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% Licensed under the Apache License, Version 2.0 (the "License"); you may not
% use this file except in compliance with the License. You may obtain a copy of
% the License at
%
% http://www.apache.org/licenses/LICENSE-2.0
%
% Unless required by applicable law or agreed to in writing, software
% distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
% WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
% License for the specific language governing permissions and limitations under
% the License.
-module(couch_hotp).
-export([generate/4]).
generate(Alg, Key, Counter, OutputLen) when
is_atom(Alg), is_binary(Key), is_integer(Counter), is_integer(OutputLen)
->
Hmac = couch_util:hmac(Alg, Key, <<Counter:64>>),
Offset = binary:last(Hmac) band 16#f,
Code =
((binary:at(Hmac, Offset) band 16#7f) bsl 24) +
((binary:at(Hmac, Offset + 1) band 16#ff) bsl 16) +
((binary:at(Hmac, Offset + 2) band 16#ff) bsl 8) +
(binary:at(Hmac, Offset + 3) band 16#ff),
case OutputLen of
6 -> Code rem 1000000;
7 -> Code rem 10000000;
8 -> Code rem 100000000
end.
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