# 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: Fall 2008 Keywords: ParticularlyConjunctionOrganizationSerial NumbersAuthenticationInfrastructureInitializationDestinationThe MessageEmployee at Will

## Sample Document Text

CMSC 414 F08 Exam 1 Page 1 of 10 Name:____________________________________ ____________________________________________________________________________________________________ Total points: 71. Total time: 75 minutes. 9 problems over 7 pages. No book, notes, or calculator 1. [14 points] a. Are n=221 and e=3 valid numbers for RSA. Explain. If you answer yes, obtain the corresponding d. b. Are n=221 and e=5 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 ?(n) (so that d, which equals e?1 mod-n, exists) First requirement [2 points] n = 221 = 13·17. 13 and 17 are primes. So this holds. Second requirement [4 points] If n =p·q where p and q are distinct primes, then ?(p?q) = (p?1)?(q?1) So ?(221) = (13?1)?(17?1) = 12·16 = 192 Part ...

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