The mission of YOON is to overcome the complexity of distributed ledger technologies providing our customers and our partners a convenient way to evidence protect their data and intellectual property, by leveraging blockchain technology.

As the landscape of technologies, especially blockchain based technologies, is constantly growing and changing, YOON is providing correspondingly scalable blockchain/data store agnostic, modularizable and extensible product landscapes based on our basic use cases which can therefore be extended. Also new use cases defined by our customer needs can be added extending our common business model for storing and validating evidence-based data.

Purpose of this document shall be the brief technical introduction on how YOON is implementing the main product-based features as well how our customers can extend and white-label our services since they want to sell own products/features based on our services.

As IT Systems are rapidly changing we try also to provide long living product focused architectures at low cost on scalability and maintainability. We choose a blockchain agnostic approach due to the fast-evolving nature of blockchain technologies.

YOON Architecture (yArch)
1. CQRS

The base architecture of our systems will be the CQRS – “Command-Query-Responsibility-Segregation” Pattern.

This pattern divides all operational use cases into a command and a query side.

Whereas the query side only handles application reads, the command side handles “well commands” only.

With this architecture we mainly want to overcome scalability issues, the complexity of our business cases and ensure transparency within the whole system landscape.

Consider following cases:

When developing within a large global team, development tasks must be split between developers, which can easily be archived when choosing the CQRS architecture. Our business developers can work on domain logic leaving routine tasks to our technology-oriented developers.
Sophisticated business logic - CQRS forces our developers to avoid mixing up domain logic and infrastructural operations.
Scalability - With CQRS excellent read and write performance as well as command handling can be achieved and scaled up on multiple nodes. Since queries are read only operations they can be optimized to do fast read operations.

As our system includes a wide range of complex subsystems which match in these patterns, implementing our logic using CQRS will be the most viable choice. In the layer diagram outlined below you will find a general overview to our CQRS-based application components.

YOONBox: Our company specific SPA frontend providing the visual appearance of our services.
Other APPs: One could provide their custom frontend.
YOON API: Our REST services with a Command and a Query API and an internal message bus.
YOON Message Bus: The system wide message bus. Internal message bus and the system wide are fully compatible.
YOON Core Engine: The YOON core functionality and home of business logic.
YOON Plugin Provider: The extensibility component for engine plugin development allowing to add additional business requirements based on the underlying immutable database technology (including blockchain).
YOON Data Layer: The main data management allowing several decentralized and centralized database and storage technologies.

Domain Driven Design

2.2.1 What is Domain-Driven Design (DDD)?

“Domain-driven design is the expansion upon and application of the domain concept, as it applies to the development of software. It aims to ease the creation of complex applications by connecting the related pieces of the software into an ever-evolving model.”¹

Why domain driven design?

As for our implementation within the design pattern CQRS, DDD fits most to business needs making it transparent implementing business driven domain models and domains using aggregates for state transitions and entities for reading out states independently which database/data storage technology we may use in the future or have been using in the past; meaning they are meant to be interchangeable, forwards and backwards compatible. An aggregate represents a bounded context which will handle a specific use case and its state transition as well spawning business events for further processing.

Events and Event Sourcing

When talking about events, we are exactly talking about a customer that has used one or more of our services and is expecting a corresponding feedback. Since we want our customers to be actively informed about their pending requests, every successful or unsuccessful command will spawn a corresponding event. And since we want to be backwards and forwards compatible to several blockchain and non-blockchain based database technologies, as well as storage providers, we want to be able to migrate to new technologies and business cases as well. Event sourcing will provide a way for auditing and replicating events based on our needs. Like the name says, event sourcing is the storing and retrieving of the occurrence of events (in detail state transitions of our aggregates) for further usage within the YOON architecture.

The process manager (Saga)

On top of supplying and sourcing events YOON needs a way of automating business processes according to the complexity of our products. The most viable way in the context of command query responsibility segregation in conjunction with using domain driven design and event sourcing is to use a process manager, some call it a saga, for combining our bounded contexts or aggregates to a state machine like behavior with the possibility of scaling all our components over more than only one physical system. This diagram shows an example process manager implementation managing the states via aggregates, where the violet arrows represents commands/write actions and the green events/read actions. This image demonstrates the use case of ordering seats e.g. for an airplane.

According to this example we must pass through the following steps:

Place an order (more abstract making a request, therefore sending a command)
The order manager creates an event for signaling that the order has been created (request accepted)
The order manager tries to book a reservation (inner message bus command)
The reservation aggregate creates an event for the reservation succeeded (inner message bus event)
The reservation aggregate creates an event for the reservation not succeeded (inner message bus event)
According to the received event reservation succeeded the order manager spawns a payment command (the critical command) and a add to waitlist command (non-critical).
The payment gets accepted by the payment aggregate spawning a payment accepted event. (critical event)
The order manager throws a order created event to the customer (external message bus)

Another brief similar example: A user uploads a document and wants his ownership clarified within our system therefore also claiming ownership.

In practice this action consists out of several actions. Some of it are and some are not mutually exclusive and usable from other subsystems. The YOON Engine will be the part were all this information’s (states) from several subsystems merge and lead to the desired output states the user expects. For instance, a user could upload a document claiming the ownership but someone else is flagging this operation as fraudulent operation. So, the engine will be able to manage each state on each time and be able to rollback previously done operations sending new commands when receiving corresponding events. Ultimately the YOON Engine is the place where our domain logic lies thus our DDD is part of the architecture outlined above. Read more about the engine, messages, commands and events in the following chapters.

