Which security strategy requires using several, varying methods to protect IT systems against attacks?

Defense in depth applies independent layers of security controls - such as firewalls, intrusion detection, encryption, and access controls - so an attacker must defeat each layer separately. Using varying methods ensures no single point of failure compromises the entire system. This layered approach is a foundational principle recognized in frameworks such as NIST SP 800-53 and CompTIA Security+.

The three-way handshake is a TCP connection establishment process (SYN, SYN-ACK, ACK) and is not a strategy for layering protective security controls.

Covert channels are hidden communication paths used to exfiltrate data, representing a security threat rather than a protective defensive strategy.

Exponential backoff is a network retry algorithm that progressively increases wait times between retries and has no relation to layered security defense.