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fix(auth): keep the full length difference in ApiKey::matches - #6
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The length difference was narrowed to u8, so it folded to zero whenever the two lengths differed by a multiple of 256. The modulo indexing then let the key repeated that many times match on every byte: a generated 64-byte key presented five or nine times over authenticated. Keep the difference as a usize and widen each byte's XOR into it. The loop still reads every byte of the longer input, so the timing is unchanged. Fixes #4 Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01VhxjRgZo4zeCeNA8rZXp7v
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Fixes #4.
The bug
ApiKey::matchesnarrowed the length difference tou8, so it became zero whenever the lengths differed by a multiple of 256. Because the loop indexes both inputs modulo their lengths, the key repeated that many times then matched on every byte. A generated 64-byte key sent five or nine times over authenticated.The existing test only tried one repeat (
abcdefabcdef). A length difference of 6 does not fold to zero, so the test passed.The fix
usize, and each byte's XOR is widened into it withusize::from.Tests
a_repeated_key_does_not_match_at_any_length: a generated key repeated 2 to 9 times, and"ab"repeated 129 times (258 bytes).key x5 matched, and passes with the fix.cargo test --workspace,cargo clippy --workspace --all-targetsandcargo fmtare all clean.🤖 Generated with Claude Code
https://claude.ai/code/session_01VhxjRgZo4zeCeNA8rZXp7v