AES (Advanced Encryption Standard) is a symmetric encryption algorithm that became the encryption standard of the United States government in 2001.

What is AES?

AES is a block cipher algorithm that uses keys of 128, 192, or 256 bits to encrypt and decrypt data in 128-bit blocks.

Main Characteristics

Key Lengths

  • AES-128: 128-bit key
  • AES-192: 192-bit key
  • AES-256: 256-bit key

Block Size

  • 128 bits: Fixed block size
  • Efficient: Fast processing
  • Standard: Widely supported

Modes of Operation

ECB (Electronic Codebook)

  • Simple: Direct block encryption
  • Insecure: Visible patterns
  • Not recommended: For sensitive data

CBC (Cipher Block Chaining)

  • IV: Initialization vector
  • Chaining: Each block depends on previous
  • Secure: Widely used

GCM (Galois/Counter Mode)

  • Authenticated: Encryption + authentication
  • Efficient: Parallelizable
  • Recommended: For modern applications

CTR (Counter Mode)

  • Stream: Works as stream cipher
  • Parallel: Parallel processing
  • Secure: No error propagation

Implementation

Key Generation

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# Example of AES key generation
from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
from cryptography.hazmat.backends import default_backend
import os

# Generate random 256-bit key
key = os.urandom(32)  # 32 bytes = 256 bits

CBC Encryption

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# AES-CBC encryption
from cryptography.hazmat.primitives import padding

# Generate random IV
iv = os.urandom(16)  # 16 bytes = 128 bits

# Create cipher
cipher = Cipher(algorithms.AES(key), modes.CBC(iv), backend=default_backend())
encryptor = cipher.encryptor()

# Apply PKCS7 padding
padder = padding.PKCS7(128).padder()
padded_data = padder.update(data)
padded_data += padder.finalize()

# Encrypt
ciphertext = encryptor.update(padded_data) + encryptor.finalize()

GCM Encryption

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# AES-GCM encryption (recommended)
cipher = Cipher(algorithms.AES(key), modes.GCM(iv), backend=default_backend())
encryptor = cipher.encryptor()

# Encrypt with authentication
ciphertext = encryptor.update(data) + encryptor.finalize()

Security

Strengths

  • Standard: Approved by NIST
  • Resistant: Resistant to known cryptanalytic attacks
  • Efficient: Fast implementation
  • Widely adopted: Widely adopted

Considerations

  • Key length: Use at least 128 bits
  • Secure mode: Prefer GCM or CBC
  • Unique IV: Never reuse IVs
  • Key management: Protect keys adequately

Applications

Data Encryption

  • Files: Encryption of sensitive files
  • Databases: Encryption of sensitive fields
  • Backups: Backup encryption
  • Communications: Channel encryption

Protocols

  • TLS/SSL: Web communication encryption
  • IPsec: Network traffic encryption
  • WPA2/WPA3: WiFi network encryption
  • BitLocker: Disk encryption

Standards

  • FIPS 140-2: Government certification
  • Common Criteria: Security evaluation
  • PCI DSS: Payment card compliance

Performance

Hardware

  • AES-NI: Specialized CPU instructions
  • Acceleration: Fast encryption/decryption
  • Efficiency: Lower power consumption

Software

  • Optimizations: Optimized implementations
  • Lookup tables: Lookup tables
  • Bit slicing: Optimization techniques

Best Practices

Configuration

  • Length: Use AES-256 for critical data
  • Mode: Prefer GCM for authentication
  • IV: Generate cryptographically secure IVs
  • Padding: Use PKCS7 for CBC

Implementation

  • Libraries: Use proven libraries
  • Testing: Test implementations
  • Audit: Review cryptographic code
  • Updates: Keep updated

Management

  • Rotation: Rotate keys regularly
  • Storage: Protect keys adequately
  • Backup: Backup keys securely
  • Revocation: Revoke compromised keys

References