Jesse Walker, Intel Corporation Russ Housley, Vigil Security March 2003 EAP Archie Jesse Walker, Intel Corporation Russ Housley, Vigil Security Walker & Housley

Background Fact: IETF EAP WG has asked IEEE 802.11 TGi for guidance March 2003 Background Fact: IETF EAP WG has asked IEEE 802.11 TGi for guidance Observation: The mandatory-to-implement EAP authentication method (MD5 Challenge) is unsuitable for 802.11  This increases market confusion around security! Question: Is there a suitable replacement algorithm? Answer: Not really Walker & Housley

Goals Design a candidate for a better EAP default: March 2003 Goals Design a candidate for a better EAP default: Based on a long-lived pre-shared secret Light weight; no public key operations Mutual authentication Prevent man-in-the-middle attacks Protect against dictionary attacks if key is not weak Guarantee a fresh session key Walker & Housley

EAP Archie Key Hierarchy March 2003 EAP Archie Key Hierarchy PSK = Long-lived Pre-Shared Key = KCK | KEK | KDK SK = Session Key = Archie-PRF(PSK, “Archie session key” | ASNonce | PeerNonce)  TLS Master Key Pairwise Key = Archie-PRF(SK, “Archie pairwise key” | BSSID | STA MAC Addr)  PMK Walker & Housley

Archie PRF Algorithm Archie-PRF Input: Key K, Label L, Nonce N, Output Length OL Output: OL-octet string Out Out = “” for i = 1 to (OL+15)/16 do Out = Out | AES-CBC-MAC(K, L | N | i | OL) return first OL octets out of Out Walker & Housley

The Archie Exchange STA AS March 2003 PSK PSK Request: AS-ID, ARandom Response: Hash1, STA-ID, SNonce, Binding, MIC1 Confirm: Hash2, Counter2, ANonce, Binding, MIC2 Finish: Hash3, MIC3 Walker & Housley

Archie Features Hash1 = SHA1(Request) Hash2 = SHA1(Response) March 2003 Archie Features Hash1 = SHA1(Request) Hash2 = SHA1(Response) Hash3 = SHA1(Confirm) Defeats replay and reflection attacks Each hash is a simple transaction id Each hash ties msg to all prior msgs of this session Explicit binding protects STA from man-in-the-middle attacks in the infrastructure Derived SK is always fresh Walker & Housley

March 2003 Status Draft-jwalker-eap-archie-00.txt to be posted after San Fransisco IETF. Attempt to stimulate discussion on what TGi needs from EAP WG. Walker & Housley

March 2003 Feedback? Walker & Housley