Which of the following is a method of defeating a cryptographic scheme by trying a large number of possibilities?

A zero-day is an undisclosed software vulnerability that has not yet been patched, not a method of cryptographic attack through exhaustive trial.

IP spoofing is a network-level attack that forges the source IP address in packets to impersonate another host, unrelated to breaking cryptographic schemes.

Brute force attacks work by systematically trying every possible combination of keys, passwords, or inputs until the correct one is discovered. This method directly targets the cryptographic scheme itself by attempting to exhaust the entire keyspace. It is the foundational concept behind key length requirements - longer keys exponentially increase the time required for a successful brute force attack.

The FMS (Fluhrer, Mantin, and Shamir) attack is a specific cryptanalytic attack targeting weak IVs in the RC4 cipher, not a general method of trying large numbers of possibilities.