feat(xmldsig): resolve RSAKeyValue keys

[polaz]

Summary

• Parse bounded XMLDSig RSAKeyValue modulus and exponent CryptoBinary parameters.
• Convert embedded RSA parameters to validated SubjectPublicKeyInfo DER and resolve them through DefaultKeyResolver.
• Verify a real RSA-2048 donor signature end-to-end without a preset key.

Security behavior

• Require ordered Modulus and Exponent children in the XMLDSig namespace.
• Reject missing, duplicated, nested, malformed, empty, and oversized parameters.
• Apply the existing RSA policy to embedded keys, including the 2048-bit minimum and exponent validation.
• Reject RSA key material for ECDSA signature methods with a typed algorithm mismatch.

Testing

• cargo check --workspace
• cargo clippy --all-targets --all-features -- -D warnings
• cargo nextest run --workspace (473/473)
• cargo test --doc --workspace (3/3)
• cargo build --workspace --all-features

Closes #67

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: 4efe72de-c857-41e9-90d8-de9eb699a8c9

📥 Commits

Reviewing files that changed from the base of the PR and between a2d958a and 2f891bc.

📒 Files selected for processing (2)

• src/xmldsig/parse.rs
• src/xmldsig/whitespace.rs

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📝 Walkthrough

Summary by CodeRabbit

• New Features
  • Added built-in resolution of XML signature verification keys from RSA KeyValue sources (in addition to existing key sources).
• Bug Fixes
  • Strengthened RSA KeyValue parsing and validation (required modulus/exponent structure and correct element ordering).
  • Improved base64 handling with whitespace normalization and length limits.
  • Rejects weak RSA keys and enforces RSA-compatible signature algorithms for verification.
• Tests
  • Expanded end-to-end and negative coverage for valid/legacy RSA KeyValue scenarios and failure modes.

Walkthrough

Adds structured RSAKeyValue parsing with bounded XML base64 decoding, resolves decoded RSA key material into verification keys, and updates verification tests, donor-suite handling, and README status text.

Changes

RSAKeyValue Parsing and Key Resolution

Layer / File(s)	Summary
Bounded XML base64 normalization src/xmldsig/whitespace.rs	Adds a bounded XML base64 normalizer, length-limited error types, and tests for capped and uncapped whitespace handling.
RSAKeyValue parser and key material shape src/xmldsig/parse.rs	Changes KeyValueInfo::Rsa to carry decoded modulus and exponent bytes, routes RSAKeyValue parsing to a strict parser, and adds tests for accepted and rejected RSAKeyValue structures and payloads.
RSA key resolution src/xmldsig/keys.rs	Adds RSA DER/SPKI imports, resolves KeyValueInfo::Rsa into a VerificationKey, and routes KeyInfoSource::KeyValue through the new resolver path.
Verification tests and donor suite src/xmldsig/keys.rs, tests/donor_full_verification_suite.rs, README.md	Adds resolver tests for valid, weak, and algorithm-mismatched RSAKeyValue inputs, updates donor-suite skip handling, and adds the README status entry.

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Possibly related PRs

• structured-world/xml-sec#22: Introduces the RSA verification path and InvalidKeyDer handling that the weak-key rejection tests exercise.
• structured-world/xml-sec#32: Touches the same key-resolution plumbing by refactoring verification around VerifyContext and KeyResolver.
• structured-world/xml-sec#41: Extends the donor verification suite skip/probe logic that this PR updates with WeakRsaKey.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 62.50% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: resolving RSAKeyValue keys in xmldsig.
Description check	✅ Passed	The description matches the implemented RSAKeyValue parsing, resolution, validation, and testing changes.
Linked Issues check	✅ Passed	The PR covers bounded RSAKeyValue parsing, RSA-only resolution, weak/incompatible key rejection, and donor-vector verification.
Out of Scope Changes check	✅ Passed	The changes stay focused on RSAKeyValue parsing, resolution, validation, tests, and related README updates.

✨ 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 feat/#67-rsa-key-value

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_{Comment @coderabbitai help to get the list of available commands.}

[greptile-apps]

Greptile Summary

This PR adds built-in XMLDSig RSA KeyValue parsing and verification-key resolution. The main changes are:

• Parses bounded RSAKeyValue Modulus and Exponent CryptoBinary values.
• Converts embedded RSA parameters into SubjectPublicKeyInfo DER for the default resolver.
• Applies existing RSA algorithm, modulus-size, and exponent checks to embedded keys.
• Adds donor-suite coverage for successful RSA KeyValue verification and weak-key rejection.

Confidence Score: 5/5

The RSA KeyValue parsing and resolver changes appear merge-safe based on the bounded parsing, algorithm-policy enforcement, and donor-suite coverage described.

No correctness or security issues were identified in the reviewed changes, and the implementation is covered by workspace checks, linting, end-to-end donor verification, and negative tests for malformed or weak embedded RSA parameters.

T-Rex Logs

What T-Rex did

• Ran the RSA keyvalue end-to-end test on the base commit and observed a failure with VerifyResult status Invalid(KeyNotFound) and exit code 101.
• Ran the RSA keyvalue end-to-end test on the head commit and observed a passing verification with status Valid and exit code 0.
• Inspected the before artifact for RSA keyvalue security to verify baseline Rust test source and environment showing base lacks KeyValueInfo::Rsa.
• Inspected the after artifact for RSA keyvalue security to verify the test source and verbose cargo output show 11 RSAKeyValue tests passed, including parser rejection cases and key resolver policy/mismatch tests, with test result: ok and exit code 0.

_{Ran code and verified through T-Rex}

_{Reviews (2): Last reviewed commit: "fix(xmldsig): bound crypto binary normal..." | Re-trigger Greptile}

[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@src/xmldsig/parse.rs`:
- Around line 592-606: The length check in the XML base64 parsing path is
happening after `normalize_xml_base64_text` has already appended the full child
text into `cleaned`, so oversized `<Modulus>`/`<Exponent>` nodes can still drive
large allocations. Update the `parse.rs` base64 normalization flow around
`normalize_xml_base64_text` and `cleaned` so the maximum decoded length is
enforced during accumulation, rejecting input before `cleaned` grows past
`max_base64_len` while preserving the existing XML-whitespace normalization
behavior.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: 4faf5dcd-520d-4314-b3d6-e30f2bd15185

📥 Commits

Reviewing files that changed from the base of the PR and between 400410b and a2d958a.

📒 Files selected for processing (4)

• README.md
• src/xmldsig/keys.rs
• src/xmldsig/parse.rs
• tests/donor_full_verification_suite.rs