The YOON Providers

Yoon providers will be an abstract concept in our application structure for accessing external technologies like storage systems (web or non-web based, blockchain or non-blockchain based), RESTful Services or reading out identity information. As they abstract common use cases they reflect external standards. On providers you possibly can think on your internet provider or telecommunication provider. Our providers differ from your provider abstracting this particular use case, like offering a bandwidth over copper and/or fiber cable for you enabling your VDSL modem connecting to the internet.

YOON Protocol (yProtocol)

The YOON Protocol will be the key part of all our systems defining our business actions as messages, commands and events.

As you can see in the diagram above all our commands and events are messages. In terms of information systems, a message is a textual information encoded into a human readable format and simultaneously as a content for machine to machine communication (e.g. E-Mail, Printer Service Protocol Messages over the Internet [IPP], WhatsApp Messages, or a CAN Bus message in your car or vehicle indicating your battery is low).

A message is the part of information without a specific action or context. It could literally be anything. An ID, a string, an object or anything else. Messages have no specific context. What provides a message with more context is a command or an event.

A command is a message indicating that something should or must happen.

An event is a message indicating that something already happened.

So, events and commands are both time relevant whereas messages are not. With the implementation of CQRS commands and events play a significant role over the whole subsystems as they decouple the “what is happening” from the “already happened” within in our systems. For example, “upload a picture with claiming ownership” and “the ownership of an uploaded picture was granted” are the messages, first the command and second the event, reflecting the use case “upload picture with ownership”. More precisely there exist 2 commands and 2 events one for upload and one for the ownership, which has to be handled in a special way. More on this circumstance later in this document.

The diagram above illustrates the usage of messages within our message bus system. Our message bus systems will span across many layers whereas one message bus is a global service like bus while subsequent internal message bus systems also exists depending on the implementation in the specific modules.

Commands

In the following table you can see our generic command structure. Commands therein are structured in the command action, the metadata, parameters and a stream websocket endpoint for uploading files (a websocket is a HTTP based protocol on top of the TCP stack allowing persistent http connections).

Command	Metadata	Parameter	Stream
Verify	User information	Restricted/Public	-
Upload	User Info, File Info	Restricted/Public	URI
Flag	User Information	Restricted/Public	-
Delete (restricted)	User Info, File Info	Restricted/Public	-
Stream	User Info, File Info	Receiving URI	-

Events

Analogous to our commands the events are describing if any of the above called actions happened and succeeded. Events occur mostly if a command has been executed or an external action has been executed within the context of our business cases, signaling readiness.

Event	Metadata	Parameter	Success
Verified	User Info, Timestamp	Restricted/Public	True, false
Uploaded	User Info, File Info, Timestamp	Restricted/Public	True, false
Flagged	User Info, Timestamp	Restricted/Public	True, false
Deleted	User Info, File Info, Timestamp	Restricted/Public	True, false
AccountCharged	Payment Info e.g. Ethereum or Altcoins, Timestamp	Payment address	True, false

YOON API (yAPI)

The YOON API defines our main endpoints for providing the communication between SPAs or APPs and our services. To obtain industry standard security and implementation of RESTful web services we were encouraged to find a solution for defining our API infrastructure dynamically and cross portable between several programming languages and hosting technologies like Windows Azure, Amazon Webservices, Apache, Docker etc.

OpenAPI

The OpenAPI standard defines a templating language for automate RESTful API development in several platforms and languages like asp core with .NET, php, apache with java. Originally developed by swagger, this standard is now licensed under open source and comes along with a broad community. Meanwhile a significant number of SDK (Source development kit) providers implemented this standard, which is one, but not the only, reason why we prefer to use swagger. It currently seems to be the most viable provider currently. The standard defines all API endpoints, parameters, bearer access tokens (JWT, OAuth2.0) and result sets as well as request models.

In general, we will expose a public and a private API. Whereas the private API is for our internal development, basically all our products and features, the public API will be the external access point for our partners which can use our services for developing their own products requiring or implementing our evidence related services.

The OpenAPI standard defines its components using JSON or YAML. Since JSON is a subset of YAML it is valid in both scenarios using either YAML or JSON. We will define our API Components with YAML and compile and store them in JSON. If our partners prefer to use JSON, they will be fully compatible with our definitions in advanced scenarios. Below you can see a global example of our parameter object which will be used by both, command and query side:

parameter:

type: object

name: string

value:

type: object

Identity Provider

The identity provider uses the OpenAPI standard and meets industry encryption standards. We encourage our partners to use our public templates to secure their evidence-based transactions over RESTful services.

In the diagram above you see a typical communication handshake for authorizing via our identity service for later accessing the YOON API.

Bearer access token (JWT)

Our public and private API will be secured by using a bearer access authentication via the OAUTH2.0. The user, or developer, must login via our identity service getting a JSON Web Token

API Key

In addition to bearer access authentication we provide a way to generate and store API keys for long-term communications via mobile apps or third-party providers. Like the bearer access token, the API key is bounded to an account.

Security Schema

For our API Key the security schema looks like this:

components:

...

securitySchemes:

YoonApiKeyAuth:

type: apiKey

description: “API key to authorize requests..”

name: yoonApiKey

in: header

Quite simple, isn’t it? That’s why we use the OpenAPI. We therefore defined our API Security with the API Key Method and Bearer Access token method.² Now we define the bearer access token authentication and OAUTH2.0:

components:

securitySchemes:

…

YoonBearerAuth:

type: http

scheme: bearer

YoonOAuth2:

type: oauth2

flows:

authorizationCode:

authorizationUrl: https://yoon.online/ouath

tokenUrl: https://yoon.online/ouath/token

scopes:

read: Grants read access

write: Grants write access

admin: Grants access to admin operations

Command API

Our command API will responsible for receiving the commands described above. In the header there must exist the specified token when using our API. We will define it at the root level. The definition files are stored in our database and on initiation the API implantation will be automatically compiled in the configured output language for clients (SPA) as well for the servers.

