Fall2011+Week+1

Here are the ideas and problems to work on for the first week of the course. You'll need the ideas from Chapters 1 and 2. I am going to present problems which do not require the book. You will need a hand-written table of A B ... Z 0 1 ... 25 in order to number 6.

1. Prove that a shift cipher followed by another shift cipher is the same as a single shift cipher.

2. Prove that an affine cipher followed by another affine cipher (with alpha mutually prime with 26 each time) is the same as another affine cipher.

3. Write an English sentence without the letter e. Your sentence must include an indefinite article, a noun, a verb and an adjective or adverb.

For lunch, dinosaurs always want small food and a drink. P.S. this was Kayla, but my account isn't right. I'm working on it. user:kml003 Write three asterisks at the end of an entry and the wiki signs off for you. It is interesting that your PS does not contain an "e".user:mcdaniel30 Can you fight a mammoth on your round sun? user:ian.hart A shark swims lazily back and forth in an aquarium tank. user:meganternes Girls laugh at boys who play with dolls. user:bea001

4. Here's a ciphertext which has been made using a shift cipher. Decrypt and describe the shift. Each letter of the ciphertext was shifted 8 places, so to find what the plaintext was, shift each letter back 8.user:meganternes XAGKPQKXCTAMQAIV psychicpulseisan ITTZQOPBIBBIKSQBQA allrightattackitis IBILCVLMZEPMTUQVO atadunderwhelming WVIXWSMUWVMFJCBB onapokemonexbutt PMXWSMXWEMZUQOP hepokepowermigh BJMOWWLMVWCOPBW tbegoodenoughto EIZZIVBQBMQBPMZBP warrantiteitherth MXWEMZKIVAMBCXN epowercansetupf WZBPMIBBIKSWZBPMIB ortheattackortheat BIKSKIVAMBCXNWZIVW tackcansetupforano BPMZCAMWNKCZAMLMGMA theruseofcursedeyesuser:meganternes

Wrote a program to decode all the shift ciphers, both for reasonable guesses and bruteforce. I got the same as above. user:ian.hart
5. Here's a ciphertext from a shift cipher. Decrypt and describe the shift.

DRKDLBSXQCECDYIYEBVKC

THATBRINGSUSTOYOURLAS

DAEOCDSYXSPGORKFODROBY

TQUESTIONIFWEHAVETHERO

MUCGRIQYSXDYCZKMOPYBW

CKSWHYGOINTOSPACEFORM

YBOMYEZVO BOKCYXCGSDRKVVBO

ORECOUPLEREASONSWITHALLRE

CZOMDDYDROQOXSECOC

SPECTTOTHEGENIUSES

GRYDRYEQRDSDEZCYWO WHOTHOUGHTITUPSOME

The whole thing: THATBRINGSUSTOYOURLASTQUESTIONIFWEHAVETHEROCKSWHYGOINTOSPACEFORMORE COUPLEREASONSWITHALLRESPECTTOTHEGENIUSESWHOTHOUGHTITUPSOME. Shift of +16/-10 user:ian.hart

6. Here's a ciphertext from a Vigenere cipher. Decrypt and see if you can find anything interesting about the encryption and plaintext which was meant to be misleading.

TTEPLPSUTJEPLNV HLAVGLMYVEKEPO IJVGZYNQIVLEVYKDFJPXUH YLSAUMOIUTLWUVLSHEWSTTFU

This message is too short for an easy Viginere attack. We'll play with a cheap version in class. Do not be frustrated!user:mcdaniel30

7. Some American Civil war personel carried an encryption device which was a wheel pinned through the middle to a larger wheel. The borders of the wheels had the alphabet written in the standard way along the perimeters. These were used for encryption and decryption. What type of cipher is this? Was it symmetric? Why or why not? It's a symmetric shift cipher. It encrypts and decrypts the in the same way. And it was before WWII when nearly everything was symmetric. user:kml003

It's a very basic symmetric shift cipher, as the method shifts all the letters the same way to encrypt, and the reverse to decrypt. user:ian.hart

Good job, everybody.user:mcdaniel30