Which key agreement protocol should a developer use for authentication, relying on elliptic curve mathematics?

Using Elliptic Curve Diffie-Hellman (ECDH) is the most appropriate choice for key agreement among the options given due to its reliance on elliptic curve cryptography, which offers enhanced security with smaller key sizes compared to traditional methods. ECDH is specifically designed for secure key exchange, allowing two parties to establish a shared secret over an insecure channel.

The elliptic curve aspect of ECDH provides an efficient and secure mechanism for generating keys, facilitating the creation of strong cryptographic keys using relatively small parameters. This capability is particularly advantageous in environments with limitations on processing power and bandwidth, making ECDH ideal for mobile and embedded systems.

Additionally, while RSA, Diffie-Hellman, and DSA are important cryptographic protocols, they do not leverage the benefits of elliptic curve mathematics in the way that ECDH does. RSA primarily focuses on public-key encryption rather than key agreement, while traditional Diffie-Hellman can require larger key sizes to maintain equivalent security levels. As for DSA, it is aimed at digital signatures rather than key agreement. Therefore, ECDH stands out as the most suitable protocol for secure authentication in this context.