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Abort extracting vk when there are no phase 2 contributions #620

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Abort extracting vk when there are no phase 2 contributions #620

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Abort extracting vk when there are no phase 2 contributions
StefanosChaliasos Feb 26, 2026
cd20312
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OBrezhniev Mar 23, 2026
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5 changes: 5 additions & 0 deletions src/groth16_verify.js
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Original file line number Diff line number Diff line change
Expand Up @@ -69,6 +69,11 @@ export default async function groth16Verify(_vk_verifier, _publicSignals, _proof
const vk_alpha_1 = curve.G1.fromObject(vk_verifier.vk_alpha_1);
const vk_beta_2 = curve.G2.fromObject(vk_verifier.vk_beta_2);

if (curve.G2.eq(vk_gamma_2, vk_delta_2)) {
if (logger) logger.error("SOUNDNESS ERROR: vk_gamma_2 and vk_delta_2 are equal. This verification key is insecure, the zkey likely has no phase 2 contribution. Proofs can be forged. Aborting verification.");
return false;
}
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Copilot AI Mar 23, 2026

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New behavior returns false when vk_gamma_2 equals vk_delta_2, but there doesn’t appear to be a test exercising this soundness guard. Adding a unit/integration test that verifies groth16.verify rejects an insecure verification key (e.g., by crafting a VK with vk_delta_2 copied from vk_gamma_2, or by exporting from an un-contributed zkey if that produces equality) would prevent regressions.

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const res = await curve.pairingEq(
curve.G1.neg(pi_a) , pi_b,
cpub , vk_gamma_2,
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4 changes: 4 additions & 0 deletions src/zkey_export_verificationkey.js
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Expand Up @@ -56,6 +56,10 @@ async function groth16Vk(zkey, fd, sections) {
const curve = await getCurve(zkey.q);
const sG1 = curve.G1.F.n8 * 2;

if (curve.G2.eq(zkey.vk_gamma_2, zkey.vk_delta_2)) {
throw new Error("SOUNDNESS ERROR: vk_gamma_2 and vk_delta_2 are equal. This zkey is insecure, it likely has no phase 2 contribution. Proofs can be forged. Run 'snarkjs zkey contribute' before exporting.");
}
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Copilot AI Mar 23, 2026

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Throwing here will skip the fd.close() in zkeyExportVerificationKey (it’s only reached on the success path), which can leak the underlying file handle when exporting a Groth16 VK from an insecure zkey. Consider wrapping the readBinFile/protocol switch in a try/finally so the descriptor is always closed, even when groth16Vk throws.

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const alphaBeta = await curve.pairing(zkey.vk_alpha_1, zkey.vk_beta_2);

let vKey = {
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