Zero Knowledge Proofs are mathematical techniques (families of cryptographic protocols) allowing someone (the prover) to prove to someone else (the verifier) that they are in possession of a secret, without actually disclosing the secret to the verifier or to some trusted third party. The secret is often a credential used for authentication (such as a password, biometric or personally identifiable information) but could equally be some other piece of sensitive/valuable information which is to remain confidential/private during the verification process, such as the person's age.

The process involves the prover (who knows the secret) convincing the verifier (who needs to check it) that the verifier’s statement/s or assertion/s concerning the secret (e.g. “The person is older than 18 years”) are either true or false, without disclosing additional information (e.g. their birthday). At the same time, the process substantially prevents malicious interference such as replay attacks (e.g. repeating a previous age-verification sequence that applied to a different person) and collusion between the parties.