<< Chapter < Page Chapter >> Page >
This module details the "attacks" used to test the three methods of encryption (frequency, phase, and echo) and how they responded to deliberate external attempts to break them. This is a continuation of the fall 2008 ELEC 301 class project.

Noise addition

We added varying amounts of Gaussian noise to our marked test signals and attempted to retrieve the hidden message with varyingsuccess.

In order to account for the noise, we adjusted the threshold we used in the decoding algorithm. From Figures 10,12, and 14, it isclear that a threshold can be drawn between the higher observed differences (one-bits) and the lower observed differences. However, in the cases where toomuch noise was added (see Figures 11,13, and 15), this threshold is not so clearly defined. In fact, for the PSA and EA, any threshold value is difficultto determine whether by calculation or by “eyeing it.”

Observed differences between frequencies of original signal and frequencies of marked signal for FMA with no added noise
Observed differences between frequencies of original signal and frequencies of marked signal for FMA with added noise of SNR 30 dB
Observed differences between frequencies of original signal and frequencies of marked signal for PSA with no added noise
Observed differences between frequencies of original signal and frequencies of marked signal for PSA with added noise of SNR 30 dB
Observed differences between frequencies of original signal and frequencies of marked signal for EA with no added noise
Observed differences between frequencies of original signal and frequencies of marked signal for EA with added noise of SNR 70 dB

Based on studying these threshold values, we found maximum noise we could add to the marked signal for each algorithm. The minimumSNR for the FMA, PSA, and EA were 30 dB, 30 dProject! ElB, and 60 dB, respectively. At these SNR values and with an input of “Elec301 Project! ”, thealgorithms output as follows:


Elec301 Pro*ect! Elec301 Project! ElB, and 60 dB, respectively. At these SNR values and with an input of “Elec301 Project! ”, thealgorithms output as follows:

ec301 Project! Elec30ec301 Project! Elec30


Elec301Elec301Elec301ELec301Elec301EleC#01Elec301Elec300Elec301El ek30qElec301Elec301Elec301Elec301El El`c 1El


Elec381 Pzg*ect!MleC343 RzebesT!eoec#p1 Psozec|#GleC#00 P2ojEct)Mmec301 QrozEkw Umea3p1'PRgbmct!Eleg:0qP2ojea4%D|

The FMA and PSA clearly outperformed the EA in the noise category. In fact, at the point that we begin to miss bits, we can alreadysignificantly hear the white noise. Because the FMA only looks at the difference between the frequencies of the original and marked signals for a small segmentof the frequency spectrum (in particular around the maximum frequency of the original signal), the noise power included in the difference is much smaller forthe FMA than for the PSA and the EA which both calculate the difference over the whole frequency range. The PSA is good because our ears cannot detectsignificant alterations in phase; in fact, the phase shift could go up to .1*pi without audible detection. This large phase shift power difference between a oneand zero is much more than the power added by the noise.

For all of our algorithms some genres of our test signals performed better in every case. We found that ‘pop’ and ‘techno’ bothfailed noise tests at least 20db SNR higher than any of the others. Examining the magnitude in the frequency domain for both of these signals (see Figure 8)shows us that the 90% power bandwidth is wider than in the others. I.e. there is significant information at higher frequencies, so more significant frequenciesare altered by the noise, which lessens the amount of tolerable SNR.

To defend against noise we encode the user-input phrase over and over as many times as will fit. This increases our chances ofgetting the phrase back since the probability of several bits being wrong is lower than the probability of one bit being judged incorrectly.

Another defense against noise was to raise our various predefined values closer to human-hearable level. For example we can increase the amount of phase shift in the PSA from .01*pi all the way to .1*pi.These increases mean that the value shifting caused by adding noise is not significant when compared to the value shifting created by encoding a one. Ingeneral, there is a balance between how much noise a marked signal can take and how audible the mark becomes. This balance is found by toying with thepredefined values for each algorithm.

Compression and decompression

We also tested an attack in which the wave file was compressed using MPEG-1 and AAC compression algorithms. In order to test whetherwe could still recover our encoded bits in MATLAB (MATLAB can only work with wave audio files), we then decompressed the files. We found that we werecompletely unable to recover our encoded message and received as output either nothing or complete garbage.

These results were not unexpected as audio compression algorithms take advantage of the same psycho-acoustical phenomenathat we used to


Our encoding scheme can survive truncation on the back end. We simply lose any bits contained in the deleted data. While we didnot implement this process, we could implement a matched filter setup to survive truncation on the front end. We could take the marked audio file and attempt toplace it in the unmarked original file using convolution.


We tested whether our algorithm could be marked with a second message and still recover either message. We provided our decoder withthe original signal and the signal that had been marked two different times. If we had provided the decoder with the once-marked signal and the original signal(cascading the decoder), we could have easily recovered our original signal; however, we felt this solution was trivial and against the point of theattack.

We found, as expected, that when encoding two different messages, we could not correctly recover either message. We, however,found that if two of the same letter were encoded in the same place, we could recover this particular letter. Remarking the signal with the same message doesnot affect our ability to decode the message, but remarking can affect the quality of the output.

Questions & Answers

what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!

Source:  OpenStax, Elec 301 projects fall 2008. OpenStax CNX. Jan 22, 2009 Download for free at http://cnx.org/content/col10633/1.1
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Elec 301 projects fall 2008' conversation and receive update notifications?