Internet DRAFT - draft-yegin-pana-encr-avp
draft-yegin-pana-encr-avp
Network Working Group A. Yegin
Internet-Draft Samsung
Intended status: Standards Track R. Cragie
Expires: March 11, 2013 Gridmerge Ltd.
September 7, 2012
Encrypting PANA AVPs
draft-yegin-pana-encr-avp-10
Abstract
This document specifies a mechanism for delivering PANA (Protocol for
Carrying Authentication for Network Access) AVPs (Attribute-Value
Pairs) in encrypted form.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on March 11, 2013.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Specification of Requirements . . . . . . . . . . . . . . 3
2. Details . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Encryption Keys . . . . . . . . . . . . . . . . . . . . . . . 3
4. Encryption-Algorithm AVP . . . . . . . . . . . . . . . . . . . 5
4.1. AES128_CTR Encryption Algorithm . . . . . . . . . . . . . 5
5. Encr-Encap AVP . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Encryption Policy . . . . . . . . . . . . . . . . . . . . . . 7
6.1. Encryption Policy Specification . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7.1. AES-CTR Security Considerations . . . . . . . . . . . . . 9
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
8.1. PANA AVP codes . . . . . . . . . . . . . . . . . . . . . . 9
8.2. PANA Encryption-Algorithm AVP values . . . . . . . . . . . 10
8.3. PANA AVP codes encryption policy . . . . . . . . . . . . . 10
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
10. Normative References . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
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1. Introduction
PANA [RFC5191] is a UDP-based protocol to perform EAP authentication
between a PaC (PANA Client) and a PAA (PANA Authentication Agent).
Various types of payloads are exchanged as part of the network access
authentication and authorization. These payloads are carried in PANA
Attribute-Value Pairs (AVPs). AVPs can be integrity-protected using
the AUTH AVP when EAP authentication generates cryptographic keying
material. AVPs are transmitted in the clear (i.e., not encrypted).
There are certain types of payloads that need to be delivered
privately (e.g., network keys, private identifiers, etc.). This
document defines a mechanism for applying encryption to selected
AVPs.
1.1. Specification of Requirements
In this document, several words are used to signify the requirements
of the specification. These words are often capitalized. 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 [RFC2119].
2. Details
This document extends the AVP set defined in Section 8 of [RFC5191]
by defining two new AVPs: the Encryption-Algorithm AVP (see
Section 4) and the Encr-Encap AVP (see Section 5). Two new
encryption keys, PANA_PAC_ENCR_KEY and PANA_PAA_ENCR_KEY, are defined
to encrypt AVPs from the PaC to the PAA and AVPs from the PAA to the
PaC respectively (see Section 3).
When encryption needs to be used, the required algorithm is
negotiated as follows: the PAA SHALL send the initial PANA-Auth-
Request carrying one or more Encryption-Algorithm AVPs supported by
it. The PaC SHALL select one of the algorithms from this AVP, and it
SHALL respond with the initial PANA-Auth-Answer carrying one
Encryption-Algorithm AVP for the selected algorithm. Once
PANA_PAC_ENCR_KEY and PANA_PAA_ENCR_KEY have been generated, a PANA
message MAY contain an Encr-Encap AVP.
3. Encryption Keys
PANA_PAC_ENCR_KEY is used for encrypting the AVP payload of the Encr-
Encap AVP sent in a PANA message from the PaC to the PAA.
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PANA_PAC_ENCR_KEY SHALL be computed according to the following
formula:
PANA_PAC_ENCR_KEY = prf+(MSK, "IETF PANA PaC Encr" | I_PAR |
I_PAN | PaC_nonce | PAA_nonce | Key_ID)
PANA_PAA_ENCR_KEY is used for encrypting the AVP payload of the Encr-
Encap AVP sent in a PANA message from the PAA to the PaC.
PANA_PAA_ENCR_KEY SHALL be computed according to the following
formula:
PANA_PAA_ENCR_KEY = prf+(MSK, "IETF PANA PAA Encr" | I_PAR |
I_PAN | PaC_nonce | PAA_nonce | Key_ID)
In both cases:
- The prf+ function is defined in IKEv2 [RFC5996].
