11 — Cryptographic Amnesia

Cryptographic amnesia gives smart contracts the ability to provably erase data — producing a ZK proof that a storage slot has been overwritten with zeros and that all historical references have been scrubbed from the Merkle trie.

This satisfies on-chain “right to be forgotten” requirements without requiring chain rollbacks or off-chain trust.

amnesia { } block

contract PrivateRecord {
  field records: Map<Address, String>

  action store(data: String) {
    self.records[msg.sender] = data;
  }

  action erase() {
    amnesia {
      // Everything inside this block is provably erased.
      // The compiler inserts a two-pass erasure:
      //   Pass 1: overwrite with random bytes
      //   Pass 2: overwrite with zeros + emit erasure proof
      delete self.records[msg.sender];
    }
    emit RecordErased(msg.sender);
  }
}

Two-pass erasure protocol

1. Pass 1 — Randomisation: the slot is overwritten with keccak256(slot . blockhash(N-1)) — ensures no value is predictable.
2. Pass 2 — Zeroing: the slot is set to 0x00…00 and a ZK proof is emitted attesting that the slot was at value V at block N-1 and is now 0.
3. Proof publication: the proof is stored in the erasure receipt log (EIP-7XX, pending) so any observer can verify erasure.

Verifying an erasure off-chain

covenant amnesia verify   --contract 0xABCD...   --slot 0x...         --block 19000000     --receipt 0xtx...

Output:

Erasure proof VALID
  Slot 0x... zeroed at block 19000001
  Pre-image hash: 0xdeadbeef...
  Prover: Halo2 recursive

What amnesia can and cannot erase

The compiler warns when an amnesia block is applied to an event-indexed field — event logs are permanent.

GDPR / regulatory context

Cryptographic amnesia satisfies “erasure” under data minimisation frameworks because:

• The current state provably contains zeros.
• The ZK proof commits to the pre-erasure value’s hash, not the value itself.
• No trusted third party is needed to certify erasure.

This is not legal advice. Consult a privacy attorney for regulatory compliance.