Hello HN,

I built this because I've become paranoid about "safe" refactors in the wake of supply chain attacks like the xz backdoor.

We spend a lot of time reviewing code for syntax, but we lack good tools for verifying that a large refactor (e.g., renaming variables, changing loop styles) preserves the exact business logic. Standard SHA256 hashes break if you change a single whitespace or variable name, which makes them useless for verifying semantic equivalence.

I built Semantic Firewall (sfw) to solve this. It is an open-source tool that fingerprints Go code based on its behavior, not its bytes.

How it works:

1. SSA Conversion: It loads the Go source into Static Single Assignment form using golang.org/x/tools/go/ssa.

2. Canonicalization: It renames registers (v0, v1) deterministically and normalizes control flow graphs. This ensures that `if a { x } else { y }` fingerprints the same even if branches are swapped with inverted conditions.

3. Scalar Evolution (SCEV): This was the hardest part. I implemented an SCEV engine that mathematically solves loop trip counts. This means a `for range` loop and a `for i++` loop that iterate N times produce the exact same fingerprint.

Here is a quick example of what it catches:

  // Implementation A
  func wipe(k []byte) {
      for i := range k { k[i] = 0 }
  }

  // Implementation B (Refactor?)
  func wipe(buf []byte) {
      for i := 0; i < len(buf); i++ { buf[i] = 0 }
  }

These two produce identical hashes. If you change the logic (e.g. `i < len(buf)-1`), the hash diverges immediately.

It’s written in Go and available as a CLI or GitHub Action. I’d love to hear your thoughts on the approach or edge cases I might have missed in the normalization phase.

Repo: https://github.com/BlackVectorOps/semantic_firewall

Show HN: Hashing Go Functions Using SSA and Scalar Evolution