Command Request Schemas

Here is our first command schema:

components:

schemas:

…

Message:

type: object

discriminator:

propertyName: messageType

properties:

name:

type: string

messageType:

type: string

required:

- name

- messageType

Command: ## "Command" will be used as the discriminator value

description: “A representation of a command.”

allOf:

- $ref: '#/components/schemas/Message'

- type: object

properties:

metadata:

type: object

description: “The user and file metadata.”

parameters:

type: array

description: “The parameters sent via the command.”

stream:

type: string

description: “The stream URL on which the stream will be pushed over WebSockets protocol.”

required:

- metadata

- parameters

Command Paths

This will be our first command path definition for our endpoints:

paths:

/commands:

post:

tags:

- Post a command

summary: "Endpoint for all commands."

description: "A generic endpoint for posting YOON commands."

parameters:

- $ref: '#/components/schemas/Command'

Query API

Our query API will provide endpoints for accessing data synchronously in an event-based manner. The events hold all information about what happened with (needed) meta information about the user himself and the uploaded files.

Query Response Schemas

Event: ## "Event" will be used as the discriminator value

description: A representation of an event. Events will be the endpoints on which you can also subscribe on this API endpoints with WebSockets.

allOf:

- $ref: '#/components/schemas/Message'

- type: object

properties:

metadata:

type: object

description: “The user and file metadata”

parameters:

type: array

description: “The parameters sent via the previously sent command.”

success:

type: boolean

description: “Indicates the operation was successful.”

required:

- metadata

- parameters

- success

Query Paths

paths:

/events:

get:

tags:

- Gets a list of chronologic ordered events for this account.

summary: "Endpoint for all events."

description: "A generic endpoint for querying YOON events from a specific time."

parameters:

- name: timestamp:

type: datetime

description: “A timestamp from where we want to receive events.”

- metadata:

type: object

description: “The events metadata information. Which user? Which file?”

…

YOON Engine (yEngine)

The YOON Engine will be the central part of our business logic. As modularized engine with subscribing on commands and events, outlined above, it does not expose direct dependencies to other modules in the application.

Core

The Engine will provide a core with all basic functionalities and will later be extended to handle more – up to an indefinite number of - use cases. In the next chapter we will explain some basic concepts we are implementing. You can also find them on the whitepaper since they directly reflect our core business concepts.

Use Cases (examples)

Our use cases all have in common that they reflect the need of evidence protection, as our major use case, so we want conceptually to extract this case in one common abstract base.

Uploading a file claiming ownership

This is the most common use case and all other use cases will at least partially derive from this one. For clarity we will describe this process here in detail.

That’s the typical workflow what happens in our application:

A customer logs in (opens the app which retrieves user secrets) and provides us with his account information.
(optional) The user can charge his account to have enough credit for to make this command.
The customer selects our copyright tool (this is just one tool within our toolbox).
The customer chooses a file, from his device, for which he wants to claim ownership.
The customer fills in required meta information according to his copyright.
The customer sends the file for which he is claiming copyright.
The engine checks the customer’s account balance. If it meets the required balance, the command gets executed, otherwise it fails. Either way, an event will be generated indicating if the operation was successful.

To be more precise, two commands (upload, verify) and two events (uploaded, verified) are generated in a sequence here. If one procedure step fails, the other fails subsequently and if all succeed, the quite process succeeds so this will be our first saga here implemented as process manager, e.g. a VerifyUploadManager.

Uploading a contractual document with multi party agreement

This case is a derived use case from the case above, with the exception, that one or more customers meta information is being added. For instance, person names as contractors and the required actions (commands) which must be executed on behalf the person(s) could be filled out and then automatically the required human (or non-human) actors could be informed about the process.

Submitting a review together with B2C Handshake

Like the multi-party document agreement (from above), the business to customer handshake will ensure that the business customer (for example the “hotel”) has sent a verification command (= “customer checked out”) before the guest account customer has done his review. We will generate guest accounts on behalf the reviewers on the fly.

Election with automated transparency events

This use case will be a bit more sophisticated since the information, we rely on, comes from a list of anonymously generated guest accounts (voters), which will then vote over a site using our endpoints for collecting all necessary data. After this process the voters get matched with a list of allowed voters internally, the election process itself is managed by an immutable smart contract. The match between the list and the vote will be done with an anonymous hash token, that we created before and then check it again against our internal database.

Upload a testament with events on specific conditions

Like the document or file upload case, outlined in the sub-chapters before, the testament upload case extends this routine with a more complex ruleset of events for notifying other customers in case of death. For this procedure we are using both, our system or an alternative communication channels like e-mail, phone, pager etc.

Basic functionality

Based on our use cases we provide an infrastructure that executes this use cases mentioned above using a payment models which calculates the current YOON Token prices for each functionality, as our primary payment method within the whole YOON ecosystem are YOON Tokens.

YOON Accounts

When using our platform, a customer or developer must register at our site and provide all account information needed like Name, Country, Payment methods (Ethereum, Stellar, Bank Account) to pass the KYC and to be able to charge his account with the desired payment method to obtain YOON Tokens. Each functionality will require a different amount of YOON Tokens, depending on it’s complexity and computational power. Business partners will be able to obtain API keys for external development within their account. A YOON account will also be represented by a Stellar Account and thus fully convertible in both directions. The Stellar Account in its simplest form is a wallet, from which you can send and receive YOON Token.

