EAP%20Generalized%20PSK%20(GPSK)%20draft-clancy-eap-gpsk-01.txt

1
EAP Generalized PSK (GPSK)draft-clancy-eap-gpsk-0
1.txt

• Editors C. Clancy, H. Tschofenig
• EMU WG, IETF 67, Montreal

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Design Team

• o Jari Arkko
• o Mohamad Badra
• o Uri Blumenthal
• o T. Charles Clancy
• o Lakshminath Dondeti
• o David McGrew
• o Joe Salowey
• o Sharma Suman
• o Hannes Tschofenig
• o Jesse Walker

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Design Goals

• Simple (fast) authentication based on a
  pre-shared symmetric key
• Design constraints
• No public-key operations
• Two round trips
• No fragmentation
• Try to support as many features as possible given
  those constraints

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Base Protocol
Client
Server
ID_Server, RAND_Server, CSuite_List
SEC_SK( ID_Client, ID_Server, RAND_Client,
RAND_Server, CSuite_List, CSuite_Sel
ENC_PK(PD_Payload_1) )
SEC_SK( RAND_Client, RAND_Server, CSuite_Sel
ENC_PK(PD_Payload_2) )
SEC_SK( ENC_PK(PD_Payload_3) )
Note SEC_K(X) X MAC_K(X)
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Base Protocol

• Simple MAC-based mutual authentication
• Supports extensibility through the use of
  encrypted Extended Data Fields (EDF)
• Possible EDF applications
• Channel binding
• Protected results indication
• Identity protection
• EDFs MUST not add round trips or cause packet
  size to exceed the EAP MTU

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Ciphersuites

• Specified as 6-octet field consisting of vendor
  OID (0x000000IETF) and 3-octet ciphersuite
  specifier
• Server sends client a list of supported
  ciphersuites and client selects one from the list
• Ciphersuites with NULL encryption provide only
  integrity and not confidentiality

Specifier KS Encryption Integrity KDF
0x000001 16 AES-EAX-128 AES-CMAC-128 GKDF-128
0x000002 32 NULL HMAC-SHA256 GKDF-256
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Key Derivation Function (KDF)

• Based on the IEEE 802.11i KDF
• Iterated MAC of input key Y and entropy Z
• Outputs X octets of keying material

GKDF-X (Y, Z) M_0 "" result ""
for i1 to (floor( X / MACsize ) 1) M_i
MAC_Y (M_i-1 Z i X) result
results M_i return truncate (result,
X)
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Key Derivation Hierarchy
PSK
Entropy, Identifiers
KDF
MK
KDF
MSK
EMSK
SK
PK
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Implementation

• Jouni Malinen produced a first implementation
  http//hostap.epitest.fi/releases/snapshots/

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Open Issues

• See http//www.tschofenig.com8080/eap-gpsk/index
  
• Error Handling
• Identities in KDF
• KDFData
• Channel Binding
• protected results indiciation

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Next Steps

• Seeking approval from EMU WG to make it a WG item
• Move forward with full WG participation