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### Course: Computer science theory > Unit 2

Lesson 3: Cryptography challenge 101# Clue #4

### Finally you approach the safe house...

The coast is clear.

Luckily you brought a flashlight...

Ah! Garbage...

These notes look like they are related to the code...

You don't want anyone to know you were here, so you return the garbage immediately and escape.

Hopefully you have enough information to break the initial

**secret code**...### Hints

1) Remember there was a newspaper clipping found inside the bag in The Discovery

2) Make sure you are comfortable with different number bases, such as binary numbers.

3) A frequency stability tool could help.

4) the XOR operation was used when constructing in this code.

2) Make sure you are comfortable with different number bases, such as binary numbers.

3) A frequency stability tool could help.

4) the XOR operation was used when constructing in this code.

### Still Stuck?

Check out the hints in the next exercise

## Want to join the conversation?

- Does anyone know the cipher that was used to make the code? And if so, what cipher is it and how do you decode it?(15 votes)
- Hint:

First, get the angles into binary.

In each angle, there is one cardinal direction and one intermediate direction. The cardinal direction is the first set of two binary digits for each angle and the intermediate direction is the second set of binary digits.

Cardinal Directions:

North=00, East=01, South=10, West=11

Intermediate Directions:

Southeast=00, Southwest=01, Northwest=10, Northeast=11

I hope this helps!(50 votes)

- So far I think they used a one time pad, using the newspaper to generate the random numbers, vowel=1, consonant=0, doing xor on message, and then converting to base 4 to encrypt using the compass rose. Not sure if the spiral on top of the arrow had anything to do with how it was encrypted. Any thoughts?

UPDATED: The third to last image has the term one time pad written on the far right about halfway down. It runs beyond the edge of the image, but one and time are able to be made out.

RE-UPDATED: I figured out the spiral, it has to do with the modification to the polybius. I've got all the pieces together, just a few bumps preventing me from getting everything right...(15 votes)- Once you get past everything you just said, you need to convert the new binary string into base-6. However, do it part by part. How big do you think each part should be? Think about how many binary digits one base-6 digit can take up. What's 4 or 5 in binary?

Once you convert it into base-6 part by part, you need to use a 6-by-6 Polybius square with letters and numbers. Can you guess which shape the letters and numbers go in? Hint: You mentioned it in your question.

I hope this helps!(23 votes)

- Regarding checkpoint 4: what seems like the only reasonable approach fails to be accepted as the answer. Therefore there must be some alternative and some hint that I must use this alternative but I'm stuck as to what that is. Here is my solution (incorrect) for checkpoint 4:

What values do you get after you XOR the following message with the given pad?

message: me I encode ME as 5,2 ; 1,0

101 010 001 000

pad: 'open me to read' Using vowels as 1,0 I get

101 001 010 110

XOR gives

000 011 011 110

when I enter that with no spaces between the triples the answer is not accepted as correct. ( I also tried 2,5; 0,1 the rotated version)

I'm thinking that perhaps there's a different polybius square than the one i inferred from the hints.(10 votes)- I think M is 2,5 while E is 1,0 but not sure yet(3 votes)

- Can someone make like a picture or something of the whole pad? I made an XORing program (but the binary message is built in, so I won't share it.), and I need the pad.(4 votes)
- Do you mean transfer the pad into binary into angles? Interesting...

Well, I'm not sure if this is going to help anybody, but here it is!

U=North

D=South

L=West

R=East

UL=Northwest

UR=Northeast

DL=Southwest

DR=Southeast

I think this would be it (a space is a new angle):