Charging and payment methods

As mentioned above YOON accounts are being charged through our charging mechanisms. We will implement also a mechanism that allows to charge accounts periodically (abonnement), incentivized by a discount. In the first releases YOON accounts will be chargeable with Stellar, Ethereum, Bitcoin and Dash. In further releases we will provide a way to customize the charging process for our partners using the Stellar Network and providing a way to implement custom currency charging methods.

YOON Token Command Price Model

Depending on the operation there will exist different fees for any of the corresponding commands (or set of commands). Subscribing to events is generally free of charge.

In our token model we issue a specific number of tokens.

After the end of our crowdfunding phase we will generate a Wei-like representation of our credits allowing to charge little or no fees for single operations up to larger fees for chained, more complex operations. For basic operations like the commands mentioned in the chapter above we charge almost no fees. Almost means that the fees charged will generate no real-world costs but need a minimum number of parts of YOON Ticks (inspired by and analogous to processor ticks) with a scaling factor to be executed. In practice it is a freemium model to execute the basic commands like “Verify” or “Upload (for small sized files)”.

Stellar Payment

The stellar payment will be our channel for tracking YOON Token based transactions. See https://www.stellar.org/developers/horizon/reference/resources/operation.html#payment for reference.

Stellar YOON Smart Contract

We will generate a Smart Contract storing and managing our business logic relevant account information replicating it also locally. Stellar Smart Contracts are represented as a composition or let’s say a series of operations (transactions, to be more precise) with two or more parties (signatures) involved. See https://www.stellar.org/developers/guides/walkthroughs/stellar-smart-contracts.html for more details.

Stellar Smart Contracts are not Turing complete, but they are fully capable or reflecting our use cases. We will translate Stellar transactions into commands and Stellar payment streams into events, so we will also be able to represent a Stellar Smart Contract as Stellar Process Manager.

Stellar Payment Command

For making a stellar payment we must translate our commands within an OpenAPI definition (external data representation) conform representation so that is understandable for Stellar and vice versa for us as well, when it comes from the stellar side.

Stellar Payment Received Event³

To react on incoming payments, we will create a corresponding payment event which will be listened on when a payment will from a customer was received and thus has the state “received”. Payments in YOON Tokens can be queried by streams over WebSocket or directly by accessing our API.

Extensibility

Depending on the underlying blockchain or non-blockchain technology we will provide a way to extend the YOON Engine with additional plugins. Our developers can easily add new functionalities for newly designed use cases or new currencies that we want to accept.

We use dependency injection mechanisms to extend our core engine with additional modules, so it will be possible to attach or detach additional business logic depending on the underlying blockchain or non-blockchain immutable database technology (see diagram above). The modules then will be called subsequently when needed by a specific event and/or command. For the execution chain and the dependency injection we will evaluate different IOC (inversion of control) Containers and choose depending on our business needs.

Yoon DataLayer (yData)

For adopting different blockchain, non-blockchain storages and databases we will design a repository that can be isolated as service or directly be attached to our API subscribing either to our external or internal message bus system.

Data Providers

The data layer will integrate different providers via dependency injection mechanisms. Analog to our extensibility of the YOON Engine, the YOON DataLayer will be extendable the same way subscribing on the corresponding events/commands the engine enqueues.

Blockchain Provider

Our main provider for storing data across the application will be the blockchain providers. This could be internally implemented with different blockchain technologies like Stellar, Ethereum or EOS. Our first supported platform will be Stellar. In the immutable ledger domain (also called blockchain) will also happen the file anchoring in composition with the storage provider.

SQL Provider

Additional to the blockchain protocol storage we will implement an SQL or NoSQL provider which mirrors the data for the possibility to migrate all data later on, when a specific platform mentioned above should die out (which seems to be very unlikely) or should run into performance problems. The mirroring is also a measure to keep us independent.

File Storage Provider

The file storage provider will handle the different file-based storage systems by abstracting them to a simple form of a folder like file system abstraction with read, write and execute rights.

JSON File Storage (OpenAPI)

We will implement a storage module which handles our OpenAPI definitions like previously mentioned. Our API is then replicable in different services and programming languages as well as client endpoint technologies (client SDKs).

Decentralized File Storage

Here we will handle our decentralized file storage. We consider first to implement a solution using Chainpoint as anchoring technology for our use cases, ⁴ but the usage of other services leveraging swarm could also be possible. We will not be enforced to use Chainpoint as the main anchoring mechanism since file anchoring is a concept or pattern of linking files to hashes. We will consider using JSON-LD as the main description language since it is programming language and technology agnostic.

YOON Message Bus (yBus)

In this section we will describe our YOON Message Bus (yBus), which is intended to be portable as internal message bus and/or external message bus system. We consider using a microservice⁵ for the external implementation.

Everything is a message

Since everything in YOON is a message, we can pass through the messages between all layers and every module, service or API implementation. Messages can be shared across the whole ecosystem. This implementation is also called message broadcasting.

Internal vs. external bus

The main difference between an internal and an external message bus will be its configuration. Every instance of a message can be configured for subscribing on, publishing and broadcasting different kinds of messages. We will store this kind of configuration within a database and a local overwritable configuration file.

Queuing messages

The message bus can enqueue messages if they are not already received from the subscribing part of the application. A message is received when all subscribing modules have flagged the messages as received. Modules which have already received a message ignore this by a message sequence implementation from the broadcasting algorithm. The message bus will therefore be able to store events and commands. For example, a transaction could be such an event.

