>>> cfb Ciphertext feeback mode >>> c[i] = f1(K, c[i-1]) ^ p[i] >>> p[i] = f1(K, c[i-1]) ^ c[i] >Suppose instead of c[i-1] you use c[i-N] where N is say 10. Wouldn't the size of your IV have to grow as N grows? Jim Russell SynData Technologies