Semantic Firewall

Next-Gen Code Integrity & Malware Detection for Go

Protect your codebase from hidden risks.

Semantic Firewall goes beyond traditional static analysis: it understands your code's intent and behavior, not just the text. Instantly spot risky changes, catch malware, and prove your code is safe--no matter how it's refactored or renamed.

No more false positives. No more missed backdoors.

---

Caution

Disclaimer: This tool is provided for defensive security research and authorized testing only. The malware scanning features are designed to help security teams detect and analyze malicious code patterns. Do not use this tool to create, distribute, or deploy malware. Users are responsible for ensuring compliance with all applicable laws and organizational policies. The author assumes no liability for misuse.

---

What is Semantic Firewall?

Semantic Firewall is a new kind of static analysis tool for Go that:

• Fingerprints code by behavior, not by text -- so you can refactor, rename, or reformat without breaking your security gates.
• Detects malware and backdoors -- even if attackers try to hide them with obfuscation or clever tricks.
• Flags risky changes in pull requests -- so you know when something really changes, not just when someone moves code around.

Why is this different?

• Traditional tools (like git diff, grep, or hash-based scanners) are easily fooled by renaming, whitespace, or code shuffling.
• Semantic Firewall understands the structure and intent of your code. It knows when a function is logically the same--even if it looks different.
• It also knows when something dangerous is added, like a hidden network call or a suspicious loop.

Key Features:

• Behavioral fingerprinting: Prove your code hasn't changed in intent, even after big refactors.
• Malware & backdoor detection: Find threats by structure, not just by name or hash.
• Risk-aware diffs: Instantly see if a PR adds risky logic, not just lines changed.
• Obfuscation & entropy analysis: Spot packed or encrypted payloads.
• Zero-config persistent database: Fast, scalable, and easy to use.

See full feature table

Feature	Description
Loop Equivalence	Proves loops are logically identical, no matter the syntax
Semantic Diff	Diffs code by behavior, not by text
Malware Indexing	Store and hunt for known malware patterns
Obfuscation Detection	Flags suspiciously complex or packed code
Dependency Scanning	Scans your code and all its dependencies

---

Getting Started

go install github.com/BlackVectorOps/semantic_firewall/v2/cmd/sfw@latest

Quick Start

# Check a file for risky changes
sfw check ./main.go

# See what *really* changed between two versions
sfw diff old_version.go new_version.go

# Index a known malware sample
sfw index malware.go --name "Beacon_v1" --severity CRITICAL

# Scan your codebase for malware (fast, O(1) matching)
sfw scan ./suspicious/

# Scan with dependency analysis
sfw scan ./cmd/myapp --deps

# See database stats
sfw stats

Show example outputs

Check Output:

{
  "file": "./main.go",
  "functions": [
    { "function": "main", "fingerprint": "005efb52a8c9d1e3...", "line": 12 }
  ]
}

Diff Output (Risk-Aware):

{
  "summary": {
    "semantic_match_pct": 92.5,
    "preserved": 12,
    "modified": 1,
    "renamed_functions": 2,
    "high_risk_changes": 1
  },
  "functions": [
    {
      "function": "HandleLogin",
      "status": "modified",
      "added_ops": ["Call <log.Printf>", "Call <net.Dial>"],
      "risk_score": 15,
      "topology_delta": "Calls+2, AddedGoroutine"
    }
  ],
  "topology_matches": [
    {
      "old_function": "processData",
      "new_function": "handleInput",
      "similarity": 0.94,
      "matched_by_name": false
    }
  ]
}

Scan Output (Malware Hunter):

{
  "target": "./suspicious/",
  "backend": "boltdb",
  "total_functions_scanned": 47,
  "alerts": [
    {
      "signature_name": "Beacon_v1",
      "severity": "CRITICAL",
      "matched_function": "executePayload",
      "confidence": 0.92,
      "match_details": {
        "topology_match": true,
        "entropy_match": true,
        "topology_similarity": 1.0,
        "calls_matched": ["net.Dial", "os.Exec"]
      }
    }
  ],
  "summary": { "critical": 1, "high": 0, "total_alerts": 1 }
}

---

Why Developers Need Semantic Firewall

• No more noisy diffs: See only what matters--real logic changes, not whitespace or renames.
• Catch what tests miss: Unit tests check correctness. Semantic Firewall checks intent and integrity.
• Malware can't hide: Renaming, obfuscation, or packing? Still detected.
• Refactor with confidence: Prove your big refactor didn't change what matters.
• CI/CD ready: Block PRs that sneak in risky logic.

