Consensus Authorization Digest (CAD) Enables Quantum-Resistant Blockchains for Any PQC Signature

Post-quantum migration requires blockchains to revisit protocol design beyond simply replacing legacy signatures. A blockchain is designed to write a globally shared ledger and to keep it identically replicated and maintained by many validators. When signature bytes inside transactions are treated as ledger data permanently committed by consensus, every validator is forced to store them. In this setting, simply substituting post-quantum signatures can sharply increase replication and storage burdens and threaten decentralization. We propose the Consensus Authorization Digest (CAD), a fixed-size summary of transaction admission outcomes computed in the execution-layer admission stage and committed to the ledger; the consensus layer agrees only on its root, CADRoot, committed in the block header. By separating and removing signature material from consensus commitments, CAD enables signature-independent consensus commitments. We analyze why this separation preserves block validity as well as consensus safety and liveness. As a result, CAD enables quantum-resistant blockchains for any PQC signature scheme.