[lisp] LISP-SEC review (finally)

[Luigi Iannone <[e-mail]>]

Dear Authors of the LISP-SEC document,

hereafter my review of the document.
This was long overdue, sorry for being so late.

I really like the solution and the majority of my comments are just clarification questions.
Let me know if my comments are clear.

ciao

L.



> 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).  
I find the above sentence confusing. Wouldn’t be better to specify that we are talking about IP addresses?

> 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 [RFC7835].
> 
>    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.  

I would put s forward reference to section 3 stating that the reader will find details about the threat model.

> 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.

Why are you considering ITR-OTK and MS-OTK sub-terms? 
I would elevate them at full terms, hence avoiding spacing and indentation.

> 
>       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.
> 
Why are you re-defining ECM? 
You do not specify other packets, e.g., Map-Reply, so why ECM?
I would drop it.


>       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.


Why are you considering OTK-AD, EID-AD, and PKT-AD sub-terms? 
I would elevate them at full terms, hence avoiding spacing and indentation.


> 
>    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 [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 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.
LISP-SEC does not require OTK confidentiality in the mapping system. This should be discussed here.


> 
>    According to the threat model described in [RFC7835] 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
You did not define HMAC acronym. Please define and add a reference.

>       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 
Why not using “MUST”???
Are you suggesting that a different way to provide confidentiality can be used (e.g. a different shared key)???
If yes, please state so.

Or are you suggesting that no encryption at all is used? But this means not providing confidentiality…
Can you clarify?

(this very same comment will appear several time in this review)
> 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 
This “should” should be a “SHOULD”  (sorry for the cacophony…)

Why not using “MUST”???
Are you suggesting that a different way to provide confidentiality can be used (e.g. a different shared key)???
If yes, please state so.

Or are you suggesting that no encryption at all is used? But this means not providing confidentiality…
Can you clarify?

> 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                           ~     |
> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ <—+
I think that “rec” is mis-aligned and should be shifted one character upward.

> 
>                      LISP-SEC ECM Authentication Data
> 
>       AD Type: 1 (LISP-SEC Authentication Data)
This is the first document starting to allocate values to the "AD Type” value. 
Why not asking IANA to create a registry??
(to be done in the IANA Considerations Section) 



> 
>       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. 
I am not sure I understand the rationale of this “SHOULD”. If for any reason the ITR does not indicate the KDF ID what are the consequences?
Is the MS free to choose the algorithm? This should be clarified.

>  The Map-
>       Server can overwrite the KDF ID if it does not support the KDF ID
>       recommended by the ITR.  
What happens if the MS will choose a KDF ID not supported by the ITR?
Can you clarify how to solve this situation or explain why this will never happen?

> 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)
Shouldn’t this be a different value? This AD  format is different from the one described in section 5.1!
Another reason to ask IANA for a registry….


> 
>       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.
“Location Data” is something nowhere defined. Can you clarify what do you mean?


> 
>       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.  
I would better explain that this document is allocating a bit marked as reserved in 6830.
Furthermore, at the cost of being redundant, I would put the packet format highlighting the position of the bit so that there is no confusion whatsoever.

> 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,
In section 4 you seem to suggest that this is not the only way to protect the OTK (see my comment).
Here instead you suggest that a shared key is the only way.
>  the ITR-OTK
>    confidentiality SHOULD be protected by wrapping the ITR-OTK with the
>    algorithm specified by the OTK Encryption ID field. 
Not clear what this “SHOULD” refers to.
IS the SHOULD related to the fact to encrypt the OTK? The ITR SHOULD encrypt.
Or the choice of the algorithm? The ITR SHOULD use the algorithm specified by the OTK Encryption ID?
The second case looks impossible since is the ITR is choosing the algorithm. May be the sentence can be rewritten.

Similarly to previous comment: Why it is not a MUST?
>  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.
> 
What happens if the MS will choose a HMAC not supported by the ETR or the ITR?
Can you clarify how to solve this situation or explain why this will never happen?

>    The KDF ID field, specifies the suggested key derivation function to
>    be used by the Map-Server to derive the MS-OTK.

What happens if the MS will choose a KDF ID not supported by the ITR?
Can you clarify how to solve this situation or explain why this will never happen?

> 
>    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.
Why a “SHOULD”? If the Map-Request has S-bit=0 it mean that there is no AD, hence no OTK, how can the ITR decrypt the reply?????
It MUST discard…..


> 
>    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
Why is this a SHOULD? If it supports the HMAC Algorithm why not decrypt? Shouldn’t this be a “MAY”, according to internal policy?
>    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.
Shouldn’t the MS do the same thing? Otherwise different values will be obtained. This is not specified in the MS functioning description.


