QSIG Handshake Reference Architecture

Abstract

Secure communication handshakes form the foundation of trust in distributed systems. As cryptographic ecosystems transition toward post-quantum readiness, handshake mechanisms must satisfy a broader set of requirements than confidentiality and authentication alone. They must be interoperable, cryptographically agile, auditable, and capable of operating across heterogeneous trust environments.

This Technical Note defines the QSIG Handshake Reference Architecture. QSIG is presented as an abstract, implementation-agnostic handshake model that separates identity, key agreement, policy enforcement, and audit evidence into explicit architectural phases. The intent is to provide a reusable reference architecture that can inform protocol design, interoperability analysis, and pre-standardization efforts without prescribing specific algorithms or wire formats.

This document is informational and pre-standard in nature. It does not define a protocol specification, mandate algorithm choices, or assert regulatory authority.

Review, version advancement, and retraction are governed by QIST-TN-2025-001.

1. Scope and Non-Goals

1.1 Scope

This Technical Note addresses:

• Architectural phases of a secure handshake
• Trust boundaries and role separation
• Cryptographic agility and post-quantum transition considerations
• Auditability and evidence generation

1.2 Non-Goals

This document does not:

• Specify a concrete protocol or message format
• Mandate cryptographic algorithms or parameters
• Claim compatibility with any existing standard
• Certify implementations or deployments

2. Architectural Principles

The QSIG Handshake Reference Architecture is guided by the following principles:

1. Explicit Phasing: Each function of the handshake is isolated into a distinct phase.
2. Separation of Identity and Keying: Identity establishment is decoupled from key agreement.
3. Cryptographic Agility: Algorithms can be replaced without redesigning the handshake structure.
4. Deterministic Commitment: Final session establishment is deterministic and verifiable.
5. Audit Evidence Generation: Handshake execution produces artifacts suitable for later audit.

3. Actors and Roles

The architecture assumes at minimum two communicating parties:

• Initiator
• Responder

Additional roles MAY include:

• Identity authorities
• Policy authorities
• Verification services

Role separation is logical rather than organizational; a single entity MAY perform multiple roles provided boundaries are preserved.

4. Handshake Phases Overview

The QSIG handshake is decomposed into the following phases:

1. Capability Discovery
2. Identity Assertion
3. Key Agreement
4. Policy Verification
5. Session Commitment
6. Evidence Recording

Each phase has defined inputs, outputs, and trust assumptions.

5. Phase Descriptions

5.1 Capability Discovery

Parties exchange supported capabilities, including:

• Cryptographic algorithms
• Protocol versions
• Policy constraints

Capability discovery enables interoperability and algorithm agility without implicit assumptions.

5.2 Identity Assertion

Identity assertion establishes who is participating in the handshake.

Key characteristics:

• Identity credentials are validated independently of key agreement
• Multiple identity schemes MAY be supported
• Failure to establish identity terminates the handshake

5.3 Key Agreement

Key agreement establishes shared cryptographic material.

Architectural requirements:

• Support for classical, hybrid, or post-quantum mechanisms
• Forward secrecy considerations
• Explicit binding to prior identity assertions

The architecture does not constrain the choice of algorithms.

5.4 Policy Verification

Policy verification evaluates whether the proposed session satisfies:

• Local security policy
• Regulatory or organizational constraints
• Risk tolerances

Policy evaluation is deterministic and produces a binary outcome: accept or reject.

5.5 Session Commitment

Session commitment finalizes the handshake.

Characteristics:

• Deterministic selection of session parameters
• Cryptographic confirmation of agreement
• Explicit transition from negotiation to active session

Once committed, session parameters are immutable for the lifetime of the session.

5.6 Evidence Recording

Evidence recording produces artifacts that may include:

• Transcript hashes
• Session identifiers
• Policy evaluation results
• Cryptographic commitments

These artifacts support later verification, dispute resolution, or audit.

6. Trust Boundaries

Each handshake phase introduces a trust boundary.

The architecture requires that:

• Trust assumptions are explicit at each boundary
• Failure in one phase does not contaminate others
• Evidence is generated at boundary transitions

7. Post-Quantum Transition Considerations

QSIG is designed to accommodate post-quantum transition scenarios, including:

• Hybrid key agreement
• Algorithm negotiation without downgrade ambiguity
• Long-term evidence durability

The architecture supports gradual migration without forcing synchronized upgrades.

8. Security Considerations

Security properties addressed include:

• Authentication
• Confidentiality
• Integrity
• Replay resistance

Implementation-specific risks remain outside the scope of this document.

9. Relationship to Other QIST Artifacts

This Technical Note aligns with:

• QIST-RA-2025-001 (Deterministic Trust Pipelines)
• QIST-TN-2025-002 (Artifact Lifecycle and Retraction Policy)

QSIG handshake artifacts are intended to be inputs into broader trust pipelines rather than standalone security claims.

10. Conclusion

The QSIG Handshake Reference Architecture provides a structured, auditable approach to secure session establishment in evolving cryptographic environments.

By separating identity, key agreement, policy, and audit concerns, the architecture enables interoperability, cryptographic agility, and institutional trust without prescribing implementation details.

The QIST Foundation publishes this Technical Note to support responsible protocol design and evaluation during the transition to post-quantum and high-assurance systems.

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End of QIST-TN-2025-001 (v0.9)