Update getLength in PDEncryprion according to specification

[LonelyMidoriya]

Summary by CodeRabbit

• Bug Fixes
  • Improved PDF encryption handling by applying the correct default key lengths for encryption algorithms V4 and V5.
  • Preserved existing behavior for other encryption configurations, including dictionary-defined and legacy defaults.
  • Enhanced compatibility when opening and processing encrypted PDF documents that use newer encryption standards.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: eefe90c3-4b39-4ea6-bdea-c3b4edc53ecb

📥 Commits

Reviewing files that changed from the base of the PR and between 3014e75 and 0ab7f42.

📒 Files selected for processing (1)

• src/main/java/org/verapdf/pd/encryption/PDEncryption.java

Included review availability: Your plan provides up to 1 included review per hour; 0 remain after this review.

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📝 Walkthrough

Walkthrough

PDEncryption.getLength() now returns 128 bits for encryption version 4 and 256 bits for version 5. Version 1 returns 40 bits. Other versions retain the existing LENGTH lookup and 40-bit fallback.

Changes

Encryption key length handling

Layer / File(s)	Summary
Version-based key length defaults src/main/java/org/verapdf/pd/encryption/PDEncryption.java	Adds default lengths for encryption versions 4 and 5. Updates getLength() to select version-specific defaults before the existing LENGTH dictionary lookup and fallback.

Estimated code review effort: 1 (Trivial) | ~3 minutes

Merge Risk: ⚪ Minimal · up to 0ab7f

The change updates encryption key-length selection for specified PDF versions without adding new dependencies, authorization paths, or entrypoints. No actionable merge-blocking risk remains beyond normal checks and review.

Suggested reviewers: maximplusov

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly identifies the main change to getLength() in PDEncryption and indicates that the implementation follows the specification. It contains a typo in PDEncryprion, but the intended …
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 1 files.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

Full details: Title check

Explanation

The title clearly identifies the main change to getLength() in PDEncryption and indicates that the implementation follows the specification. It contains a typo in PDEncryprion, but the intended class is clear.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch encryption-length

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