Message Broadcasting Algorithm

Like already described, messages are broadcasted over one or more message bus systems to other subsystems subscribing to events or commands. When speaking in physical network terms our network communicates asynchronously over a peer-to-peer network in a physically behavior. When talking in application terms, the communication spans a complete graph over all applications. Since the communication with messages over physical and application-based message bus systems is unified in application, the overall structure of communication is again peer-to-peer communication, which one could see as subset of a complete graph in union with a complete graph thus resulting in a complete graph again, since one or more processes could listen on the same message.

The formal definition of the sentence above would be as G(k) from G where G is the Complete Graph and G(k) the kth subset of direct connected network graphs so within our architecture:

G(k) ∪ G = G

We therefore reflect our message bus systems as a complete graph.

Due to reach consistency and order invariance of all messages sent over any type of media within our or the partner network systems we are forced to implement a proper broadcasting algorithm. It should be capable of handling all sending and receiving of messages in a reliable way without the need of a semaphore like mechanism which may result in blocking other messages to be received properly. On the next site we will explain how we reach consistency over all application modules. On the first version of our message broadcasting implementation we choose a Uniform reliable Broadcast.⁶

Like other distributed systems this algorithm uses consistent one way hashing for signing its data to be correct.

The massage broadcast algorithm can easily be converted into a uniform consensus algorithm, which will later be the heart of our own blockchain, which our message bus system is a subset from, since we implement a modular approach for the algorithms as described on the next pages.

Therefore, lets define some basic definitions:

Let {m} be a message or a set of messages of any type.

Let {p0} be an independent process which executes asynchronously in relation to its neighbor processes {p1…, pN}. The processes could also be data nodes N which have to replicate like this simple formula to reach overall consistency, where {W} represents a set of writes of messages and {R} a set of reads of events:

W + R > N

This means, if we run 2 processes respectively nodes, at least 1 message and 2 corresponding events must be replicated.

According to the CAP Theorem we want to ensure at least consistency and availability, so we choose a multivalued consensus for the consistency hashing. The broadcasting algorithm⁷ we use looks like outlined below:

Definitions for process {pi} ∈ {p1…, pN}.:

{M}, set of known broadcast messages of type {m}, initially empty

{D}, set of delivered messages of type {m}, initially empty

{R}, set of values representing the result of current multivalued consensus instance

{l}, non-negative integer, initially 0

Code for process {pi}:

Task 1: To execute UR-Broadcast({m}):

{M} ← {M} ∪ {m}

Task 2: Upon FL-Receive({m}):

M ← {M} ∪ {m}

Task 3: Repeat periodically:

for any value v ∈ {M}\{D}, FL-Send({m}) to all processes

Task 4: Repeat periodically:

{R} ← {M}-Con[{l}] ({M}\{D})

{R} ← {R}\{D}

UR-Deliver all values in R in some deterministic order

{D} ← {D} ∪ {R}

{l} ← {l} + 1

Message Bus Plugins

In the chapter above, we described a modular approach to broadcast messages and reach consistency over all application modules which means reliable overall consistency over all stored data, which are also stored as messages. In this chapter we want to describe the further plugin development for the message bus implementation.

When the YOON Platform evolves we will transform the multivalued consensus algorithm into a uniform multivalued consensus, which means that we can properly reflect a blockchain friendly consistency mechanism. In the next step we will create a message bus plugin, which is listening on the messages according to the storage relevant commands like file anchoring or signing concrete transactions which will then facilitate our own blockchain.

YOON Blockchain (yChain)

Like many other blockchain technologies we consider modelling our structure of our hash signing with the help of the well-known Merkle Tree⁸. As traversal algorithm for finding the next authentication node we consider using the TREEHASH algorithm⁹, more specifically a binary tree. (see Picture above) But for more complex scenarios we consider defining a Merkle Tree of higher order then 2. For the key pair generation and for signing transactions, we consider using the hash function Blake2¹⁰, since it is faster than SHA-3 (Keccak) but also remarkably strong in terms of resisting pre-image attacks¹¹ and collision detection¹².

On the next pages we will describe how we could solve this a problem in the binary tree domain. Therefore, we will define and explain some basic concepts of tree traversing within a hash binary tree and Merkle Tree signing of messages and compare them with classical concepts. One could say that blockchain technologies at a top level consists of two mechanisms, first the one-way hash function for each new state of the entire blockchain data to ensure the state of the new block is valid and secondly a public-private key pair of a one-way hash function which gets randomly generated more than once for an account, transaction, event, message or whatever to create a signature. We will discuss effective Merkle Tree traversal techniques, validation of blocks for file anchoring and the keypair generation of old and the new Merkle signature generation.

Digital Signatures

We use digital signatures to proof the validity of files as well as the authentication of one users. The signatures get generated and to be verified by one or more trusted parties. The most common signature in the web are certificate signed SSL connections in your web browser. If a trusted party is the owner of the actual (signed) connection, the signature is verified while the asynchronous encryption handshake gets initiated. You as User can verify this by checking the green lock in your browsers address bar. This kind of verification process is very similar in other cryptographic enhanced technologies like the blockchain technology.

1976 the Lamport Diffie ¹³ one-time signature method was founded, which use a one-time hash function

¹⁴

to generate a public key out of a private key. It has the form

for the normal distributed private key string and

for the encrypted public key string.

For clarity consider following scenario:

Our hash function

is a simple XOR function so that in binary format

1 XOR 1 is 0,

0 XOR 0 is 0

and 1 XOR 0 is 1.

Like in the formula above Alice encodes a 1 in a 2n + 1 (odd) and a 0 in a 2n (even) index.

