feat: support SHA-384 digests and RSA-SHA384 signatures

[cjbarth]

xml-crypto has SHA-1, SHA-256 and SHA-512, and no SHA-384. A document whose SignatureMethod is rsa-sha384 fails with signature algorithm '…#rsa-sha384' is not supported, one whose DigestMethod is sha384 fails with hash algorithm '…#sha384' is not supported, and neither name can be used to sign.

XMLDSig 1.1 lists both as optional (§6.2.4, §6.4.2), and RFC 9231 defines the identifiers (§2.1.3, §2.3.3). The implementations a signed document is likely to come from or go to have both:

Implementation	rsa-sha384	sha384 digest
xml-crypto master	no	no
.NET System.Security.Cryptography.Xml	yes	yes
JDK javax.xml.crypto.dsig	yes	yes
goxmldsig	yes	yes
xmlsec, as python3-saml uses it	yes	yes
ruby-saml	yes	yes

node-saml is the caller that needs it now. Since node-saml/node-saml#479 it takes the algorithm for a Redirect-binding signature from SignedXml's SignatureAlgorithms, and it keeps a second lookup among OpenSSL digest names only for the identifiers that map lacks. rsa-sha384 is the one of those worth keeping, so that lookup can go once this is released.

This PR adds:

• Sha384, the digest http://www.w3.org/2001/04/xmldsig-more#sha384.
• RsaSha384, the signature http://www.w3.org/2001/04/xmldsig-more#rsa-sha384: PKCS Initial support for enveloped signatures #1 v1.5, as rsa-sha256 and rsa-sha512 are.
• Both registered by default in HashAlgorithms and SignatureAlgorithms, so a document that names them verifies with no configuration, like the other SHA-2 sizes.
• The two identifiers in HashAlgorithmType and SignatureAlgorithmType, and in the README's lists. Both unions already end in string, so this changes editor completion and nothing else.

Left out on purpose:

• SHA-224. XMLDSig 1.1 lists it as optional too, but .NET, goxmldsig, python3-saml and ruby-saml don't offer it.
• The other PSS sizes (sha384-rsa-MGF1, sha512-rsa-MGF1). Nothing here needs them.

Tests

• A fixture from another implementation. test/static/rsa_sha384_signature.xml is signed by JDK 21 with client.pem, using rsa-sha384 over a sha384 digest. It verifies, and stops verifying when the signed content changes.
• Signing matches the JDK. Signing the same document with the same parameters writes the DigestValue and SignatureValue the JDK wrote. PKCS Initial support for enveloped signatures #1 v1.5 is deterministic, so they are equal byte for byte.
• rsa-sha384 joins the sign-and-verify list in test/signature-unit-tests.spec.ts.

All five tests failed before the change with the two is not supported errors above. Each also fails when SHA-256 is put in place of SHA-384 in RsaSha384's signing, in its verifying, or in Sha384.

Checks

• npm run build && npm test && npm run lint pass (555 tests).
• JDK 21 verifies a document this branch signs with rsa-sha384 and a sha384 digest over an Id reference, and rejects it after an edit.

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features
  • Added support for SHA-384 digests and RSA-SHA384 signatures when signing and verifying XML.
• Tests
  • Added coverage for verifying, creating, and rejecting modified RSA-SHA384 signatures.

[coderabbitai]

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ℹ️ Recent review info

⚙️ Run configuration

• Configuration used: defaults
• Review profile: CHILL
• Plan: Advanced
• Run ID: f3941f90-a251-4d31-ae38-e94a291c6a65

📥 Commits

Reviewing files that changed from the base of the PR and between a311adc and ea0b0a6.

📒 Files selected for processing (9)

• README.md
• src/hash-algorithms.ts
• src/signature-algorithms.ts
• src/signed-xml.ts
• src/types.ts
• test/README.md
• test/signature-integration-tests.spec.ts
• test/signature-unit-tests.spec.ts
• test/static/rsa_sha384_signature.xml

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📝 Walkthrough

Walkthrough

The change adds SHA-384 digest and RSA-SHA384 signature support. It updates the algorithm types and registries, documents the supported algorithms, and adds a signed XML fixture with integration and unit test coverage.

Changes

SHA-384 support

Layer / File(s)	Summary
Algorithm contracts and implementations src/types.ts, src/hash-algorithms.ts, src/signature-algorithms.ts, README.md	Adds SHA-384 and RSA-SHA384 algorithm types and implementations. The README lists SHA384 as a hash algorithm and RSA-SHA384 as a signature algorithm.
Registration and fixture-based tests src/signed-xml.ts, test/static/rsa_sha384_signature.xml, test/README.md, test/signature-integration-tests.spec.ts, test/signature-unit-tests.spec.ts	Registers both algorithms. Adds a JDK-signed fixture and tests for verification, modified-content rejection, and matching generated digest and signature values.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~12 minutes

Change: Feature

Suggested reviewers: shunkica

Merge Risk: ⚪ Minimal · up to ea0b0

No actionable issue remains from this review; the change is mergeable after normal checks.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 6 files. (3 skipped: 3 …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely identifies the two main changes: SHA-384 digest support and RSA-SHA384 signature support.
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: Docstring Coverage

Explanation

Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 6 files. (3 skipped: 3 unsupported.)

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