gistfile1.hrl

make_qry(Chl) ->
    %% First we compose two strings:
    %% ChlKey = Challenge + Client-Key
    %% ChlPid = Challenge + Client-Id zero padded to even 8
    Key     = "CFHUR$52U_{VIX5T",
    Pid     = "PROD0101{0RM?UBW",
    ChlKey  = Chl ++ Key,
    ChlPid0 = Chl ++ Pid,
    ChlPadL = 8 - (length(ChlPid0) rem 8),
    ChlPid1 = ChlPid0 ++ lists:duplicate(ChlPadL, $0),

    %% Chop the strings up in 4 byte parts and flip byte order.
    ChlKeyParts = split_32_little(erlang:md5(ChlKey)),
    ChlPidParts = split_32_little(ChlPid1),

    %% Calculate the two key parts.
    {Hgh, Low}  = make_qry_calc(ChlKeyParts, ChlPidParts),

    %% XOR the key parts with the ChlKey and flip byte order again.
    <<Res:128>> = <<(element(1, ChlKeyParts) bxor Hgh):32/little,
		    (element(2, ChlKeyParts) bxor Low):32/little,
		    (element(3, ChlKeyParts) bxor Hgh):32/little,
		    (element(4, ChlKeyParts) bxor Low):32/little>>,

    %% Return lower-case 32 char hex notation.
    string:to_lower(lists:flatten(io_lib:format("~32.16.0B", [Res]))).

split_32_little(<<X:32/little, T/binary>>) ->
    [X | split_32_little(T)];
split_32_little(<<>>) ->
    [].

make_qry_calc(M, CHL) ->
    make_qry_calc([X band 16#7fffffff || X <- M], CHL, 0, 0).

make_qry_calc([M1, M2, M3, M4], [C1, C2 | T], Hgh, Low) ->
     Temp = (M1 * (((16#0e79a9c1 * C1) rem 16#7fffffff) + Hgh) + M2) rem 16#7fffffff,
     Hgh1 = (M3 * ((C2 + Temp)         rem 16#7fffffff) + M4)        rem 16#7fffffff,
     Low1 = Low + Hgh1 + Temp,

    make_qry_calc([M1, M2, M3, M4], T, Hgh1, Low1);

make_qry_calc([_, M2, _, M4], [], Hgh, Low) ->
    Hgh1 = (Hgh + M2) rem 16#7fffffff,
    Low1 = (Low + M4) rem 16#7fffffff,
    {Hgh1, Low1}.