Multiplication Group Zm=a: gdd( a, m)=1) Euler phi function p(m)=Z If m is a prime then p(m)=m-1,and p(ma)Multiplication Group • Z* m = {a: gcd(a,m) = 1} • Euler phi function f(m) = | Z* m | • If m is a prime then  f(m) = m -1, and  f(md ) = md - md-1