Locator/ID Separation Protocol Security (LISP-SEC)

Introduction The Locator/ID Separation Protocol (LISP) 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 , is built on top of the LISP threat model defined in , 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 . 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 .

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 when, and only when, they appear in all capitals, as shown here.

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 , 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 .

LISP-SEC Threat Model LISP-SEC addresses the control plane threats, described in Sections and of , 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 , 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.

Protocol Operations The goal of the security mechanisms defined in 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 to address the threats described in by leveraging the trust relationships existing among the LISP entities participating in the exchange of the Map-Request/Map-Reply messages. Those trust relationships (see also and ) are used to securely distribute, as described in , 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) 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., ) 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.

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:

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.
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.
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.
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.
If the Map-Server is acting in proxy mode, as specified in , 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 .
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 .
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.
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.

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 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 .

Encapsulated Control Message LISP-SEC Extensions LISP-SEC uses the ECM defined in 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 . OTK-AD stands for One-Time Key Authentication Data and EID-AD stands for EID Authentication Data.

LISP-SEC ECM Authentication Data

ECM AD Type:: 1 (LISP-SEC Authentication Data). See .
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 ). Refer to 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 ). Refer to 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 for details.
One-Time-Key:: The OTK wrapped as specified by OTK Wrapping ID. See 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 ). Refer to for more details.
Record Count:: As defined in .
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 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 for more details.
EID mask-len:: As defined in .
EID-AFI:: As defined in .
EID-Prefix:: As defined in .
EID HMAC:: HMAC of the EID-AD computed and inserted by a Map-Server. See for more details.

Map-Reply LISP-SEC Extensions LISP-SEC uses the Map-Reply defined in , 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 . PKT-AD is the Packet Authentication Data that covers the Map-Reply payload.

LISP-SEC Map-Reply Authentication Data

MR AD Type:: 1 (LISP-SEC Authentication Data). See .
EID-AD Length:: Length (in bytes) of the EID-AD (see ).
KDF ID:: Identifier of the Key Derivation Function used to derive MS-OTK (see ).
Record Count:: The number of records in this Map-Reply message (see ).
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 ).
EID mask-len:: Mask length for EID-Prefix (see ).
EID-AFI:: See .
EID-Prefix:: See .
EID HMAC:: See .
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 ).
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.

Map-Register LISP-SEC Extensions The S-bit in the Map-Register message (see ) 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.

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 ), together with the nonce generated as specified in . 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 ). 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 ) or by enabling DTLS between the ITR and the Map-Resolver. The Map-Request (as defined in ) 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 for further details on OTK encryption. If the NULL-KEY-WRAP-128 algorithm (see ) 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 , it performs the functions of both the ITR and the Map-Resolver, forwarding the Protected Map-Request as described in . The processing performed by Proxy ITRs (PITRs) is equivalent to the processing of an ITR; hence, the procedure described above applies.

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 . 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 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 . 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:

The KDF and key wrap algorithms are identified by the value of the 'OTK Wrapping ID' field. The initial values are documented in .
If the NULL-KEY-WRAP-128 algorithm (see ) 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.
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'.
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.
The per-msg-key is then used to wrap the OTK with AES-KEY-WRAP-128, as specified in . 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.

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).

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 . 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 , the Map-Resolver originates a new ECM header with the S-bit set, which contains the unencrypted ITR-OTK, as specified in , 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.

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: Map-Request Processing

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

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 .

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 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 .

Generating a Proxy Map-Reply A LISP-SEC proxy Map-Reply is generated according to , 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 , as well as the PKT-AD computed as specified in .

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 to obtain the unencrypted MS-OTK. The ETR then generates a Map-Reply as specified in 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 .

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 , 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 , 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 , 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 . An example of Map-Reply record validation is provided in . 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.

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.

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

Mapping System Security The LISP-SEC threat model described in 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.

Random Number Generation The ITR-OTK MUST be generated by a properly seeded pseudo-random (or strong random) source. See for advice on generating security-sensitive random data.

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.

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.

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.

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.

Message Privacy DTLS SHOULD be used (conforming to ) 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.

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.

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 . 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.

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 ). Initial allocations are shown in . LISP ECM Authentication Data Types

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

Values 2-255 are unassigned.

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 ). Initial allocations are shown in . Map-Reply Authentication Data Types

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

Values 2-255 are unassigned.

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 . LISP-SEC Preferred Authentication Data HMAC IDs

Name	Number	Defined in
NOPREF	0	RFC 9303
AUTH-HMAC-SHA-1-96	1
AUTH-HMAC-SHA-256-128	2

Values 3-65535 are unassigned.

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 . LISP-SEC Authentication Data Key Wrap IDs

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			RFC 9303

Values 3-65535 are unassigned.

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 . LISP-SEC Authentication Data Key Derivation Function IDs

Name	Number	Reference
NOPREF	0	RFC 9303
HKDF-SHA1-128	1
HKDF-SHA256	2

Values 3-65535 are unassigned.

References Normative References Locator/ID Separation Protocol (LISP) Control Plane The Locator/ID Separation Protocol (LISP) Informative References

Acknowledgments The authors would like to acknowledge , , , , , , , and for their valuable suggestions provided during the preparation of this document.