U/UL R/DL U/UR U/UR U/UL R/DR R/UL R/DR D/UL D/DR R/DR U/UL D/DR D/UL R/DL R/DL U/UL U/DL U/UL D/DR D/DL U/UL D/UL D/DL R/DL U/UL U/UR R/DR D/UR U/UL U/UL U/DL U/DR D/UR U/DL U/DR L/DR D/UL U/UL D/DR D/DR D/UL U/UL D/DL U/UR R/DR D/DL U/UL R/UL U/UL R/DR U/UL D/DR D/DL U/UL R/DR D/DL R/DR D/DL R/UL D/DL R/DR D/DL R/DR R/DL U/DL R/DL L/UL R/DR D/UL U/UR R/DR L/DR D/DL R/DL U/DL L/DR R/DR R/DR D/DR L/DR L/UL D/DL R/DL R/UR D/DL R/DL U/DL R/DR D/DR L/DR D/DL R/DR R/UL U/DL D/DR D/UR U/UL U/UL D/DR D/DL U/UL D/DL U/DR D/UL R/DR D/DR D/UL D/DL U/UL R/DR D/UL R/UL R/DR D/UL R/DL U/UL R/DR D/UL U/UL R/UL L/UL R/DR L/DL R/DL R/DL U/DR D/DR R/DR D/DL R/DL U/UL D/DL U/UL R/DR R/DL U/DL D/DR D/DL U/DL U/UL U/UL U/UL U/DL U/UL U/UL U/UL D/UL D/DR L/UL D/UL R/DR R/DR D/UL D/UL D/UL D/DR D/DR D/UL U/UL R/DR D(<--this is half an angle)

I hope this helps!(16 votes)

- Hopefully the next clue or picture will give some information on how to go from binary to letters?(6 votes)
- ALERT: I updated the final code in "The Discovery"(7 votes)

- Does the code change part way through? My decoded message is readable for about 1/3 of the text and then, gibberish. Is this a typo, or are parts of the code decoded differently?(6 votes)
- Huh.... I encountered the same problem... was able to decipher.... the first 44 letters.... and then boom gibberish. I did spot a typo, but that didn't change the gibberish.(1 vote)

- I am on the verge of solving this, but could use one last tip or nudge in the right direction.

I have translated the "angle code" into binary, and agree with others posts, eg 20,33,22,21,00. (binary = 100011111010100100001111110000) I have converted the pad article(Thewholegraingoodnessofbluechi) to binary 001001010011001100100100011001

XORing these and using 3 digits per number to access the lookup table gives me

(100 011) ^ (001 001) -> 101 011 or 5,2 for the first letter. after getting the correct spiral figured out, (from one of the hints i read) this means 'S' , and the next 4 are 'tart'. All in all not surprising.

My trouble is that I have pretty much garble after that.

One specific question I have is how to handle digits in the pad phrase eg 2008. I am skipping them like any other non-alpha characters, punctuation etc.(6 votes)- I don't see any digits in the source for the pad ...

If everything is garbled after the first 5 letters it is probably:

- a missing or extra digit in the pad

(invalid numbers in your output would indicate this)

- an incorrect "spiral"

( After you attempt to decode the message:

-does the end of your message agree with the format of other messages ?

-do your most frequently occurring letters agree somewhat with the most frequent letters in English ?)

Good Luck(2 votes)

- I wonder if that spiral above the arrow in the last picture has something to do with the method of changing the original message to numbers.(4 votes)
- I have how they went between numbers and angles but not all the details of how they used the newspaper as a one time pad(3 votes)

- I think I figured out how and where hints 1, 2 and 5 are used (even if I'm not doing these steps right in my decryption). But what do 3 and 4 have to do with it? Where do random numbers vs. human generated come into the decryption?(3 votes)
- Hints 3 and 4 are not necessary as you can obtain the same information in a different way.

Here's an idea on how you would use hints 3+4:

Being able to identify the difference between random and non random numbers is useful if there are various ways of looking at or grouping the data from the code text. The idea is that the underlying frequency of a plain text message will remain after encryption. Groupings of code text that have random frequency signatures likely do not contain an underlying message, groupings that are distinctly non-random potentially have an underlying message.

Note: To apply these techniques one would typically need to apply them after reversing any step that adds**diffusion**into the decryption.**Diffusion**is a process to remove or reduce the frequency fingerprints.

Hope this makes sense(3 votes)

- Which picture is the code on? I have no idea where to start. Also, what do the numbers in the newspaper mean? Thanks!(4 votes)
- the numbers on the newspaper go with the words and numbers at the top of the last picture(1 vote)