TLS 1.3 Security in ISO 15118-20: What Changed and Why
Security is one of the biggest changes from ISO 15118-2 to ISO 15118-20. This guide covers what actually changed in the transport layer and the certificate model, and where the industry is heading next.
From TLS 1.2 to TLS 1.3
ISO 15118-20 mandates TLS 1.3, which reduces handshake round-trips and removes legacy, vulnerable cipher suites. The EV-to-EVSE channel relies on modern AEAD cipher suites, all of which provide forward secrecy:
| Cipher suite | Notes |
|---|---|
TLS_AES_128_GCM_SHA256 | Widely supported default |
TLS_CHACHA20_POLY1305_SHA256 | Efficient on lower-power controllers |
TLS_AES_256_GCM_SHA384 | Higher-strength option |
Larger Certificates
Moving to secp521r1 and Ed448 keys increases certificate size versus ISO 15118-2's secp256r1. Budget for the additional secure storage and the extra bytes on the communication link.
Mutual Authentication
- The charging station presents its certificate chain; the EV verifies it against stored V2G roots.
- The EV presents a valid contract certificate.
- Both peers verify the chain and certificate status.
Post-Quantum: Important Context
A common misconception is that secp521r1 or Ed448 are “quantum-resistant.” They are not — they are classical elliptic-curve algorithms with larger keys, which improves classical security only. True post-quantum protection requires lattice-based signature schemes such as those standardized by NIST. Hybrid classical-plus-post-quantum certificates are being studied at ISO and CharIN for future revisions, but are not part of ISO 15118-20 today.
Implementation Tips
- Use a well-maintained, constant-time cryptographic library.
- Be cautious with TLS 1.3 early data (0-RTT) — only use it in ways that cannot be replayed.
See It Working
Watch a real ISO 15118-20 Plug & Charge session end to end, or explore more EV-charging deep-dives.