Traditional Tools	Semantic Firewall
git diff	sfw diff
Sees lines changed	Sees logic changed
Fooled by renames	Survives refactors
Hash-based AV	Behavioral fingerprints
YARA/grep	Topology & intent matching

Use cases:

• Supply chain security: catch backdoors that pass code review
• Safe refactoring: prove your refactor is safe
• CI/CD gates: block risky PRs
• Malware hunting: scan codebases at scale
• Obfuscation detection: flag packed/encrypted code
• Dependency auditing: scan imported packages

---

---

Lie Detector Workflow

Worried about sneaky changes or hidden intent?

Supply chain attacks often hide behind boring commit messages like "fix typo" or "update formatting." sfw audit uses an LLM (or deterministic simulation if you dont want to bother with an api key) to compare the developer's claim against the code's reality.

Command:

# Check if the commit message matches the code changes
sfw audit old.go new.go "minor refactor of logging" --api-key sk-...

The Verdict:

{
  "inputs": {
    "commit_message": "minor refactor of logging"
  },
  "risk_filter": {
    "high_risk_detected": true,
    "evidence_count": 1
  },
  "output": {
    "verdict": "LIE",
    "evidence": "Commit claims 'minor refactor' but evidence shows addition of high-risk network calls (net.Dial) and goroutines."
  }
}

How it works:

1. Semantic Diff: Calculates exact structural changes (ignoring whitespace).
2. Risk Filter: Isolates high-risk deltas (Network, FS, Concurrency).
3. Intent Verification: Asks the AI: "Does 'fix typo' explain adding a reverse shell?"

Typical CI/CD workflow:

jobs:
  semantic-firewall:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - name: Run Semantic Firewall
        run: |
          go install github.com/BlackVectorOps/semantic_firewall/v2/cmd/sfw@latest
          sfw diff old.go new.go
          sfw scan . --deps

Result:

• PRs that only change formatting or names pass instantly.
• PRs that add risky logic or malware get flagged for review.

---

Command	Purpose	Time Complexity	Space
sfw check	Generate semantic fingerprints	O(N)	O(N)
sfw diff	Semantic delta via Zipper algorithm	O(I)	O(I)
sfw index	Index malware samples into BoltDB	O(N)	O(1) per sig
sfw scan	Hunt malware via topology matching	O(1) exact / O(M) fuzzy	O(M)
sfw migrate	Migrate JSON signatures to PebbleDB	O(S)	O(S)
sfw stats	Display database statistics	O(1)	O(1)
sfw audit	Verify commit intent (AI Lie Detector)	O(I) + API	O(I)

Where N = source size, I = instructions, S = signatures, M = signatures in entropy range.

Command Details

sfw check [--strict] [--scan --db <path>] <file.go|directory>

Generate semantic fingerprints. Use --strict for validation mode. Use --scan to enable unified security scanning during fingerprinting.

sfw diff <old.go> <new.go>

Compute semantic delta using the Zipper algorithm with topology-based function matching. Outputs risk scores and structural deltas.

sfw index <file.go> --name <name> --severity <CRITICAL|HIGH|MEDIUM|LOW> [--category <cat>] [--db <path>]

Index a reference malware sample. Generates topology hash, fuzzy hash, and entropy score.

sfw scan <file.go|directory> [--db <path>] [--threshold <0.0-1.0>] [--exact] [--deps] [--deps-depth <direct|transitive>]

Scan target code for malware signatures. Use --exact for O(1) topology-only matching. Use --deps to scan imported dependencies.

sfw migrate --from <json> --to <db>

Migrate legacy JSON database to PebbleDB format for O(1) lookups.

sfw audit <old.go> <new.go> "<commit message>" [--api-key <key>]

Verify if a commit message matches the structural code changes. Uses an LLM to detect deception (e.g., hiding a backdoor in a "typo fix").

---

Signature Database Configuration

The CLI automatically resolves the signature database location (signatures.db) in the following order:

1. Explicit Flag: --db /custom/path/signatures.db
2. Environment Variable: SFW_DB_PATH
3. Local Directory: ./signatures.db
4. User Home: ~/.sfw/signatures.db
5. System Strings: /usr/local/share/sfw/signatures.db or /var/lib/sfw/signatures.db

This allows you to manage updates independently of the binary.

sfw stats --db <path>

Display database statistics including signature count and index sizes.

