Hashing - Why this method is a bad choice

Hey guys, again a homework problem that is incredibly mind blowing to me... and help would be greatly appreciated!

Consider a version of the division method for hashing in which h(k) = k mod m, where m = (2^p) - 1 and k is a character string interpreted in radix 2^p. (That is, each character takes p bits.) Show that if string x can be derived from string y by permuting its characters, then x and y hash to the same value.

Here my main problem is i dont understand how to generally interpret a string in radix 2^p. Again, any help would be awesome!