# Primitives

Penumbra uses the following cryptographic primitives, described in the following sections:

• The Proof System section describes the choice of proving curve (BLS12-377) and proof system (Groth16, and potentially PLONK in the future);

• The decaf377 section describes decaf377, a parameterization of the Decaf construction defined over the BLS12-377 scalar field, providing a prime-order group that can be used inside or outside of a circuit;

• The Poseidon for BLS12-377 section describes parameter selection for an instantiation of Poseidon, a SNARK-friendly sponge construction, over the BLS12-377 scalar field;

• The zk555 section describes zk555, an instantiation of the STROBE protocol framework for use inside (and outside) of circuits.