---

Deep Technical Dive (Math, Graphs & Algorithms)

Persistent Signature Database (Pebble)

The scanner uses Pebble, an embedded key-value store inspired by RocksDB, for signature storage. This enables:

• O(1) exact topology lookups via indexed hash keys
• O(M) fuzzy matching via range scans on entropy indexes
• Atomic writes: no partial updates on crash
• Concurrent reads: safe for parallel scanning
• Zero configuration: single file, no server required

Database Schema

Pebble uses a flat key-space, and we simulate buckets by using prefixes:

• sig:ID -> JSON blob (full signature)
• topo:TopologyHash:ID -> ID (O(1) exact match)
• fuzzy:FuzzyHash:ID -> ID (LSH bucket index)
• entr:EntropyKey -> ID (range scan index)
• meta:key -> value (version, stats, maintenance info)

Entropy Key Encoding

Entropy scores are stored as fixed-width keys for proper lexicographic ordering:

Key: "05.1234:SFW-MAL-001"
      ├──────┤ ├─────────┤
      entropy  unique ID

This enables efficient range scans: find all signatures with entropy 5.0 ± 0.5.

Database Operations

# View statistics
sfw stats --db signatures.db
{
  "signature_count": 142,
  "topology_index_count": 142,
  "entropy_index_size": 28672,
  "file_size_human": "2.1 MB"
}

# Migrate from legacy JSON (one-time operation)
sfw migrate --from old_signatures.json --to signatures.db

# Export for backup/compatibility
# (Programmatic API: scanner.ExportToJSON("backup.json"))

Programmatic Database Access

// Open database with options
opts := semanticfw.BoltScannerOptions{
    MatchThreshold:   0.75,    // Minimum confidence for alerts
    EntropyTolerance: 0.5,     // Fuzzy entropy window
    Timeout:          5*time.Second,
    ReadOnly:         false,   // Set true for scan-only mode
}
scanner, err := semanticfw.NewBoltScanner("signatures.db", opts)
defer scanner.Close()

// Add signatures (single or bulk)
scanner.AddSignature(sig)
scanner.AddSignatures(sigs)  // Atomic batch insert

// Lookup operations
sig, _ := scanner.GetSignature("SFW-MAL-001")
sig, _ := scanner.GetSignatureByTopology(topoHash)
ids, _ := scanner.ListSignatureIDs()
count, _ := scanner.CountSignatures()

// Maintenance
scanner.DeleteSignature("SFW-MAL-001")
scanner.MarkFalsePositive("SFW-MAL-001", "benign library")
scanner.RebuildIndexes()  // Recover from corruption
scanner.Compact("signatures-compacted.db")

---

Malware Scanning: Two-Phase Detection

The Semantic Firewall includes a behavioral malware scanner that matches code by its structural topology, not just strings or hashes. The scanner uses a two-phase detection algorithm:

Phase 1: O(1) Exact Topology Match

1. Extract FunctionTopology from target SSA function
2. Compute topology hash: SHA-256(blockCount || callProfile || controlFlowFlags)
3. BoltDB lookup: idx_topology[hash] → signature IDs
4. Return exact matches with 100% topology confidence

Phase 2: O(1) Fuzzy Bucket Match (LSH-lite)

1. Compute fuzzy hash: GenerateFuzzyHash(topology) → "B3L1BR2"
2. Look up all signatures in the same fuzzy bucket
3. Verify call signature overlap and entropy distance
4. Return matches above confidence threshold

Why this survives evasion:

• Renaming evasion fails: backdoor() → helper() still matches (names aren't part of topology)
• Obfuscation-resistant: Variable renaming and code shuffling don't change block/call structure
• O(1) at scale: BoltDB indexes enable instant lookups even with thousands of signatures

Fuzzy Hash Buckets (LSH-lite)

The fuzzy hash creates locality-sensitive buckets based on quantized structural metrics:

FuzzyHash = "B{log2(blocks)}L{loops}BR{log2(branches)}"

Examples:
  B3L1BR2 = 8-15 blocks, 1 loop, 4-7 branches
  B4L2BR3 = 16-31 blocks, 2 loops, 8-15 branches

Log2 buckets reduce sensitivity to small changes while preserving structural similarity.

Dependency Scanning

Scan not just your code, but all imported dependencies:

# Scan local code + direct imports
sfw scan ./cmd/myapp --deps --db signatures.db

# Deep scan: include transitive dependencies
sfw scan . --deps --deps-depth transitive --db signatures.db

# Fast exact-match mode for large codebases
sfw scan . --deps --exact --db signatures.db

Output with dependencies:

{
  "target": "./cmd/myapp",
  "total_functions_scanned": 1247,
  "dependencies_scanned": 892,
  "scanned_dependencies": [
    "github.com/example/suspicious-lib",
    "github.com/another/dependency"
  ],
  "alerts": [...],
  "summary": { "critical": 0, "high": 1, "total_alerts": 1 }
}

Flag	Description
--deps	Enable dependency scanning
--deps-depth direct	Scan only direct imports (default)
--deps-depth transitive	Scan all transitive dependencies
--exact	O(1) exact topology match only (fastest)

Note: Dependency scanning requires modules to be downloaded (go mod download). Stdlib packages are automatically excluded.

