4.1.1. Account

An Iroha entity that is able to perform specified set of actions. Each account belongs to one of existing domains.

An account has some number of roles (can be none) — which is a collection of permissions. Only grantable permissions are assigned to an account directly.

4.1.2. Ametsuchi

Iroha storage component, which stores blocks and a state generated from blocks, called World State View. There is no way for the client to directly interact with Ametsuchi.

4.1.3. Asset

Any countable commodity or value. Each asset is related to one of existing domains. For example, an asset can represent any kind of such units - currency unit, a bar of gold, real estate unit, etc.

4.1.4. Block

Transaction data is permanently recorded in files called blocks. Blocks are organized into a linear sequence over time (also known as the block chain) [1].

Blocks are signed with the cryptographic signatures of Iroha peers, voting for this block during consensus. Signable content is called payload, so the structure of a block looks like this:

Outside payload

  • hash — SHA3-512 hash of block protobuf payload
  • signatures — signatures of peers, which voted for the block during consensus round

Inside payload

  • height — a number of blocks in the chain up to the block
  • timestamp — Unix time (in milliseconds) of block forming by a peer
  • body — transactions, which successfully passed validation and consensus step
  • transactions quantity
  • previous hash of a block

4.1.5. Block Creator

System component that forms a block from a set of transactions that have been passed stateless and stateful validation for further propagation to consensus.

4.1.6. Client

Any application that uses Iroha is treated as a client.

A distinctive feature of Iroha is that all clients are using simple client-server abstractions when they interact with a peer network: they don’t use any abstractions which are specific for blockchain-related systems. For example, in Bitcoin clients have to validate blocks, or in Fabric they need to poll several peers to make sure that a transaction was written in a block, whereas in Iroha a client interacts with any peer similarly to a single server.

4.1.7. Command

A command is an intention to change the state. For example, in order to create a new role in Iroha you have to issue Create role command.

4.1.8. Consensus

A consensus algorithm is a process in computer science used to achieve agreement on a single data value among distributed processes or systems. Consensus algorithms are designed to achieve reliability in a network involving multiple unreliable nodes. Solving that issue – known as the consensus problem – is important in distributed computing and multi-agent systems.

Consensus, as an algorithm

An algorithm to achieve agreement on a block among peers in the network. By having it in the system, reliability is increased.

Consensus, as a component

Preserves consistent state among the peers within a peer network. Iroha uses own consensus algorithm called Yet Another Consensus (aka YAC). Distinctive features of this algorithm are its scalability, performance, and Byzantine fault tolerance. If there are missing blocks, they will be downloaded from another peer via Synchronizer. Committed blocks are stored in Ametsuchi block storage.

4.1.9. Domain

A named abstraction for grouping accounts and assets.

4.1.10. Ordering Gate

Internal Iroha component that passes transactions from Peer Communication Service to Ordering Service. Ordering Gate eventually recieves proposals from Ordering Service and sends them to Simulator for stateful validation.

4.1.11. Ordering Service

Internal Iroha component that combines several transactions that have been passed stateless validation into a proposal. Proposal creation could be triggered by one of the following events:

  1. Time limit dedicated to transactions collection has expired.
  2. Ordering service has received the maximum amount of transactions allowed for a single proposal.

Both parameters (timeout and maximum size of proposal) are configurable (check environment-specific parameters page).

A common precondition for both triggers is that at least one transaction should reach ordering service. Otherwise, no proposal will be formed.

4.1.12. Peer

A node that is a part of Iroha network. It participates in consensus process.

4.1.13. Peer Communication Service

Internal component of Iroha - an intermediary that transmits transaction from Torii to Ordering Gate. The main goal of PCS is to hide the complexity of interaction with consensus implementation.

4.1.14. Permission

A named rule that gives the privilege to perform a command. Permission cannot be granted to an account directly, instead, an account has roles, which are the collection of permissions.

List of Iroha permissions.

4.1.14.1. Grantable Permission

Only grantable permission is given to an account directly. An account that holds grantable permission is allowed to perform some particular action on behalf of another account. For example, if the account a@domain1 gives the account b@domain2 a permission that it can transfer assets — then b@domain2 can transfer assets of a@domain1 to anyone.

4.1.15. Proposal

A set of transactions that have passed only stateless validation.

4.1.15.1. Verified Proposal

A set of transactions that have been passed stateless and stateful validation, but were not committed yet.

4.1.16. Query

A request to Iroha that does not change the state. By performing a query, a client can get request data from the state, for example a balance of his account, a history of transactions, etc.

4.1.17. Quorum

In the context of transactions signing, quorum number is a minimum amount of signatures required to consider a transaction signed. The default value is 1. Each account can link additional public keys and increase own quorum number.

4.1.18. Role

A named abstraction that holds a set of permissions.

