Network Working Group F. Maino
Internet-Draft V. Ermagan
Intended status: Experimental Cisco Systems
Expires: April 21, 2016 A. Cabellos
Technical University of Catalonia
D. Saucez
INRIA
October 19, 2015
LISP-Security (LISP-SEC)
draft-ietf-lisp-sec-09
Abstract
This memo specifies LISP-SEC, a set of security mechanisms that
provides origin authentication, integrity and anti-replay protection
to LISP's EID-to-RLOC mapping data conveyed via mapping lookup
process. LISP-SEC also enables verification of authorization on EID-
prefix claims in Map-Reply messages.
Requirements 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 [RFC2119].
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 April 21, 2016.
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Copyright Notice
Copyright (c) 2015 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
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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. Definition of Terms . . . . . . . . . . . . . . . . . . . . . 3
3. LISP-SEC Threat Model . . . . . . . . . . . . . . . . . . . . 4
4. Protocol Operations . . . . . . . . . . . . . . . . . . . . . 4
5. LISP-SEC Control Messages Details . . . . . . . . . . . . . . 7
5.1. Encapsulated Control Message LISP-SEC Extensions . . . . 7
5.2. Map-Reply LISP-SEC Extensions . . . . . . . . . . . . . . 9
5.3. Map-Register LISP-SEC Extentions . . . . . . . . . . . . 10
5.4. ITR Processing . . . . . . . . . . . . . . . . . . . . . 10
5.4.1. Map-Reply Record Validation . . . . . . . . . . . . . 12
5.4.2. PITR Processing . . . . . . . . . . . . . . . . . . . 13
5.5. Encrypting and Decrypting an OTK . . . . . . . . . . . . 13
5.6. Map-Resolver Processing . . . . . . . . . . . . . . . . . 14
5.7. Map-Server Processing . . . . . . . . . . . . . . . . . . 14
5.7.1. Map-Server Processing in Proxy mode . . . . . . . . . 15
5.8. ETR Processing . . . . . . . . . . . . . . . . . . . . . 15
6. Security Considerations . . . . . . . . . . . . . . . . . . . 16
6.1. Mapping System Security . . . . . . . . . . . . . . . . . 16
6.2. Random Number Generation . . . . . . . . . . . . . . . . 16
6.3. Map-Server and ETR Colocation . . . . . . . . . . . . . . 16
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
7.1. HMAC functions . . . . . . . . . . . . . . . . . . . . . 16
7.2. Key Wrap Functions . . . . . . . . . . . . . . . . . . . 17
7.3. Key Derivation Functions . . . . . . . . . . . . . . . . 17
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 18
9. Normative References . . . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
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1. Introduction
The Locator/ID Separation Protocol [RFC6830] defines a set of
functions for routers to exchange information used to map from non-
routable Endpoint Identifiers (EIDs) to routable Routing Locators
(RLOCs). If these EID-to-RLOC mappings, carried through Map-Reply
messages, are transmitted without integrity protection, an adversary
can manipulate them and hijack the communication, impersonate the
requested EID, or mount Denial of Service or Distributed Denial of
Service attacks. Also, if the Map-Reply message is transported
unauthenticated, an adversarial LISP entity can overclaim an EID-
prefix and maliciously redirect traffic directed to a large number of
hosts. A detailed description of "overclaiming" attack is provided
in [I-D.ietf-lisp-threats].
This memo specifies LISP-SEC, a set of security mechanisms that
provides origin authentication, integrity and anti-replay protection
to LISP's EID-to-RLOC mapping data conveyed via mapping lookup
process. LISP-SEC also enables verification of authorization on EID-
prefix claims in Map-Reply messages, ensuring that the sender of a
Map-Reply that provides the location for a given EID-prefix is
entitled to do so according to the EID prefix registered in the
associated Map-Server. Map-Register security, including the right
for a LISP entity to register an EID-prefix or to claim presence at
an RLOC, is out of the scope of LISP-SEC. Additional security
considerations are described in Section 6.
2. Definition of Terms
One-Time Key (OTK): An ephemeral randomly generated key that must
be used for a single Map-Request/Map-Reply exchange.
ITR-OTK: The One-Time Key generated at the ITR.
MS-OTK: The One-Time Key generated at the Map-Server.