Workflow: Lab → Hunt

flowchart LR
    subgraph Lab["Lab Phase"]
        M1["Known Malware"] --> I["sfw index"]
        I --> DB[(signatures.db)]
    end
    
    subgraph Hunt["Hunter Phase"]
        T["Target Code"] --> S["sfw scan"]
        DB --> S
        S --> A["Alerts"]
    end
    
    style Lab fill:#1e1b4b,stroke:#8b5cf6,stroke-width:2px
    style Hunt fill:#064e3b,stroke:#10b981,stroke-width:2px
    style DB fill:#7c2d12,stroke:#f97316,stroke-width:2px

Loading

Step 1: Index Known Malware (Lab Phase)

# Index a beacon/backdoor sample
sfw index samples/dirty/dirty_beacon.go \
    --name "DirtyBeacon" \
    --severity CRITICAL \
    --category malware \
    --db signatures.db

# Output:
{
  "message": "Indexed 1 functions from samples/dirty/dirty_beacon.go",
  "indexed": [{
    "name": "DirtyBeacon_Run",
    "topology_hash": "topo:9a8b7c6d5e4f3a2b...",
    "fuzzy_hash": "B3L1BR2",
    "entropy_score": 5.82,
    "identifying_features": {
      "required_calls": ["net.Dial", "os.Exec", "time.Sleep"],
      "control_flow": { "has_infinite_loop": true, "has_reconnect_logic": true }
    }
  }],
  "backend": "boltdb",
  "total_signatures": 1
}

Step 2: Scan Suspicious Code (Hunter Phase)

# Scan an entire directory
sfw scan ./untrusted_vendor/ --db signatures.db --threshold 0.75

# Fast mode: exact topology match only (O(1) per function)
sfw scan ./large_codebase/ --db signatures.db --exact

---

Shannon Entropy Analysis

The scanner calculates Shannon entropy for each function to detect obfuscation and packed code:

$$H = -\sum_{i} p(x_i) \log_2 p(x_i)$$

Where $p(x_i)$ is the probability of byte value $x_i$ appearing in the function's string literals.

Entropy Spectrum:

     LOW          NORMAL              HIGH         PACKED
  ◀─────────────────────────────────────────────────────────▶
  │    ░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░▓▓▓▓▓▓▓▓▓▓▓████████│
  0                  4.0              6.5        7.5        8.0
  │                   │                │          │          │
  │  Simple funcs     │  Normal code   │ Obfusc.  │ Encrypted│
  │  (getters/setters)│  (business     │ (base64  │ (packed  │
  │                   │   logic)       │  strings)│  payloads)│

Entropy Range	Classification	Meaning	Example
< 4.0	LOW	Simple/sparse code	func Get() int { return x }
4.0 - 6.5	NORMAL	Typical compiled code	Business logic, handlers
6.5 - 7.5	HIGH	Potentially obfuscated	Base64 blobs, encoded strings
> 7.5	PACKED	Likely packed/encrypted	Encrypted payloads, shellcode

Functions with HIGH or PACKED entropy combined with suspicious call patterns receive elevated confidence scores.

Call Signature Resolution

The topology extractor resolves call targets to stable identifiers:

Call Type	Resolution	Example
Static function	pkg.Func	net.Dial
Interface invoke	invoke:Type.Method	invoke:io.Reader.Read
Builtin	builtin:name	builtin:len
Closure	closure:signature	closure:func(int) error
Go statement	go:target	go:handler.serve
Defer statement	defer:target	defer:conn.Close
Reflection	reflect:Call	Dynamic dispatch
Dynamic	dynamic:type	Unknown target

This stable resolution ensures signatures match even when:

• Code is moved between packages
• Interface implementations change
• Method receivers are renamed

---

Topology Matching

The diff command now uses structural topology matching to detect renamed or obfuscated functions.

