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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

where we get a research paper on Nano chemistry....?
Maira Reply
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
Nasa has use it in the 60's, copper as water purification in the moon travel.
nanocopper obvius
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
analytical skills graphene is prepared to kill any type viruses .
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
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.
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Elec 301 projects fall 2008. OpenStax CNX. Jan 22, 2009 Download for free at http://cnx.org/content/col10633/1.1
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