Encapsulated Control Message (ECM): A LISP control message that is
prepended with an additional LISP header. ECM is used by ITRs to
send LISP control messages to a Map-Resolver, by Map-Resolvers to
forward LISP control messages to a Map-Server, and by Map-
Resolvers to forward LISP control messages to an ETR.
Authentication Data (AD): Metadata that is included either in a
LISP ECM header or in a Map-Reply message to support
confidentiality, integrity protection, and verification of EID-
prefix authorization.
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OTK-AD: The portion of ECM Authentication Data that contains a
One-Time Key.
EID-AD: The portion of ECM and Map-Reply Authentication Data
used for verification of EID-prefix authorization.
PKT-AD: The portion of Map-Reply Authentication Data used to
protect the integrity of the Map-Reply message.
For definitions of other terms, notably Map-Request, Map-Reply,
Ingress Tunnel Router (ITR), Egress Tunnel Router (ETR), Map-Server
(MS), and Map-Resolver (MR) please consult the LISP specification
[RFC6830].
3. LISP-SEC Threat Model
LISP-SEC addresses the control plane threats, described in
[I-D.ietf-lisp-threats], that target EID-to-RLOC mappings, including
manipulations of Map-Request and Map-Reply messages, and malicious
ETR EID prefix overclaiming. LISP-SEC makes two main assumptions:
(1) the LISP mapping system is expected to deliver a Map-Request
message to their intended destination ETR as identified by the EID,
and (2) no man-in-the-middle (MITM) attack can be mounted within the
LISP Mapping System. Furthermore, while LISP-SEC enables detection
of EID prefix overclaiming attacks, it assumes that Map-Servers can
verify the EID prefix authorization at time of registration.
According to the threat model described in [I-D.ietf-lisp-threats]
LISP-SEC assumes that any kind of attack, including MITM attacks, can
be mounted in the access network, outside of the boundaries of the
LISP mapping system. An on-path attacker, outside of the LISP
mapping system can, for example, hijack Map-Request and Map-Reply
messages, spoofing the identity of a LISP node. Another example of
on-path attack, called overclaiming attack, can be mounted by a
malicious Egress Tunnel Router (ETR), by overclaiming the EID-
prefixes for which it is authoritative. In this way the ETR can
maliciously redirect traffic directed to a large number of hosts.
4. Protocol Operations
The goal of the security mechanisms defined in [RFC6830] is to
prevent unauthorized insertion of mapping data by providing origin
authentication and integrity protection for the Map-Registration, and
by using the nonce to detect unsolicited Map-Reply sent by off-path
attackers.
LISP-SEC builds on top of the security mechanisms defined in
[RFC6830] to address the threats described in Section 3 by leveraging
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the trust relationships existing among the LISP entities
participating to the exchange of the Map-Request/Map-Reply messages.
Those trust relationships are used to securely distribute a One-Time
Key (OTK) that provides origin authentication, integrity and anti-
replay protection to mapping data conveyed via the mapping lookup
process, and that effectively prevent overclaiming attacks. The
processing of security parameters during the Map-Request/Map-Reply
exchange is as follows:
o The ITR-OTK is generated and stored at the ITR, and securely
transported to the Map-Server.
o The Map-Server uses the ITR-OTK to compute an HMAC that protects
the integrity of the mapping data known to the Map-Server to
prevent overclaiming attacks. The Map-Server also derives a new
OTK, the MS-OTK, that is passed to the ETR, by applying a Key
Derivation Function (KDF) to the ITR-OTK.
o The ETR uses the MS-OTK to compute an HMAC that protects the
integrity of the Map-Reply sent to the ITR.
o Finally, the ITR uses the stored ITR-OTK to verify the integrity
of the mapping data provided by both the Map-Server and the ETR,
and to verify that no overclaiming attacks were mounted along the
path between the Map-Server and the ITR.