How Topology Matching Works:

┌─────────────────────────────────────────────────────────────────────────────┐
│                        TOPOLOGY FINGERPRINT EXTRACTION                       │
├─────────────────────────────────────────────────────────────────────────────┤
│                                                                             │
│   func processData(input []byte) error {        ──►  TOPOLOGY VECTOR        │
│       conn, _ := net.Dial("tcp", addr)                                      │
│       for _, b := range input {                      ┌──────────────────┐   │
│           conn.Write([]byte{b})                      │ Params: 1        │   │
│       }                                              │ Returns: 1       │   │
│       return conn.Close()                            │ Blocks: 4        │   │
│   }                                                  │ Loops: 1         │   │
│                                                      │ Calls:           │   │
│                                                      │   net.Dial: 1    │   │
│   func handleInput(data []byte) error {              │   Write: 1       │   │
│       c, _ := net.Dial("tcp", server)                │   Close: 1       │   │
│       for i := 0; i < len(data); i++ {               │ Entropy: 5.2     │   │
│           c.Write([]byte{data[i]})                   └──────────────────┘   │
│       }                                                      │              │
│       return c.Close()                                       ▼              │
│   }                                              ┌──────────────────────┐   │
│                                                  │  SIMILARITY: 94%     │   │
│   Different names, SAME topology ───────────────│  ✓ MATCH DETECTED    │   │
│                                                  └──────────────────────┘   │
└─────────────────────────────────────────────────────────────────────────────┘

Topology vs Name-Based Matching:

flowchart LR
    subgraph old["Old Version"]
        O1["processData()"]
        O2["sendPacket()"]
        O3["initConn()"]
    end
    
    subgraph new["New Version (Obfuscated)"]
        N1["handleInput()"]
        N2["xmit()"]
        N3["setup()"]
    end
    
    O1 -.->|"Name: ✗"| N1
    O1 ==>|"Topology: 94%"| N1
    O2 ==>|"Topology: 91%"| N2
    O3 ==>|"Topology: 88%"| N3
    
    style old fill:#1e1b4b,stroke:#8b5cf6,stroke-width:2px
    style new fill:#064e3b,stroke:#10b981,stroke-width:2px

Loading

sfw diff old_version.go refactored_version.go

{
  "summary": {
    "preserved": 8,
    "modified": 2,
    "renamed_functions": 3,
    "topology_matched_pct": 85.7
  },
  "topology_matches": [
    {
      "old_function": "processData",
      "new_function": "handleInput",
      "similarity": 0.94,
      "matched_by_name": false
    }
  ]
}

Functions are matched by their structural fingerprint (block count, call profile, control flow features) rather than just name, enabling detection of:

• Renamed functions
• Copy-pasted code with modified names
• Obfuscated variants of known patterns

---

Library Usage

Fingerprinting

import semanticfw "github.com/BlackVectorOps/semantic_firewall/v2"

src := `package main
func Add(a, b int) int { return a + b }
`

results, err := semanticfw.FingerprintSource("example.go", src, semanticfw.DefaultLiteralPolicy)
if err != nil {
    log.Fatal(err)
}

for _, r := range results {
    fmt.Printf("%s: %s\n", r.FunctionName, r.Fingerprint)
}

Malware Scanning with BoltDB

import semanticfw "github.com/BlackVectorOps/semantic_firewall/v2"

// Open the signature database
scanner, err := semanticfw.NewBoltScanner("signatures.db", semanticfw.DefaultBoltScannerOptions())
if err != nil {
    log.Fatal(err)
}
defer scanner.Close()

// Extract topology from a function
topo := semanticfw.ExtractTopology(ssaFunction)

// O(1) exact topology match
if alert := scanner.ScanTopologyExact(topo, "suspiciousFunc"); alert != nil {
    fmt.Printf("ALERT: %s matched %s (confidence: %.2f)\n", 
        alert.MatchedFunction, alert.SignatureName, alert.Confidence)
}

// Full scan: exact + fuzzy entropy matching
alerts := scanner.ScanTopology(topo, "suspiciousFunc")
for _, alert := range alerts {
    fmt.Printf("[%s] %s: %s\n", alert.Severity, alert.SignatureName, alert.MatchedFunction)
}

Topology Extraction

import semanticfw "github.com/BlackVectorOps/semantic_firewall/v2"

// Extract structural features from an SSA function
topo := semanticfw.ExtractTopology(ssaFunction)

fmt.Printf("Blocks: %d, Loops: %d, Entropy: %.2f\n", 
    topo.BlockCount, topo.LoopCount, topo.EntropyScore)
fmt.Printf("Calls: %v\n", topo.CallSignatures)
fmt.Printf("Entropy Class: %s\n", topo.EntropyProfile.Classification)
fmt.Printf("Fuzzy Hash: %s\n", topo.FuzzyHash)

Unified Pipeline: Check + Scan

Enable security scanning during fingerprinting for a unified integrity + security workflow:

// CLI: sfw check --scan --db signatures.db ./main.go

// Programmatically:
results, _ := semanticfw.FingerprintSourceAdvanced(
    path, src, semanticfw.DefaultLiteralPolicy, strictMode)

for _, r := range results {
    // Integrity: Get fingerprint
    fmt.Printf("Function %s: %s\n", r.FunctionName, r.Fingerprint)
    