- The pseudo-random function (PRF) to be used for the prf+
function SHALL be negotiated using PRF-Algorithm AVP in the
initial PANA-Auth-Request and PANA-Auth-Answer exchange with 'S'
(Start) bit set as described in Section 4.1 of [RFC5191]
- MSK is the master session key generated by the EAP method
[RFC3748]. PANA_PAC_ENCR_KEY and PANA_PAA_ENCR_KEY MUST be
recalculated whenever a new MSK is generated by the EAP method.
- "IETF PANA PaC Encr" and "IETF PANA PAA Encr" are the ASCII code
representations of the respective non-NULL terminated strings
(excluding the double quotes around them).
- I_PAR and I_PAN are the initial PANA-Auth-Request and PANA-Auth-
Answer messages (the PANA header and the following PANA AVPs) with
'S' (Start) bit set, respectively.
- PaC_nonce and PAA_nonce are values of the Nonce AVP carried in
the first non-initial PANA-Auth-Answer and PANA-Auth-Request
messages in the authentication and authorization phase or the
first PANA-Auth-Answer and PANA-Auth-Request messages in the re-
authentication phase, respectively.
- Key_ID is the value of the Key-Id AVP.
The length of PANA_PAC_ENCR_KEY and PANA_PAA_ENCR_KEY depends on the
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encryption algorithm in use.
4. Encryption-Algorithm AVP
The Encryption-Algorithm AVP (AVP code TBD1) is used for conveying
the encryption algorithm to be used with the Encr-Encap AVP. The AVP
value data is of type Unsigned32.
Only one encryption algorithm identifier AES128_CTR (code 1) is
identified by this document. Encryption algorithm identifier values
other than 1 are reserved for future use. Future specifications are
allowed to extend this list.
AES128_CTR: 1
In the absence of an application profile specifying otherwise, all
implementations SHALL support AES128_CTR.
4.1. AES128_CTR Encryption Algorithm
The AES128_CTR encryption algorithm uses the AES-CTR (Counter)
mode of operation as specified in [NIST_SP800_38A] using the AES-
128 block cipher. The formatting function and counter generation
function as specified in Appendix A of [NIST_SP800_38C] are used,
with the following parameters:
n = 12,
q = 3
The 12-octet nonce consists of a 4-octet Key-Id, a 4-octet Session
ID and a 4-octet Sequence Number in that order where each 4-octet
value is encoded in network byte order. The Session ID and
Sequence Number values SHALL be the same as those in the PANA
message carrying the key Encr-Encap AVP. The Key-Id value SHALL
be the same as the one used for deriving PANA_PAC_ENCR_KEY and
PANA_PAA_ENCR_KEY. The output blocks of the encryption processing
are encoded as OctetString data in the Value field of a Encr-Encap
AVP.
Note the first counter block used for encryption is Ctr_1, where
"_1" denotes "subscript 1" as described in section A.3 of
[NIST_SP800_38C]. For example, given the following:
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Key-Id = 0x55667788,
Session ID = 0xaabbccdd,
Sequence Number = 0x11223344
The first counter block used for encryption will be:
0x0255667788aabbccdd11223344000001
where the initial 0x02 represents the Flags Field of the counter
block.
The nonce meets the requirement of uniqueness per key usage providing
the sequence number does not wrap. Therefore, for the purpose of
generating new keys:
- If Encr-Encap AVPs are being sent from the PaC to the PAA and
the sequence number is about to wrap, the PaC SHALL initiate PANA
re-authentication as described in Section 4.3 of [RFC5191].
- If Encr-Encap AVPs are being sent from the PAA to the PaC and
the sequence number is about to wrap, the PAA SHALL initiate PANA
re-authentication as described in Section 4.3 of [RFC5191].
Re-authentication ensures the generation of a new MSK [RFC3748] and
thus a new PANA_PAC_ENCR_KEY and PANA_PAA_ENCR_KEY.
