Post-Quantum Secure Channel Model

Abstract

The transition to post-quantum cryptography introduces new design constraints for secure communication channels. These constraints extend beyond algorithm selection to include cryptographic agility, interoperability across heterogeneous environments, long-term confidentiality, and institutional auditability.

This Pre-Standard defines an abstract model for a Post-Quantum Secure Channel (PQSC). The model specifies functional components, lifecycle stages, and security properties required to establish, maintain, and terminate secure channels in environments anticipating quantum-capable adversaries. It is intentionally non-prescriptive with respect to algorithms, wire formats, and implementations.

This document is pre-standard and informational in nature. It does not assert regulatory authority, mandate compliance, or certify implementations.

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

1. Introduction

Secure channels are a foundational primitive for distributed systems. In a post-quantum context, the longevity of protected data and the durability of cryptographic assurances must be reconsidered.

Post-quantum secure channels must support:

• Cryptographic agility across classical and post-quantum algorithms
• Interoperability during extended migration periods
• Deterministic verification and audit
• Resistance to retrospective decryption

This document defines a channel model intended to guide system architects, protocol designers, and institutions during the post-quantum transition.

2. Scope and Non-Goals

2.1 Scope

This Pre-Standard addresses:

• Functional decomposition of a secure channel
• Channel lifecycle states
• Security properties relevant to post-quantum threat models
• Interoperability and migration considerations

2.2 Non-Goals

This document does not:

• Specify cryptographic algorithms or parameters
• Define message encodings or transport bindings
• Replace or supersede existing standards
• Provide implementation guidance or certification criteria

3. Terminology

• Channel: A logical construct providing confidentiality, integrity, and authentication between endpoints.
• Session: A bounded instance of channel operation.
• Endpoint: A participant in a secure channel.
• Adversary: An entity capable of observing, modifying, or replaying communications.

Normative language (e.g., MUST, SHOULD, MAY) is used sparingly and is limited to describing properties of the abstract model.

4. Threat Model

The Post-Quantum Secure Channel model assumes adversaries with:

• Classical cryptanalytic capabilities
• Future access to quantum-capable computation
• Long-term access to recorded ciphertext

The model explicitly considers harvest now, decrypt later scenarios.

Side-channel attacks, implementation vulnerabilities, and physical compromise are acknowledged but remain outside the scope of this document.

5. Channel Functional Components

A Post-Quantum Secure Channel comprises the following abstract components:

1. Identity and Authentication Component
2. Key Establishment Component
3. Key Update and Rollover Component
4. Data Protection Component
5. Policy and Verification Component
6. Evidence and Audit Component

Each component has defined responsibilities and interfaces.

6. Channel Lifecycle

The channel lifecycle consists of the following states:

6.1 Initialization

Endpoints discover capabilities and negotiate supported mechanisms.

6.2 Establishment

Key material is established using mechanisms that MAY include classical, hybrid, or post-quantum techniques.

6.3 Active Operation

Protected data is exchanged. The channel MUST provide confidentiality and integrity during this state.

6.4 Key Update

Channels SHOULD support periodic key updates to limit exposure and support algorithm agility.

6.5 Termination

Sessions are explicitly closed, and sensitive material is destroyed.

7. Security Properties

A Post-Quantum Secure Channel MUST provide:

• Confidentiality against quantum and classical adversaries (within defined assumptions)
• Integrity of protected data
• Authentication of endpoints

A Post-Quantum Secure Channel SHOULD provide:

• Forward secrecy
• Post-compromise security
• Resistance to downgrade attacks

8. Interoperability and Migration

Post-quantum migration is expected to span extended periods.

The model supports:

• Hybrid operation
• Algorithm negotiation without silent downgrade
• Gradual transition without coordinated upgrades

Interoperability considerations are architectural rather than algorithmic.

9. Auditability and Evidence

Secure channels in institutional contexts must produce evidence suitable for later verification.

Evidence MAY include:

• Session identifiers
• Transcript commitments
• Policy evaluation results

Evidence generation MUST NOT weaken channel security.

10. Relationship to Other QIST Artifacts

This Pre-Standard aligns with:

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

The Post-Quantum Secure Channel model is intended to inform, not replace, future protocol specifications.

11. Limitations

This model provides structural guidance only. Security guarantees depend on correct algorithm selection, implementation quality, and operational practices.

12. Conclusion

The Post-Quantum Secure Channel model provides a common conceptual framework for designing and evaluating secure communication systems in anticipation of quantum-capable adversaries.

By focusing on functional decomposition, lifecycle discipline, and auditability, the model supports responsible post-quantum transition without prematurely constraining innovation or interoperability.

The QIST Foundation publishes this Pre-Standard to contribute a neutral, pre-normative reference for the global QIST community.

---

End of QIST-PS-2025-001 (v0.1)