Now Alice wants to send Bob a Message

= {0101} with the private key

= {10110010} and the public key

= {01001101} with XOR 1 and is therefore signing the message with

= {1100} and writes this with several other possible variants of a new private key and public key pair mentioned above. Its only important that its different from all the others. Bob randomly picks this one and knows the encryption method

. Since there are existing many solutions, which hit XOR to be valid some could only guess a possibly wrong combination. Now let’s assume that Bob has received Alice signed message and can proof the signature by applying her public key with the signed message and can forge the message by

= {01001101} with EVEN/ODD index {1100} and so receives {1010}, and {1010] XOR 1 is {0101}. Eureka! There exist many improvements to this methodology like for example the Winternitz improvement¹⁵, but they all have in common one major problem as you already can guess, the length (in size of data) of the private key. Considering the length of the example above much longer, then all verifiers of this public key which results in an immerse overhead of computation and space requirement when you see it as distributed system where one actor waits until the other has finished verifying. As described earlier we will use the blake2 hash function for signature generation. ¹⁶

Esoteric of Merkle Trees

As you may already guess there exists a solution to this problem, founded by Ralph Merkle¹⁷, which is and was indeed a revolutionary idea but nothing new, since it is already popular in use within the Bitcoin blockchain. In the context of blockchain technology an also revolutionary idea firstly used to describe a rich state by Vitali Butkerin¹⁸ the Merkle Tree is seen in a new light from this time. Let’s take a closer look to a simple Merkle (binary) Tree.

The principle is like the signature generation described on the previous page with one major advantage: One could verify more than one public key with only the root hash or fragments within the tree. To be more precise the bottom elements are the leaves or the tree and represents the hashed data. The middle part of the tree are the nodes and represents the combined hashes of two nodes which labels two hashed leaves and so on. The top level is called root hash and represents the generalized public key or let’s say signature of overall transactions, data, accounts. For instance, one would only need node A to verify, that h (1) and h (2) are valid signatures of the corresponding data 1 and 2 and not the quite tree.

It has the general and simple formula

which states, that the next closest parent signs the two children’s. Remember the private public key signature scheme explained above, the principle is the very same. Consider the example above as a fraction of a full Merkle Tree for an atomic transaction chain or for more inter-blockchain states of a YOON Account. The formula above is used with the blake2 hash function in three phases, key generation, output or let’s say traversal and verification. We only describe key generation and traversal, since the verification is just the application of the formula mentioned above.

Since it is a binary tree the fractal subtree height computes logarithmic with the formula

n + 1) where n is the total number of leaves and nodes. So, for instance our Merkle Tree example above has a height of

7 + 1) = 3, since 2 (h (1), h (2)) * 2 (h (3), h (4)) * 2 (A, B) = 8. The root is excluded or added synthetically since it base is 2^0 = 1.

Then for key (leaf, node) generation the following algorithm gets applied:

Key Generation and Setup

1	Initial Subtrees: For each i ∈ {1, 2, ..., L}:

Calculate all non – root nodes n in existing subtree at each logarithmic level i with hash function H(n) where H = blake2.
- Create a new desired subtree which is empty at each level i (except for i= L), with leaf position initialized to 2ih.

2	Public Key: Calculate and publish tree root.

Where L is the logarithmic count of the subtree levels.

For traversal of the fractal tree following algorithm gets applied, where Desire is a desired fractal tree and Exist is an existing fractal tree:

Fractal Merkle Tree Traversal

1	Set leaf =0.
2	Output: Authentication path for leaf with index leaf.
3	Next Subtree: For each i for which Exist is no longer needed, i.e. i ∈ {1, 2, ..., L−1} such that leaf = 2hi - 1 mod (2hi ) :
4	Grow Subtrees: For each I ∈ {1, 2, ..., L−1}: Grow tree Desirei by applying two units to TREEHASH (unless Desirei is completed) starting from leaf with index 2ih .
5	Increment leaf and loop back to step 2 (while leaf < 2H - 1).

Remove root nodes in Existi .
Rename tree Desirei as tree Existi.
Create a new, empty tree Desirei (if leaf + 2hi < 2H).

With the TREEHASH algorithm

TREEHASH (s, hmax, i, Desire[][])

1	Set leaf = s and create empty stack.
2	Consolidate: If top 2 nodes on the stack are equal height:
3	New Leaf: Otherwise:
4	Push relevant nodes in Desire: continue:

Pop node value

from stack.

Pop node value

from stack.

=

– 1, output

and terminate.

Compute new

=

If height

=

then output

Push

in to the stack and stop.

Compute new leaf with hash function

.

Push

onto the stack.

Increment leaf.
For each node value in stack

,
push {stack[s+ i-2],stack[s+i-1].stack[s+i]} in Desire[s][i].

Loop to step 2. ¹⁹

Remember this is also a one-way hash function? Alice claims the ownership of h (2) with her public key thus sending Bob h (4) only her minimum authentication path with different variants of the Merkle Tree structure and says Bob after generation: Look at {h (1) and h (h (3) + h (4))}. Since Bob is aware of his own and his parent and his neighbor, he would concatenate his h (h (3) + h (4)) result with given h (h (1) + h (2)) and check if it matches the root value.

We at YOON want to generalize this pattern again and want to sign different blockchain bound transactions, accounts, files and so on in a single round trip with different kinds of Merkle Trees, one for each blockchain technology, like Stellar, Ethereum, Bitcoin etc.

