Internet Engineering Task Force (IETF) F. Maino

Internet Engineering Task Force (IETF) F. Maino
Request for Comments: 9303 Cisco Systems
Category: Standards Track V. Ermagan
ISSN: 2070-1721 Google, Inc.
A. Cabellos
Universitat Politecnica de Catalunya
D. Saucez
Inria
October 2022

Locator/ID Separation Protocol Security (LISP-SEC)

Abstract

This memo specifies Locator/ID Separation Protocol Security (LISP-
SEC), a set of security mechanisms that provides origin
authentication, integrity, and anti-replay protection to the LISP's
Endpoint-ID-to-Routing-Locator (EID-to-RLOC) mapping data conveyed
via the mapping lookup process. LISP-SEC also enables verification
of authorization on EID-Prefix claims in Map-Reply messages.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9303.

Copyright Notice

Copyright (c) 2022 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
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in the Revised BSD License.

Table of Contents

1. Introduction
2. Requirements Notation
3. Definitions of Terms
4. LISP-SEC Threat Model
5. Protocol Operations
6. LISP-SEC Control Messages Details
6.1. Encapsulated Control Message LISP-SEC Extensions
6.2. Map-Reply LISP-SEC Extensions
6.3. Map-Register LISP-SEC Extensions
6.4. ITR Processing: Generating a Map-Request
6.5. Encrypting and Decrypting an OTK
6.5.1. Unencrypted OTK
6.6. Map-Resolver Processing
6.7. Map-Server Processing
6.7.1. Generating a LISP-SEC-Protected Encapsulated
Map-Request
6.7.2. Generating a Proxy Map-Reply
6.8. ETR Processing
6.9. ITR Processing: Receiving a Map-Reply
6.9.1. Map-Reply Record Validation
7. Security Considerations
7.1. Mapping System Security
7.2. Random Number Generation
7.3. Map-Server and ETR Colocation
7.4. Deploying LISP-SEC
7.5. Shared Keys Provisioning
7.6. Replay Attacks
7.7. Message Privacy
7.8. Denial-of-Service and Distributed Denial-of-Service Attacks
8. IANA Considerations
8.1. ECM AD Type Registry
8.2. Map-Reply AD Types Registry
8.3. HMAC Functions
8.4. Key Wrap Functions
8.5. Key Derivation Functions
9. References
9.1. Normative References
9.2. Informative References
Acknowledgments
Authors' Addresses

1. Introduction

The Locator/ID Separation Protocol (LISP) [RFC9300] [RFC9301] is a
network-layer-based protocol that enables separation of IP addresses
into two new numbering spaces: Endpoint Identifiers (EIDs) and
Routing Locators (RLOCs). EID-to-RLOC mappings are stored in a
database and the LISP Mapping System, and they are made available via
the Map-Request/Map-Reply lookup process. 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 (DoS) or Distributed Denial-of-Service (DDoS) attacks. Also,
if the Map-Reply message is transported unauthenticated, an
adversarial LISP entity can overclaim an EID-Prefix and maliciously
redirect traffic. The LISP-SEC threat model, described in Section 4,
is built on top of the LISP threat model defined in [RFC7835], which
includes a detailed description of an "overclaiming" attack.

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 the 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/Map-Notify 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, as those
protocols are protected by the security mechanisms specified in
[RFC9301]. However, LISP-SEC extends the Map-Register message to
allow an Ingress Tunnel Router (ITR) to downgrade to non-LISP-SEC
Map-Requests. Additional security considerations are described in
Section 7.

2. Requirements Notation

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.

3. Definitions of Terms

One-Time Key (OTK): An ephemeral randomly generated key that must be
used for a single Map-Request/Map-Reply exchange.

ITR One-Time Key (ITR-OTK): The One-Time Key generated at the
Ingress Tunnel Router (ITR).

MS One-Time Key (MS-OTK): The One-Time Key generated at the Map-
Server.

Authentication Data (AD): Metadata that is included either in a LISP
Encapsulated Control Message (ECM) header as defined in [RFC9301],
or in a Map-Reply message to support confidentiality, integrity
protection, and verification of EID-Prefix authorization.

OTK Authentication Data (OTK-AD): The portion of ECM Authentication
Data that contains a One-Time Key.

EID Authentication Data (EID-AD): The portion of ECM and Map-Reply
Authentication Data used for verification of EID-Prefix
authorization.

Packet Authentication Data (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
[RFC9301].

4. LISP-SEC Threat Model

LISP-SEC addresses the control plane threats, described in Sections
3.7 and 3.8 of [RFC7835], 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 on-path attack can be mounted within the LISP Mapping System. How
the Mapping System is protected from on-path attacks depends on the
particular Mapping System used and is out of the scope of this memo.
Furthermore, while LISP-SEC enables detection of EID-Prefix
overclaiming attacks, it assumes that Map-Servers can verify the EID-
Prefix authorization at registration time.

