What it does. A cryptographic audit systematically reviews an application's use of Part of mukul975/Anthropic-Cybersecurity-Skills (817 security skills) (mukul975/Anthropic-Cybersecurity-Skills).

Install

• npx skills add mukul975/Anthropic-Cybersecurity-Skills --skill performing-cryptographic-audit-of-application, or copy the skill folder into ~/.claude/skills/performing-cryptographic-audit-of-application/.
• Raw file: curl -sL https://raw.githubusercontent.com/mukul975/Anthropic-Cybersecurity-Skills/HEAD/skills/performing-cryptographic-audit-of-application/SKILL.md

SKILL.md (verbatim)

name: performing-cryptographic-audit-of-application
description: A cryptographic audit systematically reviews an application's use of
  cryptographic primitives, protocols, and key management to identify vulnerabilities
  such as weak algorithms, insecure modes, hardco
domain: cybersecurity
subdomain: cryptography
tags:
- cryptography
- audit
- security-review
- compliance
- vulnerability-assessment
version: '1.0'
author: mahipal
license: Apache-2.0
nist_csf:
- PR.DS-01
- PR.DS-02
- PR.DS-10
mitre_attack:
- T1600
- T1573
- T1553
mitre_f3:
  version: '1.1'
  tactics:
  - reconnaissance
  - initial-access
  - positioning
  techniques:
  - id: T1557
    name: Adversary-in-the-Middle
    tactic: positioning
    source: attack
  - id: T1555
    name: Credentials from Password Stores
    tactic: reconnaissance
    source: attack
  - id: F1006.001
    name: 'Account Takeover: Exposed API Key'
    tactic: initial-access
    source: f3
  - id: F1004
    name: Access with Stolen Session Cookie
    tactic: initial-access
    source: f3

Performing Cryptographic Audit of Application

Overview

A cryptographic audit systematically reviews an application's use of cryptographic primitives, protocols, and key management to identify vulnerabilities such as weak algorithms, insecure modes, hardcoded keys, insufficient entropy, and protocol misconfigurations. This skill covers building an automated crypto audit tool that scans Python and configuration files for common cryptographic weaknesses.

When to Use

• When conducting security assessments that involve performing cryptographic audit of application
• When following incident response procedures for related security events
• When performing scheduled security testing or auditing activities
• When validating security controls through hands-on testing

Prerequisites

• Familiarity with cryptography concepts and tools
• Access to a test or lab environment for safe execution
• Python 3.8+ with required dependencies installed
• Appropriate authorization for any testing activities

Objectives

• Detect usage of deprecated algorithms (MD5, SHA-1, DES, RC4)
• Identify insecure cipher modes (ECB) and padding schemes
• Find hardcoded keys, passwords, and secrets in source code
• Verify TLS/SSL configuration strength
• Check key derivation function parameters
• Validate random number generator usage
• Produce a structured audit report with findings and remediation

Key Concepts

Cryptographic Weakness Categories

Security Considerations

• Review both application code and configuration files
• Check third-party dependencies for known crypto vulnerabilities
• Verify certificates and TLS configurations on deployed servers
• Ensure secrets are loaded from environment variables or vaults
• Review key storage and rotation practices

Validation Criteria

• Scanner detects all injected test weaknesses
• MD5/SHA-1 usage for security purposes is flagged
• ECB mode usage is flagged
• Hardcoded keys/passwords are detected
• Weak KDF parameters are identified
• Report includes severity, location, and remediation
• False positive rate is below 10%

Other files in this skill

• LICENSE
• assets/template.md
• references/api-reference.md
• references/standards.md
• references/workflows.md
• scripts/agent.py
• scripts/process.py

assets/template.md (verbatim)

Cryptographic Audit Report Template

Executive Summary

Audit Scope

• Source code review (Python, JavaScript, Java, Go)
• Configuration file review (YAML, JSON, INI)
• TLS/SSL configuration assessment
• Key management practices review
• Dependency vulnerability check
• Deployed infrastructure scan

Approved Algorithms

Finding Template

### Finding F-001: [Title]

**Severity**: CRITICAL / HIGH / MEDIUM / LOW
**Category**: [Category]
**CWE**: [CWE-XXX]
**File**: [file_path:line_number]

**Description**:
[Description of the vulnerability]

**Code**:
[Code snippet]

**Remediation**:
[Steps to fix]

**References**:
- [NIST/OWASP reference]

Remediation Priority

1. CRITICAL: Hardcoded secrets, broken encryption (fix immediately)
2. HIGH: Weak algorithms, insecure modes (fix in current sprint)
3. MEDIUM: Suboptimal parameters, deprecated protocols (next release)
4. LOW: Informational, best practice improvements (backlog)

references/api-reference.md (verbatim)

