Post-Quantum Hybrid Kyber-1024 + AES-256-CTR File Encryption

Streaming hybrid file encryption combining ML-KEM-1024 (Kyber-1024) for post-quantum key encapsulation with AES-256-CTR for bulk encryption and HMAC-SHA256 for integrity verification.

Handles files larger than available RAM via chunked streaming (64 MB chunks).

Features

Post-quantum secure key exchange via liboqs Kyber-1024 KEM (~256-bit PQ security)
AES-256-CTR symmetric encryption with a streaming architecture that handles files larger than RAM (64 MB chunks)
HMAC-SHA256 authenticity tag to detect tampering or corruption

Requirements

oqs (liboqs-python)
cryptography (pyca/cryptography)

python3 -m venv venv && . venv/bin/activate
pip install -r requirements.txt

Usage

Generate a Kyber-1024 key pair

python3 gen_kyber.py

Produces:

kyber.pub - public key (1568 bytes)
kyber.sec - secret key (3168 bytes)

Encrypt a file

python3 encrypt.py archive.7z

Output: archive.7z.enc

The .enc file contains:

Section	Description
Kyber ciphertext	Encapsulated key (ciphertext from KEM)
IV	16-byte AES-CTR nonce
HMAC key	32-byte HMAC key
File ciphertext	AES-256-CTR encrypted chunks
HMAC tag	32-byte SHA-256 MAC of the file ciphertext

Decrypt a file

python3 decrypt.py archive.7z.enc

Output: archive.7z

The script automatically verifies the HMAC tag. If the file has been tampered with, you'll see:

Error: Integrity check failed. File corrupted or tampered

and the partial output gets deleted.

File formats

Key files (raw binary)

File	Content	Size (bytes)
`kyber.pub`	Kyber-1024 public key	1568
`kyber.sec`	Kyber-1024 secret key	3168

Encrypted file structure

archive.7z.enc:

┌─────────────────────────┐
│ Kyber CT length (4 B)   │  ← big-endian uint32
├─────────────────────────┤
│ Kyber ciphertext        │  ← 1568 bytes(Kyber-1024)
├─────────────────────────┤
│ IV (16 B)               │  ← AES-CTR nonce
├─────────────────────────┤
│ HMAC key (32 B)         │  ← random per file
├─────────────────────────┤
│ AES-256-CTR ciphertext  │  ← streamed in 64 MB chunks
├─────────────────────────┤
│ HMAC-SHA256 tag (32 B)  │  ← over the AES ciphertext only
└─────────────────────────┘

Security notes

A new random AES key is generated per file via Kyber encapsulation.
A new random HMAC key is generated per file.
The HMAC tag is computed over the AES ciphertext (the encrypted file data), so any tampering is detected before decryption.
Kyber-1024 is believed to offer security equivalent to ~256-bit classical keys against quantum attackers.
The secret key file (kyber.sec) should be treated like a private SSH key. Store it offline or in a secure vault.

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