The Phantom Challenge: How a Missing Hash Input in Solana's ZK Proofs Could Have Minted Unlimited Tokens

Security researcher suneal_eth from zkSecurity discovered a critical vulnerability in Solana's ZK ElGamal Proof program where a missing hash input in the Fiat-Shamir transformation allowed forging zero-knowledge proofs, potentially enabling unlimited token minting and draining confidential balances. The bug stemmed from a prover-generated challenge value not being absorbed into the Fiat-Shamir transcript hash within sigma OR proofs, breaking the critical invariant that all algebraic components must be included. This is the second critical ZK ElGamal bug found on Solana, highlighting the existential importance of correct Fiat-Shamir implementation in non-interactive zero-knowledge proof systems.