Which definition among those given below best describes a covert channel?

A server using a non-standard or little-known port is simply unconventional port usage and does not meet the definition of a covert channel, which requires misuse of a protocol's intended function.

A covert channel exploits a legitimate resource, protocol, or mechanism in a manner not intended by its designers to secretly pass information and bypass security policies. Classic examples include tunneling data inside ICMP echo packets, DNS queries, or HTTP headers - all of which repurpose standard protocols for unauthorized, hidden communication.

Multiplexing is a legitimate, intentional networking technique for sharing a communication link and has no inherent relationship to covert or unauthorized information transfer.

WEP's insecurity stems from flawed cryptographic key management and IV reuse, which is an encryption vulnerability unrelated to the concept of covert channels.