Section 5 provides the detailed description of the LISP-SEC control
messages and their processing, while the rest of this section
describes the flow of protocol operations at each entity involved in
the Map-Request/Map-Reply exchange:
o The ITR, upon needing to transmit a Map-Request message, generates
and stores an OTK (ITR-OTK). This ITR-OTK is included into the
Encapsulated Control Message (ECM) that contains the Map-Request
sent to the Map-Resolver. To provide confidentiality to the ITR-
OTK over the path between the ITR and its Map-Resolver, the ITR-
OTK SHOULD be encrypted using a preconfigured key shared between
the ITR and the Map-Resolver, similar to the key shared between
the ETR and the Map-Server in order to secure ETR registration
[RFC6833].
o The Map-Resolver decapsulates the ECM message, decrypts the ITR-
OTK, if needed, and forwards through the Mapping System the
received Map-Request and the ITR-OTK, as part of a new ECM
message. As described in Section 5.6, the LISP Mapping System
delivers the ECM to the appropriate Map-Server, as identified by
the EID destination address of the Map-Request.
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o The Map-Server is configured with the location mappings and policy
information for the ETR responsible for the EID destination
address. Using this preconfigured information, the Map-Server,
after the decapsulation of the ECM message, finds the longest
match EID-prefix that covers the requested EID in the received
Map-Request. The Map-Server adds this EID-prefix, together with
an HMAC computed using the ITR-OTK, to a new Encapsulated Control
Message that contains the received Map-Request.
o The Map-Server derives a new OTK, the MS-OTK, by applying a Key
Derivation Function (KDF) to the ITR-OTK. This MS-OTK is included
in the Encapsulated Control Message that the Map-Server uses to
forward the Map-Request to the ETR. To provide MS-OTK
confidentiality over the path between the Map-Server and the ETR,
the MS-OTK should be encrypted using the key shared between the
ETR and the Map-Server in order to secure ETR registration
[RFC6833].
o If the Map-Server is acting in proxy mode, as specified in
[RFC6830], the ETR is not involved in the generation of the Map-
Reply. In this case the Map-Server generates the Map-Reply on
behalf of the ETR as described below.
o The ETR, upon receiving the ECM encapsulated Map-Request from the
Map-Server, decrypts the MS-OTK, if needed, and originates a
standard Map-Reply that contains the EID-to-RLOC mapping
information as specified in [RFC6830].
o The ETR computes an HMAC over this standard Map-Reply, keyed with
MS-OTK to protect the integrity of the whole Map-Reply. The ETR
also copies the EID-prefix authorization data that the Map-Server
included in the ECM encapsulated Map-Request into the Map-Reply
message. The ETR then sends this complete Map-Reply message to
the requesting ITR.
o The ITR, upon receiving the Map-Reply, uses the locally stored
ITR-OTK to verify the integrity of the EID-prefix authorization
data included in the Map-Reply by the Map-Server. The ITR
computes the MS-OTK by applying the same KDF used by the Map-
Server, and verifies the integrity of the Map-Reply. If the
integrity checks fail, the Map-Reply MUST be discarded. Also, if
the EID-prefixes claimed by the ETR in the Map-Reply are not equal
or more specific than the EID-prefix authorization data inserted
by the Map-Server, the ITR MUST discard the Map-Reply.
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5. LISP-SEC Control Messages Details
LISP-SEC metadata associated with a Map-Request is transported within
the Encapsulated Control Message that contains the Map-Request.
LISP-SEC metadata associated with the Map-Reply is transported within
the Map-Reply itself.
5.1. Encapsulated Control Message LISP-SEC Extensions
LISP-SEC uses the ECM (Encapsulated Control Message) defined in
[RFC6830] with Type set to 8, and S bit set to 1 to indicate that the
LISP header includes Authentication Data (AD). The format of the
LISP-SEC ECM Authentication Data is defined in the following figure.
OTK-AD stands for One-Time Key Authentication Data and EID-AD stands
for EID Authentication Data.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AD Type |V| Reserved | Requested HMAC ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+\
| OTK Length | OTK Encryption ID | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| One-Time-Key Preamble ... | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ OTK-AD
| ... One-Time-Key Preamble | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
~ One-Time Key (128 bits) ~/
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ <---+
| EID-AD Length | KDF ID | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Record Count | Reserved | EID HMAC ID | EID-AD
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+\ |
| Reserved | EID mask-len | EID-AFI | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Rec |
~ EID-prefix ... ~ | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+/ |
~ EID HMAC ~ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ <---+
LISP-SEC ECM Authentication Data
AD Type: 1 (LISP-SEC Authentication Data)
V: Key Version bit. This bit is toggled when the sender switches
to a new OTK wrapping key
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Reserved: Set to 0 on transmission and ignored on receipt.
