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M 12/2/13
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Classes resume. No
additional HW due.
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T 12/3/13
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No class. If you wish to
stop by to discuss your project proposal and/or a switch to a different
topic, please feel free.
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W 12/4/13
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HW due: Skim this article lightly
(reading only for general background), and then consult this page in
detail regarding the Hamming 7,4 code (7 bits carrying a 4-bit payload).
Then, for each of the following, determine whether the 7-bit transmission is
(a) valid (in which case you should translate the payload as a single hex
digit)
(b) invalid but correctable (in which case you should correct the wrong bits
and state what the correct 7-bit transmission should have been, as well as
the payload as a single hex digit)
or (c) invalid and uncorrectable.
1. 0110101
2. 0101110
3. 1011101
4. 1100010
5. 1101001
6. 1001001
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Th
12/5/13
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HW due:
1. Correct the errors in the following bitstream
encoded using Hamming 7,4:
1110110 1101110 1001111 0100101 1001100 0011110
2. Take the 6 payloads you obtained in #1, and write your answer as 6 hex
digits in order from left to right.
3. Convert your answer from #2 from hex into ASCII text. If you have lost
your ASCII table, click here for
one. Your final answer should consist of 3 characters.
4. Convert each of the following 24-bit RGB colors to its appropriate color
name. The first one is done for you as an example.
0x00FF00 = GREEN
0x0000FF
0x000000
0xFFFF00
0xFFFFFF
0x00FFFF
0x808080
5. Write the short identifier of your project topic. For example, Gabe would
write, “cryptographic hash functions.” A complete sentence is not expected.
By the way, if you are still searching for a topic, here are some additional
ones to consider:
color spaces
Bitcoin
rainbow tables
viruses
Tornado codes
certificates
optical computers
6. Prove that the number of possible 2-person connections for n people attending a party is O(n2).
In other words, prove that the number of possible connections grows quadratically as the number of people increases.
Hint: For 4 people (let’s call them
A, B, C, and D), the possible 2-person connections are AB, AC, AD, BC, BD,
and CD. We don’t count BA, CA, DA, CB, DB, and DC, since those are duplicates
of the 6 connections we already listed.
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F 12/6/13
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Answer the questions below.
We will use 24-bit RGB color format throughout (8 bits for R, 8 bits for G, 8
bits for B).
1. A 6MP (6 megapixel) cell phone camera stores a single image as 6 million
RGB values. Compute the amount of storage space required. Give answer in MB.
2. Compute the amount of storage required for 2500 pictures of the size
described in #1. Give answer in MB.
3. Are images like those described in #1 and #2 stored compressed or
uncompressed? Explain your answer.
4. If compression is used to store RGB still images on a cell phone, would it
be lossy or lossless? What commercial format would
you recommend?
5. Can the human eye detect the difference between a color of 0xFFFFFF and
0xFFFFEF? Why or why not?
6. Can the human eye detect the difference between a color of 0x00002F and
0x00003F? Why or why not?
Note: You will have to do some
research in order to answer questions 5 and 6. Justify your reasoning.
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M 12/9/13
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HW due: Work on your
project. A short oral progress report is expected. Nothing in writing is
required just yet.
Here are the current topics:
Andrew: encoding and analysis of football statistics
Beau: digital signatures
Coby: audio phase and PSK
Gabe: cryptographic hash functions
James: Bitcoin
Justin: encrypted data transmission (DES, PGP?)
Matthew: man in the middle
Max: circuitry and traffic systems
Michael: circuitry in Minecraft
Nate: steganography with images and text
Ryan: PRNG statistical analysis
Shane: QR codes
Thomas: projectile rendering techniques
If you wish to change your topic, send e-mail as soon as practical to Mr.
Hansen (with a subject line beginning with 2 underscores).
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T 12/10/13
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No school (snow day).
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W 12/11/13
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HW due: Canceled on account
of Tuesday’s snow day. It would be rough to have to do additional written HW
on a snow day! However, you should continue to do some background reading
related to your project. By now, you should have a fairly coherent picture of
your topic and a focused idea that you can dig into and become knowledgeable
about.
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Th
12/12/13
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HW due: Read §3.1 (bottom
of p. 105 through middle of p. 122) and §3.2 (pp. 125-141); write p. 142 #8,
9.
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F 12/13/13
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HW due:
1. Finish yesterday’s reading if you have not already done so. Another
open-notes reading quiz is possible.
2. Read p. 143 to the middle of p. 154.
3. Write p. 142 #11.
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M 12/16/13
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HW due:
1. Read pp. 166-173, pp. 242-243, and the calendar entry for Wednesday,
12/18.
2. Write a “study guide” for Wednesday’s test. Include instructions for
yourself on how to compute your public key (see #5 in the 11/21 calendar
entry), how to use combine someone else’s public key with your own private
key to produce a shared secret (also #5 in the 11/21 calendar entry), how to
compute the ith
output of a PRNG by using the shared secret as the seed (see #3 in the 11/21
calendar entry), how to merge the output of a PRNG with a bitstream
to XOR-encrypt or XOR-decrypt it, how to compute even parity for any bitstream, how to use even parity to detect errors, how
to use the Hamming 7,4 code to correct errors, and anything from Chapter 3
and the diagram on pp. 242-243 that you think is worth knowing. If your study
guide is worthy, as judged by Mr. Hansen, then you will be permitted to use
it on Wednesday’s test. Worked examples are permitted in your study guide.
Try to limit yourself to 2 pieces of paper. You may use the front and back
sides of both sheets.
In class: Inspection of study guides, followed by general review.
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T 12/17/13
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No class.
