Which of the following attacks allows an attacker to recover the key in an RC4 encrypted stream from a large number of messages in that stream?

A rainbow attack uses precomputed hash tables to reverse cryptographic hash functions for password cracking, and does not target RC4 stream cipher key recovery.

A SYN flood attack is a denial-of-service technique that exploits the TCP handshake process to exhaust server resources, and has no relation to cryptographic key recovery.

A zero-day attack exploits a previously unknown software vulnerability before a patch is available, and is unrelated to RC4 stream cipher cryptanalysis.

The FMS attack, named after its authors Fluhrer, Mantin, and Shamir, targets the RC4 stream cipher by exploiting a weakness in how RC4 generates certain initialization vectors (IVs). By collecting a large number of encrypted messages that use these weak IVs, an attacker can perform statistical analysis to recover the secret key. This technique was famously used to break WEP wireless encryption.