According to the threat model described in [RFC7835], LISP-SEC
assumes that any kind of attack, including on-path attacks, can be
mounted 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 an on-path attack, called an
overclaiming attack, can be mounted by a malicious ETR by
overclaiming the EID-Prefixes for which it is authoritative. In this
way, the ETR can maliciously redirect traffic.

5. Protocol Operations

The goal of the security mechanisms defined in [RFC9301] is to
prevent unauthorized insertion of mapping data by providing origin
authentication and integrity protection for the Map-Register and by
using the nonce to detect an unsolicited Map-Reply sent by off-path
attackers.

LISP-SEC builds on top of the security mechanisms defined in
[RFC9301] to address the threats described in Section 4 by leveraging
the trust relationships existing among the LISP entities [RFC9301]
participating in the exchange of the Map-Request/Map-Reply messages.
Those trust relationships (see also Section 7 and [RFC9301]) are used
to securely distribute, as described in Section 8.4, a per-message
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 prevents overclaiming attacks.
The processing of security parameters during the Map-Request/Map-
Reply exchange is as follows:

* Per each Map-Request message, a new ITR-OTK is generated and
stored at the ITR and is securely transported to the Map-Server.

* The Map-Server uses the ITR-OTK to compute a Hashed Message
Authentication Code (HMAC) [RFC2104] 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) (e.g., [RFC5869]) to the ITR-OTK.

* The ETR uses the MS-OTK to compute an HMAC that protects the
integrity of the Map-Reply sent to the ITR.

* 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 6 provides the detailed description of the LISP-SEC control
messages and their processing, while the rest of this section
describes the flow of LISP protocol operations at each entity
involved in the Map-Request/Map-Reply exchange:

1. The ITR, upon needing to transmit a Map-Request message,
generates and stores an OTK (ITR-OTK). This ITR-OTK is encrypted
and included into the Encapsulated Control Message (ECM) that
contains the Map-Request sent to the Map-Resolver.

2. The Map-Resolver decapsulates the ECM, 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. The LISP
Mapping System delivers the ECM to the appropriate Map-Server, as
identified by the EID destination address of the Map-Request.

3. 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, 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 ECM
that contains the received Map-Request.

4. The Map-Server derives a new OTK, the MS-OTK, by applying a KDF
to the ITR-OTK. This MS-OTK is included in the ECM that the Map-
Server uses to forward the Map-Request to the ETR.

5. If the Map-Server is acting in proxy mode, as specified in
[RFC9301], the ETR is not involved in the generation of the Map-
Reply and steps 6 and 7 are skipped. In this case, the Map-
Server generates the Map-Reply on behalf of the ETR, as described
in Section 6.7.2.

6. The ETR, upon receiving the ECM-Encapsulated Map-Request from the
Map-Server, decrypts the MS-OTK (if needed), and originates a
Map-Reply that contains the EID-to-RLOC mapping information as
specified in [RFC9301].

7. The ETR computes an HMAC over the 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 the complete Map-Reply message to
the requesting ITR.

8. 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 (as specified in the
ECM-Encapsulated Map-Reply) used by the Map-Server and verifies
the integrity of the Map-Reply.

6. 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.

These specifications use an HMAC in various places (as described in
the following). The HMAC function AUTH-HMAC-SHA-256-128 [RFC6234]
MUST be supported in LISP-SEC implementations. LISP-SEC deployments
SHOULD use the AUTH-HMAC-SHA-256-128 HMAC function, except when
communicating with older implementations that only support AUTH-HMAC-
SHA-1-96 [RFC2104].

6.1. Encapsulated Control Message LISP-SEC Extensions

LISP-SEC uses the ECM defined in [RFC9301] with the S-bit set to 1 to
indicate that the LISP header includes Authentication Data (AD). The
format of the LISP-SEC ECM AD is defined in Figure 1. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ECM AD Type | Unassigned | Requested HMAC ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+\
| OTK Length | Key ID | OTK Wrap. ID | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| One-Time-Key Preamble ... | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+OTK-AD
| ... One-Time-Key Preamble | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
~ One-Time Key (128 bits) ~/
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ <---+
| EID-AD Length | KDF ID | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Record Count |E| Unassigned | EID HMAC ID |EID-AD
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+\ |
| Unassigned | EID mask-len | EID-AFI | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Rec |
~ EID-Prefix ... ~ | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+/ |
~ EID HMAC ~ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ <---+

Figure 1: LISP-SEC ECM Authentication Data

ECM AD Type: 1 (LISP-SEC Authentication Data). See Section 8.

Unassigned: Set to 0 on transmission and ignored on receipt.

Requested HMAC ID: The HMAC algorithm, which will be used to protect
the mappings, requested by the ITR. Permitted values are
registered in the LISP-SEC Authentication Data HMAC ID (see
Section 8.3). Refer to Section 6.4 for more details.

OTK Length: The length (in bytes) of the OTK Authentication Data
(OTK-AD), which contains the OTK Preamble and the OTK.

Key ID: The identifier of the pre-shared secret shared by an ITR and
the Map-Resolver, and by the Map-Server and an ETR. Per-message
keys are derived from the pre-shared secret to encrypt,
authenticate the origin, and protect the integrity of the OTK.
The Key ID allows to rotate between multiple pre-shared secrets in
a nondisruptive way.

