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Harden Base32 decoding validation #41

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97 changes: 85 additions & 12 deletions src/pot_base32.erl
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Original file line number Diff line number Diff line change
Expand Up @@ -89,25 +89,46 @@ decode(Bin, Opts) when is_binary(Bin) andalso is_list(Opts) ->
decode(List, Opts) when is_list(List) andalso is_list(Opts) ->
decode(list_to_binary(List), Opts).

decode(Fun, <<X, "======">>, Bits) ->
<<Bits/bits, (Fun(X) bsr 2):3>>;
decode(Fun, <<X, "====">>, Bits) ->
<<Bits/bits, (Fun(X) bsr 4):1>>;
decode(Fun, <<X, "===">>, Bits) ->
<<Bits/bits, (Fun(X) bsr 1):4>>;
decode(Fun, <<X, "=">>, Bits) ->
<<Bits/bits, (Fun(X) bsr 3):2>>;
decode(Fun, <<A, B, "======">>, Bits) ->
decode_final(Fun, [A, B], Bits, 2);
decode(Fun, <<A, B, C, D, "====">>, Bits) ->
decode_final(Fun, [A, B, C, D], Bits, 4);
decode(Fun, <<A, B, C, D, E, "===">>, Bits) ->
decode_final(Fun, [A, B, C, D, E], Bits, 1);
decode(Fun, <<A, B, C, D, E, F, G, "=">>, Bits) ->
decode_final(Fun, [A, B, C, D, E, F, G], Bits, 3);
decode(_Fun, <<"=", _Rest/binary>>, _Bits) ->
error(badarg);
decode(Fun, <<X, Rest/binary>>, Bits) ->
decode(Fun, Rest, <<Bits/bits, (Fun(X)):5>>);
decode(_Fun, <<>>, Bin) -> Bin.
decode(_Fun, <<>>, Bits) ->
trim_padding(Bits, bit_size(Bits) rem 8).

decode_final(Fun, [X | Rest], Bits, UnusedBits) ->
decode_final(Fun, Rest, <<Bits/bits, (Fun(X)):5>>, UnusedBits);
decode_final(_Fun, [], Bits, UnusedBits) ->
trim_padding(Bits, UnusedBits).

trim_padding(Bits, 0) -> Bits;
trim_padding(Bits, UnusedBits) when UnusedBits >= 1, UnusedBits =< 4 ->
BitSize = bit_size(Bits) - UnusedBits,
<<Decoded:BitSize/bits, Unused:UnusedBits>> = Bits,
case Unused of
0 -> Decoded;
_ -> error(badarg)
end;
trim_padding(_Bits, _UnusedBits) ->
error(badarg).

std_dec(I) when I >= $2 andalso I =< $7 -> I - 24;
std_dec(I) when I >= $a andalso I =< $z -> I - $a;
std_dec(I) when I >= $A andalso I =< $Z -> I - $A.
std_dec(I) when I >= $A andalso I =< $Z -> I - $A;
std_dec(_I) -> error(badarg).

hex_dec(I) when I >= $0 andalso I =< $9 -> I - 48;
hex_dec(I) when I >= $a andalso I =< $z -> I - 87;
hex_dec(I) when I >= $A andalso I =< $Z -> I - 55.
hex_dec(I) when I >= $a andalso I =< $v -> I - 87;
hex_dec(I) when I >= $A andalso I =< $V -> I - 55;
hex_dec(_I) -> error(badarg).

-ifdef(TEST).

Expand Down Expand Up @@ -147,10 +168,36 @@ std_encode_nopad_test_() ->
[ ?_assertEqual(Out, encode(In, [nopad]))
|| {In, Out} <- nopad_cases(std_cases()) ].

std_decode_nopad_test_() ->
[ ?_assertEqual(Out, decode(In))
|| {Out, In} <- nopad_cases(std_cases()) ].

std_decode_nopad_byte_aligned_test_() ->
[ ?_assertEqual(8 * byte_size(Out), bit_size(decode(In)))
|| {Out, In} <- nopad_cases(std_cases()) ].

std_encode_lower_nopad_test_() ->
[ ?_assertEqual(Out, encode(In, [lower,nopad]))
|| {In, Out} <- nopad_cases(lower_cases(std_cases())) ].

std_decode_malformed_padding_test_() ->
[ ?_assertError(badarg, decode(<<"M=">>)),
?_assertError(badarg, decode(<<"MY=">>)),
?_assertError(badarg, decode(<<"MY=====">>)),
?_assertError(badarg, decode(<<"M=Y=====">>)) ].

std_decode_non_zero_unused_bits_test_() ->
[ ?_assertError(badarg, decode(<<"MZ======">>)),
?_assertError(badarg, decode(<<"MZXZ====">>)),
?_assertError(badarg, decode(<<"MZXW7===">>)),
?_assertError(badarg, decode(<<"MZXW6YZ=">>)) ].

std_decode_invalid_alphabet_test_() ->
[ ?_assertError(badarg, decode(<<"M0======">>)),
?_assertError(badarg, decode(<<"M1======">>)),
?_assertError(badarg, decode(<<"M8======">>)),
?_assertError(badarg, decode(<<"M+======">>)) ].

std_encode_string_test_() ->
[ ?_assertEqual(Out, encode(In))
|| {In, Out} <- stringinput_cases(std_cases()) ].
Expand Down Expand Up @@ -186,10 +233,36 @@ hex_encode_nopad_test_() ->
[ ?_assertEqual(Out, encode(In, [hex,nopad]))
|| {In, Out} <- nopad_cases(hex_cases()) ].

hex_decode_nopad_test_() ->
[ ?_assertEqual(Out, decode(In, [hex]))
|| {Out, In} <- nopad_cases(hex_cases()) ].

hex_decode_nopad_byte_aligned_test_() ->
[ ?_assertEqual(8 * byte_size(Out), bit_size(decode(In, [hex])))
|| {Out, In} <- nopad_cases(hex_cases()) ].

hex_encode_lower_nopad_test_() ->
[ ?_assertEqual(Out, encode(In, [hex,lower,nopad]))
|| {In, Out} <- nopad_cases(lower_cases(hex_cases())) ].

hex_decode_malformed_padding_test_() ->
[ ?_assertError(badarg, decode(<<"C=">>, [hex])),
?_assertError(badarg, decode(<<"CO=">>, [hex])),
?_assertError(badarg, decode(<<"CO=====">>, [hex])),
?_assertError(badarg, decode(<<"C=O=====">>, [hex])) ].

hex_decode_non_zero_unused_bits_test_() ->
[ ?_assertError(badarg, decode(<<"CP======">>, [hex])),
?_assertError(badarg, decode(<<"CPNH====">>, [hex])),
?_assertError(badarg, decode(<<"CPNMV===">>, [hex])),
?_assertError(badarg, decode(<<"CPNMUOH=">>, [hex])) ].

hex_decode_invalid_alphabet_test_() ->
[ ?_assertError(badarg, decode(<<"CW======">>, [hex])),
?_assertError(badarg, decode(<<"CX======">>, [hex])),
?_assertError(badarg, decode(<<"CY======">>, [hex])),
?_assertError(badarg, decode(<<"CZ======">>, [hex])) ].

hex_encode_string_test_() ->
[ ?_assertEqual(Out, encode(In, [hex]))
|| {In, Out} <- stringinput_cases(hex_cases()) ].
Expand Down