MTLS-SPEC

Bidirectional TLS client + server.

Definition

mTLS relies on X.509 v3 certificate chains and the TLS 1.2/1.3 handshake CertificateRequest extension (RFC 8446 §4.3.2). Widely used in AS2/AS4 EDI, mTLS service mesh (Istio), critical B2B APIs. Client certificate management (rotation, revocation, HSM) is more complex than server-only TLS.

Origin

TLS 1.0 RFC 2246 (1999) already introduces CertificateRequest ; mTLS popularised with FAPI 2.0 Open Banking.

Example in context

A PEPPOL Access Point B verifies the client certificate of Access Point A during the AS4 mTLS handshake.

Related terms

• X.509 PKI — certificate infrastructure.