Internet DRAFT - draft-ietf-hokey-erp-aak
draft-ietf-hokey-erp-aak
Network Working Group Z. Cao
Internet-Draft H. Deng
Intended status: Standards Track China Mobile
Expires: November 3, 2012 Q. Wu
Huawei
G. Zorn, Ed.
Network Zen
May 2, 2012
EAP Re-authentication Protocol Extensions for Authenticated Anticipatory
Keying (ERP/AAK)
draft-ietf-hokey-erp-aak-11
Abstract
The Extensible Authentication Protocol (EAP) is a generic framework
supporting multiple types of authentication methods.
The EAP Re-authentication Protocol (ERP) specifies extensions to EAP
and the EAP keying hierarchy to support an EAP method-independent
protocol for efficient re-authentication between the peer and an EAP
re-authentication server through any authenticator.
Authenticated Anticipatory Keying (AAK) is a method by which
cryptographic keying material may be established upon one or more
candidate attachment points (CAPs) prior to handover. AAK uses the
AAA infrastructure for key transport.
This document specifies the extensions necessary to enable AAK
support in ERP.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 3, 2012.
Cao, et al. Expires November 3, 2012 [Page 1]
Internet-Draft ERP/AAK May 2012
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Standards Language . . . . . . . . . . . . . . . . . . . . 3
2.2. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. ERP/AAK Description . . . . . . . . . . . . . . . . . . . . . 4
4. ERP/AAK Key Hierarchy . . . . . . . . . . . . . . . . . . . . 7
4.1. Derivation of the pRK and pMSK . . . . . . . . . . . . . . 8
5. Packet and TLV Extension . . . . . . . . . . . . . . . . . . . 9
5.1. EAP-Initiate/Re-auth-Start Packet and TLV Extension . . . 9
5.2. EAP-Initiate/Re-auth Packet and TLV Extension . . . . . . 10
5.3. EAP-Finish/Re-auth packet and TLV extension . . . . . . . 12
5.4. TV and TLV Attributes . . . . . . . . . . . . . . . . . . 14
6. Lower Layer Considerations . . . . . . . . . . . . . . . . . . 15
7. AAA Transport Considerations . . . . . . . . . . . . . . . . . 15
8. Security Considerations . . . . . . . . . . . . . . . . . . . 15
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 18
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
11.1. Normative References . . . . . . . . . . . . . . . . . . . 18
11.2. Informative References . . . . . . . . . . . . . . . . . . 18
Cao, et al. Expires November 3, 2012 [Page 2]
Internet-Draft ERP/AAK May 2012
1. Introduction
The Extensible Authentication Protocol (EAP) [RFC3748] is a generic
framework supporting multiple types of authentication methods. In
systems where EAP is used for authentication, it is desirable to not
repeat the entire EAP exchange with another authenticator. The EAP
Re-authentication Protocol (ERP) [RFC5296] specifies extensions to
EAP and the EAP keying hierarchy to support an EAP method-independent
protocol for efficient re-authentication between the EAP re-
authentication peer and an EAP re-authentication server through any
authenticator. The re-authentication server may be in the home
network or in the local network to which the mobile host (i.e., the
EAP re-authentication peer) is connecting.
Authenticated Anticipatory Keying (AAK) [RFC5836] is a method by
which cryptographic keying materials may be established prior to
handover upon one or more candidate attachment points (CAPs). AAK
utilizes the AAA infrastructure for key transport.
This document specifies the extensions necessary to enable AAK
support in ERP.
2. Terminology
2.1. Standards Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2.2. Acronyms
The following acronyms are used in this document; see the references
for more details.
AAA
Authentication, Authorization and Accounting [RFC3588]
CAP
Candidate Attachment Point [RFC5836]
EA
Abbreviation for "ERP/AAK"
EA Peer
An EAP peer that supports the ERP/AAK. Note that all references
to "peer" in this document imply an EA peer, unless specifically
noted otherwise.