OTK Wrapping ID (OTK Wrap. ID): The identifier of the Key Derivation
Function and of the key wrapping algorithm used to encrypt the
One-Time-Key. Permitted values are registered in the LISP-SEC
Authentication Data Key Wrap ID (see Section 8.4). Refer to
Section 6.5 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 a Map-Resolver, the OTK Preamble is set to
0x0000000000000000 (64 bits). See Section 6.5.1 for details.

One-Time-Key: The OTK wrapped as specified by OTK Wrapping ID. See
Section 6.5 for details.

EID-AD Length: Length (in bytes) of the EID Authentication Data
(EID-AD). The ITR MUST set the 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 bytes long, plus the length of
the AFI-encoded EID-Prefix.

KDF ID: Identifier of the Key Derivation Function used to derive the
MS-OTK. Permitted values are registered in the LISP-SEC
Authentication Data Key Derivation Function ID (see Section 8.5).
Refer to Section 6.7 for more details.

Record Count: As defined in Section 5.2 of [RFC9301].

E: ETR-Cant-Sign bit. If this bit is set to 1, it signals to the
ITR that at least one of the ETRs that is authoritative for the
EID-Prefixes of this Map-Reply has not enabled LISP-SEC. Only a
Map-Server can set this bit. See Section 6.7 for more details.

Unassigned: 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 the Map-Server
that computed the EID-Prefix HMAC. See Section 6.7.1 for more
details.

EID mask-len: As defined in Section 5.2 of [RFC9301].

EID-AFI: As defined in Section 5.2 of [RFC9301].

EID-Prefix: As defined in Section 5.2 of [RFC9301].

EID HMAC: HMAC of the EID-AD computed and inserted by a Map-Server.
See Section 6.7.1 for more details.

6.2. Map-Reply LISP-SEC Extensions

LISP-SEC uses the Map-Reply defined in [RFC9301], 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 Figure 2. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MR AD Type | Unassigned |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ <---+
| EID-AD Length | KDF ID | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Record Count | Unassigned | EID HMAC ID |EID-AD
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+\ |
| Unassigned | EID mask-len | EID-AFI | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Rec |
~ EID-Prefix ... ~ | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+/ |
~ EID HMAC ~ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ <---+
| PKT-AD Length | PKT HMAC ID |\
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
~ PKT HMAC ~PKT-AD
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+/

Figure 2: LISP-SEC Map-Reply Authentication Data

MR AD Type: 1 (LISP-SEC Authentication Data). See Section 8.

EID-AD Length: Length (in bytes) of the EID-AD (see Section 6.1).

KDF ID: Identifier of the Key Derivation Function used to derive MS-
OTK (see Section 6.1).

Record Count: The number of records in this Map-Reply message (see
Section 6.1).

Unassigned: 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 6.1).

EID mask-len: Mask length for EID-Prefix (see Section 6.1).

EID-AFI: See Section 6.1.

EID-Prefix: See Section 6.1.

EID HMAC: See Section 6.1.

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 (see Section 6.5).

PKT HMAC: HMAC of the whole Map-Reply packet to protect its
integrity, including the LISP-SEC Authentication Data (from the
'Map-Reply Type' field to the 'PKT HMAC' field), which allow
message authentication.

6.3. Map-Register LISP-SEC Extensions

The S-bit in the Map-Register message (see [RFC9301]) 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.

6.4. ITR Processing: Generating a Map-Request

Upon creating a Map-Request, the ITR generates a random ITR-OTK that
is stored locally, until the corresponding Map-Reply is received (see
Section 6.9), together with the nonce generated as specified in
[RFC9301].

The ITR MAY use the 'KDF ID' 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 6.7). A KDF value of NOPREF (0) may be used to specify
that the ITR has no preferred KDF ID.

ITR-OTK confidentiality and integrity protection MUST be provided in
the path between the ITR and the Map-Resolver. This can be achieved
either by encrypting the ITR-OTK with the pre-shared secret known to
the ITR and the Map-Resolver (see Section 6.5) or by enabling DTLS
[RFC9147] between the ITR and the Map-Resolver.

The Map-Request (as defined in [RFC9301]) MUST be encapsulated as a
LISP Control Message in an ECM, with the S-bit set to 1, to indicate
the presence of Authentication Data. Such a message is also called a
"Protected Map-Request" in this memo.

The ITR-OTK is wrapped with the algorithm specified by the 'OTK
Wrapping ID' field. See Section 6.5 for further details on OTK
encryption. If the NULL-KEY-WRAP-128 algorithm (see Section 8.4) is
selected, and no other encryption mechanism (e.g., DTLS) is enabled
in the path between the ITR and the Map-Resolver, the Map-Request
MUST be dropped, and an appropriate log action SHOULD be taken.
Implementations may include mechanisms (which are beyond the scope of
this document) to avoid log resource exhaustion attacks.

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. A HMAC ID value of
NONE (0) MAY be used to specify that the ITR has no preferred HMAC
ID.