    // Security: Scan for malware
    fn := r.GetSSAFunction()
    topo := semanticfw.ExtractTopology(fn)
    alerts := scanner.ScanTopology(topo, r.FunctionName)
    for _, alert := range alerts {
        fmt.Printf("ALERT: %s\n", alert.SignatureName)
    }
}

Signature Structure

type Signature struct {
    ID                  string              // "SFW-MAL-001"
    Name                string              // "Beacon_v1_Run"
    Description         string              // Human-readable description
    Severity            string              // "CRITICAL", "HIGH", "MEDIUM", "LOW"
    Category            string              // "malware", "backdoor", "dropper"
    TopologyHash        string              // SHA-256 of topology vector
    FuzzyHash           string              // LSH bucket key "B3L1BR2"
    EntropyScore        float64             // 0.0-8.0
    EntropyTolerance    float64             // Fuzzy match window (default: 0.5)
    NodeCount           int                 // Basic block count
    LoopDepth           int                 // Maximum nesting depth
    IdentifyingFeatures IdentifyingFeatures // Behavioral markers
    Metadata            SignatureMetadata   // Provenance info
}

type IdentifyingFeatures struct {
    RequiredCalls  []string          // Must be present (VETO if missing)
    OptionalCalls  []string          // Bonus if present
    StringPatterns []string          // Suspicious strings
    ControlFlow    *ControlFlowHints // Structural patterns
}

type ControlFlowHints struct {
    HasInfiniteLoop   bool  // Beacon/C2 indicator
    HasReconnectLogic bool  // Persistence indicator
}

---

Architecture & Algorithms

Pipeline Overview

flowchart LR
    A["Source"] --> B["SSA"]
    B --> C["Loop Analysis"]
    C --> D["SCEV"]
    D --> E["Canonicalization"]
    E --> F["SHA-256"]
    
    B -.-> B1["go/ssa"]
    C -.-> C1["Tarjan's SCC"]
    D -.-> D1["Symbolic Evaluation"]
    E -.-> E1["Virtual IR Normalization"]
    
    style A fill:#4c1d95,stroke:#8b5cf6,stroke-width:2px,color:#e9d5ff
    style B fill:#1e3a8a,stroke:#3b82f6,stroke-width:2px,color:#dbeafe
    style C fill:#064e3b,stroke:#10b981,stroke-width:2px,color:#d1fae5
    style D fill:#7c2d12,stroke:#f97316,stroke-width:2px,color:#ffedd5
    style E fill:#701a75,stroke:#d946ef,stroke-width:2px,color:#fae8ff
    style F fill:#0f766e,stroke:#14b8a6,stroke-width:2px,color:#ccfbf1
    
    style B1 fill:transparent,stroke:#3b82f6,color:#93c5fd
    style C1 fill:transparent,stroke:#10b981,color:#6ee7b7
    style D1 fill:transparent,stroke:#f97316,color:#fdba74
    style E1 fill:transparent,stroke:#d946ef,color:#f0abfc

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1. SSA Construction: golang.org/x/tools/go/ssa converts source to Static Single Assignment form with explicit control flow graphs
2. Loop Detection: Natural loop identification via backedge detection (edge B->H where H dominates B)
3. SCEV Analysis: Algebraic characterization of loop variables as closed-form recurrences
4. Canonicalization: Deterministic IR transformation: register renaming, branch normalization, loop virtualization
5. Fingerprint: SHA-256 of canonical IR string

Scalar Evolution (SCEV) Engine

The SCEV framework (scev.go, 746 LOC) solves the "loop equivalence problem" -- proving that syntactically different loops compute the same sequence of values.

Core Abstraction: Add Recurrences

An induction variable is represented as ${Start, +, Step}_L$, meaning at iteration $k$ the value is:

$$Val(k) = Start + (Step \times k)$$

This representation is closed under affine transformations:

Operation	Result
${S, +, T} + C$	${S+C, +, T}$
$C \times {S, +, T}$	${C \times S, +, C \times T}$
${S_1, +, T_1} + {S_2, +, T_2}$	${S_1+S_2, +, T_1+T_2}$

IV Detection Algorithm (Tarjan's SCC)

1. Build dependency graph restricted to loop body
2. Find SCCs via Tarjan's algorithm (O(V+E))
3. For each SCC containing a header Phi:
   a. Extract cycle: Phi -> BinOp -> Phi
   b. Classify: Basic ({S,+,C}), Geometric ({S,*,C}), Polynomial
   c. Verify step is loop invariant
4. Propagate SCEV to derived expressions via recursive folding

