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The CGGMP21 threshold ECDSA protocol utilizes Zero-Knowledge (ZK) proofs to allow multiple parties to collaboratively generate signatures without any single party holding the complete private key. A critical vulnerability exists due to a missing verification step within these proofs. Specifically, the protocol fails to adequately validate a specific commitment during the signature generation process. This flaw breaks the fundamental security guarantee of the threshold scheme. A single malicious participant can exploit this omission by submitting a specially crafted, invalid ZK proof. By observing the signature output and the protocol’s failure to reject their bad input, the attacker can perform a key reconstruction attack. Through linear algebra, they can compute the secret shares held by other honest parties. This allows the malicious actor to piece together the entire group’s private signing key, completely compromising the wallet or system protected by the threshold signature scheme.
Platform: CGGMP21 Library
Version: < v0.6.3
Vulnerability: Key Reconstruction
Severity: Critical
date: 2025-11-24
Prediction: Patch Available
What Undercode Say:
git clone https://github.com/LFDT-Lockness/cggmp21.git cd cggmp21 git checkout v0.6.3 cargo build --release
// Example of a missing check in proof verification (pseudo-code)
fn verify_zk_proof(proof: &Proof, commitment: &Commitment) -> bool {
// ... existing checks ...
// MISSING: if !validate_dlog_proof(proof, commitment) { return false; }
true // Incorrectly returns true even if proof is invalid
}
How Exploit:
Malicious signer submits invalid ZK proof. Observes signature output. Computes others’ secret shares. Reconstructs full private key.
Protection from this CVE:
Upgrade to cggmp21 v0.6.3. Migrate to cggmp24 v0.7.0-alpha.2. Apply the security patch.
Impact:
Full private key compromise. Loss of secured funds. Broken threshold security guarantees.
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Sources:
Reported By: github.com
Extra Source Hub:
Undercode