Economic verification algorithm or „Proof of the tasty Steak “

Like many other providers for our verification on top of the Merkle Signatures we consider implementing a Proof of Stake-like algorithm which should be suitable enough for our business needs. Since it is more an economy related conceptual algorithm (and is quite far too complex to explain it here within 3 sites), we won’t go deeper in that here. Let’s state that everyone participating at the YOON Blockchain will receive a first positive stake, so that the “there is nothing to stake” argument won’t quite fit, but we will implement a malus for each malicious and/or suspicious action (which later results in a malicious one) resulting in an event which leaves unvalidated/corrupt blocks of data once submitted to validate. So, we also talk about (signature) validators, not block miners. There exist also plenty of (economic) attack scenarios, like the 51% attack, we will consider choosing one of the known algorithms.

For more information see https://blog.ethereum.org/2014/01/15/slasher-a-punitive-proof-of-stake-algorithm/.

Decentralized File Storage and Anchoring

The YOON Blockchain will be able to address and sign big data across different storage systems, like cloud storage, our local storage or any arbitrary traditionally file-based storage systems. In the first run we will use Chainpoint as external data anchoring provider being able to anchor large files with Merkle Tree signatures at the root level for different files. In the previous section of this white paper we talked about JSON-LD as markup language for generic blockchain agnostic anchoring. In this section we will give a brief example how we use this technology in conjunction with our blockchain or let’s say Merkle Tree abstraction.

In this example we will use Ethereum Swarm as decentralized file storage technology. We define the following JSON-LD file:

{

"@context": "{EthereumSwarmSchema}",

"@id": "{DataId}",

"name": "{DataName}",

"type": "{DataType}",

"Created": "{Date}",

"YoonAccount" : {PublicKey} (owner),

"MerkleRoot": "{RootHash}"

}

In this simple example we demonstrate a generic file, which will be mapped to Ethereum swarm with data type, name and a global unique id. The bridge between our blockchain and underlying technology happens with their and our Merkle Root or let’s say Merkle Root fragment.

In the next step we want to build our own distributed file system with a classical peer-to-peer network approach allowing third party providers to host a peer node for distributing and signing files backed by our blockchain client. Like other blockchain based peer-to-peer networking models we want to apply a reward system for the participants getting them YOON Tokens for transmitting data fragments, signing file-based transactions and flagging suspicious actions on the network.

8.5 Introducing the YOON peer to peer (in short p2p) model

The early ages of peer to peer networking are already known by a broad mass as the popular bit torrent clients which already have made use of distributed hash tables (in short DHT) ²⁰, for example eDonkey which represents one of these distributed file sharing systems. As a peer node you offered your computational power as well as your bandwidth for allowing others to share hashed file artifacts through your peer node and allows yourself to import seeds to download a specific file at whole (if you paid sufficient funds in YOON). Our peer-to-peer model will be a pure p2p model, in which we also serve with some strong nodes offering you the computational power for the daily use. As a contributor you can earn YOON Tokens as a reward for hosting a node. You will be paid for uptime as well as for your bandwidth throughput, proper consistency checks with Merkle Signatures for the corresponding artifacts (top root hash in the JSON-LD document) and name resolves for querying new nodes. For clarity consider following scenario. A YOON Account owner wants to upload a file, an image for instance, which has a size of 10 Mbytes. Now your image gets split into 10 even sized chunks (if it were 11 Mbytes big, there would be 11 chunks with the last one having 1Mb). First, a JSON-LD file gets generated with the following information:

{

"@context": "{YoonP2PSchema}",

"@id": "{ImageId}",

"name": "{ImageName}",

"type": "jpeg",

"size": "10Mb",

"Created": "{TodayDate}",

"YoonAccount" : {PublicKey} (owner),

"MerkleRoot": "{RootHash}"

}

Additionally, the owner wants to claim the ownership according to our business use case No. 1 “Uploading a file claiming the ownership”. First, a series of identifying immutable transactions will be generated in an inter-blockchain scenario. For the image fragments a Merkle signature with root hash will be generated and each chunk will be signed by the corresponding Merkle Tree leaf. Then the root hash becomes an anchor for the corresponding data like you have seen in the JSON-LD document.

In the next step the file chunks will be distributed with their corresponding Merkle Signatures and gets converted in a distributed hash table form, like {Key1, Data1}, {Key2, Data2}, {Key3, Data3} … {Keyn, Datan}.

9 YOON Streaming Services (ySS)

With the Yoon Streaming Services, we want to provider a way to open a stream from one of file providers mentioned above to stream large files over web-based technologies like state of the art browsers like Google Chrome on Windows as well as lightweight smart phone browser within iOS or Android operating systems.

The Streaming Server

The core concept of our streaming will be a standalone streaming server which registers on our message bus systems. Once registered the server can listen to corresponding stream control commands as well to events signaling file-based operations on our blockchain bound file system abstractions.

Authentication Flow

The authentication flow works transparently according to our OpenAPI standard mentioned above. Once authenticated a web client (single page application) or any other app can use our streaming API commands.

Streaming Command and Streaming Via WebSocket

For streaming we will use WebSocket²¹ for the transport of our streaming data and the normal OpenAPI standard for abstracting (file)stream control commands. For a concrete implementation in PHP in the first version we consider using Ratched as library for the server part. ²² The most WebSocket implementations naturally support messages, events and commands within their implementation as well as the most JavaScript SPA frameworks implement a publish subscriber pattern on top of a JavaScript web socket API.

In the diagram underneath we will explain a sample scenario how we would implement a typical use of WebSocket for our streaming.

