A covert channel is a channel that

A covert channel is specifically defined as a communication path that transfers information in a manner not sanctioned by the security policy of the system or network. This distinguishes it from legitimate channels, which are authorized and controlled. The key attribute is the violation or circumvention of the security policy, not merely the medium or method of transfer.

This describes a legitimate, authorized channel that operates within policy boundaries, which is the opposite of a covert channel.

This describes a generic communication path and omits the defining characteristic that a covert channel operates outside the security policy.

Encryption is a property of data protection and does not define a covert channel - a covert channel can be unencrypted, and an encrypted channel can still be legitimate and policy-compliant.