gh-146311: Reject non-zero padding bits in base64/base32 decoding#146312
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gpshead wants to merge 3 commits intopython:mainfrom
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gh-146311: Reject non-zero padding bits in base64/base32 decoding#146312gpshead wants to merge 3 commits intopython:mainfrom
gpshead wants to merge 3 commits intopython:mainfrom
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RFC 4648 section 3.5 allows decoders to reject encoded data containing non-zero pad bits. Both a2b_base64 (strict_mode=True) and a2b_base32 currently silently discard non-zero trailing bits instead of raising binascii.Error. These tests document the expected behavior. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Add leftchar validation after the main decode loop in a2b_base64 (strict_mode only) and a2b_base32 (always). Fix existing test data that incidentally had non-zero padding bits to use characters with zero trailing bits while preserving the same decoded output. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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discussing if base32 needs strict_mode on the issue. not adding a NEWS entry until that is decided. |
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Summary
a2b_base64: reject non-zero padding bits whenstrict_mode=Truea2b_base32: reject non-zero padding bits unconditionallyPer RFC 4648 section 3.5, decoders MAY reject encodings where pad bits are not zero.