Requested HMAC ID: The HMAC algorithm requested by the ITR. See
Section 5.4 for details.
OTK Length: The length (in bytes) of the OTK Authentication Data
(OTK-AD), that contains the OTK Preamble and the OTK.
OTK Encryption ID: The identifier of the key wrapping algorithm
used to encrypt the One-Time-Key. When a 128-bit OTK is sent
unencrypted by the Map-Resolver, the OTK Encryption ID is set to
NULL_KEY_WRAP_128. See Section 5.5 for more details.
One-Time-Key Preamble: set to 0 if the OTK is not encrypted. When
the OTK is encrypted, this field may carry additional metadata
resulting from the key wrapping operation. When a 128-bit OTK is
sent unencrypted by Map-Resolver, the OTK Preamble is set to
0x0000000000000000 (64 bits). See Section 5.5 for details.
One-Time-Key: the OTK encrypted (or not) as specified by OTK
Encryption ID. See Section 5.5 for details.
EID-AD Length: length (in bytes) of the EID Authentication Data
(EID-AD). The ITR MUST set EID-AD Length to 4 bytes, as it only
fills the KDF ID field, and all the remaining fields part of the
EID-AD are not present. An EID-AD MAY contain multiple EID-
records. Each EID-record is 4-byte long plus the length of the
AFI-encoded EID-prefix.
KDF ID: Identifier of the Key Derivation Function used to derive
the MS-OTK. The ITR SHOULD use this field to indicate the
recommended KDF algorithm, according to local policy. The Map-
Server can overwrite the KDF ID if it does not support the KDF ID
recommended by the ITR. See Section 5.4 for more details.
Record Count: The number of records in this Map-Request message.
A record is comprised of the portion of the packet that is labeled
'Rec' above and occurs the number of times equal to Record Count.
Reserved: Set to 0 on transmission and ignored on receipt.
EID HMAC ID: Identifier of the HMAC algorithm used to protect the
integrity of the EID-AD. This field is filled by Map-Server that
computed the EID-prefix HMAC. See Section 5.4 for more details.
EID mask-len: Mask length for EID-prefix.
EID-AFI: Address family of EID-prefix according to [RFC5226]
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EID-prefix: The Map-Server uses this field to specify the EID-
prefix that the destination ETR is authoritative for, and is the
longest match for the requested EID.
EID HMAC: HMAC of the EID-AD computed and inserted by Map-Server.
Before computing the HMAC operation the EID HMAC field MUST be set
to 0. The HMAC covers the entire EID-AD.
5.2. Map-Reply LISP-SEC Extensions
LISP-SEC uses the Map-Reply defined in [RFC6830], with Type set to 2,
and S bit set to 1 to indicate that the Map-Reply message includes
Authentication Data (AD). The format of the LISP-SEC Map-Reply
Authentication Data is defined in the following figure. PKT-AD is
the Packet Authentication Data that covers the Map-Reply payload.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AD Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ <---+
| EID-AD Length | KDF ID | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Record Count | Reserved | EID HMAC ID | EID-AD
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+\ |
| Reserved | EID mask-len | EID-AFI | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Rec |
~ EID-prefix ... ~ | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+/ |
~ EID HMAC ~ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ <---+
| PKT-AD Length | PKT HMAC ID |\
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
~ PKT HMAC ~ PKT-AD
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+/
LISP-SEC Map-Reply Authentication Data
AD Type: 1 (LISP-SEC Authentication Data)
EID-AD Length: length (in bytes) of the EID-AD. An EID-AD MAY
contain multiple EID-records. Each EID-record is 4-byte long plus
the length of the AFI-encoded EID-prefix.
KDF ID: Identifier of the Key Derivation Function used to derive
MS-OTK. See Section 5.7 for more details.
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Record Count: The number of records in this Map-Reply message. A
record is comprised of the portion of the packet that is labeled
'Rec' above and occurs the number of times equal to Record Count.
Reserved: Set to 0 on transmission and ignored on receipt.
EID HMAC ID: Identifier of the HMAC algorithm used to protect the
integrity of the EID-AD. See Section 5.7 for more details.
EID mask-len: Mask length for EID-prefix.
EID-AFI: Address family of EID-prefix according to [RFC5226].