The 'KDF ID' field specifies the suggested Key Derivation Function to
be used by the Map-Server to derive the MS-OTK. A KDF value of NONE
(0) may be used to specify that the ITR has no preferred KDF ID.

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.

If the ITR is directly connected to a Mapping System, such as
LISP+ALT [RFC6836], it performs the functions of both the ITR and the
Map-Resolver, forwarding the Protected Map-Request as described in
Section 6.6.

The processing performed by Proxy ITRs (PITRs) is equivalent to the
processing of an ITR; hence, the procedure described above applies.

6.5. Encrypting and Decrypting an OTK

MS-OTK confidentiality and integrity protection MUST be provided in
the path between the Map-Server and the ETR. This can be achieved
either by enabling DTLS between the Map-Server and the ETR or by
encrypting the MS-OTK with the pre-shared secret known to the Map-
Server and the ETR [RFC9301].

Similarly, ITR-OTK confidentiality and integrity protection MUST be
provided in the path between the ITR and the Map-Resolver. This can
be achieved either by enabling DTLS between the Map-Server and the
ITR or by encrypting the ITR-OTK with the pre-shared secret known to
the ITR and the Map-Resolver. The ITR/Map-Resolver pre-shared key is
similar to the Map-Server/ETR pre-shared key.

This section describes OTK processing in the ITR/Map-Resolver path,
as well as in the Map-Server/ETR path.

It's important to note that, to prevent ETR's overclaiming attacks,
the ITR/Map-Resolver pre-shared secret MUST be independent from the
Map-Server/ETR pre-shared secret.

The OTK is wrapped using the algorithm specified in the 'OTK Wrapping
ID' field. This field identifies both the:

* Key Encryption Algorithm used to encrypt the wrapped OTK and

* Key Derivation Function used to derive a per-message encryption
key.

Implementations of this specification MUST support the OTK Wrapping
ID AES-KEY-WRAP-128+HKDF-SHA256, which specifies the use of the HKDF-
SHA256 Key Derivation Function specified in [RFC5869] to derive a
per-message encryption key (per-msg-key), as well as the AES-KEY-
WRAP-128 key wrap algorithm used to encrypt a 128-bit OTK, according
to [RFC3394].

Implementations of this specification MUST support OTK Wrapping NULL-
KEY-WRAP-128. NULL-KEY-WRAP-128 is used to carry an unencrypted
128-bit OTK, with a 64-bit preamble set to 0x0000000000000000 (64
bits).

The key wrapping process for OTK Wrapping ID AES-KEY-WRAP-128+HKDF-
SHA256 is described below:

1. The KDF and key wrap algorithms are identified by the value of
the 'OTK Wrapping ID' field. The initial values are documented
in Table 5.

2. If the NULL-KEY-WRAP-128 algorithm (see Section 8.4) is selected
and DTLS is not enabled, the Map-Request MUST be dropped and an
appropriate log action SHOULD be taken. Implementations may
include mechanisms (which are beyond the scope of this document)
to avoid log resource exhaustion attacks.

3. The pre-shared secret used to derive the per-msg-key is
represented by PSK[Key ID], which is the pre-shared secret
identified by the 'Key ID'.

4. The 128-bit-long per-message encryption key is computed as:

per-msg-key = KDF( nonce + s + PSK[Key ID] )

where the nonce is the value in the 'Nonce' field of the Map-
Request, 's' is the string "OTK-Key-Wrap", and the operation'+'
just indicates string concatenation.

5. The per-msg-key is then used to wrap the OTK with AES-KEY-WRAP-
128, as specified in Section 2.2.1 of [RFC3394]. The AES Key
Wrap Initialization Value MUST be set to 0xA6A6A6A6A6A6A6A6 (64
bits). The output of the AES key wrap operation is 192 bits
long. The most significant 64 bits are copied in the 'One-Time
Key Preamble' field, while the 128 least 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
operation is equal to 0xA6A6A6A6A6A6A6A6. If this verification
fails, the receiver MUST discard the entire message.

6.5.1. Unencrypted OTK

However, when DTLS is enabled, the OTK MAY be sent unencrypted as
transport layer security is providing confidentiality and integrity
protection.

When a 128-bit OTK is sent unencrypted, the OTK Wrapping ID is set to
NULL_KEY_WRAP_128, and the OTK Preamble is set to 0x0000000000000000
(64 bits).

6.6. Map-Resolver Processing

Upon receiving a Protected Map-Request, the Map-Resolver decapsulates
the ECM. The ITR-OTK, if encrypted, is decrypted as specified in
Section 6.5.

Protecting the confidentiality of the ITR-OTK and, in general, the
security of how the Map-Request is handed by the Map-Resolver to the
Map-Server is specific to the particular Mapping System used and is
outside of the scope of this memo.

In Mapping Systems where the Map-Server is compliant with [RFC9301],
the Map-Resolver originates a new ECM header with the S-bit set,
which contains the unencrypted ITR-OTK, as specified in Section 6.5,
and the other data derived from the ECM Authentication Data of the
received Encapsulated Map-Request.

