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GHSA-7p92-x423-vwj6 json

Plonk verifier KZG multi point verification

published 3y ago modified 2y ago also GO-2023-2119

cvss
—
not scored
cisa kev
Not listed
not in CISA's catalog
epss
—
no score, EPSS covers CVEs only
public exploits
0
none known

Summary

### 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).

Patch / fix

  • go github.com/consensys/gnark 0.9.1

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Affected packages

ecosystem package affected fixed in
go github.com/consensys/gnark
<0.9.1
0.9.1

References

Sources

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