Java Security

Hi

I performed Enc/dec using AES, hashing, then digital sig of hash, and succesfuly did the reverse of all these on reciver side. now i want to hide the source and destination ids, is there any function/class which genertae pseudonym or alternativevly i want to perform this function

Pseonym Pu= H(r.Id)

where H= hash
r= genertaing random no
Id= opt@a.com

I want to first genatere a random no and then concatenate it with id and then taking hash of all thses to get pseodnym.

can anyone help me while coding this or direct function of pesdonym

thanks.