Correct the modular fourth-roots function

[beaurancourt]

The original explanation implied that x^(1/4) mod N = x^(((p-1)*(q-1)+4)/8) mod N, but checking fact 2.160 from the Handbook of Applied Cryptography:

the text says that this is a formula for square roots not fourth roots. Thus, to get the fourth root, we apply the formula twice.

[CLAassistant]

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[mhluongo]

Can confirm, this tripped us up!

[fcasal]

Great catch! I've added the explicit formula to your edit and mentioned that the exponent only needs to be computed once as it does not depend on the input.