We revisit the design of light-client blockchain protocols from the perspective of classical proof-system theory, and explain the role that proofs of sequential work (PoSWs) can play in it. To this end, we define a new primitive called succinct non-interactive argument of chain knowledge (SNACK), a non-interactive proof system that provides clear security guarantees to a verifier (a light client) even when interacting only with a single dishonest prover (a full node). We show how augmenting any blockchain with any graph-labeling PoSW (GL-PoSW) enables SNACK proofs for this blockchain. We also provide a unified and extended definition of GL-PoSWs covering all existing constructions, and describe two new variants. We then show how SNACKs can be used to construct light-client protocols, and highlight some deficiencies of existing designs, along with mitigations. Finally, we introduce incremental SNACKs which could provide a new approach to light mining.
Category / Keywords: cryptographic protocols / blockchain, light clients, proof of sequential work Date: received 24 Feb 2022 Contact author: hamzaabusalah at gmail com, peter gazi at iohk io, georg fuchsbauer at tuwien ac at, karen klein at inf ethz ch Available format(s): PDF | BibTeX Citation Version: 20220225:081218 (All versions of this report) Short URL: ia.cr/2022/240