GHSA-7p92-x423-vwj6

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GHSA-7p92-x423-vwj6

Summary: Plonk verifier KZG multi point verification

Details: ### Impact The vulnerability allows a third party to derive a valid proof from a valid initial tuple {proof, public_inputs}, corresponding to the same public inputs as the initial proof. It is due to a randomness being generated using a small part of the scratch memory describing the state, allowing for degrees of freedom in the transcript. Note that the impact is limited to the PlonK verifier smart contract. ### Patches We still use a hash function on some data to have a pseudo rng, but instead of hashing the first 32 bytes of the state ( ` let random := mod(keccak256(state, 0x20), r_mod)` ) we hash the whole state at this point of the verifier as if it was a Fiat Shamir transcript: ``` mstore(mPtr, mload(add(state, STATE_FOLDED_DIGESTS_X))) mstore(add(mPtr, 0x20), mload(add(state, STATE_FOLDED_DIGESTS_Y))) mstore(add(mPtr, 0x40), calldataload(add(aproof, PROOF_BATCH_OPENING_AT_ZETA_X))) mstore(add(mPtr, 0x60), calldataload(add(aproof, PROOF_BATCH_OPENING_AT_ZETA_Y))) mstore(add(mPtr, 0x80), calldataload(add(aproof, PROOF_GRAND_PRODUCT_COMMITMENT_X))) mstore(add(mPtr, 0xa0), calldataload(add(aproof, PROOF_GRAND_PRODUCT_COMMITMENT_Y))) mstore(add(mPtr, 0xc0), calldataload(add(aproof, PROOF_OPENING_AT_ZETA_OMEGA_X))) mstore(add(mPtr, 0xe0), calldataload(add(aproof, PROOF_OPENING_AT_ZETA_OMEGA_Y))) mstore(add(mPtr, 0x100), mload(add(state, STATE_ZETA))) mstore(add(mPtr, 0x120), mload(add(state, STATE_GAMMA_KZG))) let random := staticcall(gas(), 0x2, mPtr, 0x140, mPtr, 0x20) ``` ### Workarounds In the function `batch_verify_multi_points`, the variable `random` (corresponding to `u` in the paper, step 12 of the [plonk](https://eprint.iacr.org/2019/953.pdf) verification process) should depend on `state_folded_digests_x`, `state_folded_digests_y`, `proof_grand_product_commitment_x`, `proof_grand_product_commitment_y` and `state_zeta` (by hashing those values for instance).

References: https://github.com/Consensys/gnark/security/advisories/GHSA-7p92-x423-vwj6, https://github.com/Consensys/gnark/commit/3421eaa7d544286abf3de8c46282b8d4da6d5da0, https://github.com/Consensys/gnark