The Map-Resolver then forwards to the Map-Server the received Map-
Request, which is encapsulated in the new ECM header that includes
the newly computed 'Authentication Data' fields.

6.7. Map-Server Processing

Upon receiving a Protected Map-Request, the Map-Server processes it
according to the setting of the S-bit and the P-bit in the Map-
Register received from the ETRs authoritative for that prefix, as
described below.

While processing the Map-Request, the Map-Server can overwrite the
'KDF ID' field if it does not support the KDF ID recommended by the
ITR. Processing of the Map-Request MUST proceed in the order
described in the table below, applying the process corresponding to
the first rule that matches the conditions indicated in the first
column:

+=================+==============================================+
| Matching | Processing |
| Condition | |
+=================+==============================================+
| 1. At least | The Map-Server MUST generate a LISP-SEC- |
| one of the ETRs | protected Map-Reply, as specified in |
| authoritative | Section 6.7.2. The ETR-Cant-Sign E-bit in |
| for the EID- | the EID Authentication Data (EID-AD) MUST be |
| Prefix included | set to 0. |
| in the Map- | |
| Request | |
| registered with | |
| the P-bit set | |
| to 1 | |
+-----------------+----------------------------------------------+
| 2. At least | The Map-Server MUST generate a LISP-SEC- |
| one of the ETRs | protected Encapsulated Map-Request (as |
| authoritative | specified in Section 6.7.1) to be sent to |
| for the EID- | one of the authoritative ETRs that |
| Prefix included | registered with the S-bit set to 1 (and the |
| in the Map- | P-bit set to 0). If there is at least one |
| Request | ETR that registered with the S-bit set to 0, |
| registered with | the ETR-Cant-Sign E-bit of the EID-AD MUST |
| the S-bit set | be set to 1 to signal the ITR that a non- |
| to 1 | LISP-SEC Map-Request might reach additional |
| | ETRs that have LISP-SEC disabled. |
+-----------------+----------------------------------------------+
| 3. All the | The Map-Server MUST send a Negative Map- |
| ETRs | Reply protected with LISP-SEC, as described |
| authoritative | in Section 6.7.2. The ETR-Cant-Sign E-bit |
| for the EID- | MUST be set to 1 to signal the ITR that a |
| Prefix included | non-LISP-SEC Map-Request might reach |
| in the Map- | additional ETRs that have LISP-SEC disabled. |
| Request | |
| registered with | |
| the S-bit set | |
| to 0 | |
+-----------------+----------------------------------------------+

Table 1: Map-Request Processing

In this way, the ITR that sent a LISP-SEC-protected Map-Request
always receives a LISP-SEC-protected Map-Reply. However, the ETR-
Cant-Sign E-bit set to 1 specifies that a non-LISP-SEC Map-Request
might reach additional ETRs that have LISP-SEC disabled. This
mechanism allows the ITR to downgrade to non-LISP-SEC requests, which
does not protect against threats described in Section 4.

6.7.1. Generating a LISP-SEC-Protected Encapsulated Map-Request

The Map-Server decapsulates the ECM and generates new ECM
Authentication Data. The Authentication Data includes the OTK-AD and
the EID-AD, which contains EID-Prefix authorization information that
are eventually received by 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 by
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.

The Map-Request MUST be encapsulated in an ECM, with the S-bit set to
1, to indicate the presence of Authentication Data.

MS-OTK is wrapped with the algorithm specified by the 'OTK Wrapping
ID' field. See Section 6.5 for further details on OTK encryption.
If the NULL-KEY-WRAP-128 algorithm is selected and DTLS is not
enabled in the path between the Map-Server and the ETR, the Map-
Request MUST be dropped and an appropriate log action SHOULD be
taken.

In the EID-AD, 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 MUST cover 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, which contains the OTK-AD, the EID-AD, and the received Map-
Request to an authoritative ETR as specified in [RFC9301].

6.7.2. Generating a Proxy Map-Reply

A LISP-SEC proxy Map-Reply is generated according to [RFC9301], with
the Map-Reply S-bit set to 1. The Map-Reply includes the
Authentication Data that contains the EID-AD computed as specified in
Section 6.7.1, as well as the PKT-AD computed as specified in
Section 6.8.

6.8. ETR Processing

Upon receiving an ECM-Encapsulated Map-Request with the S-bit set,
the ETR decapsulates the ECM. The 'OTK' field, if encrypted, is
decrypted as specified in Section 6.5 to obtain the unencrypted MS-
OTK.

The ETR then generates a Map-Reply as specified in [RFC9301] 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 HMAC operation MUST cover the entire Map-Reply,
where the 'PKT HMAC' field MUST be set to 0 before the computation.

Finally, the ETR sends the Map-Reply to the requesting ITR as
specified in [RFC9301].

6.9. ITR Processing: Receiving a Map-Reply

In response to a Protected Map-Request, an ITR expects a Map-Reply
with the S-bit set to 1, including an EID-AD and a PKT-AD. The ITR
MUST discard the Map-Reply otherwise.

