# Past Exam for CMSC 414 - CMPTR & NETWORK SECURITY with Shankar at Maryland (UMD)

## Exam Information

 Material Type: Exam 1 Professor: Shankar Class: CMSC 414 - CMPTR & NETWORK SECURITY Subject: Computer Science University: University of Maryland Term: -- Keywords: AuthenticatesParticularlyAuthenticationConvenienceEnvironmentNo CorrelationInitializationPermutationThe MessageRandom Number      ## Sample Document Text

CMSC 414 F06 Exam 1 Page 1 of 8 Name:_________________________ _____________________________________________________________________________________ Total points: 40. Total time: 75 minutes. 6 problems over 6 pages. No book, notes, or calculator 1. [14 points] Are n=187 and e=9 valid numbers for RSA. Explain. If you answer yes, obtain the corresponding d. _____________________________________________________________________ Solution There are two requirements:  n must be a product of two primes  e must be relatively prime to f(n) (so that d, which equals e-1 mod-n, exists) First requirement [2 points] n = 187 = 11�17. 11 and 17 are primes. So this holds. Second requirement [6 points] Recall that if n =p�q where p and q are distinct primes, then f(p q) = (p-1) (q-1) So f(187) = (11-1) (17-1) = 160. e, which equals 9, is relatively prime to 160 (because 9=32 and 160=10�16=2�5�24=25�5) So this requirement holds. Obtaining d ...

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