Detecting weak cryptography

Skill jeremylongshore/claude-code-plugins-plus-skills/plugins/security/penetration-tester/skills/detecting-weak-cryptography

425 plugins, 2,810 skills, 200 agents for Claude Code. Open-source marketplace at tonsofskills.com with the ccpi CLI package manager.

Install

npx -y skills add jeremylongshore/claude-code-plugins-plus-skills --skill detecting-weak-cryptography

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What its author says it does

Copied from the file, not written here

Scan a source tree for weak cryptographic primitives: MD5 / SHA-1 used for security purposes, DES / 3DES / RC4 ciphers, ECB block mode, custom-built crypto (XOR loops, hand-rolled HMAC), hardcoded IVs, predictable random (Math.random / java.util.Random for crypto seeds), missing certificate verification (verify=False, rejectUnauthorized: false). Use when: pre-merge gate on crypto-touching code, audit before SOC2 / PCI assessment, post-incident review when "we found a weakness in our token signing." Threshold: any call to a known-weak algorithm with non-test context, OR cert verification explicitly disabled, OR a custom crypto loop pattern. Trigger with: "scan weak crypto", "find MD5 usage", "check ECB mode", "audit ssl verify", "weak random".

The file declares its own license as MIT. That is the author’s claim about this one file, and it is not the same thing as the license GitHub reports for the repository, which is listed with the other numbers below.

SKILL.md

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Detecting Weak Cryptography

Overview

Weak cryptography (CWE-327 Use of a Broken or Risky Cryptographic Algorithm, CWE-330 Use of Insufficiently Random Values) shows up when engineers use the convenient API instead of the cryptographic one. hashlib.md5(password) is faster to type than the correct bcrypt/argon2 invocation; Math.random() returns a number quickly without needing to know about crypto.randomBytes().

The fix is universal: use the modern primitive. SHA-256 for general hashing, bcrypt/argon2/scrypt for passwords, AES-GCM for encryption, HMAC-SHA256 for signing, secrets / crypto.randomBytes / SecureRandom for randomness.

When the skill produces findings

Finding	Severity	Threshold	Affected control
MD5 used in security context	HIGH	hashlib.md5, MessageDigest.MD5, CryptoJS.MD5	CWE-327
SHA-1 used in security context	HIGH	hashlib.sha1, etc.	CWE-327
DES / 3DES cipher	CRITICAL	DESCrypto, "DES/CBC", "DESede"	CWE-327
RC4 cipher	CRITICAL	"ARC4", "RC4"	CWE-327
AES ECB mode	CRITICAL	"AES/ECB" or `MODE_ECB`	CWE-327
Hardcoded IV (initialization vector)	CRITICAL	IV literal in source	CWE-329
Custom XOR-based "encryption"	CRITICAL	XOR loop over bytes	CWE-327
Predictable random for crypto seed	CRITICAL	Math.random / java.util.Random / random.random for keys	CWE-330
TLS cert verification disabled	CRITICAL	verify=False, rejectUnauthorized:false, ServerCertificateValidationCallback returning true	CWE-295
Hardcoded HMAC secret	HIGH	Long literal in HMAC constructor	CWE-321
Insecure password hashing (no salt, no KDF)	CRITICAL	hashlib.sha256(password) without bcrypt/argon2	CWE-916

Prerequisites

Python 3.9+
Source tree on local filesystem

Instructions

Run

python3 ${CLAUDE_PLUGIN_ROOT}/skills/detecting-weak-cryptography/scripts/scan_weak_crypto.py /path/to/repo

Options: --output, --format, --min-severity, --include-tests, --languages, --allow-md5-checksums (excludes MD5 used in non-security contexts like content-addressable storage).

Interpret

CRITICAL = direct cryptographic break available against the algorithm. CVEs, public attack tools, sometimes pre-computed tables (rainbow tables for MD5/SHA-1).

HIGH = algorithm collision-broken (MD5, SHA-1) but the specific use case may tolerate the weakness (file-deduplication checksums, non-security HMAC). Verify the usage context.

Remediation

See references/PLAYBOOK.md for per-primitive migration. Modern defaults: SHA-256/SHA-3 for hashing, AES-256-GCM for encryption, HMAC-SHA-256 for signing, secrets-grade random for keys, bcrypt / argon2id for password storage.

Examples

Pre-merge gate

python3 ${CLAUDE_PLUGIN_ROOT}/skills/detecting-weak-cryptography/scripts/scan_weak_crypto.py \
    --min-severity high $(git diff --name-only main...HEAD | tr '\n' ' ')

CI

- name: Weak-crypto scan
  run: |
    python3 plugins/security/penetration-tester/skills/detecting-weak-cryptography/scripts/scan_weak_crypto.py \
        . --min-severity high

Output

JSON / JSONL / Markdown. Exit codes: 0 / 1 / 2.

Error Handling

False positives common on:

MD5 used for content-addressable storage (caches, content hashes) where collision resistance against ATTACKERS isn't needed — use --allow-md5-checksums.
HMAC-MD5 — broken against adversaries but acceptable as an integrity check inside a TLS session where the channel is already authenticated.

Verify each finding by reading whether the algorithm's failure mode (collision, preimage, etc.) is actually exploitable in context.

Resources

references/THEORY.md — Per-primitive attack model (why MD5 / SHA-1 are collision-broken, why ECB leaks structure, why Math.random is non-crypto-grade)
references/PLAYBOOK.md — Per-language modern-crypto recipes (Python cryptography library, Node crypto, Java JCA with modern algorithms, Go crypto/rand + crypto/cipher AEAD)