Cao, et al. Expires November 3, 2012 [Page 3]
Internet-Draft ERP/AAK May 2012
SAP
Serving Attachment Point [RFC5836]
3. ERP/AAK Description
ERP/AAK is intended to allow the establishment of cryptographic
keying materials on a single Candidate Attachment Point prior to the
arrival of the peer at the Candidate Access Network (CAN) upon
request by the peer.
In this document, ERP/AAK support by the peer is assumed. Also it is
assumed that the peer has previously completed full EAP
authentication and that either the peer or SAP knows the identities
of neighboring attachment points. Note that the behavior of a peer
that does not support the ERP-AAK scheme defined in this
specification is out of the scope of this document. Figure 1 shows
the general protocol exchange by which the keying material is
established on the CAP.
Cao, et al. Expires November 3, 2012 [Page 4]
Internet-Draft ERP/AAK May 2012
+------+ +-----+ +-----+ +-----------+
| Peer | | SAP | | CAP | | EA Server |
+--+---+ +--+--+ +--+--+ +-----+-----+
| | | |
a. | [EAP-Initiate/ | | |
| Re-auth-start | | |
| (E-flag)] | | |
|<---------------| | |
| | | |
b. | EAP-Initiate/ | | |
| Re-auth | | |
| (E-flag) | | |
|--------------->| | |
c. | | AAA(EAP-Initiate/Re-auth(E-flag))|
| |--------------------------------->|
| | | +---------+---------+
| | | | CA authorized & |
d. | | | | and EA Keying |
| | | | Distribution |
| | | +---------+---------+
| | | |
| | | |
f. | | AAA (EAP-Finish/Re-auth(E-flag)) |
| |<---------------------------------|
g. | EAP-Finish/ | | |
| Re-auth(E-flag)| | |
|<---------------| | |
| | | |
Figure 1: ERP/AAK Exchange
Cao, et al. Expires November 3, 2012 [Page 5]
Internet-Draft ERP/AAK May 2012
+-----------+ +---------+
| | | |
| EA Server | | CAP |
| | | |
+-----|-----+ +----|----+
| |
| |
| AAA Request(pMSK) |
e.1|------------------------->|
| |
| |
| |
| AAA Response (Success) |
e.2|<-------------------------|
| |
| |
| |
Figure 2: Key Distribution for ERP/AAK
ERP/AAK re-uses the packet format defined by ERP, but specifies a new
flag to differentiate EAP early-authentication from EAP re-
authentication. The peer initiates ERP/AAK itself, or does so in
response to an EAP-Initiate/Re-Auth-Start message from the SAP.
In the latter case, the SAP MAY send the identity of one or more
Candidate Attachment Points to which the SAP is adjacent to the peer
in the EAP-Initiate/Re-auth-Start message (see a. in Figure 1). The
Peer SHOULD override the identity of CAP(s) carried in EAP-Initiate/
Re-auth-Start message by sending EAP-Initiate/Re-auth with the 'E'
flag set if it knows to which CAP it will move. If the EAP-Initiate/
Re-auth-Start packet is not supported by the peer, it MUST be
silently discarded.
If the peer initiates ERP/AAK, the peer MAY send an early-
authentication request message (EAP-Initiate/Re-auth with the 'E'
flag set) containing the keyName-NAI, the CAP-Identifier, rIK and
sequence number (see b. in Figure 1). The realm in the keyName-NAI
field is used to locate the peer's ERP/AAK server. The CAP-
Identifier is used to identify the CAP. The rIK is defined in
Narayanan & Dondeti [RFC5296] and used to protect the integrity of
the message. The sequence number is used for replay protection.
The SAP SHOULD verify the integrity of thus message at step b. If
this verification fails, the SAP MUST send an EAP-Finish/Re-auth
message with the Result flag set to '1' (Failure). If the
verification succeeds, the SAP SHOULD encapsulate the early-
authentication message into a AAA message and send it to the peer's
Cao, et al. Expires November 3, 2012 [Page 6]
Internet-Draft ERP/AAK May 2012
ERP/AAK server in the realm indicated in the keyName-NAI field (see
c. in Figure 1).
