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• Homework 3 Solutions Error for #4a ElGammal?
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layla08
Posts: 70
Posted 14:40 Mar 11, 2016 |

Is there an error in the Solutions for Homework 3 that Dr. Guo posted?

For #4a where you encrypt 'phone', I agree with the solutions that:

p = 15   (P1 = 15)

h = 7     (P2 = 7)

o = 14   (P3 = 14)

n = 13   (P4 = 13)

e = 4     (P5 = 4)

HOWEVER, when we're calculating the C2 for each of them, the solution says that:

for P2, which is 7,

C2 = (P2 * e2^r) mod p = (2*1117^103) mod 1327 = 7* 437 mod 1327 = 405  (should't it be 7, not 2?)

for P3, which is 14,

C2 = (P3 * e2^r) mod p = (18*1117^103) mod 1327 = 14* 437 mod 1327 = 810  (shouldn't it be 14, not 18?)

(same for P4, and for P5)

This are mistakes in the solutions, right? Would love some confirmation. Thanks!

dle35
Posts: 22
Posted 14:50 Mar 11, 2016 |

yes i think it is a mistake

layla08
Posts: 70
Posted 14:53 Mar 11, 2016 |

Thanks! I'm 98% sure they are typos too.

dle35
Posts: 22
Posted 14:53 Mar 11, 2016 |

U know how to get Rc1 and Rc2 in Question #1 ?

layla08
Posts: 70
Posted 15:05 Mar 11, 2016 |

Are you talking about #1a S-AES? There are way too many steps to list on this forum, but PowerPoint 9 has everything you need. Here is an overview map: Try it (it takes about 2 pages to do 1 S-AES problem) and write back with a specific problem if you get stuck somewhere!

dle35
Posts: 22
Posted 15:06 Mar 11, 2016 |

I got the problem but the Rc1 = 80 and Rc2 = 30 IDK where she get the number from

layla08
Posts: 70
Posted 15:08 Mar 11, 2016 |

OH! Okay, those are constants. They never change. It's always going to be 80 the first time and 30 the second time. For every single problem :)

Last edited by layla08 at 15:09 Mar 11, 2016.
dle35
Posts: 22
Posted 20:21 Mar 11, 2016 |

In the homework 3 solution for this question the Round 2 and round 3 they use SR then SN but in the Power Point they use the SN then SR. So which version is correct.

Last edited by dle35 at 20:22 Mar 11, 2016.