A Full Threshold NIST PQC-Compliant Framework for Distributed Trust in Federal Public Key Infrastructure
Abstract
The U.S. Federal PKI (FPKI) relies on digital certificates and a network of certificate authorities (CAs) to build trust between federal agencies and their commercial partners. However, CAs’ current certificate generation faces two critical threats: The imminent quantum threats that jeopardize classical digital signatures and the systemic vulnerabilities introduced by centralized signing operations. While threshold-compatible post-quantum (PQ) signatures offer a promising foundation for compromise-resilient trust, their adoption within the FPKI remains constrained by strict standard compliance requirements. ML-DSA is a prominent construction for thresholding within the NIST-PQC standards. However, current efforts to threshold ML-DSA achieve functional interchangeability by sacrificing full compliance. This is done by either skipping essential steps or modifying the signing process to improve performance. Hence, no fully standard-compliant threshold PQ solution currently meets FPKI’s need for a distributed and quantum-resistant trust infrastructure.
We introduce SHIELD, an efficient threshold NIST-PQC-compliant signature framework that replaces its classical centralized counterpart in certificate generation within the FPKI. SHIELD provides several key properties that overcome the limitations of prior approaches. First, it achieves full compliance with FIPS-204 and seamless functional interchangeability with standard ML-DSA, without altering the signing algorithm. Second, it conforms to FPKI’s structural and operational requirements, provides high security against highly adversarial environments, and prevents fraudulent certificates by eliminating single-key compromise risks. Finally, SHIELD provides the first open-source implementation of a FIPS-204-compliant threshold signature. We also empirically evaluated its performance under diverse network latency conditions to validate its practical conformance with FPKI operational needs.