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. After processing the Map-Reply, the ITR
MUST discard the <nonce,ITR-OTK> pair associated to the Map-Reply.

The integrity of the EID-AD is verified using the ITR-OTK (stored
locally for the duration of this exchange) to recompute the HMAC of
the EID-AD using the algorithm specified in the 'EID HMAC ID' field.
If the ITR did indicate a Requested HMAC ID in the Map-Request and
the PKT HAMC ID in the corresponding Map-Reply is different, or if
the ITR did not indicate a Requested HMAC ID in the Map-Request and
the PKT HMAC ID in the corresponding Map-Reply is not supported, then
the ITR MUST discard the Map-Reply and send, according to rate-
limitation policies defined in [RFC9301], a new Map-Request with a
different 'Requested HMAC ID' field, according to ITR's local policy.
The scope of the HMAC operation covers the entire EID-AD, from the
'EID-AD Length' field to the 'EID HMAC' field.

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 ITR did indicate a recommended KDF ID in
the Map-Request and the KDF ID in the corresponding Map-Reply is
different or if the ITR did not indicate a recommended KDF ID in the
Map-Request and the KDF ID in the corresponding Map-Reply is not
supported, then the ITR MUST discard the Map-Reply and send,
according to rate-limitation policies defined in [RFC9301], a new
Map-Request with a different KDF ID, according to ITR's local policy.
The Key Derivation Function HKDF-SHA256 MUST be supported in LISP-SEC
implementations. LISP-SEC deployments SHOULD use the HKDF-SHA256
HKDF function, unless older implementations using HKDF-SHA1-128 are
present in the same deployment. Without consistent configuration of
involved entities, extra delays may be experienced. However, since
HKDF-SHA1-128 and HKDF-SHA256 are supported, the process will
eventually converge.

The derived MS-OTK is then used to recompute 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
MUST discard the Map-Reply and send, according to rate-limitation
policies defined in [RFC9301], a new Map-Request with a different
Requested HMAC ID, according to ITR's local policy or until all HMAC
IDs supported by the ITR have been attempted. When the 'PKT HMAC ID'
field does not match the Requested HMAC ID, it is not possible to
validate the Map-Reply.

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 Map-Cache, as described
in [RFC9301]. An example of Map-Reply record validation is provided
in Section 6.9.1.

[RFC9301] allows ETRs to send Solicit-Map-Requests (SMRs) directly to
the ITR. The corresponding SMR-invoked Map-Request will be sent
through the Mapping System, hence, secured with the specifications of
this memo if in use. If an ITR accepts Map-Replies piggybacked in
Map-Requests and its content is not already present in its EID-to-
RLOC Map-Cache, it MUST send a Map-Request over the Mapping System in
order to verify its content with a secured Map-Reply before using the
content.

6.9.1. 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 action SHOULD be taken and the
Map-Reply MUST NOT be processed any further. Implementations may
include mechanisms (which are beyond the scope of this document) to
avoid log resource exhaustion attacks. 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-Prefixes
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; otherwise, a log
action MUST be taken and the EID-Record MUST be discarded.
Implementations may include mechanisms (which are beyond the scope of
this document) to avoid log resource exhaustion attacks.

For instance, the Map-Reply payload contains 3 mapping record EID-
Prefixes:

2001:db8:102::/48

2001:db8:103::/48

2001:db8:200::/40

The EID-AD contains two EID-Prefixes:

2001:db8:103::/48

2001:db8:203::/48

The EID-Record with EID-Prefix 2001:db8:102::/48 is not eligible to
be used by the ITR, since it is not included in any of the EID-ADs
signed by the Map-Server. A log action MUST be taken, and the EID-
Record MUST be discarded. Implementations may include mechanisms
(which are beyond the scope of this document) to avoid log resource
exhaustion attacks.

The EID-Record with EID-Prefix 2001:db8:103::/48 is eligible to be
used by the ITR because it matches the second EID-Prefix contained in
the EID-AD.

The EID-Record with EID-Prefix 2001:db8:200::/40 is not eligible to
be used by the ITR, since it is not included in any of the EID-ADs
signed by the Map-Server. A log action MUST be taken and the EID-
Record MUST be discarded. Implementations may include mechanisms
(which are beyond the scope of this document) to avoid log resource
exhaustion attacks. In this last example, the ETR is trying to over
claim the EID-Prefix 2001:db8:200::/40, but the Map-Server authorized
only 2001:db8:203::/48; hence, the EID-Record is discarded.

7. Security Considerations

This document extends the LISP control plane defined in [RFC9301];
hence, its security considerations apply to this document as well.

7.1. Mapping System Security

The LISP-SEC threat model described in Section 4 assumes that the
LISP Mapping System is working properly and delivers Map-Request
messages to a Map-Server that is authoritative for the requested EID.

It is assumed that the Mapping System ensures the confidentiality of
the OTK and the integrity of the Map-Reply data. However, how the
LISP Mapping System is secured is out of the scope of this document.

Similarly, 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.

