Final answer:
The statement is true; an asymmetric key pair, composed of a secret (or private) key and a public key, is required when using RS256 for digital signatures, which is part of asymmetric cryptography.
Step-by-step explanation:
The statement that a secret or public key must be an asymmetric key when using RS256 is indeed true. RS256 is a standard for digital signature algorithms that stands for RSA Signature with SHA-256. It is a type of asymmetric cryptography which means it uses a pair of keys, a secret (or private) key and a public key, for encryption and decryption processes. In this context, the secret key is used to create a digital signature which can be verified by others using the corresponding public key. This ensures that the data originates from the holder of the private key and hasn't been tampered with. Asymmetric keys are essential to this process because they allow for a secure means of transmitting information where the sender and receiver do not need to share a secret key beforehand.