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Algorithm Derivation

Our goal is to determine . Let us assume we have a prime number p and that p-1 can be factored in the following way:

then we can say that

Thus if one can find for all i, one could use the Chinese Remainder Theorem to combine them and obtain . In order to do this consider expanding as follows

Then it is possible to show that

In order to show this, we have to see that

Multiplying out Eq (6) one obtains

Applying Eq(7) (one can apply to Eq(7) since it represents the exponent of Eq(5) which is all done in )

Therefore Eq(5) becomes

Let and . Then

Using Shank's algorithm we find given , , and p (notice that there are only possible values for ). Now let . Then

Considering only the exponents

Then,

and we can use Shank's algorithm to find given , , and p. We now repeat the same procedure to obtain as follows.

Doing p-1 modular arithmetic, one finds that

Then if one lets

We then apply Shank's algorithm to find . This process is continued to obtain all coefficients in Eq(4). From these coefficients, we can find for all and finally combine them using the Chinese Remainder Theorem to obtain . [4]



Pedro Soria-Rodriguez
Sat Mar 16 16:13:36 EST 1996