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Real-Life Math -- Solution

Here is one way to figure out this problem:

1. (14 x 4) mod 55 = 56 mod 55
55 x 1 = 55
55 + 1 = 56
56 mod 55 = 1
2. (42 x 4) mod 55 = 168 mod 55
55 x 3 = 165
165 + 3 = 168
168 mod 55 = 3
3. (43 x 4) mod 55 = 172 mod 55
55 x 3 = 165
165 + 7 = 172
172 mod 55 = 7
4. (58 x 4) mod 55 = 232 mod 55
55 x 4 = 220
220 + 12 = 232
232 mod 55 = 12
5. (35 x 4) mod 55 = 140 mod 55
55 x 2 = 110
110 + 30 = 140
140 mod 55 = 30

So the modified public key is: 1 - 3 - 7 - 12 - 30. Good work! Knowing how to find the "mod" makes the rest of the job easy. You nail down the PIN number and unscramble the company records. You're a cipher hero!

As you can see, cryptographers use math skills every day.

"There isn't any 'number crunching' to do," says Anna Lysyanskaya. She's a cryptography professor at Brown University. "The chief math skill required is the ability to think logically and rigorously and to come up with mathematical proofs."


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