What characterizes a half-open attack or SYN flood?

A half-open attack, commonly referred to as a SYN flood, is characterized by the attacker sending a large volume of SYN (synchronize) packets to a targeted server as part of the TCP handshake process without completing the handshake. This results in the server becoming overwhelmed as it allocates resources to manage these requests.

When the server receives a SYN packet, it responds with a SYN-ACK (synchronize acknowledgment) packet and waits for an ACK (acknowledgment) packet to finalize the connection. In a SYN flood scenario, the attacker never sends the final ACK packet, leaving many half-open connections. Because the server allocates memory and resources for these requests, a flood of such packets can lead to resource exhaustion, ultimately preventing legitimate users from establishing connections, which can disrupt services or even cause server crashes.

In contrast, other choices either describe unrelated processes, such as data encryption or user authentication, or imply a positive function that is not associated with the disruptive nature of a SYN flood attack. Therefore, option B accurately captures the essence of a half-open attack by emphasizing its goal of overwhelming a server through repeated, incomplete connection requests.