Computer Hacking Forensic Investigator (CHFI) Practice Exam 2025 – The Complete All-in-One Guide to Exam Mastery!

The medium referred to in the context of an echo data hiding technique is indeed the cover audio signal. This technique involves concealing a secret message within an existing audio file, where the original audio acts as the medium for hiding the data. The cover audio signal is manipulated in such a way that the embedded information remains imperceptible to the human ear while still being retrievable by software designed to extract it.

In echo data hiding, the hidden message is typically encoded by introducing subtle modifications to the audio waves, creating variations in its natural echo patterns. This process relies on the characteristics of sound and human auditory perception, which allows the embedded information to remain as inconspicuous as possible.

The other concepts mentioned, such as the phase spectrum, pseudo-random signal, and pseudo-spectrum signal, do not serve as the medium for embedding messages in this specific method. Instead, they pertain to different aspects of signal processing and data representation, rather than functioning as the actual carrier of the hidden information in echo data hiding. Thus, the cover audio signal is the appropriate term for describing the medium in this technique.