Anthropic-Cybersecurity-Skills/skills/implementing-aes-encryption-for-data-at-rest/assets/template.md

AES Encryption Implementation Template

Pre-Implementation Checklist

• Identify data classification level and regulatory requirements
• Determine key management strategy (local, HSM, KMS)
• Select AES mode (GCM recommended for authenticated encryption)
• Define key derivation parameters (algorithm, iterations)
• Plan nonce/IV generation strategy
• Determine encrypted file format and metadata storage
• Review compliance requirements (PCI-DSS, HIPAA, GDPR)

Configuration Parameters

encryption:
  algorithm: AES-256-GCM
  key_length: 256
  nonce_length: 96  # bits
  tag_length: 128   # bits

key_derivation:
  algorithm: PBKDF2-SHA256
  iterations: 600000
  salt_length: 128  # bits

file_format:
  magic_bytes: "AES256GCM"
  version: 1
  header: "magic || version || salt || nonce"
  body: "ciphertext || tag"

Integration Code Template

from cryptography.hazmat.primitives.ciphers.aead import AESGCM
from cryptography.hazmat.primitives.kdf.pbkdf2 import PBKDF2HMAC
from cryptography.hazmat.primitives import hashes
import os

def encrypt_data(plaintext: bytes, password: str) -> bytes:
    """Encrypt data with AES-256-GCM."""
    salt = os.urandom(16)
    kdf = PBKDF2HMAC(
        algorithm=hashes.SHA256(),
        length=32,
        salt=salt,
        iterations=600_000,
    )
    key = kdf.derive(password.encode())
    nonce = os.urandom(12)
    aesgcm = AESGCM(key)
    ciphertext = aesgcm.encrypt(nonce, plaintext, None)
    return salt + nonce + ciphertext

def decrypt_data(data: bytes, password: str) -> bytes:
    """Decrypt AES-256-GCM encrypted data."""
    salt = data[:16]
    nonce = data[16:28]
    ciphertext = data[28:]
    kdf = PBKDF2HMAC(
        algorithm=hashes.SHA256(),
        length=32,
        salt=salt,
        iterations=600_000,
    )
    key = kdf.derive(password.encode())
    aesgcm = AESGCM(key)
    return aesgcm.decrypt(nonce, ciphertext, None)

Testing Checklist

• Encrypt and decrypt a small text file
• Encrypt and decrypt a large binary file (>100MB)
• Verify wrong password raises authentication error
• Verify tampered ciphertext raises authentication error
• Verify nonce uniqueness across multiple encryptions
• Measure encryption throughput (MB/s)
• Test with empty files and edge cases

Common Pitfalls

Pitfall	Impact	Mitigation
Nonce reuse with same key	Complete loss of confidentiality in GCM	Always generate random nonce per encryption
Low PBKDF2 iterations	Brute-force password attacks	Use minimum 600,000 iterations
ECB mode usage	Pattern leakage in ciphertext	Always use GCM or CBC (never ECB)
No authentication	Undetected ciphertext modification	Use AEAD modes (GCM, CCM)
Hardcoded keys	Key compromise	Use KMS, HSM, or environment variables
No key rotation	Extended exposure window	Implement periodic key rotation policy