Name:

1/ / 2/ / 3/ / 4/ / 5/ / 6/ / 7/ / 8/ / Total/

Please do not write in the spaces above.

Directions: This exam must be handed in at the beginning of the in-class exam on Friday. You may not use anything but your class notes, class book, and the maplets. You may not discuss the problems with anyone (other than me).
Make sure to break the plaintext into individual words. Show work on the cryptanalysis problems.
Please attach this signed cover sheet to your work.
Good luck!

Please sign:

I, , affirm that I have not discussed this exam, its questions, or its content, with anyone.

Note: These are all to be done on maplets – do not attempt to do these by hand, unless I explicitly tell you to do so. Also, make sure you break these up into words in English.

1.  Break the following cipher, which was made using a random substitution cipher:

URTLT EAPP HT PAUUPT LWHK MJQ QAKMCCYAJUSTJUK TVTLXERTLT MJQ ET MLT MPP MCU UY TOCTBU UYY SWBR HWU URTJ AG YJT KBRTST YG RMCCAJTKK GMAPK RWSMJ JMUWLT UWLJK UY MJYURTL AG URT GALKU BMPBWPMUAYJ AK ELYJZ ET SMFT M KTBYJQ HTUUTL ET GAJQ BYSGYLU KYSTERTLT

Hint: The most common letter of the ciphertext is the most common English letter.

Give a detailed description of your process here, including any steps that didn’t work.

2.  Break the following cipher, which was made using a keyword columnar cipher, and with crib “and courage as”:

ESEHR DSTUT ETISE SAENC AYULK FSATA AESHM WNTNR GOSGS EAEIG SHRHT NFWIE TRNGD OHIHR SHEDE AN

Give a detailed description of your process here, including any steps that didn’t work.

3.  Break the following phase shift cipher: ALAKL GLZWU JWVAL GXZME SFFSL MJWLZ SLWPU WHLOZ WJWAL KKWDX AKZFW KKAKT JGMYZ LAFLG HDSQA LDGNW KEGJW JWSVA DQLZS FALZS LWK

Give a detailed description of your process here, including any steps that didn’t work.

4.  Break the following affine cipher, where it is somehow known that the plaintext letter y corresponds to the ciphertext letter D and the plaintext letter o corresponds to the ciphertext letter J: DJVIH KPWCH XURXU DJVCI PHADJ VIHKP EPPGX UDJVC RIJPR DJVLH URGPP CDJVC RPQEH UDAXC PLGXJ UDJVL IJJRP DJVCP JUDJV CJZUH UADJV BUJZZ IHGDJ VBUJZ HUADJ VHCPG IPJUP ZIJQQ APLXA PZIPC PGJTJ

Give a detailed description of your process here, including any steps that didn’t work.

5.  Break the following hill cipher, which came from a 4x4 matrix, with a crib at the end of the message containing the words “cause for pride and contentment”.

WGOPA FBHPP JHZOL MSBFP ZISDX PNVNO ESIKM IKEIV XCILO QZYHY NTWZV YBMRH PJWVV MVMIG KTNFN DLMIS ZEGUO MEUBA TTUPY VKCWX EECYA CSXHO CHXYS BARXX TFYYE GDGUY KSLEX ZYLBC ILTKE PBZWM FKAMG KRQOB IHPPW HVBUY DOCDW DXPRK DWXGW OOMVO HAKHB UUJTR UHPPS JQJIS FUSOE WROTX BHGKK QCPOJ PSLZZ CXDPR MEMON XAMZV TXVLE GCLRE SQPCK QYCBD PVOQF OCDWD VJJWG OEJIY VYGSP WQXTS EMBYJ NUYTQ LVVOF JAMEC PYSNF PWJUV YZGRU TDNSC WNLV

6.  a. Find the gcd(232455556,63846837). Then find s and t. If exists, find it.

b. Find

c. Find

7.  Alice wants to communicate with Bob using RSA. Bob chooses primes p=435374537459 and q=2352673529. He also chooses e=994123.

a.  Find m,f,d.

b.  List out Bob’s public and private keys (along with their values)

c.  Encrypt the plaintext “not all those who wander are lost”

d.  Decrypt the ciphertext

[622823715889542502968, 613954354866029247777, 910340334116712592683, 453362927578325616029, 867981567811892203920, 414603520096219515970, 468332412731590148803]

8.  I want you to do the following by hand, showing all work:

This is another RSA example. With smaller numbers, but still not the “light” version from the last exam.

Alice wants to communicate with Bob using RSA. Bob chooses primes p=331, q=163. Additionally, he chooses e=233.

a.  Find m, f by hand, showing all work.

b.  Use the Euclidean algorithm to find the gcd of e and f, showing all work.

c.  Use the Euclidean algorithm to find d, showing all work.

d.  Write the message “him!” in ASCII, breaking it into blocks that are all less than m.

e.  Encrypt your work from part d, using modular exponentiation, showing all work. . (OK. So if you encrypt “hi” you will get full credit. If you encrypt “him!” you will get extra credit.)