Trust Spanning Protocol

Identity Protocol

Specification for the protocol at the center of the ToIP hourglass model — the "trust spanning" layer (Layer 2) intended to be "to digital trust what IP is to digital data." Facilitates secure, message-based communication between endpoints with potentially different identifier types (W3C DIDs, KERI AIDs, URNs, etc.), as long as those identifiers are based on public-key cryptography with a verifiable trust root. Provides three core properties: authenticity (mandatory), confidentiality (optional), and metadata privacy (optional, against correlation attacks). Verifiable identifiers (VIDs) form authentic relationships via TSP messages serving as virtual trust channels

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Details

License Spec: open under ToIP IPR framework; Rust open-source reference implementation hosted at OpenWallet Foundation (sponsored by Futurewei, Gen, Accenture); Python implementation by Sam Smith / Web of Trust community
Dev Status 📝 Draft
Dev Status Detail Implementers Draft — vs1.0 Experimental Rev 2; first official version target 1.0.0 upon spec release
Owner Trust Over IP Foundation (project of Linux Foundation Decentralized Trust); developed by the Trust Spanning Protocol Task Force (TSPTF) within the Technology Stack Working Group
Governing Body ToIP / LF Decentralized Trust (Trust Spanning Protocol Task Force, within the Technology Stack Working Group)
Country International (Linux Foundation; global membership)
Start Year 2023
Stack Specification only; reference implementations in Rust (Futurewei/Gen/Accenture-sponsored implementation at OpenWallet Foundation) and Python (Web of Trust GitHub community); CESR (Composable Event Streaming Representation) proposed as encoding format
Funding Trust Over IP Foundation member contributions; reference implementation funded by OpenWallet Foundation Premier members (Futurewei, Gen, Accenture)
Last Investigated Jul 1, 2026

Use Case Domains

Identity & Trust

Affordances

Trust graph portability Sovereign identity

Identity Protocol Attributes

Origins ToIP TSPTF — design synthesized from four overall proposals submitted by Sam Smith, Daniel Hardman, Wenjing Chu, Michael Herman (early 2023)
Database N/A — TSP is a transport-layer trust spanning protocol; persistence is implementation/application concern
Query Language N/A — TSP is message-oriented (Direct Mode endpoint-to-endpoint, Routed Mode via intermediaries); query patterns belong at higher ToIP layers
Data Formats TSP messages with VID_String length-prefixed identifiers; supports DID and URN syntaxes (extensible)
Mobile Support Designed to be lightweight enough for mobile and constrained devices; transport-agnostic so messages can run over Bluetooth, HTTP, or other transports suitable for mobile
Web Support Transport-agnostic — designed to be carried over any transport (HTTPS, DIDComm, raw sockets)
Native Apps Implementation-dependent; reference Rust and Python libraries are embeddable in native apps; expected wallet integrations via OpenWallet Foundation reference implementation
Terms Open standard, free to implement (under ToIP IPR framework requiring contributor membership)
Funds Unknown — ToIP/LF Decentralized Trust funded by member dues; specific TSPTF budget not separately published; four years of cumulative person-hours invested by ToIP members and sponsoring organizations (Futurewei, Gen, Accenture)
Based On W3C DIDs (DID method-agnostic); KERI Autonomic Identifiers (AIDs); IETF URN spec (RFC 8141); public-key cryptography
Permissions Out of scope for TSP itself — permission and authorization semantics belong at higher ToIP layers
Authentication & Identity VID-rooted — endpoints identified by Verifiable Identifiers (DIDs, AIDs, or URN-based PKC identifiers)
Storage Model N/A — transport protocol; storage of messages, keys, and credentials is implementation concern at higher layers
Interoperability Designed as a "spanning layer" for maximum interoperability across decentralized digital trust infrastructure; can bridge centralized, federated, and decentralized identifier architectures
Data Portability High — VIDs and TSP-channel relationships are portable across transports and ecosystems; any VID type can communicate with any other VID type through the spanning protocol
Governance & Decision Making ToIP TSWG governance — open weekly meetings, consensus-driven, IPR-protected under LF Decentralized Trust; cross-organization collaboration with DIF, Hyperledger, OpenWallet Foundation, W3C Credentials Community Group; Implementers Drafts iterated through public review
Protocol Maturity / Standardization Implementers Draft (current); pre-1.0; Rust and Python reference implementations in development
Identity Standards W3C DIDs, KERI AIDs, ToIP Technology Architecture Specification
DID Methods Supported Any (method-agnostic by design)
Key Management Per VID system (DID method or KERI key event log)
Credential Types N/A at the spanning protocol layer — credentials are exchanged at higher ToIP Layer 3 Trust Tasks (DIDComm-style credential exchange, OpenID4VC, etc.)
Verification Method Cryptographic verification using keys associated with senders VID
Privacy Features Optional confidentiality (encryption); optional metadata privacy (anti-correlation measures)
Authentication Methods Mandatory authenticity via cryptographic signatures rooted in VID
Revocation Mechanism Underlying VID system's revocation — KERI key rotation events, DID document update, X.509 CRL/OCSP — TSP itself does not define revocation, deferring to the VID's trust root
Agent Types Supported Humans, institutions, devices, AI agents — TSP April 2025 white paper explicitly extends to AI and human trust interactions
Wallet/Client Types Implementation-dependent — expected wallet integrations via OpenWallet Foundation reference implementation; KERI-style agent infrastructure compatible
Recovery Mechanisms Underlying VID system's recovery — KERI rotation events, DID rotation, X.509 reissuance — TSP itself does not define recovery
Compliance / Regulations Designed to support eIDAS, EUDI Wallet, and GLEIF (Global Legal Entity Identifier Foundation) use cases; GLEIF actively participating in TSPTF
Credential Exchange Protocols TSP is not a credential exchange protocol itself; credential exchange protocols including DIDComm subprotocols and OpenID4VC can run over TSP
Trust Framework Layer 2 of ToIP four-layer stack; complemented by TRQP (Layer 1) for trust registry queries; supports any governance framework above it
Cost Model Free — open standard, royalty-free implementation under ToIP/LF Decentralized Trust IPR
Censorship Resistance Strong — transport-agnostic, messages can traverse any underlying transport without prior assumption of trust; Routed Mode supports intermediary-mediated circumvention