1. Concepts

Fundamental concepts of post-quantum cryptography and this library.

Topic	Description
1.1 Algorithms	ML-DSA, ML-KEM, NIST standards
1.2 Security	Threat model, Harvest-Now-Decrypt-Later
1.3 Comparison with .NET 10	Why WvdS instead of Microsoft PQC?

Why Post-Quantum?

The Problem: Classical cryptography (RSA, ECDSA) can be broken by quantum computers. Data intercepted today could be decrypted in the future.

The Solution: Post-quantum algorithms (ML-DSA, ML-KEM) are resistant to quantum attacks. They are standardized by NIST¹⁾ and implemented in OpenSSL 3.6+.

Our Approach: Hybrid cryptography - classical and PQ algorithms in parallel. Backward compatible, future-proof.

Library Scope

WvdS.System.Security.Cryptography.Extensions focuses on asymmetric post-quantum cryptography:

In Scope (WvdS)	Out of Scope (.NET Built-in)
ML-DSA signatures	AES-GCM encryption
ML-KEM key exchange	ChaCha20-Poly1305
Hybrid certificates	Symmetric encryption
X.509 PQ extensions	Hash functions (SHA-256/384/512)

Rule of thumb: Use WvdS only for asymmetric operations (signatures, key exchange, certificates). For symmetric encryption, use the .NET standard library directly.

The Three Crypto Modes

Mode	Algorithms	Compatibility	Usage
Classic	RSA, ECDSA, ECDH	Universal	Legacy systems
Hybrid	RSA + ML-DSA, ECDH + ML-KEM	Forward/Backward	Migration (recommended)
PostQuantum	ML-DSA, ML-KEM	PQ-capable only	New PQ-only systems

flowchart TD START(["Which mode to choose?"]) --> Q1{"All systems
PQ-capable?"} Q1 -->|Yes| Q2{"Backward
compatibility
needed?"} Q1 -->|No| Q3{"OpenSSL 3.6
available?"} Q2 -->|No| PQ["PostQuantum
ML-DSA / ML-KEM"] Q2 -->|Yes| HYB["Hybrid
RSA+ML-DSA / ECDH+ML-KEM"] Q3 -->|Yes| HYB Q3 -->|No| CLS["Classic
RSA / ECDSA / ECDH"] style PQ fill:#4caf50,color:#fff style HYB fill:#2196f3,color:#fff style CLS fill:#ff9800,color:#fff style START fill:#9c27b0,color:#fff

Classic Mode

CryptoConfig.DefaultMode = CryptoMode.Classic;

Only classical algorithms. For legacy compatibility or systems without OpenSSL 3.6.

Hybrid Mode (recommended)

CryptoConfig.DefaultMode = CryptoMode.Hybrid;

Both algorithms in parallel. Legacy clients ignore PQ extension, modern ones validate both.

PostQuantum Mode

CryptoConfig.DefaultMode = CryptoMode.PostQuantum;

Only use when all participating systems are PQ-capable!

Override Per-Operation

// Global: Hybrid
CryptoConfig.DefaultMode = CryptoMode.Hybrid;
 
// This operation: PostQuantum
var cert = request.CreateSelfSigned(notBefore, notAfter, CryptoMode.PostQuantum);

Algorithm Overview

→ Details: Algorithms

Signatures (ML-DSA):

Replaces RSA/ECDSA for digital signatures
NIST FIPS 204²⁾

Key Exchange (ML-KEM):

Replaces ECDH for key agreement
NIST FIPS 203³⁾

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