Features of RGB State

Strict Type System

As described in the previous sections, the state represents a set of conditions that are subjected to validation against both the business logic and ordered history of commitments.

In RGB, this set of data is actually an arbitrary rich set of data which:

• Are strongly typed, meaning that each variable has a clear type definition (e.g. u8) and lower and upper bounds.

• Can be nested, meaning that a type can be constructed from other types.

• Can be organized in lists, sets or maps.

To properly encode data in the state in a reproducible way, a Strict Type System has been adopted in RGB along with Strict Encoding. This means that:

• Encoding of the data is done following some Schema structure which, unlike JSON or YAML, defines a precise layout of the data, thus also allowing deterministic ordering of each data element.

• The ordering of elements within each collection (i.e., in lists, sets or maps) is also deterministic.

• Bounds (lower and upper) are defined for each variable or data structure. This property is also applied to the number of elements in each collection (the so called Confinement).

• All data fields are byte-aligned.

• Data serialization and hashing are performed deterministically (Strict Encoding), allowing reproducible commitments of the data to be created regardless of the system on which that operation is performed.

• Data creation according to the schema is performed through a simple description language which compiles to binary form from the Rust Language. Extension to other languages will be supported in the future.

• In addition, compilation according to the Strict Type System produces two types of output:

  • A compile-time Memory Layout.

  • Semantic identifiers associated with memory layout (i.e., the commitment to the name of each data field). For instance, this type of construction is able to make detectable the change of a single variable name, which doesn't change the memory layout but changes the semantics.

• Finally, Strict Type System allows for versioning of the compilation schema, thus enabling the tracking of consensus changes in contracts and the compilation engine. To this end each compilation of an RGB object, being it a Schema, an Interface, an Implementation, or RGB libraries themselves produce an unique fingerprint such as:

BEiLYE-am9WhTW1-oK8cpvw4-FEMtzMrf-mKocuGZn-qWK6YF#ginger-parking-nirvana

As a matter of fact, Strict Encoding is defined both at an extremely pure functional level (thus far away from object-oriented programming (OOP) philosophy) and at a very low level (almost a hardware definition, thus far removed from more abstract structures and languages).

Size limitation of validated data

Regarding data participating in state validation, the RGB protocol consensus rule applies a maximum size limit of 2^16 bytes (64 KiB):

• To the size of any type of data participating in state validation (e.g. a maximum of 65536 x u8, 32768 x u16, etc...)

• To the number of elements of each collection employed in state validation. This is designed to:

  • Avoid unlimited growth of client-side validated data per each state transition.

  • Ensure that this size fits the register size of a particular virtual machine AluVM that is capable of performing complex validations along with RGB.

The Validation != Ownership Paradigm in RGB

One of the most important features of RGB compared to most blockchain-based smart contract systems is based on the clear separation between the validation task and ownership that are defined by the protocol at the most fundamental level.

In practice:

• The Validation task, performed by users and observers of the protocol, ensures how the properties of a smart contract can change and thus the internal consistency and adherence of state transitions to the smart contract rule. This process is fully realized by the stratification of the stack of RGB-specific libraries.

• The Ownership property, which, through the definition of the seal pointing to a Bitcoin UTXO, defines who can change the state. The security level of this property depends entirely on the security model of Bitcoin itself.

This type of separation prevents the possibility of mixing the non-Turing complete capabilities of smart contracts with the public access to contract states that is embedded in almost all blockchains with advanced programming capabilities. In contrast, the use of these common "mixed" architectures has led to frequent and notable hacks in which yet unknown vulnerabilities of smart contracts have been exploited by publicly accessing the contract state encoded in the blockchain.

Moreover, based on Bitcoin's transaction structure, RGB can exploit the features of the Lightning Network directly.

RGB Consensus Changes

As another important feature, RGB has, in addition to Semantic Versioning of data, a Consensus Update System, which tracks changes in consent in contracts and contract operations.

There are basically two ways to update the consent rule embedded in the protocol.

Fast-forward

A fast-forward update occurs when some previously invalid rule becomes valid. Despite the similarities, this kind of update is NOT comparable to a blockchain hardfork. The chronological history of this kind of changes is mapped into the contract through the Ffv field of Contract Operation. Specifically, it is characterized by the following properties:

• Existing owners are not affected.

• New beneficiaries must upgrade their wallets.

Push-back

A push-back update occurs when some previously valid state becomes invalid. Despite the similarities, this kind of update is NOT comparable to a blockchain softfork, and furthermore:

• Existing owners can lose assets if they update their wallets.

• It's actually a new protocol, no longer the same version of RGB.

• Can only occur through issuers reissuing assets on a new protocol and users using two wallets (for both the old and new protocols).