EID-prefix: This field contains an EID-prefix that the destination
ETR is authoritative for, and is the longest match for the
requested EID.
EID HMAC: HMAC of the EID-AD, as computed by the Map-Server.
Before computing the HMAC operation the EID HMAC field MUST be set
to 0. The HMAC covers the entire EID-AD.
PKT-AD Length: length (in bytes) of the Packet Authentication Data
(PKT-AD).
PKT HMAC ID: Identifier of the HMAC algorithm used to protect the
integrity of the Map-reply Location Data.
PKT HMAC: HMAC of the whole Map-Reply packet, including the LISP-
SEC Authentication Data. The scope of the authentication goes
from the Map-Reply Type field to the PKT HMAC field included.
Before computing the HMAC operation the PKT HMAC field MUST be set
to 0. See Section 5.8 for more details.
5.3. Map-Register LISP-SEC Extentions
The second bit after the Type field in a Map-Register message is
allocated as the S bit. The S bit indicates to the Map-Server that
the registering ETR is LISP-SEC enabled. An ETR that supports LISP-
SEC MUST set the S bit in its Map-Register messages.
5.4. ITR Processing
Upon creating a Map-Request, the ITR generates a random ITR-OTK that
is stored locally, together with the nonce generated as specified in
[RFC6830].
The Map-Request MUST be encapsulated in an ECM, with the S-bit set to
1, to indicate the presence of Authentication Data. If the ITR and
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the Map-Resolver are configured with a shared key, the ITR-OTK
confidentiality SHOULD be protected by wrapping the ITR-OTK with the
algorithm specified by the OTK Encryption ID field. See Section 5.5
for further details on OTK encryption.
The Requested HMAC ID field contains the suggested HMAC algorithm to
be used by the Map-Server and the ETR to protect the integrity of the
ECM Authentication data and of the Map-Reply.
The KDF ID field, specifies the suggested key derivation function to
be used by the Map-Server to derive the MS-OTK.
The EID-AD length is set to 4 bytes, since the Authentication Data
does not contain EID-prefix Authentication Data, and the EID-AD
contains only the KDF ID field.
In response to an encapsulated Map-Request that has the S-bit set, an
ITR MUST receive a Map-Reply with the S-bit set, that includes an
EID-AD and a PKT-AD. If the Map-Reply does not include both ADs, the
ITR MUST discard it. In response to an encapsulated Map-Request with
S-bit set to 0, the ITR expects a Map-Reply with S-bit set to 0, and
the ITR SHOULD discard the Map-Reply if the S-bit is set.
Upon receiving a Map-Reply, the ITR must verify the integrity of both
the EID-AD and the PKT-AD, and MUST discard the Map-Reply if one of
the integrity checks fails.
The integrity of the EID-AD is verified using the locally stored ITR-
OTK to re-compute the HMAC of the EID-AD using the algorithm
specified in the EID HMAC ID field. If the EID HMAC ID field does
not match the Requested HMAC ID the ITR SHOULD discard the Map-Reply
and send, at the first opportunity it needs to, a new Map-Request
with a different Requested HMAC ID field, according to ITR's local
policy. The ITR MUST set the EID HMAC ID field to 0 before computing
the HMAC.
To verify the integrity of the PKT-AD, first the MS-OTK is derived
from the locally stored ITR-OTK using the algorithm specified in the
KDF ID field. This is because the PKT-AD is generated by the ETR
using the MS-OTK. If the KDF ID in the Map-Reply does not match the
KDF ID requested in the Map-Request, the ITR SHOULD discard the Map-
Reply and send, at the first opportunity it needs to, a new Map-
Request with a different KDF ID, according to ITR's local policy.
The derived MS-OTK is then used to re-compute the HMAC of the PKT-AD
using the Algorithm specified in the PKT HMAC ID field. If the PKT
HMAC ID field does not match the Requested HMAC ID the ITR SHOULD
discard the Map-Reply and send, at the first opportunity it needs to,
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a new Map-Request with a different Requested HMAC ID according to
ITR's local policy.
