pdftract/notes/pdftract-15cs8.md

pdftract-15cs8: Crypt Filter Implementation Verification

Task Summary

Implement Crypt filter (identity only, custom rejected with ENCRYPTION_UNSUPPORTED)

Finding

The Crypt filter implementation was already complete in the codebase. No changes were required.

Implementation Location

• File: crates/pdftract-core/src/parser/stream.rs
• Lines: 795-885 (CryptDecoder struct and implementation)
• Registered in get_decoder: line 960
• Orchestrator error handling: lines 1460-1471

Acceptance Criteria Status

Criteria	Status	Location
/Crypt with /Name /Identity passes through unchanged	✅ PASS	Lines 850-851
/Crypt with /Name /MyCustom returns ENCRYPTION_UNSUPPORTED	✅ PASS	Lines 853-854
/Crypt with no /DecodeParms defaults to /Identity	✅ PASS	Lines 822-825
/Crypt with /Identity + FlateDecode works correctly	✅ PASS	Test line 2678
proptest never panics	✅ PASS	Tests lines 2879, 2892
INV-8 maintained (no panics)	✅ PASS	Returns Err for hard errors

Test Coverage

The implementation includes comprehensive tests:

• test_crypt_decode_identity - Line 2579
• test_crypt_decode_custom_rejected - Line 2605
• test_crypt_decode_no_params - Line 2632
• test_crypt_decode_missing_name - Line 2652
• test_crypt_identity_then_flate - Line 2678
• test_crypt_decoder_invalid_params - Line 2709
• test_crypt_decode_bomb_limit - Line 2755
• test_crypt_decoder_name - Line 2778
• test_crypt_custom_names_rejected - Line 2784
• proptest_crypt_decode_no_panic - Line 2879
• proptest_crypt_decode_with_params_no_panic - Line 2892
• proptest_crypt_decode_bomb_limit_no_panic - Line 2926

Implementation Details

Public API

• CryptDecoder implements StreamDecoder trait
• decode() method checks /DecodeParms /Name
• /Identity (or missing): pass through unchanged
• Custom name: returns FilterError::EncryptionUnsupported

Orchestrator Integration

The orchestrator catches FilterError::EncryptionUnsupported and:

1. Emits ENCRYPTION_UNSUPPORTED diagnostic
2. Returns empty bytes for the stream
3. Marks the stream as undecryptable

INV-8 Compliance

• No panics in the implementation
• Hard errors return Err(FilterError::EncryptionUnsupported)
• Corrupt data mid-stream would return Ok(partial) with diagnostic (not applicable for Crypt since it's a no-op)

Conclusion

The Crypt filter is fully implemented per PDF spec 7.4.10 and meets all acceptance criteria. No changes required.