First, a single page application (authenticated), in this case our own YOON Box pushes a stream command and an authentication token to our API. For further processing the client opens a web socket to our web socket hub implementation with the API. In the next step our API internally generates a stream command for our streaming use case and generates a corresponding stream ID sending it to the client via web sockets. The API pushes the generates a stream command into to the message bus. The stream command gets received by our YOON Engine, which generates a corresponding saga to our business-related use case. If the saga succeeds, a stream event is generated and pushed to the message bus. The stream server listens on the stream event and once received it opens the stream by our file system abstracting data layer. The stream could come from everywhere, e.g. from Swarm, our P2P network or even amazon web services. The streaming server generates a push stream command and opens a WebSocket Hub exclusively for the client with a hash-based URL out of the client’s token and the stream id and pushes the command to the message bus with the previously generated stream id and token. The WebSocket Hub within the API receives this command and informs the client the stream being ready. The client initiates a new WebSocket connection to the streaming server with the supplied stream id and the token.

References

https://en.wikipedia.org/wiki/Collision_resistance

https://en.wikipedia.org/wiki/Lamport_signature

https://en.wikipedia.org/wiki/PreimageAttack

www.tierion.com

www.stellar.org

https://github.com/shelby3/winternitz/blob/master/Winternitz.md

https://airbrake.io/blog/software-design/domain-driven-design

Bachelor Thesis, Boris Ederov, Merkle Tree traversal techniques

https://blake2.net/

https://blog.ethereum.org

Robter C. Martin, Clean Architecture

http://socketo.me/

Initially introduced and made popular by programmer Eric Evans in his 2004 book, Domain-Driven Design: Tackling Complexity in the Heart of Software - https://airbrake.io/blog/software-design/domain-driven-design ↩
See https://swagger.io/docs/specification/authentication/api-keys/ for more information. ↩
The payment received event reflects if a stellar payment with a stellar wallet was successful. ↩
Chainpoint is a product of Tierion (www.tierion.com) implementing a service for multiple blockchains for timestamping and anchoring data within them. ↩
A microservice is a use case specific application encapsulated as a single service. ↩
See https://ieeexplore.ieee.org/document/7284349/ for more information. ↩
Source https://pdfs.semanticscholar.org/9a89/6c6b332b0a37ad4a9c7c099636a23764d68a.pdf ↩
A Merkle Tree represents a uniform graph with nodes and leafs, which identities have been encrypted by an arbitrary hash function. A good hash function should be easy (fast) to compute, but hard to solve (hard to find collisions and valid pre-images). A full path of a Merkle Tree represented by leafs and nodes can only be reconstructed in its raw form with the originating signing message or key. The key gets encrypted by the corresponding hash function(s). ↩
The TREEHASH algorithm we propose is a well know technique to traverse a sub Merkle tree of interest while ignoring the rest of the tree already processed. ↩
Blake2 is a new encryption standard which was proposed 2012 at NIST -> https://blake2.net/ ↩
https://en.wikipedia.org/wiki/Preimage_attack ↩
https://en.wikipedia.org/wiki/Collision_resistance ↩
Founded by Leslie Lamport, Whitfield Diffie. Ralph Merkle was later the cofounder of the Diffie Hellman encryption ↩
https://en.wikipedia.org/wiki/Lamport_signature ↩
https://github.com/shelby3/winternitz/blob/master/Winternitz.md ↩
https://www.cdc.informatik.tu-darmstadt.de/reports/reports/Boris_Ederov.bachelor.Merkle-Tree-Traversal-Techniques.pdf ↩
https://de.wikipedia.org/wiki/Ralph_Merkle ↩
https://en.wikipedia.org/wiki/Vitalik_Buterin ↩
https://www.cdc.informatik.tu-darmstadt.de/reports/reports/Boris_Ederov.bachelor.Merkle-Tree-Traversal-Techniques.pdf ↩
Distributed hash tables are hash tables like on a local node or network but distributed over one or more peers. A peer could therefore be a client, server or a service hosted by a cloud provider. Hash tables are data structures, which provider fast indexing and verification of data and can be linked by cascading hashes. ↩
https://tools.ietf.org/html/rfc6455 ↩
http://socketo.me/ ↩

Content

Introduction

Domain Driven Design

2.2.1 What is Domain-Driven Design (DDD)?

Why domain driven design?

Events and Event Sourcing

The process manager (Saga)

The YOON Providers

YOON Protocol (yProtocol)

Commands

Events

YOON API (yAPI)

OpenAPI

Identity Provider

Bearer access token (JWT)

API Key

Security Schema

Command API

Command Request Schemas

Command Paths

Query API

Query Response Schemas

Query Paths

YOON Engine (yEngine)

Core

Use Cases (examples)

Uploading a file claiming ownership

Uploading a contractual document with multi party agreement

Submitting a review together with B2C Handshake

Election with automated transparency events

Upload a testament with events on specific conditions

Basic functionality

YOON Accounts

Charging and payment methods

YOON Token Command Price Model

Stellar Payment

Stellar YOON Smart Contract

Stellar Payment Command

Stellar Payment Received Event3

Extensibility

Yoon DataLayer (yData)

Data Providers

Blockchain Provider

SQL Provider

File Storage Provider

JSON File Storage (OpenAPI)

Decentralized File Storage

YOON Message Bus (yBus)

Everything is a message

Internal vs. external bus

Queuing messages

Message Broadcasting Algorithm

Message Bus Plugins

YOON Blockchain (yChain)

Digital Signatures

Esoteric of Merkle Trees

Economic verification algorithm or „Proof of the tasty Steak “

Decentralized File Storage and Anchoring

8.5 Introducing the YOON peer to peer (in short p2p) model

9 YOON Streaming Services (ySS)

The Streaming Server

Authentication Flow

Streaming Command and Streaming Via WebSocket

Footnotes

About

Languages

Stellar Payment Received Event³