Upon receiving the message, the ERP/AAK server MUST first use the
keyName indicated in the keyName-NAI to look up the rIK and check the
integrity and freshness of the message. Then the ERP/AAK server MUST
verify the identity of the peer by checking the username portion of
the KeyName-NAI. If any of the checks fail, the server MUST send an
early- authentication finish message (EAP-Finish/Re-auth with E-flag
set) with the Result flag set to '1'. Next, the server MUST
authorize the CAP specified in the CAP-Identifier TLV. In the
success case, the server MUST derive a pMSK from the pRK for the CAP
carried in the the CAP-Identifier field using the sequence number
associated with CAP-Identifier as an input to the key derivation.
(see d. in Figure 1).
Then the ERP/AAK server MUST transport the pMSK to the authorized CAP
via AAA Section 7 as illustrated above (see e.1 and e.2 in Figure 2).
Note that key distribution in Figure 2 is one part of step d. in
Figure 1.
Finally, in response to the EAP-Initiate/Re-auth message, the ERP/AAK
server SHOULD send the early-authentication finish message (EAP-
Finish/ Re-auth with E-flag set) containing the identity of the
authorized CAP to the peer via the SAP along with the lifetime of the
pMSK. If the peer also requests the rRK lifetime, the ERP/AAK server
SHOULD send the rRK lifetime in the EAP-Finish/Re-auth message. (see
f. and g. in Figure 1).
4. ERP/AAK Key Hierarchy
ERP/AAK uses a key hierarchy similar to that of ERP. The ERP/AAK
pre-established Root Key (pRK) is derived from either the EMSK or the
DSRK as specified below (see Section 4.1). In general, the pRK is
derived from the EMSK if the peer is located in the home AAA realm
and derived from the DRSK if the peer is in a visited realm. The
DSRK is delivered from the EAP server to the ERP/AAK server as
specified in [I-D.ietf-dime-local-keytran]. If the peer has
previously been authenticated by means of ERP or ERP/AAK, the DSRK
SHOULD be directly re-used.
DSRK EMSK
| |
+---+---+---+---+
|
pRK ...
Figure 3: ERP/AAK Root Key Derivation
Cao, et al. Expires November 3, 2012 [Page 7]
Internet-Draft ERP/AAK May 2012
Similarly, the pre-established Master Session Key (pMSK) is derived
from the pRK. The pMSK is established for the CAP when the peer
early authenticates to the network. The hierarchy relationship is
illustrated Figure 4,
pRK
|
+--------+--------+
|
pMSK ...
Figure 4: ERP/AAK Key Hierarchy
below.
4.1. Derivation of the pRK and pMSK
The rRK is derived as specified in [RFC5295].
pRK = KDF (K, S), where
K = EMSK or K = DSRK and
S = pRK Label | "\0" | length
The pRK Label is an IANA-assigned 8-bit ASCII string:
EAP Early-Authentication Root Key@ietf.org
assigned from the "USRK key labels" name space in accordance with
Salowey, et al. [RFC5295]. The KDF and algorithm agility for the
KDF are also defined in RFC 5295. The KDF algorithm is indicated in
the cryptosuit field or list of cryptosuits TLV payload as specified
in the section 5.2 and section 5.3.
The pMSK uses the same PDF as pRK and is derived as follows:
pMSK = KDF (K, S), where
K = pRK and
S = pMSK label | "\0" | SEQ | length
The pMSK label is the 8-bit ASCII string:
EAP Early-Authentication Master Session Key@ietf.org
The length field refers to the length of the pMSK in octets encoded
Cao, et al. Expires November 3, 2012 [Page 8]
Internet-Draft ERP/AAK May 2012
as specified in RFC 5295. SEQ is sent by either the peer or the
server in the ERP/AAK message using the SEQ field or the Sequence
number TLV and encoded as an 16-bit number as specified in
Section 5.2 and Section 5.3.
