How does SSH key authentication function?

SSH key authentication is a security protocol that allows users to access remote servers without the need for a password by using a pair of cryptographic keys—a public key and a private key. In scenarios where SSH key authentication is implemented, the following occurs:

When the client attempts to connect to the server, it uses the public key that is stored on the server for authentication. The server creates a challenge, which typically involves generating a random piece of data (a prime number or similar) and encrypting it with the public key. This encrypted piece of data is then sent to the client. The client decrypts this challenge using its private key and generates a hash (such as an MD5 hash) of the decrypted result. This hashed response is sent back to the server for verification.

In this process, the security relies on the private key remaining confidential and only known to the client; thus, without it, the server cannot validate the authenticity of the user trying to connect. This method significantly strengthens security because even if the server's public key is known, it provides no advantage in decrypting communications without the private key.

Choosing the option stating that the client decrypts a prime number using the private key and sends an MD5 hash back accurately describes the mechanism of