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W 12/18/13
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Test (100 pts.) on PKI, parity, error correction
(Hamming 7,4 only), and most of Chapter 3, plus the diagram described on pp.
242-243. Omit pp. 154-158 and
161-165. You may use your study guide if it was approved on Monday.
Question: What do I need to
understand regarding the diagram on p. 243?
Answer: Let us assume that
24-bit RGB digital video is used throughout. A foreground image (such as a
star, or a TV weatherman who thinks he’s a star) is to be superimposed on a
background image (such as a weather map or a scene of Capitol Hill). Call the
foreground/star image S and the
background image B. The star is
photographed against a blue (or sometimes green) screen, and from the digital
image S we compute an image S' as follows: each pixel in S' is 0x000001 if the corresponding
pixel in S is the color of the
bluescreen, otherwise 0x000000. When S'
is multiplied, pixel by pixel, with B,
we get the image shown in the lower right corner of the diagram on p. 243,
which we may call M since it’s a mask that the star can be
merged with. Formula: M = S'B.
Meanwhile, the negation of S', which we might call ~S', has 0x000000 (pure black) for each
bluescreen color pixel and 0x000001 for everything else (the star). When ~S' is multiplied, pixel by pixel, with
S, we get an image (see upper right
corner of diagram on p. 243) that keeps only the star against a perfectly
black background. Let us call that digital image ~S'S, or I for short.
Formula: I = ~S'S. We’ll use the letter I
to remind us that this image is to be injected
into the mask M that we prepared
earlier.
I is mostly pure black. The only
pixels of I that are nonzero, in
fact, are the pixels corresponding to the star’s image.
M is mostly background. The only
pixels of M that are nonzero are
the background where the star’s image doesn’t exist.
Therefore, by adding I + M, pixel by pixel, we get a digital
image that shows the star against the desired background. The pure black
parts are 0x000000 in RGB, and therefore they do not affect the sum.
Formula: output = I + M = ~S'S + S'B.
Question: OK, so I “sort
of” understood all of that. But what the heck would I be expected to do on
the test?
Answer: You might be given
the diagram on p. 243 and asked to identify what the purpose of one of the
intermediate images is. Or, you might be given a formula such as I + M = ~S'S + S'B and asked to explain what part of
it meant. Or, you might be given the diagram on p. 243 with some of the
operation names (such as “map negative” or “multiply” or “add”) missing, and
you would have to explain not only what the missing operation was, but why it needed to be there.
In other words, you won’t be able to pass by copying the diagram and the
formulas and regurgitating them on the test. You’re actually going to have to
invest 20 or 30 minutes in understanding
what the diagram means and working through the explanations above.
Question: Why is Mr. Hansen
so demanding?
Answer: Regardless of what
you study in college, and regardless of what job you ultimately end up
having, nobody is going to pay you any money to memorize things that can
simply be looked up on Wikipedia.org or in some reference book. You have to
be able to think about what things
mean and explain them to other
people, so that you or they can make
decisions with that information. That’s what we call critical thinking.
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Th
12/19/13
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HW due: Fill out this blank copy of yesterday’s test. At a
minimum, work all the problems that you had trouble with. (If time permits,
fill out the entire test.) We will check answers in class.
After the HW check, we will welcome our guest speaker, Ms. Suzanne Schroer
from the Nuclear Regulatory Commission.
Tonight: Please attend Lessons & Carols.
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F 12/20/13
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Optional Test, 7:00-7:50 a.m., MH-102. This is an opportunity to improve your score. The
problems will have different numbers, and the fill-in-the-blanks may be
somewhat different, but the test will otherwise be almost a clone of
Wednesday’s test.
If your score happens to be lower on the optional test, you will not be
penalized.
In class: More about aliasing and Nyquist’s
Theorem. There is no additional HW due, but you will be asked to give a short
oral progress report on your project.
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Christmas Break
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Work on your project. There are two (2) components required.
1. In-class (oral) presentation.
Your in-class presentation should be between 5 minutes long (minimum) and 10
minutes long (maximum). Do not attempt to describe, or even to summarize,
everything that you learned. Set as your goal describing one aspect of your project in sufficient detail that we can all
see that you learned something interesting.
For example, if your topic is on
bar codes, you would not want to give an overview of everything on the
subject of bar codes. Instead, you might give a minute on history (year of
the first bar code, location where the first UPC scanner was installed,
maybe) followed by a description of how one particular type of bar code
format implements error correction. Leave a minute at the end of your
presentation for Q & A.
2. Written presentation. You need
to submit something in writing. It does not need to be long. If you use a
PowerPoint slide show for your in-class presentation, a printout of your
slides, accompanied by an additional page to document your references, is
sufficient. “Four-up” format is preferred (i.e., 4 slides per printed page).
If you wrote a program, a listing of the commented source code and a
description of the resources you used to learn from would suffice. If you are
giving an in-class presentation with no visual aids, your written presentation
should be 2 to 5 pages long. Anything
that is quoted verbatim, or used as a chart or an illustration that you did
not personally create, must be footnoted and acknowledged. Your footnote
style can be anything reasonable that you wish to use, as long as it is
consistent. At the end of your written presentation, include a short
bibliography in which you document the sources that you drew from, even if
you did not quote verbatim from them. You may not use Wikipedia for more than
one of your sources. A minimum of three (3) resources are expected. Personal
interviews are acceptable as resources; in that case, you would name the
person that you interviewed, and give the date of the interview.
Write your name and your presentation
date on the upper right corner of your first page. Your written presentation
is preferred to be turned in with your in-class presentation, but you may
delay it until Thursday, 1/9/14, if you wish.
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