5. Packet and TLV Extension
This section describes the packet and TLV extensions for the ERP/AAK
exchange.
5.1. EAP-Initiate/Re-auth-Start Packet and TLV Extension
Figure 5 shows the new parameters contained in the EAP-Initiate/
Re-auth-Start packet defined in RFC 5296 [RFC5296].
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code | Identifier | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type |E| Reserved | 1 or more TVs or TLVs ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5
Flags
'E' - The E flag is used to indicate early-authentication. This
field MUST be set to '1' if early authentication is in use and MUST
be set to '0' otherwise.
The rest of the 7 bits (Reserved ) MUST be set to 0 and ignored on
reception.
TVs and TLVs
CAP-Identifier: Carried in a TLV payload. The format is identical to
that of a DiameterIdentity [RFC3588]. It is used by the SAP to
advertise the identity of the CAP to the peer. Exactly one CAP-
Identifier TLV MAY be included in the EAP-Initiate/Re-auth-Start
packet if the SAP has performed CAP discovery.
If the EAP-Initiate/Re-auth-Start packet is not supported by the
peer, it SHOULD be discarded silently.
Cao, et al. Expires November 3, 2012 [Page 9]
Internet-Draft ERP/AAK May 2012
5.2. EAP-Initiate/Re-auth Packet and TLV Extension
Figure 6 illustrates the new parameters contained in the EAP-
Initiate/Re-auth packet defined in RFC 5296 [RFC5296].
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code | Identifier | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type |R|x|L|E|Resved | SEQ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 or more TVs or TLVs ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cryptosuite | Authentication Tag ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6
Flags
'x' - The x flag is reserved. It MUST be ignored on receipt.
'L' - As defined in section 5.3.2 of [RFC5296], this bit is used to
request the key lifetimes from the server.
'E' - The E flag is used to indicate early-authentication.
The first bit(R) and final 4 bits (Resved) MUST be set to 0 and
ignored on reception.
SEQ
As defined in Section 5.3.2 of [RFC5296],this field is 16-bit
sequence number and used for replay protection.
TVs and TLVs
keyName-NAI: As defined in RFC 5296 [RFC5296], this is carried in a
TLV payload. The Type is 1. The NAI is variable in length, not
exceeding 253 octets. The username part of the NAI is the EMSKname
used to identify the peer. The realm part of the NAI is the peer's
home domain name if the peer communicates with the home EA server or
the domain to which the peer is currently attached (i.e., local
domain name) if the peer communicates with a local EA server. The
SAP knows whether the KeyName-NAI carries the local domain name by
comparing the domain name carried in KeyName-NAI with the local
domain name which is associated with the SAP. Exactly one keyName-
Cao, et al. Expires November 3, 2012 [Page 10]
Internet-Draft ERP/AAK May 2012
NAI attribute SHALL be present in an EAP-Initiate/Re-auth packet and
the realm part of it SHOULD follow the use of internationalized
domain names defined in RFC5890 [RFC5890].
CAP-Identifier: Carried in a TLV payload.The Type is TBD (less than
128). This field is used to indicate the FQDN of a CAP. The value
field MUST be encoded as specified in Section 8 of RFC 3315
[RFC3315]. Exactly one instance of the CAP-Identifier TLV MUST be
present in the ERP/AAK-Key TLV.
Sequence number: The Type is TBD (less than 128). The value field is
a 16-bit field and used in the derivation of the pMSK for a CAP.
Cryptosuite
This field indicates the integrity algorithm used for ERP/AAK. Key
lengths and output lengths are either indicated or obvious from the
cryptosuite name, e.g., HMAC-SHA256-128 denotes HMAC computed using
the SHA-256 function [RFC4868] with 256-bit key length and the output
truncated to 128 bits [RFC2104]. We specify some cryptosuites below:
0-1 RESERVED
2 HMAC-SHA256-128
3 HMAC-SHA256-256
HMAC-SHA256-128 is REQUIRED to implement and SHOULD be enabled in the
default configuration.
