Secure aggregation in domains such as federated learning, Internet of Things, and voting requires operating on private inputs while preserving confidentiality, verifying that each input satisfies constraints, and avoiding trusted parties. Existing protocols achieve at most two of these requirements. We present zk-DEAP, a protocol combining lifted ElGamal homomorphic encryption, FROST threshold cryptography, and zero-knowledge proofs (Bulletproofs, zk-SNARKs, or zk-STARKs) for fully decentralized, verifiable, privacy-preserving aggregation. Our core technical contribution is a cryptographic binding mechanism preventing substitution attacks, where a valid proof for one input is paired with a ciphertext encrypting a different, malicious value. For Bulletproofs, we bind via ciphertext-derived randomness modification. For zk-SNARKs/zk-STARKs, to bind across algebraic structures (a well-known challenge in practical cryptography), we introduce a novel blinded arithmetic hash commitment with an embedded Schnorr constraint. These binding techniques force the ZKP's private witness to equal the encrypted value, ensuring any circuit-verified constraint applies to the ciphertext. We implement three production-ready, defense-in-depth variants in Rust and evaluate across 5-500 participants. Compared to unverified aggregation, zk-DEAP adds modest overhead while providing cryptographic guarantees against input manipulation that statistical defenses cannot match.

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