ElGamal finds various applications beyond just message encryption. Which of the following is NOT a typical use case for ElGamal?

Select one:

a$.$ Key exchange protocols, establishing secure communication channels between parties.

b$.$ Anonymous communication protocols, hiding the sender$\text{'}$s identity in online interactions.

c$.$ Digital signatures, ensuring the authenticity of a document and identifying the signer.

d$.$ Secure logins for websites and applications, where passwords are never directly transmitted.