Authentication Tag
This field contains an integrity checksum over the ERP/AAK packet
from the first bit of the Code field to the last bit of the
Cryptosuite field, excluding the Authentication Tag field itself.
The value field is calculated using the integrity algorithm indicated
in the Cryptosuite field and rIK specified in [RFC5296] as the secret
key. The length of the field is indicated by the Cryptosuite.
The peer uses the Authentication Tag to determine the validity of the
EAP-Finish/Re-auth message from the server.
If the message doesn't pass verification or the Authentication Tag is
not included in the message, the message SHOULD be discarded
silently.
If the EAP-Initiate/Re-auth packet is not supported by the SAP, it
SHOULD be discarded silently. The peer MUST maintain retransmission
Cao, et al. Expires November 3, 2012 [Page 11]
Internet-Draft ERP/AAK May 2012
timers for reliable transport of the EAP-Initiate/Re-auth message.
If there is no response to the EAP-Initiate/Re-auth message from the
server after the necessary number of retransmissions (see Section 6),
the peer MUST assume that ERP/AAK is not supported by the SAP.
5.3. EAP-Finish/Re-auth packet and TLV extension
Figure 7 shows the new parameters contained in the EAP-Finish/Re-auth
packet defined in [RFC5296].
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code | Identifier | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type |R|x|L|E|Resved | SEQ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 or more TVs or TLVs ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cryptosuite | Authentication Tag ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7
Flags
'R' - As defined in Section 5.3.3 of [RFC5296], this bit is used to
used as the Result flag. This field MUST be set to '1' if indicates
success and MUST be set to '0' otherwise.
'x' - The x flag is reserved. It MUST be ignored on receipt.
'L' - As defined in section 5.3.3 of [RFC5296], this bit is used to
request the key lifetimes from the server.
'E' - The E flag is used to indicate early-authentication.
The final 4 bits (Resved) MUST be set to 0 and ignored on reception.
SEQ
As defined in Section 5.3.3 of [RFC5296], this field is a 16-bit
sequence number and used for replay protection.
TVs and TLVs
keyName-NAI: As defined in RFC 5296 [RFC5296], this is carried in a
TLV payload. The Type is 1. The NAI is variable in length, not
Cao, et al. Expires November 3, 2012 [Page 12]
Internet-Draft ERP/AAK May 2012
exceeding 253 octets. Exactly one keyName-NAI attribute SHALL be
present in an EAP-Finish/Re-auth packet.
ERP/AAK-Key: Carried in a TLV payload for the key container. The
type is TBD. Exactly one ERP/AAK-key SHALL only be present in an
EAP-Finish/Re-auth packet.
ERP/AAK-Key ::=
{ sub-TLV: CAP-Identifier }
{ sub-TLV: pMSK-lifetime }
{ sub-TLV: pRK-lifetime }
{ sub-TLV: Cryptosuites }
CAP-Identifier
Carried in a sub-TLV payload. The Type is TBD (less than 128).
This field is used to indicate the identifier of the candidate
authenticator. The value field MUST be encoded as specified in
Section 8 of RFC 3315 [RFC3315]. There at least one instance of
the CAP-Identifier TLV MUST be present in the ERP/AAK-Key TLV.
pMSK-lifetime
Carried in a sub-TLV payload of the EAP-Finish/Re-auth message.
The Type is TBD. The value field is an unsigned 32-bit field and
contains the lifetime of the pMSK in seconds. This value is
calculated by the server after pRK-lifetime computation upon
receiving the EAP-Initiate/Re-auth message. The rIK SHOULD share
the same lifetime as the pMSK. If the 'L' flag is set, the pMSK-
Lifetime attribute MUST be present.
pRK-lifetime
Carried in a sub-TLV payload of EAP-Finish/Re-auth message. The
Type is TBD. The value field is an unsigned 32-bit field and
contains the lifetime of the pRK in seconds. This value is
calculated by the server before pMSK-lifetime computation upon
receiving a EAP-Initiate/Re-auth message. If the 'L' flag is set,
the pRK-Lifetime attribute MUST be present.
