Privately determining whether a password satisfies a constraint without having to divulge the password itself to a third party that evaluates the constraint, and without the third party even being aware of the result of the evaluation. After the user selects a password, private communication (e.g., private information retrieval) is used to determine whether the selected password satisfies password constraints. For instance, the password might be encrypted (e.g., homomorphically), and then the encrypted password and a function definition (e.g., a homomorphic function definition) is then provided to the third party. The third party then performs the function and returns an already encrypted result. The third party generated the encrypted result directly, without having access to the result in the clear. Upon receiving the encrypted result, the user's computing system may then decrypt the result, to find out whether the password satisfies the constraints, and thus is sufficiently safe.