5. Encr-Encap AVP
The Encr-Encap AVP (AVP code TBD2) is used to encrypt one or more
PANA AVPs. Format of the Encr-Encap AVP depends on the negotiated
encryption algorithm.
When the negotiated encryption algorithm identifier is AES128_CTR
(code 1), AVP data payload is occupied by the encrypted AVPs.
There SHALL be only one Encr-Encap AVP in a PANA message. All AVPs
that require encryption SHALL be encapsulated within the Encr-Encap
AVP.
The Encr-Encap AVP uses either PANA_PAC_ENCR_KEY or PANA_PAA_ENCR_KEY
and the encryption algorithm negotiated by the Encryption-Algorithm
AVP. The Encr-Encap AVP SHALL only be used if the EAP method
generates cryptographic keys (specifically the MSK [RFC3748]).
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The Encr-Encap AVP MAY be used in a PANA message from the PaC to the
PAA when the encryption algorithm has been successfully negotiated
and once PANA_PAC_ENCR_KEY has been generated.
The Encr-Encap AVP MAY be used in a PANA message from the PAA to the
PaC when the encryption algorithm has been successfully negotiated
and once PANA_PAA_ENCR_KEY has been generated.
The Encr-Encap AVP MAY be used in the very first PANA message
carrying the Result-Code AVP set to PANA_Success value, and any
subsequent message within the same PANA session.
6. Encryption Policy
The specification of any AVP SHOULD state that the AVP either shall
or shall not be encrypted using Encr-Encap AVP. The specification of
an AVP MAY state that the AVP may (or may not) be encrypted using
Encr-Encap AVP. The specification SHOULD use a table in the format
specified in Section 6.1. If the specification of an AVP is silent
about whether the AVP shall or shall not be encrypted using Encr-
Encap AVP, this implies that the AVP MAY be encrypted using Encr-
Encap AVP.
6.1. Encryption Policy Specification
This section defines a table format for the specification of whether
an AVP shall or shall not be encrypted using Encr-Encap AVP.
The table uses the following symbols:
Y: The AVP SHALL be encrypted using Encr-Encap AVP. If the AVP is
encountered not encrypted using Encr-Encap AVP, it SHALL be
considered invalid and the message containing the AVP SHALL be
discarded.
N: The AVP SHALL NOT be encrypted using Encr-Encap AVP. If the AVP
is encountered encrypted using Encr-Encap AVP, it SHALL be
considered invalid and the message containing the AVP SHALL be
discarded.
X: The AVP MAY be encrypted using Encr-Encap AVP. If the AVP is
encountered either encrypted or not encrypted using Encr-Encap
AVP, it SHALL be considered valid.
The legitimate occurrence of unencrypted AVPs and AVPs after
decryption and unencapsulation SHALL be subject to the AVP Occurrence
Table (Figure 4 in [RFC5191]).
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The following table shows the encryption requirements for the
existing AVPs defined in [RFC5191]:
Attribute Name |Enc|
----------------------+---+
AUTH | N |
EAP-Payload | X |
Integrity-Algorithm | N |
Key-Id | N |
Nonce | N |
PRF-Algorithm | N |
Result-Code | N |
Session-Lifetime | X |
Termination-Cause | X |
----------------------+---+
The following table shows the encryption requirements for the AVPs
defined in [RFC6345]:
Attribute Name |Enc|
----------------------+---+
PaC-Information | N |
Relayed-Message | N |
----------------------+---+
The following table shows the encryption requirements for the AVPs
defined in this document:
Attribute Name |Enc|
----------------------+---+
Encr-Algorithm | N |
Encr-Encap | N |
----------------------+---+
The following table is an example of showing the encryption
requirements for a newly-defined AVP, Example-AVP:
Attribute Name |Enc|
----------------------+---+
Example-AVP | Y |
----------------------+---+
The guidance for specifying the encryption requirements for a newly-
defined AVP is as follows:
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Y: If the payload needs privacy against eavesdroppers (e.g., carrying
a secret key).
N: If the payload may need to be observed by on-path network elements
(i.e., subject to deep packet inspection).
