Diameter EAP Application (draft-ietf-aaa-eap-02.txt)

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Diameter EAP Application(draft-ietf-aaa-eap-02.tx
t)

• Jari.Arkko_at_ericsson.com on behalf of
  ...Pasi.Eronen_at_nokia.com

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Outline of the Presentation

• Part 1 Introduction
• Part 2 Redirects
• Part 3 Protocol details
• Part 4 Security considerations
• Part 5 Next Steps

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Part 1 Introduction
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Introduction

• 2869bis plus key AVPs for Diameter
• Scope
• One EAP conversation, no role reversal
• One NAS, no handoffs or key distribution to
  multiple NASes
• No new NAS-to-home-server security mechanisms,
  but works end-to-end between the NAS and the home
  server

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Basic sequence
Client
Server
NAS
(initiate EAP)
Diameter-EAP-RequestEAP-Payload(EAP start)

Diameter-EAP-AnswerResult-CodeMULTI_ROUND_AUTHE
AP-Payload(Request())
EAPOL(Request())
EAPOL(Response ())
Diameter-EAP-RequestEAP-Payload(Response())
Diameter-EAP-AnswerResult-CodeSUCCESSEAP-Master
-Session-Key EAP-Payload(Success)
EAPOL(Success)
(4-way handshake)
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Changes in -02

• Redirects / NASREQ interaction
• Added various protocol details
• RADIUS translation
• RFC 2548 translation desirable, too
• Security considerations

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Part 2 Redirects
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Redirects and NASREQ interaction

• Without CMS, proxy agents can see the EAP MSK
• Solution in 02 for avoiding proxies
• NAS contacts the home server directly redirects
  used if there would otherwise be a proxy
• An optional separate request to retrieve
  authorization AVPs through the proxy chain

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Finding server with redirects
NAS
Server
Proxy
Diameter-EAP-RequestEAP-Payload(EAP start)

Diameter-EAP-AnswerRedirect-HostRedirect-Host-
UsageREALM_AND_APPLICATION
Diameter-EAP-RequestEAP-Payload(EAP start)
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Separate Authorization AVP Retrieval
NAS
Server
Diameter-EAP-RequestAuth-Request-TypeAUTHORIZE_A
UTHENTICATE

Diameter-EAP-AnswerResult-CodeDIAMETER_LIMITED_S
UCCESSEAP-Master-Session-Key(some authorization
AVPs)
NASREQ-AA-RequestAuth-Request-TypeAUTHORIZE_ONLY
(some AVPs from previous message)
Proxy
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Separate Authorization AVP Retrieval
Proxy
NAS
Server
Diameter-EAP-RequestAuth-Request-TypeAUTHENTICAT
E_ONLY

Diameter-EAP-AnswerResult-CodeDIAMETER_SUCCESSE
AP-Master-Session-Key(possibly some
authorization AVPs)
NASREQ-AA-RequestAuth-Request-TypeAUTHORIZE_ONLY
(some AVPs from previous message)
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Issues in Redirects

• The authorization AVP retrieval uses NASREQ,
  since Diameter realm routing table isnt
  command-specific
• Who decides whether the separate proxy pass is
  needed?
• What exactly does a redirect elimination of
  proxies buy us?

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Proxy Elimination

• Key is not shown to other parties
• Lengthy EAP runs become faster
• We authenticate the node on the other side
• - But untrusted proxies can still misbehave!
• Proxy might not send a Redirect
• Proxy might send the wrong servers address
• gt We need additional authorization
• Configuration
• Attributes in server certs?
• NAI realm vs. FQDN in server check

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Diameter authorization

• TLS authenticates Diameter nodes, but
• When the NAS talks to foo.example.com, is this
  actually the server for realm example.com?
• Local configuration
• Trust redirect agent
• Trust DNS
• Separate CA for servers
• Certificate name matching (possibly separate CA)
• Certificate extensions
• When the server gets a connection from
  bar.example.com, is this a valid access point?
• Separate CA for access points
• Certificate extensions

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Part 3 Protocol Details
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Protocol details

• Invalid packets
• Fragmentation
• EAP retransmission
• Accounting-EAP-Auth-Method
• EAP-Master-Session-Key

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Protocol details Invalid packets

• In RADIUS, this message contains a copy of the
  previous EAP Request, but we dont want to keep
  inter-request state
• Some alternatives
• EAP-Reissued-Payload AVP (instead of
  EAP-Payload), and normal DIAMETER_MULTI_ROUND_AUTH
  Result-Code
• New DIAMETER_EAP_INVALID_PACKET Result-Code, and
  normal EAP-Payload AVP
• But BASE and NASREQ contain multiple statements
  like if Result-Code is DIAMETER_MULTI_ROUND_AUTH,
  then

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Protocol details Fragmentation

• New AVP EAP-MTU
• Link MTU ! max. size of EAP packet
• E.g., IKEv2 can carry large EAP packets, but the
  MTU of the IPsec tunnel set up by IKEv2 is
  something different
• RADIUS translation waiting for clarification of
  2869bis and/or draft-congdon-radius-8021x

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Protocol detailsAccounting-EAP-Auth-Method

• How NAS determines the method?
• Not specified for MS-Acct-EAP-Type
• Proposed solution server returns it in
  successful Diameter-EAP-Answer
• RFC2548 has also MS-Acct-Auth-Type
• PAP/CHAP/EAP/MS-CHAP-2/etc.
• Should we add Accounting-Auth-Method to NASREQ or
  here?

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Protocol detailsEAP-Master-Session-Key

• Simple AVP (OctetString)
• Can be translated to MS-MPPE-
• But EAP WG is discussing key naming! We may need
  more AVPs

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Part 4 Security Considerations
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Security considerations System perspective

• No document contains security considerations for
  the whole system?
• Gets even more complex if we have handoffs or key
  distribution to multiple NASes
• (May require changes not just to all three
  components, but to interfaces between them)

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Part 5 Next Steps
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Next steps

• Very much dependent on EAP keying framework
  security discussion Russ requirements from
  IETF-56
• Finish that discussion first
• Identify other issues that still need work
• Comments really welcome!
• Finish document
• Keep current scope