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:

┌────────────────────────────────────────────────────────┐
│     Customer Hardware Security Module (HSM / KMS)      │
│            Key Encrypting Key (KEK) — Sovereign        │
└──────────────────────────┬─────────────────────────────┘
                           │ Wraps / Encrypts
                           ▼
┌────────────────────────────────────────────────────────┐
│             Ephemeral Data Encryption Key (DEK)        │
│          Unique 256-bit AES-GCM Key per Object         │
└──────────────────────────┬─────────────────────────────┘
                           │ Encrypts
                           ▼
┌────────────────────────────────────────────────────────┐
│                Object Chunks & Cauchy Stripes          │
│            Ciphertext Stored across Storage Nodes      │
└────────────────────────────────────────────────────────┘

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 Microsoft SQL Server are transparently encrypted at the entity level via custom EF Core EncryptionConverter attributes, 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();
}