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🔒 Authenticated Encryption (AEAD)

Integrated Encryption + Integrity

A CLI-based collection of 4 AEAD implementations that combine encryption and authentication into a single operation. Unlike plain encryption (AES-CBC, AES-CTR), AEAD schemes guarantee confidentiality, integrity, and authenticity simultaneously — if the ciphertext is tampered with even by a single bit, decryption fails.

📁 Module Structure

modules/
└── Authenticated_Encryption(AEAD)/
    └──Integrated_Encryption_Integrity/
        ├── aesgcm.py
        ├── aesccm.py
        ├── chacha20poly1305.py
        └── ocb.py

⚙️ Supported Schemes

Scheme Module Library Nonce Tag AAD Standard
AES-GCM aesgcm.py pycryptodome 96-bit 128-bit ✅ NIST SP 800-38D
AES-CCM aesccm.py pycryptodome 88-bit 128-bit ✅ NIST SP 800-38C
ChaCha20-Poly1305 chacha20poly1305.py pycryptodome 96-bit 128-bit ✅ RFC 8439
OCB ocb.py pycryptodome 120-bit 128-bit ✅ RFC 7253

All schemes use AES-256 (or ChaCha20 with 256-bit key) and produce a 16-byte authentication tag.

📦 Installation

pip install pycryptodome

🔑 Key & Nonce Reference

Scheme Key Size Nonce Size Tag Size Notes
AES-GCM 128/192/256-bit 96-bit (12 B) 128-bit 12-byte nonce strongly recommended
AES-CCM 128/192/256-bit 56–104-bit 64–128-bit Default: 88-bit nonce, 128-bit tag
ChaCha20-Poly1305 256-bit only 96-bit (12 B) 128-bit Key must be exactly 32 bytes
OCB 128/192/256-bit 1–120-bit 128-bit Default: 120-bit (15-byte) nonce

🖥️ CLI Menu Structure

Every module follows the same consistent pattern:

--- <SCHEME NAME> ---
  Type     : AEAD
  Cipher   : <cipher>
  Nonce    : <nonce size>
  Auth Tag : <tag size>
  AAD      : Supported

  1. Generate Key
  2. Encrypt Message
  3. Decrypt + Verify Message
  4. How <SCHEME> Works
  5. Back

🔐 AEAD Encrypt / Decrypt Flow

Encryption output (all schemes)

  Nonce      (hex): a3f1c29d...       ← required for decryption
  Ciphertext (hex): 9e27bd44...       ← encrypted data
  Auth Tag   (hex): f83a1d8e...       ← integrity proof (16 bytes)
  AAD              : user-id:42        ← only shown if AAD was provided

Decryption — success

  ✅ Authentication PASSED
  Decrypted Message: Hello, World!

Decryption — failure (tampered data)

  ❌ Authentication FAILED — ciphertext tampered or wrong key/tag.

🧩 AAD — Additional Authenticated Data

All four schemes support AAD — data that is authenticated but NOT encrypted. This is useful for:

  • Protocol headers or version numbers
  • Sender/receiver identifiers
  • Metadata that must be integrity-protected but readable in plaintext
  Enter AAD (or leave blank): session-id:abc123

AAD is fed into the authentication function alongside the ciphertext. Any modification to AAD during transit will cause authentication to fail, even if the ciphertext itself is untouched.

📊 Scheme Comparison

Architecture

Scheme Encryption Authentication Passes over data
AES-GCM CTR mode GHASH (GF(2¹²⁸)) Single (parallel)
AES-CCM CTR mode CBC-MAC Two (sequential)
ChaCha20-Poly1305 ChaCha20 Poly1305 (GF(2¹³⁰−5)) Single
OCB XOR-Encrypt-XOR Checksum + AES Single (fastest)

Performance & Use Cases

Scheme Best For Parallelizable HW Accel
AES-GCM Servers, TLS, general purpose ✅ Full ✅ AES-NI
AES-CCM IoT, Bluetooth LE, ZigBee ❌ Sequential ✅ AES-NI
ChaCha20-Poly1305 Mobile, embedded, no HW AES ✅ Partial ❌ Not req.
OCB High-speed, latency-critical ✅ Full ✅ AES-NI

Real-World Deployments

Scheme Used In
AES-GCM TLS 1.3, HTTPS, SSH, IPsec, WPA3, DTLS
AES-CCM WPA2 (CCMP), IEEE 802.15.4, Bluetooth LE, Matter (IoT), ZigBee
ChaCha20-Poly1305 TLS 1.3, WireGuard, Signal, WhatsApp, Android HTTPS, QUIC
OCB High-performance custom protocols, OpenSSH (optional)

🔄 How AEAD Works (Overview)

All AEAD schemes share the same conceptual interface:

  Encrypt(key, nonce, plaintext, AAD)
    ──► ciphertext || auth_tag

  Decrypt(key, nonce, ciphertext, auth_tag, AAD)
    ──► plaintext   (if tag valid)
    ──► ERROR       (if tag invalid — reject and discard)

The critical guarantee: the receiver never processes unauthenticated plaintext. Decryption only succeeds if the tag is valid.

Internal Architectures

AES-GCM

  Nonce||0 ──► AES ──► H (auth key for GHASH)
  Nonce||1 ──► AES ──► XOR(P1) ──► C1 ──► GHASH
  Nonce||2 ──► AES ──► XOR(P2) ──► C2 ──► GHASH
                                     └──► Auth Tag

AES-CCM

  Pass 1: CBC-MAC(Nonce || AAD || Plaintext) ──► Tag T
  Pass 2: CTR-Encrypt(Plaintext) ──► Ciphertext
          CTR-Encrypt(T, ctr=0)  ──► Encrypted Tag

ChaCha20-Poly1305

  ChaCha20(key, nonce, ctr=0) ──► Poly1305 key (32 bytes)
  ChaCha20(key, nonce, ctr=1+) ──► XOR(P) ──► Ciphertext
  Poly1305(AAD || Ciphertext)  ──► Auth Tag

OCB

  Per block: Offset_i = Offset_{i-1} XOR L_{ntz(i)}
             C_i = Offset_i XOR AES(P_i XOR Offset_i)
             Checksum ^= P_i
  Tag = AES(Checksum XOR Offset_n XOR L_$) XOR Hash(AAD)
  ← Encryption + auth computed in single AES pass

⚠️ Security Notes

Scheme Critical Warning
AES-GCM Nonce reuse leaks GHASH key H → enables forgery. Always use random 12-byte nonce.
AES-CCM Message length must be declared before encryption. No streaming support.
ChaCha20-Poly1305 Nonce reuse destroys confidentiality AND authenticity. Use random nonces.
OCB Nonce reuse breaks security. Patent-cleared but less deployed than GCM.

Nonce Reuse — Always Catastrophic

Every AEAD scheme in this module is broken if a nonce is reused with the same key. Always generate nonces with a cryptographically secure random generator — never use a counter unless you can guarantee counter state is never reset or duplicated.

If nonce reused Consequence
GCM GHASH key H revealed → full message forgery possible
CCM Keystream reuse → plaintext XOR recoverable
ChaCha20-Poly1305 Poly1305 key reuse → MAC forgery + plaintext exposure
OCB Offset collisions → block-level plaintext recovery

🔌 Integration (Menu System)

from modules.aead import (
    aesgcm_menu,
    aesccm_menu,
    chacha20poly1305_menu,
    ocb_menu,
)

# Example: launch AES-GCM menu
aesgcm_menu()

🗂️ Category Navigation

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Message Authentication (MAC) Authenticated Encryption (AEAD) Post-Quantum Cryptography