Trip Count Derivation

For a loop for i := Start; i < Limit; i += Step:

$$TripCount = \left\lceil \frac{Limit - Start}{Step} \right\rceil$$

Computed via ceiling division: (Limit - Start + Step - 1) / Step

The engine handles:

• Upcounting (i < N) and downcounting (i > N) loops
• Inclusive bounds (i <= N -- add 1 to numerator)
• Negative steps (normalized to absolute value)
• Multi-predecessor loop headers (validates consistent start values)

Canonicalization Engine

The canonicalizer (canonicalizer.go, 1162 LOC) transforms SSA into a deterministic string representation via five phases:

Phase 1: Loop & SCEV Analysis

c.loopInfo = DetectLoops(fn)
AnalyzeSCEV(c.loopInfo)

Phase 2: Semantic Normalization

• Invariant Hoisting: Pure calls like len(s) are virtually moved to preheader
• IV Virtualization: Phi nodes for IVs are replaced with SCEV notation {0, +, 1}
• Derived IV Propagation: Expressions like i*4 become {0, +, 4} in output

Phase 3: Register Renaming

Parameters: p0, p1, p2, ...
Free Variables: fv0, fv1, ...
Instructions: v0, v1, v2, ... (DFS order)

Phase 4: Deterministic Block Ordering

Blocks are traversed in dominance-respecting DFS order, ensuring identical output regardless of SSA construction order. Successor ordering is normalized:

• >= branches are rewritten to < with swapped successors
• > branches are rewritten to <= with swapped successors

Phase 5: Virtual Control Flow

Branch normalization is applied virtually (no SSA mutation) via lookup tables:

virtualBlocks map[*ssa.BasicBlock]*virtualBlock  // swapped successors
virtualBinOps map[*ssa.BinOp]token.Token         // normalized operators

The Semantic Zipper

The Zipper (zipper.go, 568 LOC) computes a semantic diff between two functions -- what actually changed in behavior, ignoring cosmetic differences.

Algorithm: Parallel Graph Traversal

PHASE 0: Semantic Analysis
  - Run SCEV on both functions independently
  - Build canonicalizers for operand comparison

PHASE 1: Anchor Alignment
  - Map parameters positionally: oldFn.Params[i] <-> newFn.Params[i]
  - Map free variables if counts match
  - Seed entry block via sequential matching (critical for main())

PHASE 2: Forward Propagation (BFS on Use-Def chains)
  while queue not empty:
    (vOld, vNew) = dequeue()
    for each user uOld of vOld:
      candidates = users of vNew with matching structural fingerprint
      for uNew in candidates:
        if areEquivalent(uOld, uNew):
          map(uOld, uNew)
          enqueue((uOld, uNew))
          break

PHASE 2.5: Terminator Scavenging
  - Explicitly match Return/Panic instructions via operand equivalence
  - Handles cases where terminators aren't reached via normal propagation

PHASE 3: Divergence Isolation
  - Added = newFn instructions not in reverse map
  - Removed = oldFn instructions not in forward map

Equivalence Checking

Two instructions are equivalent iff:

1. Same Go type (reflect.TypeOf)
2. Same SSA value type (types.Identical)
3. Same operation specific properties (BinOp.Op, Field index, Alloc.Heap, etc.)
4. All operands equivalent (recursive, with commutativity handling for ADD/MUL/AND/OR/XOR)

Structural Fingerprinting (DoS Prevention)

To prevent $O(N \times M)$ comparisons on high fanout values, users are bucketed by structural fingerprint:

fp := fmt.Sprintf("%T:%s", instr, op)  // e.g., "*ssa.BinOp:+"
candidates := newByOp[fp]              // Only compare compatible types

Bucket size is capped at 100 to bound worst case complexity.

Security Hardening

Threat	Mitigation
Algorithmic DoS (exponential SCEV)	Memoization cache per loop: loop.SCEVCache
Quadratic Zipper (5000 identical ADDs)	Fingerprint bucketing + MaxCandidates=100
RCE via CGO	CGO_ENABLED=0 during packages.Load
SSRF via module fetch	GOPROXY=off prevents network calls
Stack overflow (cyclic graphs)	Visited sets in all recursive traversals
NaN comparison instability	Branch normalization restricted to IsInteger | IsString types
IR injection (fake instructions in strings)	Struct tags and literals sanitized before hashing
TypeParam edge cases	Generic types excluded from branch swap (may hide floats)

Complexity Analysis

Operation	Time	Space
SSA Construction	$O(N)$	$O(N)$
Loop Detection	$O(V+E)$	$O(V)$
SCEV Analysis	$O(L \times I)$ amortized	$O(I)$ per loop
Canonicalization	$O(I \times \log B)$	$O(I + B)$
Zipper	$O(I^2)$ worst, $O(I)$ typical	$O(I)$
Topology Extract	$O(I)$	$O(C)$
Scan (BoltDB exact)	$O(1)$	$O(1)$
Scan (fuzzy entropy)	$O(M)$	$O(M)$

Where $N$ = source size, $V$ = blocks, $E$ = edges, $L$ = loops, $I$ = instructions, $B$ = blocks, $C$ = unique calls, $M$ = signatures in entropy range.

