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Fix addwindow #19

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Fix addwindow #19

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1 change: 1 addition & 0 deletions .gitignore
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Original file line number Diff line number Diff line change
@@ -1,3 +1,4 @@
.rebar3
.eunit
.rebar
ebin
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25 changes: 12 additions & 13 deletions src/pot.erl
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Expand Up @@ -106,7 +106,7 @@ valid_totp(Token, Secret, Opts) ->
Token ->
true;
_ ->
Window = proplists:get_value(window, Opts, 0),
Window = proplists:get_value(addwindow, Opts, 0),
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This looks wrong to me. window is the parameter that expands the number of allowed interval tokens to be used (basically +/- window intervals are considered valid). addwindow is supposed to offset the interval that you check.

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Hi @nalundgaard, that's very useful to know! It would be great if the docs described these options in a bit more detail?

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@danturn Indeed! It's definitely worth tracking separately. The examples hint at what the options do, but they really don't explain in detail their intention, so you kind of have to piece it together from reading the code and being familiar with the hotp/totp RFC nomenclature.

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@danturn maybe you will like #22.

case check_candidate(Token, Secret, IntervalsNo - Window, IntervalsNo + Window, Opts) of
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Isn't addwidow a number that should multiply the interval_length? This is now subtracting/adding the result of time_interval(Opts) (big number like 52357080) by a relatively small number, Window = addwindow (-2-1,0,1,2,3).
Also if you really plan to remove support of window option, can you update the references of it in the README?

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addwindow is supposed to offset the interval for checking the totp, not change the interval_length.

false ->
false;
Expand All @@ -119,21 +119,20 @@ valid_totp(Token, Secret, Opts) ->
-spec time_interval(proplist()) -> time().
time_interval(Opts) ->
IntervalLength = proplists:get_value(interval_length, Opts, 30),
AddSeconds = proplists:get_value(addwindow, Opts, 0) * proplists:get_value(interval_length, Opts, 30),
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Could you please explain to me why this behavior should be changed? We extensively use this in our application tests.

{MegaSecs, Secs, _} = proplists:get_value(timestamp, Opts, os:timestamp()),
trunc((MegaSecs * 1000000 + (Secs + AddSeconds)) / IntervalLength).
trunc((MegaSecs * 1000000 + (Secs)) / IntervalLength).

check_candidate(Token, Secret, Current, Last, Opts) when Current =< Last ->
case Current of
Last ->
false;
check_candidate(_, _, Current, Last, _) when Current > Last ->
false;

check_candidate(Token, Secret, Current, Last, Opts) ->
Candidate = hotp(Secret, Current, Opts),
case Candidate of
Token ->
Current;
_ ->
Candidate = hotp(Secret, Current, Opts),
case Candidate of
Token ->
Current;
_ ->
check_candidate(Token, Secret, Current + 1, Last, Opts) end end.
check_candidate(Token, Secret, Current + 1, Last, Opts) end.


-spec prepend_zeros(token(), non_neg_integer()) -> token().
prepend_zeros(Token, N) ->
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