List of Cryptosuites
Carried in a sub-TLV payload. The Type is 5 [RFC5296]. The value
field contains a list of cryptosuites (at least one cryptosuite
SHOULD be included), each 1 octet in length. The allowed
cryptosuite values are as specified in Section 5.2, above. The
server SHOULD include this attribute if the cryptosuite used in
the EAP-Initiate/Re-auth message was not acceptable and the
message is being rejected. The server MAY include this attribute
in other cases. The server MAY use this attribute to signal to
the peer about its cryptographic algorithm capabilities.
Cao, et al. Expires November 3, 2012 [Page 13]
Internet-Draft ERP/AAK May 2012
Cryptosuite
This field indicates the integrity algorithm and PRF used for ERP/
AAK. HMAC-SHA256-128 is REQUIRED to implement and SHOULD be enabled
in the default configuration. Key lengths and output lengths are
either indicated or obvious from the cryptosuite name.
Authentication Tag
This field contains the integrity checksum over the ERP/AAK packet
from the first bit of the Code field to the last bit of the
Cryptosuite field excluding the Authentication Tag field itself. The
value field is calculated using the integrity algorithm indicated in
the Cryptosuite field and the rIK [RFC5296] as the integrity key.
The length of the field is indicated by the corresponding
Cryptosuite.
The peer uses the authentication tag to determine the validity of the
EAP-Finish/Re-auth message from a server.
If the message doesn't pass verification or the authentication tag is
not included in the message, the message SHOULD be discarded
silently.
If the EAP-Initiate/Re-auth packet is not supported by the SAP, it is
discarded silently. The peer MUST maintain retransmission timers for
reliable transport of EAP-Initiate/Re-auth message. If there is no
response to the EAP-Initiate/Re-auth message from the server after
the necessary number of retransmissions (See Section 6), the peer
MUST assume that ERP/AAK is not supported by the SAP.
5.4. TV and TLV Attributes
With the exception of the rRK-Lifetime and rMSK-Lifetime TV payloads,
the attributes specified in Section 5.3.4 of [RFC5296] also apply to
this document. In this document, new attributes which may be present
in the EAP-Initiate and EAP-Finish messages are defined as below:
o Sequence number: This is a TV payload. The type is 7.
o ERP/AAK-Key: This is a TLV payload. The type is 8.
o pRK-Lifetime: This is a TV payload. The type is 9.
o pMSK-Lifetime: This is a TV payload. The type is 10.
o CAP-Identifier: This is a TLV payload. The type is 11.
Cao, et al. Expires November 3, 2012 [Page 14]
Internet-Draft ERP/AAK May 2012
6. Lower Layer Considerations
Similar to ERP, some lower layer specifications may need to be
revised to support ERP/AAK; refer to Section 6 of [RFC5296] for
additional guidance.
7. AAA Transport Considerations
The AAA transport of ERP/AAK messages is the same as that of the ERP
message [RFC5296]. In addition, this document requires AAA transport
of the ERP/AAK keying materials delivered by the ERP/AAK server to
the CAP. Hence, a new AAA message for the ERP/AAK application should
be specified to transport the keying materials.
8. Security Considerations
This section provides an analysis of the protocol in accordance with
the AAA key management requirements specified in RFC 4962 [RFC4962].
o Cryptographic algorithm independence: ERP-AAK satisfies this
requirement. The algorithm chosen by the peer for calculating the
authentication tag is indicated in the EAP-Initiate/Re-auth
message. If the chosen algorithm is unacceptable, the EAP server
returns an EAP-Finish/Re-auth message with a Failure indication.
o Strong, fresh session keys: ERP-AAK results in the derivation of
strong, fresh keys that are unique for the given CAP. An pMSK is
always derived on-demand when the peer requires a key with a new
CAP. The derivation ensures that the compromise of one pMSK does
not result in the compromise of a different pMSK at any time.
o Limit key scope: The scope of all the keys derived by ERP-AAK is
well defined. The pRK is used to derive the pMSK for the CAP.
