Chapter 17: Substitution Ciphers Answer the Following Questions Based on the Discussions from Class

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Chapter 17: Substitution Ciphers Answer the Following Questions Based on the Discussions from Class

Math for Liberal Studies – Fall 2007 Dr. Hamblin Chapter 17: Substitution Ciphers Answer the following questions based on the discussions from class. 1. Use the Caesar cipher (shift 3) to encode the message “ET TU BRUTUS.” 2. Use the Caesar cipher (shift 3) to decode the message “BRX MXVW VWDEEHG PH.” 3. Use the ROT13 cipher to encode the message “HASTA LA VISTA BABY.” 4. Encode the message “AFFINE CIPHER” using an affine cipher where you multiply by 5 and add 2. 5. The quotation below has been encrypted using a substitution cipher. Use frequency analysis and your knowledge of English to decrypt the message. UGSXQXAI XI QEZ WZYQSZ PVQ GJ WZQQXYW FGQZI JVGL QEZ UGGV PYH APLUPXWY JDYHI JVGL QEZ VXAE OM UVGLXIXYW QG UVGQZAQ ZPAE JVGL QEZ GQEZV. Hints: GJ and QG are both words, so there are very few possibilities for what these words can be. Also, Q appears very frequently. Math for Liberal Studies – Fall 2007 Dr. Hamblin 6. Encode the message “DRINK YOUR OVALTINE” using a Vignère cipher with key word “RALPH.” 7. The message “LFNRQ ZLQER REXWQ STHTM BSNHG AA” was encoded using a Vignère cipher with the keyword “GONE.” Decode the message. 8. Encode the message “HERE’S LOOKING AT YOU, KID” using an Autokey cipher with keyword “RICK.” 9. The message “IOWGG VBQWA OIAEW RJFLT D” was encoded using an Autokey cipher with keyword “BACON.” Decode the message. Solutions 1. HW WX EUXWXV 2. YOU JUST STABBED ME 3. UNFGN YN IVFGN ONOL 4. CBBQPW MQZLWJ 5. Politics is the gentle art of getting votes from the poor and campaign funds from the rich by promising to protect each from the other. 6. VKWEI QHII MNTZKGFX 7. Frankly, my dear, I don’t give a damn. 8. YMTO’Z PFSCTBU KB LUU, DGR 9. Houston, we have a problem .

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PROLOGUE - I. Decrypt cryptotexts: Part IV GBLVMUB JOGPSNBUJLZ Secret-key cryptosystems VMNIR RPNBMZ EBMFLP OFABKEFT prof. Jozef Gruska IV054 4. Secret-key cryptosystems 2/99 PROLOGUE - II. CHAPTER 4: SECRET-KEY (SYMMETRIC) CRYPTOGRAPHY Decrypt: In this chapter we deal with some of the very old, or quite old, classical (secret-key or symmetric) cryptosystems and their cryptanalysis that were primarily used in the pre-computer era. VHFUHW GH GHXA These cryptosystems are too weak nowadays, too easy to break, especially VHFUHW GH GLHX, with computers. However, these simple cryptosystems give a good illustration of several of the VHFUHW GH WURLV important ideas of the cryptography and cryptanalysis. Moreover, most of them can be very useful in combination with more modern VHFUHW GH WRXV. cryptosystem - to add a new level of security. prof. Jozef Gruska IV054 4. Secret-key cryptosystems 3/99 prof. Jozef Gruska IV054 4. Secret-key cryptosystems 4/99 BASICS CRYPTOLOGY - HISTORY + APPLICATIONS Cryptology (= cryptography + cryptanalysis) has more than four thousand years long history. Some historical observation People have always had fascination with keeping information away from others. Some people – rulers, diplomats, military people, businessmen – have always had needs to keep some information away from others. BASICS Importance of cryptography nowadays Applications: cryptography is the key tool to make modern information transmission secure, and to create secure information society. Foundations: cryptography gave rise to several new key concepts of the foundation of informatics: one-way functions, computationally perfect pseudorandom generators, zero-knowledge proofs, holographic proofs, program self-testing and self-correcting, . prof. Jozef Gruska IV054 4. Secret-key cryptosystems 5/99 prof.
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