EAP%20Password%20Authenticated%20eXchange%20(PAX)

1
EAP Password Authenticated eXchange (PAX)
draft-clancy-eap-pax-01

• T. Charles Clancy William A. Arbaugh
• clancy,waa_at_cs.umd.edu
• Department of Computer Science
• University of Maryland, College Park
• IETF 61, EAP WG
• November 10, 2004

2
PAX Introduction

• 2 round-trip MAC-based mutual authentication
• Supports provisioning with a weak pre-shared key
• Optional server-side certificate provides secure
  provisioning
• Supports key management with forward secrecy
  using Diffie-Hellman
• Optional support for identity protection
  (requires server-side certificate)
• Extensible ciphersuite

3
Major Changes from -00 to -01

• Address Crypto Concerns
• mutual authentication
• multiple uses of certain keys with different
  primitives
• Protocol Implementation Issues
• identity protection paradox
• new identity protection subprotocol
• Paranoia with MD5 and TLS-PRF
• extensible key derivation function
• support for HMAC-SHA1 and AES-CBC-MAC

4
PAX_STD (no identity protection)
X, Y rand(2256) If keyUpdate then A gX, B
gY, E gXY else A X, B Y, E (X
Y) AK, CK, SessionKeys KDF(AK E
KeyName)
Server
Client
A, SID, PK, CertPK
EncPK (B, CID, MACCK(A, B, CID, SID))
MACCK(B, CID, SID)
ACK
5
PAX_IDP (identity protection)
M, N, X, Y rand(2256) If keyUpdate then A
gX, B gY, E gXY else A X, B Y, E (X
Y) AK, CK, SessionKeys KDF(AK E
KeyName)
Server
Client
M, SID, PK, CertPK
EncPK (M, N, CID)
A, MACN(A, CID, SID)
B, MACCK(A, B, CID, SID)
6
Cryptographic Primitives

• Extensible
• Key Derivation Function
• KDF16X(Y) MACX(Y 1)
• KDF64X(Y) MACX(Y 1) MACX(Y 2)
• MACX(Y 3) MACX(Y 4)
• Currently supported
• MAC HMAC-SHA1-128
• AES-CBC-MAC-128
• DH 3072-bit MODP Group RFC3526
• PubKey RSA-OAEP-2048

7
PAX Implementation

• Currently Supports
• FreeRADIUS 1.0.1
• XSupplicant 1.0.1
• Authentication, Key Update
• Plan to Support
• Microsoft IAS
• Windows XP Supplicant
• Provisioning, Identity Protection
• Timings Experiment
• Cisco 1200 AP
• Pentium 3 1.2GHz, Linux 2.4.26

8
PAX Implementation Timings
Protocol PK Crypto RT Time (ms)
PAX, no update PAX, key update PAX, provision - DH-3072 DH-3072/RSA-2048 2 2 3 9.6 127.3 N/A
EAP-TLS EAP-TLS DH-512/RSA-512 DH-3072/RSA-2048 5 7 89.8 1076.7
PEAP-MSCHAPv2 PEAP-MSCHAPv2 DH-512/RSA-512 DH-3072/RSA-2048 8 10 90.4 1027.3
TLS/PEAP used OpenSSL DSA-DH parameters, PAX used
3072-bit prime and 256-bit exponent as
recommended in RFC3766