7.2. 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.

7.3. 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.

7.4. Deploying LISP-SEC

Those deploying LISP-SEC according to this memo should carefully
weigh how the LISP-SEC threat model applies to their particular use
case or deployment. If they decide to ignore a particular
recommendation, they should make sure the risk associated with the
corresponding threats is well understood.

As an example, in certain other deployments, attackers may be very
sophisticated and force the deployers to enforce very strict policies
in terms of HMAC algorithms accepted by an ITR.

Similar considerations apply to the entire LISP-SEC threat model and
should guide the deployers and implementors whenever they encounter
the key word SHOULD across this memo.

7.5. Shared Keys Provisioning

Provisioning of the keys shared between ITR and Map-Resolver pairs as
well as between ETR and Map-Server pairs should be performed via an
orchestration infrastructure, and is out of the scope of this memo.
It is recommended that both shared keys be refreshed at periodical
intervals to address key aging or attackers gaining unauthorized
access to the shared keys. Shared keys should be unpredictable
random values.

7.6. Replay Attacks

An attacker can capture a valid Map-Request and/or Map-Reply and
replay it; however, once the ITR receives the original Map-Reply, the
<nonce,ITR-OTK> pair stored at the ITR will be discarded. If a
replayed Map-Reply arrives at the ITR, there is no <nonce,ITR-OTK>
that matches the incoming Map-Reply and the replayed Map-Reply will
be discarded.

In the case of a replayed Map-Request, the Map-Server, Map-Resolver,
and ETR will have to do a LISP-SEC computation. This is equivalent,
in terms of resources, to a valid LISP-SEC computation and, beyond a
risk of DoS attack, an attacker does not obtain any additional
effect, since the corresponding Map-Reply is discarded as previously
explained.

7.7. Message Privacy

DTLS [RFC9147] SHOULD be used (conforming to [RFC7525]) to provide
communication privacy and to prevent eavesdropping, tampering, or
message forgery to the messages exchanged between the ITR, Map-
Resolver, Map-Server, and ETR, unless the OTK is encrypted in another
way, e.g., using a pre-shared secret. DTLS has the responder be
verified by the initiator, which enables an ITR to authenticate the
Map-Resolver and the Map-Server to authenticate the responding ETR.

7.8. Denial-of-Service and Distributed Denial-of-Service Attacks

LISP-SEC mitigates the risks of DoS and DDoS attacks by protecting
the integrity and authenticating the origin of the Map-Request/Map-
Reply messages and by preventing malicious ETRs from overclaiming
EID-Prefixes that could redirect traffic directed to a potentially
large number of hosts.

8. IANA Considerations

IANA has created the subregistries listed in the following sections
in the "Locator/ID Separation Protocol (LISP) Parameters" registry.

For all of the subregistries, new values are assigned according to
the Specification Required policy defined in [RFC8126]. Expert
Review should assess the security properties of newly added functions
so that encryption robustness remains strong. For instance, at the
time of this writing, the use of SHA-256-based functions is
considered to provide sufficient protection. Consultation with
security experts may be needed.

8.1. ECM AD Type Registry

IANA has created the "LISP ECM Authentication Data Types" registry
with values 0-255 for use in the ECM LISP-SEC extensions (see
Section 6.1). Initial allocations are shown in Table 2.

+==================+========+============+
| Name | Number | Defined in |
+==================+========+============+
| Reserved | 0 | RFC 9303 |
+------------------+--------+------------+
| LISP-SEC-ECM-EXT | 1 | RFC 9303 |
+------------------+--------+------------+

Table 2: LISP ECM Authentication Data
Types

Values 2-255 are unassigned.

8.2. Map-Reply AD Types Registry

IANA has created the "LISP Map-Reply Authentication Data Types"
registry with values 0-255 for use in the Map-Reply LISP-SEC
extensions (see Section 6.2). Initial allocations are shown in
Table 3.

+=================+========+============+
| Name | Number | Defined in |
+=================+========+============+
| Reserved | 0 | RFC 9303 |
+-----------------+--------+------------+
| LISP-SEC-MR-EXT | 1 | RFC 9303 |
+-----------------+--------+------------+

Table 3: Map-Reply Authentication
Data Types

Values 2-255 are unassigned.

8.3. HMAC Functions

IANA is requested to create the "LISP-SEC Preferred Authentication
Data HMAC IDs" registry with values 0-65535 for use as Requested HMAC
IDs, EID HMAC IDs, and PKT HMAC IDs in the LISP-SEC Authentication
Data. Initial allocations are shown in Table 4.

+=======================+========+============+
| Name | Number | Defined in |
+=======================+========+============+
| NOPREF | 0 | RFC 9303 |
+-----------------------+--------+------------+
| AUTH-HMAC-SHA-1-96 | 1 | [RFC2104] |
+-----------------------+--------+------------+
| AUTH-HMAC-SHA-256-128 | 2 | [RFC6234] |
+-----------------------+--------+------------+

Table 4: LISP-SEC Preferred Authentication
Data HMAC IDs

Values 3-65535 are unassigned.

