7. Which cipher is based on the clues of the physical factors, rather than the hardware or a software cryptosystem

The concealment cipher.

Explanation:

A concealment cipher also known as null cipher can be defined as an obsolete encryption format that typically involves the mixture of plaintext with non-cipher elements. This ultimately implies that, the plaintext is hidden in another message through encryption.

The concealment cipher is based on the clues of the physical factors, rather than the hardware or a software cryptosystem.

Basically, the concealment cipher is solely dependent on the clues of the physical factors that mainly affects the sender and receiver in a communication system.