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83 lines
3.3 KiB
Markdown
83 lines
3.3 KiB
Markdown
---
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name: implementing-aes-encryption-for-data-at-rest
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description: AES (Advanced Encryption Standard) is a symmetric block cipher standardized by NIST (FIPS 197) used to protect classified and sensitive data. This skill covers implementing AES-256 encryption in GCM m
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domain: cybersecurity
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subdomain: cryptography
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tags: [cryptography, encryption, aes, data-at-rest, symmetric-encryption]
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version: "1.0"
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author: mahipal
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license: Apache-2.0
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---
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# Implementing AES Encryption for Data at Rest
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## Overview
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AES (Advanced Encryption Standard) is a symmetric block cipher standardized by NIST (FIPS 197) used to protect classified and sensitive data. This skill covers implementing AES-256 encryption in GCM mode for encrypting files and data stores at rest, including proper key derivation, IV/nonce management, and authenticated encryption.
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## Objectives
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- Implement AES-256-GCM encryption and decryption for files
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- Derive encryption keys from passwords using PBKDF2 and Argon2
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- Manage initialization vectors (IVs) and nonces securely
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- Encrypt and decrypt entire directory trees
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- Implement authenticated encryption to detect tampering
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- Handle large files with streaming encryption
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## Key Concepts
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### AES Modes of Operation
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| Mode | Authentication | Parallelizable | Use Case |
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|------|---------------|----------------|----------|
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| GCM | Yes (AEAD) | Yes | Network data, file encryption |
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| CBC | No | Decrypt only | Legacy systems, disk encryption |
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| CTR | No | Yes | Streaming encryption |
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| CCM | Yes (AEAD) | No | IoT, constrained environments |
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### Key Derivation
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Never use raw passwords as encryption keys. Always derive keys using:
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- **PBKDF2**: NIST-approved, widely supported (minimum 600,000 iterations as of 2024)
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- **Argon2id**: Winner of Password Hashing Competition, memory-hard
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- **scrypt**: Memory-hard, good alternative to Argon2
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### Nonce/IV Management
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- GCM requires a 96-bit (12-byte) nonce that must NEVER be reused with the same key
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- Generate nonces using `os.urandom()` (CSPRNG)
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- Store nonce alongside ciphertext (it is not secret)
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## Workflow
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1. Install the `cryptography` library: `pip install cryptography`
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2. Generate or derive an encryption key
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3. Create a random nonce for each encryption operation
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4. Encrypt data using AES-256-GCM with the key and nonce
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5. Store nonce + ciphertext + authentication tag together
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6. For decryption, extract nonce, verify tag, and decrypt
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## Encrypted File Format
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```
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[salt: 16 bytes][nonce: 12 bytes][ciphertext: variable][tag: 16 bytes]
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```
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## Security Considerations
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- Always use authenticated encryption (GCM, CCM) to prevent tampering
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- Never reuse a nonce with the same key (catastrophic in GCM)
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- Use at least 256-bit keys for long-term data protection
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- Securely wipe keys from memory after use when possible
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- Rotate encryption keys periodically per organizational policy
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- For disk-level encryption, consider XTS mode (AES-XTS)
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## Validation Criteria
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- [ ] AES-256-GCM encryption produces valid ciphertext
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- [ ] Decryption recovers original plaintext exactly
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- [ ] Authentication tag detects any ciphertext modification
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- [ ] Key derivation uses sufficient iterations/parameters
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- [ ] Nonces are never reused for the same key
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- [ ] Large files (>1GB) can be processed via streaming
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- [ ] Encrypted file format includes all necessary metadata
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