On 09/27/2018 05:22 AM, Ivan Ivanov wrote: 
I suspect: despite that the "PC Speaker"-style beeping output is
working fine at this laptop/speakers while we are using Linux or even
some very simple OS like FreeDOS or Kolibri - that coreboot's spkmodem
might be buggy at G505S laptop, since there are only a few distinct
beeps (a couple of them are long enough to be visible at Soundcloud's
waveform) - everything else sounds like maybe an encrypted message but
could be just garbage (far from being similar to some morse code)

Hi Ivan,

sorry to say that I'm de facto illiterate when it comes to CoreBoot or even spkmodem.

What I can say, though, is that regarding transmitting hidden information through sound, the best way-to-go IMO would be piggybacking scattered, high-tuned and encrypted pieces of data on otherwise unsuspected waves. The frequencies would preferably be between what human ears can hear and what loudspeakers can transmit. Unfortunately, this is where compression algorithms come into play. So, any compressed file types (like ogg or mp3) may not convey sufficient suspicious data and therefore are no reliable grounds for checks/audits.

Directly seeing magnified waves seems to be required here. I'm not even sure if any software based tools like Audacity or any other vulnerable-to-attacks tools are suitable for those audits. Well, despite their huge budgets, **they** are sloppy or out-dated sometimes. So, using software based tools may be useful or not. Definitely better would be old-school analog oscilloscopes, and then go further from there.

Hoping I could be helpful in some way despite my illiteracy on CoreBoot.

Sincerely!