X: If neither concern applies.
7. Security Considerations
PANA_PAC_ENCR_KEY and PANA_PAA_ENCR_KEY are secret keys shared
between the PaC and the PAA. They SHALL NOT be used for purposes
other than those specified in this document. Compromise of these
keys would lead to compromise of the secret information protected by
these keys.
7.1. AES-CTR Security Considerations
The use of AES-CTR encryption has its own security considerations,
which are detailed in the Security Considerations section of
[RFC3686]. Specifically:
- The nonce specified in Section 4.1 meets the requirement of
uniqueness per key usage.
- Section 4.1 of [RFC5191] states that if the EAP method generates
cryptographic keys, an AUTH AVP will always be present in every
PANA message after key generation. Therefore, an Encr-Encap AVP
will always be sent in conjunction with an AUTH AVP. This meets
the requirement of a companion authentication function.
8. IANA Considerations
As described in Section 4 and Section 5, and following the new IANA
allocation policy on PANA messages [RFC5872], two PANA AVP codes and
one set of AVP values are requested. An additional encryption policy
for AVP codes is also requested.
8.1. PANA AVP codes
The following AVP codes are requested in the PANA Parameters - AVP
Codes registry:
o A standard AVP code of TBD1 (suggested value 12) for Encr-Encap
AVP.
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o A standard AVP code of TBD2 (suggested value 13) for Encryption-
Algorithm AVP.
8.2. PANA Encryption-Algorithm AVP values
The following AVP values representing the encryption algorithm
identifier for the Encryption-Algorithm AVP code are requested as a
sub-registry under the PANA Parameters - AVP Codes registry:
o An AVP value of 1 for AES128_CTR.
o All other AVP values (0, 2-4294967295) are unassigned
The registration procedures are IETF Review or IESG Approval in
accordance with [RFC5872].
8.3. PANA AVP codes encryption policy
The additional encryption policy defined in Section 6.1 is requested
to be assigned as an additional column labeled "Enc" to the PANA AVP
Codes parameter, applied to all existing AVP codes and those defined
in this specification.
9. Acknowledgments
The authors would like to thank Yoshihiro Ohba, Yasuyuki Tanaka,
Adrian Farrel, Brian Carpenter, Yaron Sheffer, Ralph Droms, Stephen
Farrell, Barry Leiba and Sean Turner for their valuable comments.
10. Normative References
[NIST_SP800_38A]
Dworkin, M., "Recommendation for Block Cipher Modes of
Operation: Methods and Techniques", December 2001.
[NIST_SP800_38C]
Dworkin, M., "Recommendation for Block Cipher Modes of
Operation: The CCM Mode for Authentication and
Confidentiality", May 2004.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3686] Housley, R., "Using Advanced Encryption Standard (AES)
Counter Mode With IPsec Encapsulating Security Payload
(ESP)", RFC 3686, January 2004.
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[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
Levkowetz, "Extensible Authentication Protocol (EAP)",
RFC 3748, June 2004.
[RFC5191] Forsberg, D., Ohba, Y., Patil, B., Tschofenig, H., and A.
Yegin, "Protocol for Carrying Authentication for Network
Access (PANA)", RFC 5191, May 2008.
[RFC5872] Arkko, J. and A. Yegin, "IANA Rules for the Protocol for
Carrying Authentication for Network Access (PANA)",
RFC 5872, May 2010.
[RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
"Internet Key Exchange Protocol Version 2 (IKEv2)",
RFC 5996, September 2010.
[RFC6345] Duffy, P., Chakrabarti, S., Cragie, R., Ohba, Y., and A.
Yegin, "Protocol for Carrying Authentication for Network
Access (PANA) Relay Element", RFC 6345, August 2011.
Authors' Addresses
Alper Yegin
Samsung
Istanbul
Turkey
Email: alper.yegin@yegin.org
Robert Cragie
Gridmerge Ltd.
89 Greenfield Crescent
Wakefield, WF4 4WA
UK
Email: robert.cragie@gridmerge.com
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