In Trojan terminology, what is a covert channel?

A covert channel exploits mechanisms not originally intended for communication, such as timing variations or shared resources, to transmit data in ways that bypass security controls. Trojans commonly use covert channels to exfiltrate data or receive commands while evading detection by firewalls and intrusion detection systems. The defining characteristic is that the channel violates the security policy of the system or network it operates within.

This describes an overt or legitimate communication channel, which is an authorized path explicitly permitted by security policy, the opposite of a covert channel.

Hiding boot processes and services describes rootkit behavior, specifically kernel-level rootkits, which is a separate concept from covert channel communication.

Reverse HTTP tunneling using HTTPS describes a specific tunneling technique used for firewall evasion, which may utilize a covert channel but is not the definition of a covert channel itself.