binary_to_integer, integer_to_binary

binary_to_integer(Bin)-> erlang:list_to_integer(bin_to_hex(Bin), 16).

bin_to_hex(Bin) -> [hd(erlang:integer_to_list(I, 16)) || << I:4 >> <= Bin ].

integer_to_binary(Int)-> hex_to_bin(erlang:integer_to_list(Int, 16)).

hex_to_bin(Str) -> << << (erlang:list_to_integer([H], 16)):4 >> || H <- Str >>.

Hint from : http://stackoverflow.com/questions/965038/hex-to-64-signed-decimal