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Fix hex_repo:fingerprint #177

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Merged
ericmj merged 1 commit into from
Apr 11, 2026
Merged

Fix hex_repo:fingerprint #177

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2 changes: 1 addition & 1 deletion src/hex_core.app.src
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,7 @@
{description, "Reference implementation of Hex specifications"},
{vsn, "0.15.0"},
{registered, []},
{applications, [kernel, stdlib, inets, ssl]},
{applications, [kernel, stdlib, inets, ssl, ssh]},
{licenses, ["Apache-2.0"]},
{include_paths, ["CHANGELOG.md"]},
{exclude_paths, ["src/safe_erl_term.erl"]},
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6 changes: 4 additions & 2 deletions src/hex_repo.erl
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Expand Up @@ -240,18 +240,20 @@ fingerprint(PublicKeyPem) when is_binary(PublicKeyPem) ->
%% true
%% '''
%% @end
-spec fingerprint_equal(binary(), string()) -> boolean().
-spec fingerprint_equal(binary(), iodata()) -> boolean().
fingerprint_equal(PublicKeyPem, ExpectedFingerprint) when is_binary(PublicKeyPem) ->
ActualFingerprint = fingerprint(PublicKeyPem),
constant_time_compare(
list_to_binary(ActualFingerprint),
list_to_binary(ExpectedFingerprint)
iolist_to_binary(ExpectedFingerprint)
).

%% @private
%% Constant-time comparison to prevent timing attacks.
%% Uses crypto:hash_equals/2 on OTP 25+, falls back to manual comparison on older versions.
-if(?OTP_RELEASE >= 25).
constant_time_compare(A, B) when byte_size(A) =/= byte_size(B) ->
false;
constant_time_compare(A, B) ->
crypto:hash_equals(A, B).
-else.
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4 changes: 3 additions & 1 deletion test/hex_repo_SUITE.erl
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Original file line number Diff line number Diff line change
Expand Up @@ -165,7 +165,9 @@ fingerprint_equal_test(_Config) ->
"-----END PUBLIC KEY-----\n"
>>,
CorrectFingerprint = "SHA256:O1LOYhHFW4kcrblKAxROaDEzLD8bn1seWbe5tq8TRsk",
WrongFingerprint = "SHA256:WrongFingerprint123456789012345678901234567",
WrongFingerprint = <<"SHA256:WrongFingerprint123456789012345678901234567">>,
DifferentLengthFingerprint = "SHA256:TooShort",
?assert(hex_repo:fingerprint_equal(PublicKeyPem, CorrectFingerprint)),
?assertNot(hex_repo:fingerprint_equal(PublicKeyPem, WrongFingerprint)),
?assertNot(hex_repo:fingerprint_equal(PublicKeyPem, DifferentLengthFingerprint)),
ok.
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