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CodesInChaos
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Here is an excellent paper on the math of asymmetric key encryption: http://www.mathaware.org/mam/06/Kaliski.pdf‎

See the example on Page 6.

The public key = 55$$55$$ Primes used to calculate public key are 5$$5$$ and 11$$11$$. e = 3

$$e = 3$$

Now see the appendix: L = LCM (p-1, q-1) = 20$$L = \mathrm{LCM}(p-1, q-1) = 20$$

The paper states de = 1 mod L$$de = 1 \mod L$$

I can't figure out how he gets the value of d = 7$$d = 7$$

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# how do you calculate the private exponent in asymmetric key encryption

Here is an excellent paper on the math of asymmetric key encryption: http://www.mathaware.org/mam/06/Kaliski.pdf‎

See the example on Page 6.

The public key = 55 Primes used to calculate public key are 5 and 11. e = 3

Now see the appendix: L = LCM (p-1, q-1) = 20

The paper states de = 1 mod L

I can't figure out how he gets the value of d = 7