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Motivation: Data(base64Encoded:) accepts excess padding and non-zero trailing bits, so several distinct PEM strings decode to the same DER bytes. RFC 4648 section 3.5 allows rejecting such input, and PEM carries signed material, so we should. Modifications: Validate the body before decoding: length a multiple of four, padding only at the end and at most twice, trailing bits zero. Add a test covering canonical and non-canonical encodings of the same bytes. Result: Only canonical base64 is accepted in PEM bodies.
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Motivation:
PEM bodies are decoded with Data(base64Encoded:), which accepts non-canonical input: "QUJ=" decodes to the same bytes as "QUI=", and "QUJD====" decodes the same as "QUJD". Several distinct PEM strings therefore map to one DER blob. RFC 4648 section 3.5 allows rejecting such input, and PEM carries signed material, so we should.
Modifications:
Validate the body before decoding it: the length must be a multiple of four, padding may only appear at the end and at most twice, and the bits beyond the last encoded byte must be zero. Add a test with canonical and non-canonical encodings of the same bytes.
Result:
Only canonical base64 is accepted in PEM bodies. The new test fails before this patch and passes after it.