Single-Use Seals¶

Overview¶

Single-use seals are a cryptographic primitive proposed by Peter Todd around 2016 and serve as a core technical foundation for the RGB protocol. Single-use seals are analogous to physical seals applied to containers in the real world - once opened, they cannot be re-sealed, and anyone can tell that the container has been opened.

In the digital world, a single-use seal is a cryptographic commitment to make a one-time-only commitment to a (currently unknown) message at some future point, and this commitment is provable to a specific audience.

Technical Principles¶

Definition A single-use seal is a formal commitment guaranteeing: 1. A message will be committed at some future point 2. It can only be committed once (single use) 3. The fact of commitment is provable to all relevant parties 4. The commitment is irreversible and final

Implementation on Bitcoin - Seal Definition: Bitcoin UTXO - Commitment: Hash value embedded in a Bitcoin transaction - Opening the Seal: Spending that UTXO - Uniqueness Guarantee: Bitcoin's consensus mechanism ensures a UTXO can only be spent once

Application in the RGB Protocol¶

State Transitions RGB uses single-use seals defined on Bitcoin transaction outputs: 1. Each state change of a smart contract is bound to a Bitcoin UTXO 2. The commitment for the state change is embedded in the transaction that spends that UTXO 3. UTXO uniqueness guarantees state transition uniqueness

Ownership Mapping - RGB state ownership maps to Bitcoin UTXO ownership - The Bitcoin system guarantees RGB state ownership - All state changes can be traced through UTXO history

Verification Mechanism Any party possessing the smart contract state history can verify its uniqueness: 1. Check that each state transition is bound to a valid UTXO 2. Verify that the UTXO has been correctly spent 3. Confirm there is no double-spending or state forking

Client-Side Validation¶

Single-use seals are a key component of the Client-Side Validation (CSV) paradigm:

Traditional Model (Global Consensus) - Everyone verifies all transactions - State stored on the blockchain - Limited scalability

CSV Model (Single-Use Seals) - Only relevant parties verify relevant transactions - State stored off-chain - Single-use seals guarantee uniqueness - Highly scalable

Advantages¶

Privacy - Contract state is not publicly disclosed on the blockchain - Only participants know the complete contract history - Only ordinary Bitcoin transactions are visible on-chain

Scalability - Significantly reduces on-chain data volume - Verification costs do not grow with global state - Can support large-scale applications

Security - Inherits Bitcoin's security guarantees - Double-spending is impossible - Finality of state transitions

Use Cases¶

RGB Smart Contracts - Asset issuance and transfer - Complex smart contract logic - DeFi applications

Other CSV Protocols - Taproot Assets - RGB++ (extension on CKB) - Future client-side validation systems

Theoretical Significance¶

Single-use seals represent a paradigm shift in blockchain design: - From global consensus to local verification - From on-chain state to off-chain state - From transparency to privacy - From low scalability to high scalability

This design philosophy may influence the future direction of blockchain protocol development.