Implementation of the Oblivious Pseudo Random Function (OPRF) protocol defined in RFC 9497.

The introduction of RFC 9497 puts it best:

A Pseudorandom Function (PRF) F(k, x) is an efficiently computable function taking a private key k and a value x as input. This function is pseudorandom if the keyed function K(_) = F(k, _) is indistinguishable from a randomly sampled function acting on the same domain and range as K(). An Oblivious PRF (OPRF) is a two-party protocol between a server and a client, wherein the server holds a PRF key k and the client holds some input x. The protocol allows both parties to cooperate in computing F(k, x), such that the client learns F(k, x) without learning anything about k and the server does not learn anything about x or F(k, x).

The scope of RFC 9497 and this crate covers three types of OPRFs:

• Base OPRF: The basic OPRF protocol, as described above.
• Verifiable OPRF (VOPRF): An extension of the base OPRF protocol where the server also provides a proof that it used the correct key k in the computation of F(k, x), which the client can verify without learning k.
• Partial OPRF (POPRF): An extension to VOPRF where a shared input y between the client and server is also used in the computation: F(k, x, y).

• Main crate documentation (100% coverage).
• Benchmarks.
• Examples.