API Reference: Application Cryptographic Audit

Libraries Used

Installation

pip install cryptography

TLS Configuration Audit

Check TLS Version and Cipher Suite

import ssl
import socket

def check_tls_config(hostname, port=443):
    context = ssl.create_default_context()
    with socket.create_connection((hostname, port), timeout=10) as sock:
        with context.wrap_socket(sock, server_hostname=hostname) as ssock:
            return {
                "hostname": hostname,
                "protocol": ssock.version(),
                "cipher": ssock.cipher()[0],
                "cipher_bits": ssock.cipher()[2],
                "compression": ssock.compression(),
            }

Test for Weak TLS Versions

WEAK_PROTOCOLS = {
    ssl.PROTOCOL_TLSv1: "TLSv1.0",
    ssl.PROTOCOL_TLSv1_1: "TLSv1.1",
}

def test_weak_tls(hostname, port=443):
    findings = []
    for protocol_const, name in WEAK_PROTOCOLS.items():
        try:
            ctx = ssl.SSLContext(protocol_const)
            ctx.check_hostname = False
            ctx.verify_mode = ssl.CERT_NONE
            with socket.create_connection((hostname, port), timeout=5) as sock:
                with ctx.wrap_socket(sock) as ssock:
                    findings.append({
                        "protocol": name,
                        "supported": True,
                        "severity": "high",
                        "issue": f"{name} is supported — deprecated and insecure",
                    })
        except (ssl.SSLError, ConnectionRefusedError, OSError):
            findings.append({"protocol": name, "supported": False})
    return findings

Enumerate Supported Cipher Suites

WEAK_CIPHERS = {
    "RC4", "DES", "3DES", "MD5", "NULL", "EXPORT", "anon", "CBC",
}

def check_cipher_suites(hostname, port=443):
    context = ssl.create_default_context()
    context.set_ciphers("ALL:COMPLEMENTOFALL")
    findings = []
    try:
        with socket.create_connection((hostname, port), timeout=10) as sock:
            with context.wrap_socket(sock, server_hostname=hostname) as ssock:
                cipher_name, protocol, bits = ssock.cipher()
                is_weak = any(w in cipher_name for w in WEAK_CIPHERS)
                findings.append({
                    "cipher": cipher_name,
                    "bits": bits,
                    "weak": is_weak,
                    "severity": "high" if is_weak else "pass",
                })
    except ssl.SSLError as e:
        findings.append({"error": str(e)})
    return findings

Certificate Analysis

Parse and Audit Certificate

from cryptography import x509
from cryptography.hazmat.primitives.asymmetric import rsa, ec
from datetime import datetime, timezone

def audit_certificate(hostname, port=443):
    context = ssl.create_default_context()
    with socket.create_connection((hostname, port), timeout=10) as sock:
        with context.wrap_socket(sock, server_hostname=hostname) as ssock:
            der_cert = ssock.getpeercert(binary_form=True)

    cert = x509.load_der_x509_certificate(der_cert)
    pub_key = cert.public_key()

    findings = []
    # Key strength check
    if isinstance(pub_key, rsa.RSAPublicKey):
        key_size = pub_key.key_size
        if key_size < 2048:
            findings.append({
                "check": "key_size",
                "severity": "critical",
                "detail": f"RSA key {key_size} bits — minimum 2048 required",
            })
    elif isinstance(pub_key, ec.EllipticCurvePublicKey):
        key_size = pub_key.curve.key_size
        if key_size < 256:
            findings.append({
                "check": "key_size",
                "severity": "high",
                "detail": f"EC key {key_size} bits — minimum 256 required",
            })

    # Signature algorithm
    sig_algo = cert.signature_algorithm_oid._name
    if "sha1" in sig_algo.lower():
        findings.append({
            "check": "signature_algorithm",
            "severity": "high",
            "detail": f"SHA-1 signature ({sig_algo}) — deprecated",
        })

    # Validity period
    now = datetime.now(timezone.utc)
    days_remaining = (cert.not_valid_after_utc - now).days
    if days_remaining < 0:
        findings.append({"check": "expiry", "severity": "critical", "detail": "Certificate expired"})
    elif days_remaining < 30:
        findings.append({"check": "expiry", "severity": "warning", "detail": f"Expires in {days_remaining} days"})

    return {
        "subject": cert.subject.rfc4514_string(),
        "issuer": cert.issuer.rfc4514_string(),
        "not_before": cert.not_valid_before_utc.isoformat(),
        "not_after": cert.not_valid_after_utc.isoformat(),
        "days_remaining": days_remaining,
        "serial_number": hex(cert.serial_number),
        "signature_algorithm": sig_algo,
        "key_type": "RSA" if isinstance(pub_key, rsa.RSAPublicKey) else "EC",
        "key_size": key_size,
        "findings": findings,
    }