Malware Scanner Architecture

The scanner (scanner_bolt.go, 780 LOC) provides two-phase detection with ACID-compliant persistence:

Phase 1: O(1) Exact Topology Match

1. Extract FunctionTopology from target SSA function
2. Compute topology hash: SHA-256(blockCount || callProfile || controlFlowFlags)
3. BoltDB lookup: idx_topology[hash] → signature ID
4. Return exact matches with 100% topology confidence

Phase 2: O(1) Fuzzy Bucket Match (LSH-lite)

1. Compute fuzzy hash: GenerateFuzzyHash(topo) → "B3L1BR2"
2. BoltDB prefix scan: idx_fuzzy[fuzzyHash:*] → candidate IDs
3. For each candidate:
   a. Load signature from signatures bucket
   b. Verify call signature overlap
   c. Check entropy distance within tolerance
   d. Compute composite confidence score
4. Return matches above threshold

BoltDB Storage Schema

Bucket: signatures     → ID → JSON blob (full signature)
Bucket: idx_topology   → TopologyHash → ID (exact match index)
Bucket: idx_fuzzy      → FuzzyHash:ID → ID (LSH bucket index)
Bucket: idx_entropy    → "08.4321:ID" → ID (range scan index)
Bucket: meta           → version, stats, maintenance info

Entropy Key Encoding

Entropy is stored as a fixed-width key for proper lexicographic ordering:

key := fmt.Sprintf("%08.4f:%s", entropy, id)  // "05.8200:SFW-MAL-001"

This enables efficient range scans and ensures uniqueness even for identical entropy values.

False Positive Feedback Loop

The scanner supports learning from mistakes:

// Mark a signature as generating false positives
scanner.MarkFalsePositive("SFW-MAL-001", "benign crypto library")

// This appends a timestamped note to the signature's metadata:
// "FP:2026-01-12T15:04:05Z:benign crypto library"

Confidence Score Calculation

The final confidence score is computed as a weighted average:

confidence = avg(
    topologySimilarity,      // 1.0 if exact hash match
    entropyScore,            // 1.0 - (distance / tolerance)
    callMatchScore,          // len(matched) / len(required)
    stringPatternScore,      // bonus for matched patterns
)

// VETO: If ANY required call is missing, confidence = 0.0

Topology Matching Algorithm

The topology matcher (topology.go, 673 LOC) enables function matching independent of names:

Feature Vector

type FunctionTopology struct {
    FuzzyHash      string              // LSH bucket key
    ParamCount     int                 // Signature: param count
    ReturnCount    int                 // Signature: return count
    BlockCount     int                 // CFG complexity
    InstrCount     int                 // Code size
    LoopCount      int                 // Iteration patterns
    BranchCount    int                 // Decision points
    PhiCount       int                 // SSA merge points
    CallSignatures map[string]int      // "net.Dial" → 2
    BinOpCounts    map[string]int      // "+" → 5
    HasDefer       bool                // Error handling
    HasRecover     bool                // Panic recovery
    HasPanic       bool                // Failure paths
    HasGo          bool                // Concurrency
    HasSelect      bool                // Channel ops
    HasRange       bool                // Iteration style
    EntropyScore   float64             // Obfuscation indicator
    EntropyProfile EntropyProfile      // Detailed entropy analysis
}

Similarity Score

Functions are compared via weighted Jaccard similarity:

$$Similarity = \frac{\sum_i w_i \cdot match_i}{\sum_i w_i}$$

Where weights prioritize:

1. Call profile (w=3): Most discriminative feature
2. Control flow (w=2): defer/recover/panic/select/go
3. Metrics (w=1): Block/instruction counts within 20% tolerance

Risk-Aware Diff Scoring

When comparing function versions, structural changes receive risk scores:

Change	Risk Points
New call	+5 each
New loop	+10 each
New goroutine	+15
New defer	+3
New panic	+5
Entropy increase >1.0	+10

High cumulative risk scores flag changes that warrant extra review.

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License

MIT License. See LICENSE for details.

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