Each individual Map-Reply EID-record is considered valid only if: (1)
both EID-AD and PKT-AD are valid, and (2) the intersection of the
EID-prefix in the Map-Reply EID-record with one of the EID-prefixes
contained in the EID-AD is not empty. After identifying the Map-
Reply record as valid, the ITR sets the EID-prefix in the Map-Reply
record to the value of the intersection set computed before, and adds
the Map-Reply EID-record to its EID-to-RLOC cache, as described in
[RFC6830]. An example of Map-Reply record validation is provided in
Section 5.4.1.
The ITR SHOULD send SMR triggered Map-Requests over the mapping
system in order to receive a secure Map-Reply. If an ITR accepts
piggybacked Map-Replies, it SHOULD also send a Map-Request over the
mapping system in order to securely verify the piggybacked Map-Reply.
5.4.1. Map-Reply Record Validation
The payload of a Map-Reply may contain multiple EID-records. The
whole Map-Reply is signed by the ETR, with the PKT HMAC, to provide
integrity protection and origin authentication to the EID-prefix
records claimed by the ETR. The Authentication Data field of a Map-
Reply may contain multiple EID-records in the EID-AD. The EID-AD is
signed by the Map-Server, with the EID HMAC, to provide integrity
protection and origin authentication to the EID-prefix records
inserted by the Map-Server.
Upon receiving a Map-Reply with the S-bit set, the ITR first checks
the validity of both the EID HMAC and of the PKT-AD HMAC. If either
one of the HMACs is not valid, a log message is issued and the Map-
Reply is not processed any further. If both HMACs are valid, the ITR
proceeds with validating each individual EID-record claimed by the
ETR by computing the intersection of each one of the EID-prefix
contained in the payload of the Map-Reply with each one of the EID-
prefixes contained in the EID-AD. An EID-record is valid only if at
least one of the intersections is not the empty set.
For instance, the Map-Reply payload contains 3 mapping record EID-
prefixes:
1.1.1.0/24
1.1.2.0/24
1.2.0.0/16
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The EID-AD contains two EID-prefixes:
1.1.2.0/24
1.2.3.0/24
The EID-record with EID-prefix 1.1.1.0/24 is not processed since it
is not included in any of the EID-ADs signed by the Map-Server. A
log message is issued.
The EID-record with EID-prefix 1.1.2.0/24 is stored in the map-cache
because it matches the second EID-prefix contained in the EID-AD.
The EID-record with EID-prefix 1.2.0.0/16 is not processed since it
is not included in any of the EID-ADs signed by the Map-Server. A
log message is issued. In this last example the ETR is trying to
over claim the EID-prefix 1.2.0.0/16, but the Map-Server authorized
only 1.2.3.0/24, hence the EID-record is discarded.
5.4.2. PITR Processing
The processing performed by a PITR is equivalent to the processing of
an ITR. However, if the PITR is directly connected to the ALT, the
PITR performs the functions of both the ITR and the Map-Resolver
forwarding the Map-Request encapsulated in an ECM header that
includes the Authentication Data fields as described in Section 5.6.
5.5. Encrypting and Decrypting an OTK
MS-OTK confidentiality is required in the path between the Map-Server
and the ETR, the MS-OTK SHOULD be encrypted using the preconfigured
key shared between the Map-Server and the ETR for the purpose of
securing ETR registration [RFC6833]. Similarly, if ITR-OTK
confidentiality is required in the path between the ITR and the Map-
Resolver, the ITR-OTK SHOULD be encrypted with a key shared between
the ITR and the Map-Resolver.
The OTK is encrypted using the algorithm specified in the OTK
Encryption ID field. When the AES Key Wrap algorithm is used to
encrypt a 128-bit OTK, according to [RFC3339], the AES Key Wrap
Initialization Value MUST be set to 0xA6A6A6A6A6A6A6A6 (64 bits).
The output of the AES Key Wrap operation is 192-bit long. The most
significant 64-bit are copied in the One-Time Key Preamble field,
while the 128 less significant bits are copied in the One-Time Key
field of the LISP-SEC Authentication Data.
When decrypting an encrypted OTK the receiver MUST verify that the
Initialization Value resulting from the AES Key Wrap decryption
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operation is equal to 0xA6A6A6A6A6A6A6A6. If this verification fails
the receiver MUST discard the entire message.
When a 128-bit OTK is sent unencrypted the OTK Encryption ID is set
to NULL_KEY_WRAP_128, and the OTK Preamble is set to
0x0000000000000000 (64 bits).