Check HSTS Header

import requests

def check_hsts(url):
    resp = requests.get(url, timeout=10, allow_redirects=True)
    hsts = resp.headers.get("Strict-Transport-Security", "")
    findings = []
    if not hsts:
        findings.append({"check": "hsts", "severity": "medium", "detail": "HSTS header missing"})
    else:
        if "includeSubDomains" not in hsts:
            findings.append({"check": "hsts", "severity": "low", "detail": "HSTS missing includeSubDomains"})
        max_age = 0
        for part in hsts.split(";"):
            if "max-age" in part:
                max_age = int(part.split("=")[1].strip())
        if max_age < 31536000:
            findings.append({"check": "hsts_max_age", "severity": "low", "detail": f"max-age {max_age} < 1 year"})

    return {"hsts_header": hsts, "findings": findings}

Output Format

{
  "hostname": "example.com",
  "tls_version": "TLSv1.3",
  "cipher": "TLS_AES_256_GCM_SHA384",
  "certificate": {
    "subject": "CN=example.com",
    "issuer": "CN=R3,O=Let's Encrypt",
    "days_remaining": 62,
    "key_type": "EC",
    "key_size": 256
  },
  "weak_tls_supported": ["TLSv1.0"],
  "hsts_enabled": true,
  "findings": [
    {
      "check": "weak_tls",
      "severity": "high",
      "detail": "TLSv1.0 is supported — deprecated and insecure"
    }
  ]
}

references/standards.md (verbatim)

Standards and References - Cryptographic Audit

NIST Guidelines

NIST SP 800-131A Rev. 2 - Transitioning Cryptographic Algorithms

• URL: https://csrc.nist.gov/publications/detail/sp/800-131a/rev-2/final
• Description: Defines deprecated, legacy, and acceptable algorithms

NIST SP 800-57 Part 1 Rev. 5 - Key Management

• URL: https://csrc.nist.gov/publications/detail/sp/800-57-part-1/rev-5/final
• Description: Minimum key sizes and algorithm recommendations

OWASP References

OWASP Cryptographic Failures

• URL: https://owasp.org/Top10/A02_2021-Cryptographic_Failures/
• Description: OWASP Top 10 #2 - Cryptographic Failures

OWASP Cheat Sheet - Cryptographic Storage

• URL: https://cheatsheetseries.owasp.org/cheatsheets/Cryptographic_Storage_Cheat_Sheet.html
• Description: Guidelines for secure cryptographic storage

OWASP Cheat Sheet - Password Storage

• URL: https://cheatsheetseries.owasp.org/cheatsheets/Password_Storage_Cheat_Sheet.html
• Description: Password hashing best practices

Tools

Bandit

• URL: https://bandit.readthedocs.io/
• Description: Python security linter with crypto checks

Semgrep

• URL: https://semgrep.dev/
• Crypto rules: https://semgrep.dev/r?q=crypto
• Description: Static analysis with crypto-specific rules

CryptoGuard

• URL: https://github.com/AkshayaVS/CryptoGuard
• Description: Specialized cryptographic misuse detector

references/workflows.md (verbatim)

Workflows - Cryptographic Audit

Workflow 1: Automated Source Code Scan

[Target Application Source]
      |
[Scan for Crypto Patterns]:
  - Deprecated algorithms (MD5, SHA-1, DES, RC4)
  - Insecure modes (ECB)
  - Hardcoded secrets (keys, passwords, tokens)
  - Weak KDF parameters
  - Insecure random number generation
      |
[Scan Configuration Files]:
  - TLS/SSL settings
  - Cipher suite configurations
  - Certificate paths and validity
      |
[Generate Findings with Severity]
      |
[Produce Audit Report]

Workflow 2: Manual Crypto Review

[Identify All Crypto Touchpoints]:
  - Encryption/decryption operations
  - Hashing operations
  - Key generation and storage
  - TLS/SSL connections
  - Token generation (JWT, API keys)
  - Password handling
      |
[For Each Touchpoint]:
  [Verify algorithm choice]
  [Verify mode/padding]
  [Verify key management]
  [Verify entropy sources]
  [Verify error handling]
      |
[Document Findings]

Workflow 3: Remediation Prioritization

[All Findings]
      |
[Classify by Severity]:
  CRITICAL: Hardcoded keys, broken encryption
  HIGH: Weak algorithms, ECB mode, weak KDF
  MEDIUM: Short key sizes, deprecated protocols
  LOW: Missing best practices, informational
      |
[Prioritize by Risk]:
  1. CRITICAL findings (immediate fix)
  2. HIGH findings (fix in current sprint)
  3. MEDIUM findings (plan for next release)
  4. LOW findings (backlog)

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