Enable GODEBUG=fips140=only with systemcrypto backends

[gdams]

Fixes: #1656

Will need documentation before merging but pushing up the code changes for testing/review

[gdams]

@qmuntal I wanted you to sanity check this increase in allocations please :)

[github-actions]

Patch Consistency Review - PR #2149

I've completed a thorough review of the patch file changes in this PR. Here are my findings:

✅ Vendor Patch Consistency (0001-Vendor-external-dependencies.patch)

The vendor patch properly updates all three backend dependencies:

• ✅ go.mod updated with new versions
• ✅ go.sum updated with new checksums
• ✅ modules.txt updated with version references

Version updates:

• golang-fips/openssl/v2: v2.0.4-0.20260217140351 → v2.0.4-0.20260218141142
• go-crypto-darwin: v0.0.3-0.20260130143703 → v0.0.3-0.20260223145157
• go-crypto-winnative: v0.0.0-20260127024749 → v0.0.0-20260218135539

✅ Cross-Backend Consistency

The changes add new FIPS 140-only mode support across backends:

1. FIPSApproved() method: Added consistently to all three backends (openssl, darwin, winnative) with correct backend-specific logic:

   • OpenSSL includes SHA224, SHA512_224, SHA512_256 (because it supports them)
   • Darwin/CNG exclude SHA224, SHA512_224, SHA512_256 (because they don't support these variants)

2. NewFIPSCBC methods: Added consistently across all backends that support CBC:

   • NewFIPSCBCEncrypter() ✅
   • NewFIPSCBCDecrypter() ✅

3. NewFIPSCTR method: Only added to OpenSSL backend (correct, as darwin/winnative don't implement CTR mode)

✅ Backend Implementation Patch (0003-Implement-crypto-internal-backend.patch)

• Adds SHA512_224/SHA512_256 stubs to darwin backend (correctly marked as "not available")
• Updates file statistics (432 vs 430 lines) to reflect additions

✅ Usage Patch (0004-Use-crypto-backends.patch)

• Integrates FIPS 140-only mode enforcement throughout crypto packages
• Adds proper SHA512_224/256 support with boring crypto fallbacks
• Moves FIPS enforcement checks to correct locations (before boring checks)

📋 Summary

No consistency issues found. The patches maintain proper cross-backend consistency while respecting backend-specific capabilities. The changes implement FIPS 140-only mode support (GODEBUG=fips140=only) in a well-structured manner across all three system crypto backends.

The PR is ready from a patch consistency perspective. ✅

AI generated by Patch Consistency Review Agent