5.6. Map-Resolver Processing
Upon receiving an encapsulated Map-Request with the S-bit set, the
Map-Resolver decapsulates the ECM message. The ITR-OTK, if
encrypted, is decrypted as specified in Section 5.5.
The Map-Resolver, as specified in [RFC6833], originates a new ECM
header with the S-bit set, that contains the unencrypted ITR-OTK, as
specified in Section 5.5, and the other data derived from the ECM
Authentication Data of the received encapsulated Map-Request.
The Map-Resolver then forwards the received Map-Request, encapsulated
in the new ECM header that includes the newly computed Authentication
Data fields.
5.7. Map-Server Processing
Upon receiving an ECM encapsulated Map-Request with the S-bit set,
the Map-Server process the Map-Request according to the value of the
S-bit contained in the Map-Register sent by the ETR during
registration.
If the S-bit contained in the Map-Register was clear the Map-Server
decapsulates the ECM and generates a new ECM encapsulated Map-Request
that does not contain an ECM Authentication Data, as specified in
[RFC6830]. The Map-Server does not perform any further LISP-SEC
processing.
If the S-bit contained in the Map-Register was set the Map-Server
decapsulates the ECM and generates a new ECM Authentication Data.
The Authentication Data includes the OTK-AD and the EID-AD, that
contains EID-prefix authorization information, that are ultimately
sent to the requesting ITR.
The Map-Server updates the OTK-AD by deriving a new OTK (MS-OTK) from
the ITR-OTK received with the Map-Request. MS-OTK is derived
applying the key derivation function specified in the KDF ID field.
If the algorithm specified in the KDF ID field is not supported, the
Map-Server uses a different algorithm to derive the key and updates
the KDF ID field accordingly.
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The Map-Server and the ETR MUST be configured with a shared key for
mapping registration according to [RFC6833]. If MS-OTK
confidentiality is required, then the MS-OTK SHOULD be encrypted, by
wrapping the MS-OTK with the algorithm specified by the OTK
Encryption ID field as specified in Section 5.5.
The Map-Server includes in the EID-AD the longest match registered
EID-prefix for the destination EID, and an HMAC of this EID-prefix.
The HMAC is keyed with the ITR-OTK contained in the received ECM
Authentication Data, and the HMAC algorithm is chosen according to
the Requested HMAC ID field. If The Map-Server does not support this
algorithm, the Map-Server uses a different algorithm and specifies it
in the EID HMAC ID field. The scope of the HMAC operation covers the
entire EID-AD, from the EID-AD Length field to the EID HMAC field,
which must be set to 0 before the computation.
The Map-Server then forwards the updated ECM encapsulated Map-
Request, that contains the OTK-AD, the EID-AD, and the received Map-
Request to an authoritative ETR as specified in [RFC6830].
5.7.1. Map-Server Processing in Proxy mode
If the Map-Server is in proxy mode, it generates a Map-Reply, as
specified in [RFC6830], with the S-bit set to 1. The Map-Reply
includes the Authentication Data that contains the EID-AD, computed
as specified in Section 5.7, as well as the PKT-AD computed as
specified in Section 5.8.
5.8. ETR Processing
Upon receiving an ECM encapsulated Map-Request with the S-bit set,
the ETR decapsulates the ECM message. The OTK field, if encrypted,
is decrypted as specified in Section 5.5 to obtain the unencrypted
MS-OTK.
The ETR then generates a Map-Reply as specified in [RFC6830] and
includes the Authentication Data that contains the EID-AD, as
received in the encapsulated Map-Request, as well as the PKT-AD.
The EID-AD is copied from the Authentication Data of the received
encapsulated Map-Request.
The PKT-AD contains the HMAC of the whole Map-Reply packet, keyed
with the MS-OTK and computed using the HMAC algorithm specified in
the Requested HMAC ID field of the received encapsulated Map-Request.
If the ETR does not support the Requested HMAC ID, it uses a
different algorithm and updates the PKT HMAC ID field accordingly.
The scope of the HMAC operation covers the entire PKT-AD, from the
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Map-Reply Type field to the PKT HMAC field, which must be set to 0
before the computation.
Finally the ETR sends the Map-Reply to the requesting ITR as
specified in [RFC6830].
