Introduction

In today's digital landscape, numerous key exchange protocols are widely used; examples include the mechanisms found in secure networking protocols such as TLS, PGP, and SSH. These protocols define methods for exchanging secret keys between devices, typically as part of a larger scheme that also incorporates authentication and establishes an encrypted tunnel for communication. In such systems, the shared secret is used to key symmetric ciphers for encrypting and decrypting traffic.

About QSMP

QSMP is a complete specification that not only defines a robust key exchange function but also integrates authentication mechanisms and an encrypted tunnel within a single protocol. Rather than retrofitting existing schemes with quantum-strength primitives, QSMP breaks new ground by introducing an entirely new set of mechanisms designed from the ground up for security and performance in the post-quantum era.

Design Philosophy

Recognizing that a large-scale migration to post-quantum cryptography is inevitable, QSMP was developed without the constraints of backward compatibility or the unnecessary complexity of legacy protocols. This new design avoids artifacts from older systems, such as outdated APIs, cumbersome versioning, and compatibility issues, and instead focuses on modern, streamlined solutions.

Cryptographic Primitives

QSMP employs state-of-the-art cryptographic algorithms to ensure high levels of security:

Asymmetric Ciphers: QSMP supports the Kyber and McEliece asymmetric ciphers with the full range of parameter sets.
Signature Schemes: QSMP can use Dilithium or Sphincs+ signature schemes, which were both standardized by NIST.
Symmetric Cipher: For symmetric encryption, QSMP uses the authenticated symmetric stream cipher RCS, which is based on the wide-block Rijndael cipher. This cipher is enhanced with increased rounds, a strong key-schedule, and AEAD authentication using KMAC or QMAC message authentication functions.

Protocol Specifications

QSMP defines two complete protocol specifications that cater to different trust and performance requirements:

SIMPLEX Protocol: This protocol defines a streamlined, one-way authenticated key exchange. In SIMPLEX, the client trusts the server. As part of the exchange, the server signs its public asymmetric key, and the client verifies the signature using the server's public signature-verification key. This protocol establishes a 256-bit secure two-way encrypted network stream between the server and client in just two round trips, making it ideal for scenarios where an efficient and secure encrypted channel is needed between a server and a client.
DUPLEX Protocol: In contrast, the DUPLEX protocol implements a bi-directional trust model. Both hosts authenticate each other by exchanging signed public asymmetric cipher keys and verifying them using pre-shared public signature-verification keys. Each host then creates and exchanges a shared secret, and these secrets are combined to key 512-bit secure symmetric cipher instances. The DUPLEX protocol is best suited for high-security communications between remote hosts and can be used alongside SIMPLEX to register hosts, distribute public signature keys, and establish a secure network.

QSMP offers a modern, flexible, and secure alternative to traditional key exchange protocols that are now being retrofitted with quantum-safe algorithms. Designed specifically for the post-quantum era, QSMP integrates robust key exchange, authentication, and encryption into a single protocol. It is ideally suited for any environment where strong post-quantum security is a priority.

Cryptographic Dependencies

QSTP uses the QSC cryptographic library: The QSC Library

Conclusion

Author: John G. Underhill

Date: 2025-02-10