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10.14.2008 at 02:08PM PDT, ID: 23814541
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9.0

simple question about an affine cipher

Asked by jtiernan2008 in Encryption for Network Security, Math & Science

Tags:

I have a question from college. Simple one as I am new to the subject.

2.      An affine cipher with a modulus m=31 is used. Given the encryption function

E(x) = (ax+b) mod 31

Determine which of the following values for a and b yield a valid decryption function
------------------------      
a      B
20      4
21      5
13      7
1      5
------------------------
I have found that the invertible integers mod31 are {1,3,5,7,9,11,15,17,19,21,23,25}
so must utilize one of the invertible integers for a.
any value of b is acceptable, however since everything is mod31 so need to use a
number between 0 and 25.

So I would take it that the answer is 21, 5 i.e. the second one?

I just want to make sure that I am correct and that I am understanding the question correctly.
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[+][-]10.14.2008 at 06:09PM PDT, ID: 22717381

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[+][-]10.15.2008 at 07:11AM PDT, ID: 22721246

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[+][-]10.15.2008 at 07:30AM PDT, ID: 22721476

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[+][-]10.16.2008 at 10:07AM PDT, ID: 22733294

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About this solution

Zones: Encryption for Network Security, Math & Science
Tags: cryptology
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Solution Provided By: NovaDenizen
Participating Experts: 2
Solution Grade: A
 
 
[+][-]10.17.2008 at 02:07PM PDT, ID: 22745307

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[+][-]10.17.2008 at 02:17PM PDT, ID: 22745383

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