6. Security Considerations
6.1. Mapping System Security
The LISP-SEC threat model described in Section 3, assumes that the
LISP Mapping System is working properly and eventually delivers Map-
Request messages to a Map-Server that is authoritative for the
requested EID.
Map-Register security, including the right for a LISP entity to
register an EID-prefix or to claim presence at an RLOC, is out of the
scope of LISP-SEC.
6.2. Random Number Generation
The ITR-OTK MUST be generated by a properly seeded pseudo-random (or
strong random) source. See [RFC4086] for advice on generating
security-sensitive random data
6.3. Map-Server and ETR Colocation
If the Map-Server and the ETR are colocated, LISP-SEC does not
provide protection from overclaiming attacks mounted by the ETR.
However, in this particular case, since the ETR is within the trust
boundaries of the Map-Server, ETR's overclaiming attacks are not
included in the threat model.
7. IANA Considerations
7.1. HMAC functions
The following HMAC ID values are defined by this memo for use as
Requested HMAC ID, EID HMAC ID, and PKT HMAC ID in the LISP-SEC
Authentication Data:
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Name Number Defined In
-------------------------------------------------
NONE 0
AUTH-HMAC-SHA-1-96 1 [RFC2104]
AUTH-HMAC-SHA-256-128 2 [RFC4634]
values 2-65535 are reserved to IANA.
HMAC Functions
AUTH-HMAC-SHA-1-96 MUST be supported, AUTH-HMAC-SHA-256-128 should be
supported.
7.2. Key Wrap Functions
The following OTK Encryption ID values are defined by this memo for
use as OTK key wrap algorithms ID in the LISP-SEC Authentication
Data:
Name Number Defined In
-------------------------------------------------
NULL-KEY-WRAP-128 1
AES-KEY-WRAP-128 2 [RFC3394]
values 0 and 3-65535 are reserved to IANA.
Key Wrap Functions
NULL-KEY-WRAP-128, and AES-KEY-WRAP-128 MUST be supported.
NULL-KEY-WRAP-128 is used to carry an unencrypted 128-bit OTK, with a
64-bit preamble set to 0x0000000000000000 (64 bits).
7.3. Key Derivation Functions
The following KDF ID values are defined by this memo for use as KDF
ID in the LISP-SEC Authentication Data:
Name Number Defined In
-------------------------------------------------
NONE 0
HKDF-SHA1-128 1 [RFC5869]
values 2-65535 are reserved to IANA.
Key Derivation Functions
HKDF-SHA1-128 MUST be supported
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8. Acknowledgements
The authors would like to acknowledge Pere Monclus, Dave Meyer, Dino
Farinacci, Brian Weis, David McGrew, Darrel Lewis and Landon Curt
Noll for their valuable suggestions provided during the preparation
of this document.
9. Normative References
[I-D.ietf-lisp-threats]
Saucez, D., Iannone, L., and O. Bonaventure, "LISP Threats
Analysis", draft-ietf-lisp-threats-13 (work in progress),
August 2015.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104, February
1997.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3394] Schaad, J. and R. Housley, "Advanced Encryption Standard
(AES) Key Wrap Algorithm", RFC 3394, September 2002.
[RFC4086] Eastlake, D., Schiller, J., and S. Crocker, "Randomness
Requirements for Security", BCP 106, RFC 4086, June 2005.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
Key Derivation Function (HKDF)", RFC 5869, May 2010.
[RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
Locator/ID Separation Protocol (LISP)", RFC 6830, January
2013.
[RFC6833] Fuller, V. and D. Farinacci, "Locator/ID Separation
Protocol (LISP) Map-Server Interface", RFC 6833, January
2013.
Authors' Addresses
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Fabio Maino
Cisco Systems
170 Tasman Drive
San Jose, California 95134
USA
Email: fmaino@cisco.com
Vina Ermagan
Cisco Systems
170 Tasman Drive
San Jose, California 95134
USA
Email: vermagan@cisco.com
Albert Cabellos
Technical University of Catalonia
c/ Jordi Girona s/n
Barcelona 08034
Spain
Email: acabello@ac.upc.edu
Damien Saucez
INRIA
2004 route des Lucioles - BP 93
Sophia Antipolis
France
Email: damien.saucez@inria.fr
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