4.1.19. Signatory

Represents an entity that can confirm multisignature transactions for some account. It can be attached to account via AddSignatory and detached via RemoveSignatory.

4.1.20. Simulator

See Verified Proposal Creator.

4.1.21. Synchronizer

Is a part of consensus. Adds missing blocks to peers’ chains (downloads them from other peers).

4.1.22. Torii

⛩. Entry point for clients. Uses gRPC as a transport. In order to interact with Iroha anyone can use gRPC endpoints, described in Commands and Queries sections, or use client libraries.

4.1.23. Transaction

An ordered set of commands, which is applied to the ledger atomically. Any nonvalid command within a transaction leads to rejection of the whole transaction during the validation process.

4.1.23.1. Transaction Structure

Payload stores all transaction fields, except signatures:

  • Time of creation (unix time, in milliseconds)
  • Account ID of transaction creator (username@domain)
  • Quorum field (indicates required number of signatures)
  • Repeated commands which are described in details in commands section
  • Batch meta information (optional part). See Batch of Transactions for details

Signatures contain one or many signatures (ed25519 public key + signature)

4.1.23.1.1. Reduced Transaction Hash

Reduced hash is calculated over transaction payload excluding batch meta information. Used in Batch of Transactions.

4.1.23.2. Transaction Statuses

Hyperledger Iroha supports both push and pull interaction mode with a client. A client that uses pull mode requests status updates about transactions from Iroha peer by sending transaction hashes and awaiting a response. In contrary push interaction is done over the listening of an event stream for each transaction. In any of these modes, the set of transaction statuses is the same:

../_images/tx_status.png

4.1.23.2.1. Transaction Status Set

  • NOT_RECEIVED: requested peer does not have this transaction.
  • MST_EXPIRED: this transactions is a part of MST pipeline and has expired.
  • STATELESS_VALIDATION_FAILED: the transaction was formed with some fields, not meeting stateless validation constraints. This status is returned to a client, who formed transaction, right after the transaction was sent. It would also return the reason — what rule was violated.
  • STATELESS_VALIDATION_SUCCESS: the transaction has successfully passed stateless validation. This status is returned to a client, who formed transaction, right after the transaction was sent.
  • STATEFUL_VALIDATION_FAILED: the transaction has commands, which violate validation rules, checking state of the chain (e.g. asset balance, account permissions, etc.). It would also return the reason — what rule was violated.
  • STATEFUL_VALIDATION_SUCCESS: the transaction has successfully passed stateful validation.
  • COMMITTED: the transaction is the part of a block, which gained enough votes and is in the block store at the moment.

4.1.23.2.2. Pending Transactions

Any transaction that has lesser signatures at the moment than quorum of transaction creator account is considered as pending. Pending transaction will be submitted for stateful validation as soon as multisignature mechanism will collect required amount of signatures for quorum.

Transaction that already has quorum of signatures can also be considered as pending in cases when the transaction is a part of batch of transactions and there is a not fully signed transaction.

4.1.24. Batch of Transactions

The feature is to be released.

Transactions batch is a feature that allows sending several transactions to Iroha at once preserving their order.

Each transaction within a batch includes batch meta information. Batch meta contains batch type identifier (atomic or ordered) and a list of reduced hashes of all transactions within a batch. The order of hashes prescribes transactions sequence.

Batch can contain transactions created by different accounts. Any transaction within a batch can require single or multiple signatures (depends on quorum set for an account of transaction creator). At least one transaction inside a batch should have at least one signature to let the batch pass stateless validation.

4.1.24.1. Atomic Batch

All the transactions within an atomic batch should pass stateful validation for the batch to be applied to a ledger.

4.1.24.2. Ordered Batch

Ordered batch preserves only the sequence of transactions applying to a ledger. All the transactions that able to pass stateful validation within a batch will be applied to a ledger. Validation failure of one transaction would NOT directly imply the failure of the whole batch.

4.1.25. Multisignature Transactions

A transaction which has the quorum greater than one is considered as multisignature (also called mst). To achieve stateful validity the confirmation is required by the signatories of the creator account. These participants need to send the same transaction with their signature.

4.1.26. Validator

There are two kinds of validation - stateless and stateful.

4.1.26.1. Stateless Validation

Performed in Torii. Checks if an object is well-formed, including the signatures.

4.1.26.2. Stateful Validation

Performed in Verified Proposal Creator. Validates against World State View.

4.1.27. Verified Proposal Creator

Internal Iroha component that performs stateful validation of transactions contained in received proposal. On the basis of transactions that have been passed stateful validation verified proposal will be created and passed to Block Creator. All the transactions that have not passed stateful validation will be dropped and not included in a verified proposal.

4.1.28. World State View

WSV reflects the current state of the system, can be considered as a snapshot. For example, WSV holds information about an amount of assets that an account has at the moment but does not contain any info history of transaction flow.

[1]https://en.bitcoin.it/wiki/Block