Nobauer proofed in (Nobauer, 1954) that the power function x f--7 xk mod n is a permutation on Zn for a positive integer n iff n is squarefree and (k, .\(n)) = 1, where .\(n) denotes the Carmichael function and (a, b) the greatest common divisor of a and b. The RSA-cryptosystem uses this property for n = pq, where p, q are distinct primes. Hence the modul cannot be chosen arbitrarily. If we consider permutations on prime residue classes, there is no restriction for the module anymore. In order to find criteria for power permutations on Z~ we first deal with the fixed point problem. As a consequence we get the condition for k : r (k,[cfJ(p~', ... ,p~"])=1 for n=IJpf', i=l where q, denotes the Euler totient function and [a, b] the least common multiple of a and b.