Zero-Knowledge Envelope Encryption

Aarkam implements a strict Zero-Knowledge Envelope Encryption architecture. All data ingested into the storage fabric is encrypted client-side at the gateway layer before any chunk touches internal network switches or physical disks.

1. Two-Tier Envelope Encryption Hierarchy

Aarkam decouples data encryption into a two-tier key hierarchy:

1. Key Encrypting Key (KEK): The master key, hosted exclusively inside customer-operated Hardware Security Modules (HSMs) or enterprise KMS (e.g., Thales CipherTrust, Entrust nShield, AWS KMS, HashiCorp Vault). KEKs never leave the secure hardware boundary.
2. Data Encryption Key (DEK): An ephemeral, cryptographically random 256-bit key generated uniquely for each uploaded object. The DEK is encrypted with the KEK and stored in object metadata.

2. Cryptographic Implementation Details

AES-256-GCM Authenticated Encryption

All object chunks are encrypted using AES-256-GCM (Galois/Counter Mode), providing confidentiality, forward secrecy, and built-in cryptographic authentication via a 128-bit authentication tag:

• Key Size: 256 bits (32 bytes)
• Nonce/IV: 96 bits (12 bytes), generated via RandomNumberGenerator
• Authentication Tag: 128 bits (16 bytes), verifying ciphertext integrity against tampering

Transparent Entity-Level Database Encryption

Internal metadata and tenant registries stored in the relational database (PostgreSQL / EF Core) or embedded Kdouja LSM tables are transparently encrypted at the entity level via custom EF Core EncryptionConverter attributes and AES-256-GCM, guaranteeing zero plaintext credentials even during raw database file inspection.

3. Side-Channel Timing Attack Prevention

In high-assurance security environments, variable-time string comparisons allow attackers to infer cryptographic secrets through timing discrepancies. Aarkam mitigates this across all authentication paths (such as Node Agent API keys and HMAC signatures) using constant-time verification:

// Verification in NodeAgentController.cs preventing side-channel attacks
if (!CryptographicOperations.FixedTimeEquals(
        Encoding.UTF8.GetBytes(providedApiKey),
        Encoding.UTF8.GetBytes(expectedApiKey)))
{
    return Unauthorized();
}