instances

A short recap of how the ByzCoin blockchain works. From a data perspective, ByzCoin is inspired heavily from Ethereum. Every ByzCoin node holds a copy of the Global State that reflects all the data known to the nodes. To change the global state, a client must send a Transaction to one of the nodes. All Transactions are collected in Blocks that describe how the Global State evolves. Once all nodes accepted the new Block, the new Global State is available.

The Global State holds a number of Instances. Every Instance holds the following information (summarized):

• ContractID: points to the hardcoded behaviour of this instance
• Data: holds the updated state of this instance
• DARC: defines the invokable methods on this instance and how the rights are verified

The ByzCoin blockchain has a fixed number of Contracts that can only be changed by modifying the code of the nodes. To allow for user-defined contracts, ByzCoin includes a full-fledged Ethereum Virtual Machine, EVM.

Caching of the instances

A simple cache keeps track of all known instances and stores them locally. Whenever a new block is created, the library is informed and updates all instances that have been changed. Every update to an instance triggers a next on all Observables that are linked to it. Using a web-frontend that is aware of Observables, e.g., Angular, you can keep all values up-to-date by using the cred.alias | sync pipeline.

If the library starts with a warm cache, all information is already available to the app. As this information might be outdated, the first step is to fetch all updates from the blockchain. Only the updated parts will be contacted.

Modifying the Global State

Every method in dynacred that modifies the Global State needs to create an instruction. All instructions are collected in a ClientTransaction and then sent to one of the nodes of ByzCoin. To simplify the collection and the signature of these Instructions, dynacred uses the CredentialTransaction class. It abstracts the collection of the instructions and the signing of the final ClientTransaction.

The following is an example of the caller creating an observable on the user.coinBS, and then sending some coins to another account:

Details of Transactions and Instructions

A Transaction is made up of one or more Instructions. Every Instruction has a Type and is sent to an existing Instance. The Type can be one of:

• Spawn: create a new instance
• Invoke: call a method on an existing instance
• Delete: remove an instance

Every Instruction needs to be signed by a key that can be verified by the corresponding Rule of the DARC.

Class structure

User is the basic class that holds references to all other classes that make up a user:

User
  + credStructBS: CredentialStructBS        // Holds all publicly available data from the user
  + coinBS: CoinBS                          // The coin instance of this user
  + addressBook: AddressBook                // A list of all other credentials known to this user, including
                                            // groups and actions
  + credSignerBS: CredentialSignerBS        // All devices having access to this credential
  + spawnerInstanceBS: SpawnerInstanceBS    // A link to the spawnerInstance for creating new instances
  + kpp: KeyPair                            // The keypair for this device

All the user's information are represented by the CredentialStructBS class. This structure holds different information about the user and IDs of instances that also belong to the user. All other instances of the user are represented by their own class:

• coinBS: is the main coin of the user
• addressbook: holds the CredentialStructBSs of the addresses found in credStructBS.credPublic.contacts
• credSignerBS: references all device-DARCs that can modify this credential
• spawnerInstanceBS: holds the spawner that can spawn new instances if paid for with the coin

The following two helper classes are used throughout the code. ByzCoinBuilder can retrieve existing instances from ByzCoin to make them available locally.

ByzCoinBuilder > ByzCoinBS
  - retrieveUser(|By(Ephemeral|URL|Migration|DB))
  - retrieveAddressBook
  - retrieveUserKeyCredID
  - retrieveCoinBS
  - retrieveCredentialSignerBS
  - retrieveDarcsBS
  - retrieveDarcBS
  - retrieveSignerDarcBS

CredentialTransaction is a helper-class to change the state of ByzCoin.

CredentialTransaction > Transaction
  - sendCoins
  - spawnDarc(|Basic)
  - spawnCoin
  - spawnCredential
  - createUser

Basic credential structure definitions

These all stem from the CredentialStruct class and allow an easy way to access eventual updates to the values. No interpretation is done that requires to query byzcoin. So you'll find Buffer and InstanceMap, but no Darc or Coin in these definitions.

CredentialStructBS > BS<CredentialStruct>
  + id, darcID
  + CredentialPublic
  + CredentialConfig
  + credDevices: CredentialInstanceMapBS
  + credRecoveries: CredentialInstanceMapBS
  - getCredential(|InstanceMap)BS
  - (update|set)Credentials

CredentialBS > BS<Credential>
  - getAttribute(|BS|Buffer|String|InstanceSet)
  - setValue
  - rmValue

CredentialInstanceMapBS > BS<InstanceMap>
  - setInstanceSet
  - setValue
  - rmValue

Attribute(Buffer|String|Long|Point|Bool|Number|InstanceSet)BS > BS<*>
  - setValue(T)

CredentialPublic
  + contacts, alias, ...: Attribute*BS

CredentialConfig
  + view, spawner: Attribute*BS

InstanceSet

InstanceMap

Structures that fetch more information from ByzCoin

As the CredentialStruct class points to other byzcoin-instances, these classes allow to interact directly with these instances. Every one of these classes gives a BehaviorSubject access to the underlying byzcoin-instances, as well as methods to WORM the bc-instances.

AddressBook

The AddressBook represents the following DARCs of the CredentialStruct:

• credPublic.contacts as ABContactsBS - links to other credentials the user knows
• credPublic.groups as ABGroupsBS - groups the user follows
• credPublic.actions as ABActionsBS - actions, which are DARCs + a coin-instance for actions like login

Every field is set up as a BehaviorSubject, which means that there is a getValue() method to get the current value, but also a .subscribe() to be informed if anything changes. If an element is removed or added, the BehaviorSubject calls next method on all observers. If an element is changed, only the BehaviorSubject of this element is updated.

AddressBook
  + ABContactsBS
  + ABGroupsBS
  + ABActionsBS

ABContactsBS > BS<CredentialStructBS[]>
  - create, link, unlink, rename

ABGroupsBS > BS<DarcsBS>
  - create, link, unlink, rename

ABActionsBS > BS<ActionBS[]>
  - create, link, unlink, rename

ActionBS
  + DarcBS
  + CoinBS

CredentialSigner

This class holds all devices and recovery darcs. The CredentialSigner class itself inherits DarcBS, so it follows changes to the class itself. A device and a recovery are quite similar, in that both allow full control of the CredentialDarc

CredentialSigner > DarcBS
  + devices: CSTypesBS
  + recoveries: CSTypesBS

CSTypesBS > DarcsBS
  - create, link, unlink, rename

Classes that could be integrated in dedis/cothority

The following classes are generic and could find their way into @dedis/cothority npm. Every class representing an instance is a BehaviorSubject that gives an eventually cached version of the instance, and calls next for every new version of the instance.

DarcsBS > BS<DarcBS[]>

DarcBS > BS<Darc>
  - evolve
  - (set|add|rm)signEvolve

CoinBS
  - transfer

Transaction
  - send
  - (spawn|invoke|delete)

Next steps

• calypso support for identity attributes (email, webpage)
• sharable address-book
• BEvm support