EAP-TTLS Status draft-funk-eap-ttls-v0-00.txt draft-funk-eap-ttls-v1-00.txt draft-funk-tls-inner-application-extension-01.txt Paul Funk Funk Software

Overview of Draft Set Names have changed –Previous name: draft-ietf-pppext-eap-ttls-nn. –Changed to individual submission, since pppext doesn’t do EAP any more. –Draft version reverted to 00. Relationship between drafts –TTLS v0 is original protocol –TTLS v1 is new version TTLS v1 is defined over TLS extension called TLS/IA –TLS/IA defined in separate draft: draft-funk-tls-inner-application-extension-01.txt

EAP-TTLS v1 Overview A version field is now defined in the Flag bits. EAP-TTLS v1 is defined over TLS/IA. –It’s a much shorter draft. –But the new TLS/IA draft more than makes up for this. –The same AVP encapsulation defined in EAP- TTLS v0 is now defined in TLS/IA. –TLS/IA includes enhanced security features.

TLS “InnerApplication” Extension (TLS/IA) TLS/IA defines a mechanism for embedding EAP authentication and other negotiations in TLS itself. –Allows any TLS-based protocol to use inner EAP authentication. Uses standard RFC 3546 extension mechanism –Inner Application extension appended to ClientHello, confirmed in ServerHello Defines new “Inner Application” record type. –Inner Application records follow immediately after TLS handshake, but prior to upper-layer data exchange. –New record type carries one or more “phases”. –Each phase consists of: exchange of AVPs permutation of Inner Secret exchange of PhaseFinished messages for confirmation. –TLS handshake plus Inner Application records can be thought of as an “extended handshake”.

Comparison of TLS Encapsulation Handshake msgsCCS/FinishedAVPs Handshake msgs CCS/FinishedAVPsPhaseFinishedThis space available In EAP-TTLS version 0 (as well as EAP-PEAP/FAST) In TLS/IA TLS handshakedata TLS handshake data Inner application Handshake msgs CCS/FinishedAVPsPhaseFinished In EAP-TTLS version 1 TLS handshake Inner application

TLS/IA Security Optional multi-phase negotiation. –Allows subsequent exchange to be predicated on success of prior exchange –Phases are optional in resumed sessions Additional “Inner Secret” is computed. –Mixes TLS master secret and all session keys from inner authentications. Prevents MitM attack. –Inner Secret is mutually confirmed at the end each phase. Result of inner authentication is securely exchanged. Prevents truncation attack. No change to TLS handshake itself or cipher usage within TLS.

Session Key Binding Inner Secret is initialized to master secret at conclusion of TLS handshake. Inner Secret is permuted in each phase –All inner session keys developed during phase are concatenated into a vector in order of value –PRF is applied to label, randoms, and session key vector, using current Inner Secret as key –48-octet result is new Inner Secret Inner Secret is confirmed by PhaseFinished message. Final Inner Secret from last phase is exported. –EAP-TTLS v1 derives MSK (i.e. MPPE keys) from Inner Secret.

Uses of TLS/IA Beyond TTLS TLS/IA can provide inner AVP capabilities to other protocols besides EAP-TTLS. Inner AVPs can be use for various purposes: –authentication –key exchange –endpoint integrity attestation –etc. Possible other applications for TLS/IA: –HTTP with EAP authentication –Alternative to IKE for IPsec key establishment –Setting up SSL VPN