Chapter 4: Orders of Growth and Tree Recursion

Making the Signing and Verification Functions Inverses

Suppose x is a message, represented as a number.

Then the signature s is computed by the signing function:

     s = x^e mod m

for a chosen signing exponent e and modulus m.

This function is private because e is known only to the author.

The modulus m must be public because it is used by the receiver of the message in the verification function:

     x = s³ mod m

This works because m and e are chosen in such a way that: x = (x^e mod m)³ mod m