8.4. Key Wrap Functions

IANA has created the "LISP-SEC Authentication Data Key Wrap IDs"
registry with values 0-65535 for use as OTK key wrap algorithm IDs in
the LISP-SEC Authentication Data. Initial allocations are shown in
Table 5.

+==============================+======+=========+=========+=========+
| Name |Number|Key Wrap |KDF |Reference|
+==============================+======+=========+=========+=========+
| Reserved | 0 |None |None |RFC 9303 |
+------------------------------+------+---------+---------+---------+
| NULL-KEY-WRAP-128 | 1 |RFC 9303 |None |RFC 9303 |
+------------------------------+------+---------+---------+---------+
| AES-KEY-WRAP-128+HKDF-SHA256 | 2 |[RFC3394]|[RFC4868]|RFC 9303 |
+------------------------------+------+---------+---------+---------+

Table 5: LISP-SEC Authentication Data Key Wrap IDs

Values 3-65535 are unassigned.

8.5. Key Derivation Functions

IANA has created the "LISP-SEC Authentication Data Key Derivation
Function IDs" registry with values 0-65535 for use as KDF IDs.
Initial allocations are shown in Table 6.

+===============+========+===========+
| Name | Number | Reference |
+===============+========+===========+
| NOPREF | 0 | RFC 9303 |
+---------------+--------+-----------+
| HKDF-SHA1-128 | 1 | [RFC5869] |
+---------------+--------+-----------+
| HKDF-SHA256 | 2 | [RFC5869] |
+---------------+--------+-----------+

Table 6: LISP-SEC Authentication
Data Key Derivation Function IDs

Values 3-65535 are unassigned.

9. References

9.1. Normative References

[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104,
DOI 10.17487/RFC2104, February 1997,
<https://www.rfc-editor.org/info/rfc2104>.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.

[RFC3394] Schaad, J. and R. Housley, "Advanced Encryption Standard
(AES) Key Wrap Algorithm", RFC 3394, DOI 10.17487/RFC3394,
September 2002, <https://www.rfc-editor.org/info/rfc3394>.

[RFC4868] Kelly, S. and S. Frankel, "Using HMAC-SHA-256, HMAC-SHA-
384, and HMAC-SHA-512 with IPsec", RFC 4868,
DOI 10.17487/RFC4868, May 2007,
<https://www.rfc-editor.org/info/rfc4868>.

[RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
Key Derivation Function (HKDF)", RFC 5869,
DOI 10.17487/RFC5869, May 2010,
<https://www.rfc-editor.org/info/rfc5869>.

[RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and SHA-based HMAC and HKDF)", RFC 6234,
DOI 10.17487/RFC6234, May 2011,
<https://www.rfc-editor.org/info/rfc6234>.

[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <https://www.rfc-editor.org/info/rfc7525>.

[RFC7835] Saucez, D., Iannone, L., and O. Bonaventure, "Locator/ID
Separation Protocol (LISP) Threat Analysis", RFC 7835,
DOI 10.17487/RFC7835, April 2016,
<https://www.rfc-editor.org/info/rfc7835>.

[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.

[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.

[RFC9147] Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version
1.3", RFC 9147, DOI 10.17487/RFC9147, April 2022,
<https://www.rfc-editor.org/info/rfc9147>.

[RFC9300] Farinacci, D., Fuller, V., Meyer, D., Lewis, D., and A.
Cabellos, Ed., "The Locator/ID Separation Protocol
(LISP)", RFC 9300, DOI 10.17487/RFC9300, October 2022,
<https://www.rfc-editor.org/info/rfc9300>.

[RFC9301] Farinacci, D., Maino, F., Fuller, V., and A. Cabellos,
Ed., "Locator/ID Separation Protocol (LISP) Control
Plane", RFC 9301, DOI 10.17487/RFC9301, October 2022,
<https://www.rfc-editor.org/info/rfc9301>.

9.2. Informative References

[RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker,
"Randomness Requirements for Security", BCP 106, RFC 4086,
DOI 10.17487/RFC4086, June 2005,
<https://www.rfc-editor.org/info/rfc4086>.

[RFC6836] Fuller, V., Farinacci, D., Meyer, D., and D. Lewis,
"Locator/ID Separation Protocol Alternative Logical
Topology (LISP+ALT)", RFC 6836, DOI 10.17487/RFC6836,
January 2013, <https://www.rfc-editor.org/info/rfc6836>.

Acknowledgments

The authors would like to acknowledge Luigi Iannone, 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.

Authors' Addresses

Fabio Maino
Cisco Systems
San Jose, CA
United States of America
Email: [email protected]

Vina Ermagan
Google, Inc.
1600 Amphitheatre Parkway
Mountain View, CA 94043
United States of America
Email: [email protected]

Albert Cabellos
Universitat Politecnica de Catalunya
c/ Jordi Girona s/n
08034 Barcelona
Spain
Email: [email protected]

Damien Saucez
Inria
2004 route des Lucioles - BP 93
Sophia Antipolis
France
Email: [email protected]