reverse-skills-max: initial public release (restored, redacted, hardened)

vendor-new/analyst-ai-pack/skills/analyzing-authenticode-signatures/SKILL.md

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+---
+name: analyzing-authenticode-signatures
+description: 'Analyzes Windows Authenticode signatures on PE files: checking for a signature,
+  reading the signer certificate chain, detecting revoked/expired/stolen certs, and recognizing
+  signature-stripping and catalog-signing abuse. Activates for requests to analyze a code
+  signature, verify Authenticode, or assess signer trust on a PE.'
+domain: cybersecurity
+subdomain: malware-analysis
+tags:
+  - malware-analysis
+  - authenticode
+  - code-signing
+  - pe
+  - certificates
+version: 1.0.0
+author: analyst-ai-pack
+license: Apache-2.0
+mitre_attack:
+  - T1553.002
+  - T1036.001
+d3fend:
+  - D3-FCR
+references:
+  - 'Windows Authenticode PE signature format — https://learn.microsoft.com/windows-hardware/drivers/install/authenticode'
+  - 'Microsoft PE/COFF specification (security directory) — https://learn.microsoft.com/windows/win32/debug/pe-format'
+---
+
+# Analyzing Authenticode Signatures
+
+## When to Use
+
+- You need to know whether a PE is signed and whether the signer is trustworthy.
+- You suspect a stolen/abused code-signing certificate or a forged/invalid signature.
+- You are distinguishing legitimately signed software from signed malware.
+
+**Do not use** "is signed" as "is safe" — adversaries use stolen certs, abuse catalog signing,
+and append invalid signatures; a valid signature only attests the signer, not benignity.
+
+## Prerequisites
+
+- Access to the PE security directory (Python `struct`/`pefile`); on Windows, `signtool`/PowerShell
+  `Get-AuthenticodeSignature` for authoritative verification.
+
+## Safety & Handling
+
+- Parse the signature statically; never execute the sample.
+- Keep the sample password-protected at rest and reference it by hash.
+
+## Workflow
+
+### Step 1: Check for a signature
+
+Read the PE security directory (certificate table). Absent entry = unsigned; present = embedded
+PKCS#7. Note that valid signing can also be via a catalog file (not embedded).
+
+```bash
+python scripts/analyst.py check sample.exe
+```
+
+### Step 2: Extract signer details
+
+Parse the PKCS#7 to read the signer certificate: subject, issuer, validity dates, and serial.
+Cross-reference against known-abused/stolen certs.
+
+### Step 3: Verify, do not just read
+
+On Windows, verify the signature cryptographically and check revocation
+(`Get-AuthenticodeSignature`). A present-but-invalid signature is a strong red flag.
+
+### Step 4: Assess trust in context
+
+Weigh signer reputation, certificate age, and whether the signed file's behavior matches the
+purported publisher. Treat anomalies (recently issued cert, mismatched publisher) as suspicious.
+
+## Validation
+
+- Signature presence is determined from the security directory, and verified (not just read) on
+  Windows.
+- Signer certificate details are extracted and checked against abuse intel.
+- The trust conclusion accounts for revocation/validity, not mere presence.
+
+## Pitfalls
+
+- Equating a present signature with safety; stolen-cert malware is common.
+- Missing catalog-signed files by only checking embedded signatures.
+- Reading the signature without cryptographically verifying it.
+
+## References
+
+- See [`references/api-reference.md`](references/api-reference.md) for the signature checker.
+- Authenticode format and the PE/COFF security directory (linked in frontmatter).