Integration Patterns

PQC algorithms don’t exist in isolation — they plug into protocols you already use. This page shows how PQC fits into TLS, SSH, and VPN, and what changes at each layer.

The Good News

For most engineers, PQC adoption means updating your TLS/SSH library and changing a configuration line. You don’t implement the algorithms yourself. The protocol libraries handle the hard parts.

TLS 1.3 with PQC

TLS 1.3 already supports PQC through hybrid key exchange. Chrome, Firefox, and Cloudflare have deployed it in production.

How It Works

The TLS handshake uses ML-KEM alongside X25519 (classical ECDH) in hybrid mode — both run in parallel, and the shared secret combines both results. If either algorithm is secure, the connection is secure.

sequenceDiagram
    participant C as Client
    participant S as Server

    C->>S: ClientHello<br/>+ X25519 key share<br/>+ ML-KEM-768 encaps key
    S->>C: ServerHello<br/>+ X25519 key share<br/>+ ML-KEM-768 ciphertext
    Note over C,S: Shared secret = HKDF(X25519_secret || ML-KEM_secret)
    S->>C: Certificate (ML-DSA signature)<br/>+ CertificateVerify
    C->>S: Finished
    S->>C: Finished
    Note over C,S: Encrypted application data

What Changes vs. Classical TLS

Component	Classical	PQC Hybrid	Impact
Key exchange	X25519 (32 B each)	X25519 + ML-KEM-768 (~2.3 KB)	+2.2 KB in handshake
Server signature	ECDSA (64 B)	ML-DSA-65 (3,309 B)	+3.2 KB per cert
Certificate chain	~128 B sigs total	~6.6 KB sigs total	+6.5 KB (2 certs)
Handshake latency	~1 RTT	~1 RTT (same)	No change
Total handshake overhead	—	~9 KB extra	—

The extra ~9 KB adds negligible latency on broadband. For satellite or IoT links, consider Level 1 parameters or certificate compression.

Enabling PQC in Your TLS Stack

OpenSSL 3.2+ (with oqs-provider):

# In openssl.cnf or via API
Groups = X25519MLKEM768:x25519

BoringSSL (used by Chrome, gRPC):

# Enabled by default since Chrome 124
# X25519Kyber768 hybrid

Go 1.23+ (crypto/tls):

// Hybrid X25519+ML-KEM-768 is the default key exchange
tls.Config{
    // PQC is enabled automatically
}

Rust (rustls with aws-lc-rs):

// aws-lc-rs supports ML-KEM hybrid
let config = rustls::ServerConfig::builder()
    .with_no_client_auth()
    .with_single_cert(certs, key)?;

SSH with PQC

OpenSSH 9.0+ supports post-quantum key exchange using a hybrid of X25519 and a streamlined NTRU Prime scheme.

What Changes

Component	Classical	PQC	Impact
Key exchange	curve25519-sha256	sntrup761x25519-sha512	+1.2 KB
Host key auth	ssh-ed25519	ssh-ed25519 (unchanged for now)	No change yet

# ~/.ssh/config — prefer PQC key exchange
Host *
    KexAlgorithms sntrup761x25519-sha512@openssh.com,curve25519-sha256

SSH signature algorithms haven’t migrated to PQC yet. Host keys and user keys still use Ed25519/RSA. This is the next frontier — expect ML-DSA integration in future OpenSSH releases.

VPN with PQC

WireGuard

WireGuard uses Noise protocol with X25519. PQC integration is in progress:

Rosenpass project provides a PQC wrapper for WireGuard using Classic McEliece + ML-KEM
Not yet upstream in WireGuard — requires a separate daemon

IPsec / IKEv2

RFC 9370 defines PQC key exchange for IKEv2
strongSwan 6.0+ supports ML-KEM hybrid key exchange
Cisco and Juniper have announced PQC support timelines

What You Don’t Need to Change

Layer	PQC Impact	Action
Application code	None	No code changes
Symmetric encryption (AES)	None (use AES-256)	Config change at most
Hash functions (SHA)	None	No change
TLS library	Update to PQC-capable version	Library upgrade
TLS configuration	Enable hybrid key exchange	Config change
Certificates	Reissue with PQC signatures	CA-dependent

flowchart TD
    APP[Your Application Code<br/>NO CHANGES] --> LIB[TLS/SSH Library<br/>UPDATE VERSION]
    LIB --> CONF[Configuration<br/>ENABLE PQC HYBRID]
    CONF --> CERT[Certificates<br/>REISSUE WITH PQC]
    CERT --> DONE[PQC Protected]

    classDef nochange fill:#6b8e6b,stroke:#4a6a4a,color:#2c3e50
    classDef update fill:#5a8eaa,stroke:#3a6e8a,color:#2c3e50
    classDef config fill:#8e7060,stroke:#6e5040,color:#2c3e50
    classDef cert fill:#8e6b8e,stroke:#6e4a6e,color:#2c3e50

    class APP nochange
    class LIB update
    class CONF config
    class CERT cert
    class DONE nochange

Next: Find the right PQC library for your language in Libraries & Tools.

Sources: Cloudflare PQC Deployment

OpenSSH 9.0 Release

RFC 9370

Last updated: 2026-02-13