Different sequence numbers for each CAP MUST be used to derive a
unique pMSK.
o Replay detection mechanism: For replay protection a sequence
number associated with the pMSK is used.The peer increments the
sequence number by one after it sends an ERP/AAK message. The
server sets the expected sequence number to the received sequence
number plus one after verifying the validity of the received
message and responds to the message.
o Authenticate all parties: The EAP Re-auth Protocol provides mutual
authentication of the peer and the server. The peer and SAP are
authenticated via ERP. The CAP is authenticated and trusted by
the SAP.
Cao, et al. Expires November 3, 2012 [Page 15]
Internet-Draft ERP/AAK May 2012
o Peer and authenticator authorization: The peer and authenticator
demonstrate possession of the same keying material without
disclosing it, as part of the lower layer secure authentication
protocol.
o Keying material confidentiality: The peer and the server derive
the keys independently using parameters known to each entity.
o Uniquely named keys: All keys produced within the ERP context can
be referred to uniquely as specified in this document.
o Prevent the domino effect: Different sequence numbers for each CAP
MUST be used to derive the unique pMSK. So the compromise of one
pMSK does not hurt any other CAP.
o Bind key to its context: the pMSK are bound to the context in
which the sequence numbers are transmitted.
o Confidentiality of identity: this is the same as with the ERP
protocol [RFC5296].
o Authorization restriction: All the keys derived are limited in
lifetime by that of the parent key or by server policy. Any
domain-specific keys are further restricted to be used only in the
domain for which the keys are derived. Any other restrictions of
session keys may be imposed by the specific lower layer and are
out of scope for this specification.
9. IANA Considerations
IANA is requested to assign five TLV type values from the registry of
EAP Initiate and Finish Attributes maintained at
http://www.iana.org/assignments/eap-numbers/eap-numbers.xml.
with the following numbers:
o Sequence number: This is a TV payload. The type is 7.
o ERP/AAK-Key: This is a TLV payload. The type is 8.
o pRK Lifetime: This is a TLV payload. The type is 9.
o pMSK Lifetime: This is a TLV payload. The type is 10.
o CAP-Identifier: This is a TLV payload. The type is 11.
This document reuses the crytosuites have already created for 'Re-
authentication Cryptosuites' in [RFC5296].
Cao, et al. Expires November 3, 2012 [Page 16]
Internet-Draft ERP/AAK May 2012
Further, this document instructs IANA to add a new label in the User
Specific Root Keys (USRK) Key Labels of the Extended Master Session
Key (EMSK) Parameters registry, as follows:
EAP Early-Authentication Root Key@ietf.org
This document creates a new registry for the flags in the EAP
Initiate/Re-auth-Start message called the "EAP Initiate/Re-auth-Start
Flags" and assigns a new flag (E) as follows:
(E) 0x80
The rest of the values in the 8-bit field are reserved. New values
can be assigned by Standards Action or IESG approval.
This document also creates a new registry for the flags in the EAP
Initiate/Re-auth message called the "EAP Initiate/Re-auth Flags".
The following flag are reserved:
(R) 0x80 [RFC5296]
(B) 0x40 [RFC5296]
(L) 0x20 [RFC5296]
This document assigns a new flag (E) as follows:
(E) 0x10
The rest of the values in the 8-bit field are reserved. New values
can be assigned by Standards Action or IESG approval.
Further,this document creates a new registry for the flags in the EAP
Finish/Re-auth message called the "EAP Finish/Re-auth Flags". The
following values are reserved.
(R) 0x80 [RFC5296]
(B) 0x40 [RFC5296]
(L) 0x20 [RFC5296]
This document assigns a new flag (E) as follows:
(E) 0x10
The rest of the values in the 8-bit field are reserved. New values
can be assigned by Standards Action or IESG approval.
