SPHINCS+ is primarily which type of primitive?

• A. Hash-based digital signature
• B. Key exchange
• C. Encryption
• D. Message authentication code

Answer: (A)

SPHINCS+ is a hash-based digital signature scheme. It uses cryptographic hash functions to build a signature system—often with a tree structure and hash-based one-time signing components—that provides authenticity and non-repudiation for messages without encrypting them. The security rests on the properties of hash functions (preimage and collision resistance) rather than on factoring or discrete logarithms, which is why it’s considered post-quantum secure. It does not provide encryption of data, it does not establish a shared secret for secure communication (key exchange), and it is not a MAC, which would be a symmetric-key tag for a message. Therefore, SPHINCS+ is best described as a hash-based digital signature primitive.