Public Parameters Lifecycle

Public Parameters (PP) are the cryptographic foundation of a Token Management System (TMS). They define the rules of the token system, including the cryptographic curves, generators, and authorized participants (issuers, auditors).

This document describes the lifecycle of public parameters in the Fabric Token SDK, from generation to dynamic updates.

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Generation

Public parameters are generated using the tokengen CLI tool. The generation process is driver-specific because different drivers require different cryptographic setups.

Command Example

# Generate FabToken public parameters
tokengen gen fabtoken.v1 --auditors ./msp/auditor --issuers ./msp/issuer --output ./params

# Generate ZKAT-DLOG public parameters
tokengen gen zkatdlognogh.v1 --curve bls12_381_bbs --idemix-issuer-pk ./msp/idemix --output ./params

Driver-Specific Details:

• FabToken: Focuses on auditor and issuer identities (X.509).
• DLOG w/o Graph Hiding: Includes Pedersen generators, range proof parameters, and Idemix issuer keys for privacy.

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Publication and Management

The publication mechanism varies depending on the network driver being used (Fabric vs. FabricX).

Fabric (Standard)

In a standard Hyperledger Fabric network, public parameters are managed by the Token Chaincode (TCC).

1. Embedding: The parameters are typically embedded into the TCC source code (params.go) or provided as transient data during chaincode Init/Upgrade.
2. Ledger State: The TCC writes the parameters to a specific "Setup Key" in its world state.
3. Validation: The TCC uses these parameters to validate all incoming token requests.

FabricX

In FabricX, public parameters are managed through a dedicated Public Parameters Service and the Vault.

1. Publication: Parameters are written to the ledger under a well-known setup key within the token namespace.
2. Query Service: FSC nodes use the FabricX Query Service to fetch these parameters directly from the vault's world state.

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Discovery and Fetching

When an FSC node starts or connects to a TMS, it must fetch the current public parameters to initialize its local drivers.

• Fetching: The node uses the PublicParamsFetcher (provided by the Network Service) to query the ledger (via TCC or the Query Service).
• Local Cache: Fetched parameters are cached in the node's local PublicParametersStorage to ensure they are available even if the network is temporarily unreachable.

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Dynamic Updates and Synchronization

The SDK supports dynamic synchronization of public parameter updates across the entire network without requiring node restarts.

The Role of the Network Service

The Network Service is responsible for monitoring the ledger for changes to the public parameters.

1. Event Listening: For each connected TMS, the Network Service registers a PermanentLookupListener (using the setupListener) on the Setup Key.
2. Notification: When a transaction updates the public parameters on the ledger (e.g., rotating an auditor's key or upgrading the protocol), the underlying blockchain platform triggers an event.
3. Auto-Reload: The setupListener receives the new raw parameters and triggers TMSProvider.Update(tmsID, newParams).
4. Driver Refresh: The node transparently unloads the old driver instance and hot-swaps it with a new instance configured with the updated parameters.

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Summary of Roles

Stage	Tool/Component	Responsibility
Generation	tokengen	Creates the cryptographic blob for a specific driver version.
Publication	tcc (Fabric) / Vault (FabricX)	Persists the blob to the ledger's world state.
Monitoring	Network Service	Listens for ledger events on the Setup Key.
Synchronization	TMSProvider	Hot-swaps the driver instance in the FSC node upon update.