Definition
A zero-knowledge proof (ZKP) is an interactive or non-interactive protocol in which a prover convinces a verifier that a statement is true while leaking no information about the witness behind it. Goldwasser, Micali, and Rackoff introduced the concept in 1985; modern formulations require completeness, soundness, and zero-knowledge.
Most production deployments are non-interactive (NIZK). SNARK families (Groth16, PLONK, Halo2) and STARK families dominate, each trading proof size, verification time, and trusted-setup requirements. Any computation expressed as a constraint system can be proven over private inputs.
ZKP serves two distinct purposes: proving properties without disclosing the underlying values (privacy), and replacing heavy verification with short proofs (scalability). Lemma uses the privacy axis as its primary lever.
Lemma implementation
Lemma's core architecture pins provenance, attributes, and AI inference traces as a docHash and emits proofs over a ZK circuit that exposes only the facts that matter — "a provenance chain exists," "an attribute is within a range" — without leaking the underlying content or PII to the verifier.
The stack combines Poseidon hashing for circuit-internal efficiency, commitments for staged disclosure, and selective disclosure for attribute-level granularity. Final proofs verify cheaply on EVM-compatible chains.
ZKP is the substrate for every Lemma product (Civic / Critical / Compliance / Trust402). Hiding the evidence while exposing the verification is the only path that satisfies regulatory adherence and confidentiality at once.