Cao, et al. Expires November 3, 2012 [Page 17]
Internet-Draft ERP/AAK May 2012
10. Acknowledgement
In writing this document, Yungui Wang contributed to early versions
of this document and we have received reviews from many experts in
the IETF, including Tom Taylor, Tena Zou, Tim Polk, Tan Zhang, Semyon
Mizikovsky, Stephen Farrell, Radia Perlman, Miguel A. Garcia and
Sujing Zhou. We apologize if we miss some of those who have helped
us.
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in
RFCs to Indicate Requirement Levels",
BCP 14, RFC 2119, March 1997.
[RFC3315] Droms, R., Ed., Bound, J., Volz, B.,
Lemon, T., Perkins, C., and M. Carney,
"Dynamic Host Configuration Protocol
for IPv6 (DHCPv6)", RFC 3315,
July 2003.
[RFC5295] Salowey, J., Dondeti, L., Narayanan,
V., and M. Nakhjiri, "Specification
for the Derivation of Root Keys from
an Extended Master Session Key
(EMSK)", August 2008.
[RFC5296] Narayanan, V. and L. Dondeti, "EAP
Extensions for EAP Re-authentication
Protocol (ERP)", RFC 5296,
August 2008.
11.2. Informative References
[I-D.ietf-dime-local-keytran] Zorn, G., Wu, W., and V. Cakulev,
"Diameter Attribute-Value Pairs for
Cryptographic Key Transport",
draft-ietf-dime-local-keytran-14 (work
in progress), August 2011.
[RFC2104] Krawczyk, H., Bellare, M., and R.
Canetti, "HMAC: Keyed-Hashing for
Message Authentication", RFC 2104,
February 1997.
[RFC3588] Calhoun, P., Loughney, J., Guttman,
Cao, et al. Expires November 3, 2012 [Page 18]
Internet-Draft ERP/AAK May 2012
E., Zorn, G., and J. Arkko, "Diameter
Base Protocol", RFC 3588,
September 2003.
[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J.,
Carlson, J., and H. Levkowetz,
"Extensible Authentication Protocol
(EAP)", RFC 3748, June 2004.
[RFC4868] Kelly, S. and S. Frankel, "Using HMAC-
SHA-256, HMAC-SHA-384, and HMAC-SHA-
512 with IPsec", RFC 4868, May 2007.
[RFC4962] Housley, R. and B. Aboba, "Guidance
for Authentication, Authorization, and
Accounting (AAA) Key Management",
BCP 132, RFC 4962, July 2007.
[RFC5836] Ohba, Y., Wu, Q., and G. Zorn,
"Extensible Authentication Protocol
(EAP) Early Authentication Problem
Statement", RFC 5836, April 2010.
[RFC5890] Klensin, J., "Internationalized Domain
Names for Applications (IDNA):
Definitions and Document Framework",
RFC 5890, August 2010.
Authors' Addresses
Zhen Cao
China Mobile
53A Xibianmennei Ave., Xuanwu District
Beijing, Beijing 100053
P.R. China
EMail: zehn.cao@gmail.com
Hui Deng
China Mobile
53A Xibianmennei Ave., Xuanwu District
Beijing, Beijing 100053
P.R. China
EMail: denghui02@gmail.com
Cao, et al. Expires November 3, 2012 [Page 19]
Internet-Draft ERP/AAK May 2012
Qin Wu
Huawei
Floor 12, HuiHong Mansion, No.91 BaiXia Rd.
Nanjing, Jiangsu 210001
P.R. China
Phone: +86 25 56623633
EMail: sunseawq@huawei.com
Glen Zorn (editor)
Network Zen
227/358 Thanon Sanphawut
Bang Na, Bangkok 10260
Thailand
Phone: +66 (0) 87-040-4617
EMail: glenzorn@gmail.com
Cao, et al. Expires November 3, 2012 [Page 20]
