Compact Shielded CSV: Post-Quantum, Private, Lightweight Client-Side Validation Blockchain

We propose Compact Shielded CSV, a private client-side validation blockchain for peer-to-peer payments designed for the postquantum era. Upgrading existing blockchains to quantum-resistant cryptography substantially increases on-chain overhead. By keeping all large cryptographic artifacts off-chain, Compact Shielded CSV keeps a minimal on-chain footprint independent of the size of the underlying cryptographic proofs and signatures. For a single input transaction, the onchain footprint is just 3 hashes (3x32 bytes): a nullifier, a degriefer, and a commitment to the transaction. We introduce the degriefer - a novel mechanism that enforces ownership and prevents double-spending using only hash commitments, eliminating the need for on-chain signatures entirely. These properties make Compact Shielded CSV a promising foundation for private, scalable, post-quantum digital payments.