Solana
Proof of Replication
Context
This figure appears in the 'Streaming Proof of Replication' section, specifically in the description of how storage challenges are issued and verified using Merkle proofs. The section explains that the network periodically selects random positions in each validator's encrypted ledger and requests the encrypted block at that position along with a Merkle proof of its inclusion in the validator's published encrypted ledger root.
What This Figure Shows
The diagram shows the Fast Proof of Replication verification scheme: the validator maintains a Merkle hash tree over its encrypted ledger, with the Merkle root published on-chain as a commitment to the full encrypted dataset. When challenged at position k, the validator returns the encrypted block C_k and a Merkle branch proof from C_k to the root. The verifier recomputes the expected encryption key from the validator's public key and the PoH-derived seed, decrypts C_k to recover the expected plaintext P_k, and verifies the Merkle branch against the published root. The entire verification requires O(log n) hashes rather than the full encrypted dataset, making challenge-response efficient even for large ledgers. Challenge positions are derived from the PoH state, which the validator cannot predict in advance, forcing storage of the complete encrypted dataset.
Significance
This Merkle-based challenge scheme is what makes Proof of Replication cryptographically sound in the presence of rational (economically motivated) adversaries. The unpredictability of challenge positions prevents selective storage, and the Merkle tree commitment allows efficient verification without the verifier downloading the entire encrypted ledger. Together with the CBC encryption mechanism, this creates a complete accountability system where any validator that discards data will eventually fail a challenge and lose its stake.
