Trust Spanning Protocol (TSP) Specification

The Trust Spanning Protocol (TSP) is a message-based communication protocol designed to facilitate secure communication between endpoints with different identifier types. It provides a universal method for interconnecting various decentralized identifiers while preserving trust properties and enabling metadata privacy protection.

Key features include:

• Authenticity and optional confidentiality for all messages
• Support for multiple Verifiable Identifier (VID) types
• Metadata privacy protection through nested messaging
• Routed communication capabilities through intermediaries
• Relationship-based trust model

Core Technical Components:

1. Message Structure:

   • TSP Envelope: Contains version, sender/receiver VIDs
   • TSP Payload: Includes confidential and non-confidential fields
   • TSP Signature: Ensures message authenticity

2. Cryptographic Foundation:

   • Uses Ed25519 for signatures
   • Supports HPKE (Hybrid Public Key Encryption)
   • Implements public-key authenticated encryption

3. Verifiable Identifiers (VIDs):

   • Must support cryptographic non-correlation
   • Require resolution to transport addresses
   • Map to necessary cryptographic keys
   • Support verification operations

4. Relationship Types:

   • Direct relationships between endpoints
   • Nested relationships for privacy
   • Routed relationships through intermediaries

Implementation Requirements:

1. Protocol Support:

   • Must implement TSP_SEAL and TSP_OPEN primitives
   • Must support CESR encoding
   • Must handle relationship management

2. Cryptographic Requirements:

   • Must support Ed25519 signatures
   • Must implement HPKE-Base and HPKE-Auth modes
   • Must support specified hash functions

3. Transport Layer:

   • Must implement defined transport service interface
   • Must handle message routing appropriately
   • Must support asynchronous messaging

Security Considerations:

• Provides end-to-end authenticity and optional confidentiality
• Protects against metadata correlation attacks
• Supports privacy-preserving routing
• Implements strong cryptographic primitives

Current Status:

The protocol is in experimental status (v1.0 Implementor's Draft)
Being developed under the Trust Over IP Foundation
Actively evolving with ongoing specification refinements

The TSP represents a significant advancement in digital identity protocols by providing a universal method for secure communication while maintaining strong privacy and security properties. Its flexible architecture allows for future expansion and adaptation to emerging requirements.