> 
>    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.  
I do not understand this “SHOULD”.  This has consequences in the choice how to react to SMR. This is a local policy.
_If_ the ITR wants to protect Map-Requests using LISP-SEC, than SMR triggered Map-Request MUST be sent through the mapping system.


> 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.
Same as above.

> 
> 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.  
I think “log message" is too much implementation specific. 
If there is a notification, and how this notification is done, is implementation specific IMHO.

> 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.
I think “log message" is too much implementation specific. 
If there is a notification, and how this notification is done, is implementation specific IMHO.

> 
>    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.
I think “log message" is too much implementation specific. 
If there is a notification, and how this notification is done, is implementation specific IMHO.

>   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.
Reading the example I am not sure I would follow this behaviour.
Only 1 record out of 3 is valid so why should I actually trust the ETR instead of throwing everything away?
Can you explain ???



> 
> 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, 
This would be LISP+ALT. Pleas add a reference to 6836.

> 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
If confidentiality is required why there is not a MUST?

>  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 
Again, if confidentiality is required why there is not a MUST?

> 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 correct RFC is 3394.

>  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.
Few points on this last paragraph:
- You assume that there is no need of confidentiality inside the Mapping System?
- Why not stating that encryption inside the mapping system is mapping system specify and out of scope of this document?
- Why are you assuming that all of the Mapping system will use ECM? Future Mapping system may use soemthos different. The important point is to ship the AD along.
> 
>    The Map-Resolver then forwards
to whom?
>  the received Map-Request, encapsulated
>    in the new ECM header that includes the newly computed Authentication
>    Data fields.
As for my comment of the previous paragraph I would be more generic stating that the MR will hand over the request to the mapping system.

You can still provide the example of DDT using ECM.

> 
> 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.
This equivalent to not using LISP-SEC. Please specify that the Map-Reply will be not protected.

> 
>    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,
Again, if confidentiality is required why there is not a MUST?
>  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.
> 

As for a previous comment, can you elaborate if OTK confidentiality is required in the mapping system and what are the consequences?


>    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
This section is not conform to RFC 5226.

There right way to go is to ask IANA to create three new registries, for HMAC, Key Wrap, and Key Derivation functions.
Define what is the allocation process (in light of the size of the field FCFS should not cause any problem IMHO)

Then ask to populate the registries as already described.


> 
> 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


Please Check your reference, this is the output if the nits tool:


Checking references for intended status: Experimental
  ----------------------------------------------------------------------------

  == Missing Reference: 'RFC3339' is mentioned on line 602, but not defined

  == Missing Reference: 'RFC4634' is mentioned on line 752, but not defined

  ** Obsolete undefined reference: RFC 4634 (Obsoleted by RFC 6234)

> 
>    [RFC2104]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
>               Hashing for Message Authentication", RFC 2104,
>               DOI 10.17487/RFC2104, February 1997,
>               <http://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,
>               <http://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, <http://www.rfc-editor.org/info/rfc3394>.
> 
>    [RFC4086]  Eastlake 3rd, D., Schiller, J., and S. Crocker,
>               "Randomness Requirements for Security", BCP 106, RFC 4086,
>               DOI 10.17487/RFC4086, June 2005,
>               <http://www.rfc-editor.org/info/rfc4086>.
> 
>    [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
>               IANA Considerations Section in RFCs", BCP 26, RFC 5226,
>               DOI 10.17487/RFC5226, May 2008,
>               <http://www.rfc-editor.org/info/rfc5226>.
> 
>    [RFC5869]  Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
>               Key Derivation Function (HKDF)", RFC 5869,
>               DOI 10.17487/RFC5869, May 2010,
>               <http://www.rfc-editor.org/info/rfc5869>.
> 
>    [RFC6830]  Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
>               Locator/ID Separation Protocol (LISP)", RFC 6830,
>               DOI 10.17487/RFC6830, January 2013,
>               <http://www.rfc-editor.org/info/rfc6830>.
> 
>    [RFC6833]  Fuller, V. and D. Farinacci, "Locator/ID Separation
>               Protocol (LISP) Map-Server Interface", RFC 6833,
>               DOI 10.17487/RFC6833, January 2013,
>               <http://www.rfc-editor.org/info/rfc6833>.
> 
> 
> 
> 
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> 
> 
>    [RFC7835]  Saucez, D., Iannone, L., and O. Bonaventure, "Locator/ID
>               Separation Protocol (LISP) Threat Analysis", RFC 7835,
>               DOI 10.17487/RFC7835, April 2016,
>               <http://www.rfc-editor.org/info/rfc7835>.
> 
> Authors' Addresses
> 
>    Fabio Maino
>    Cisco Systems
>    170 Tasman Drive
>    San Jose, California  95134
>    USA
> 
>    Email: [e-mail]
> 
> 
>    Vina Ermagan
>    Cisco Systems
>    170 Tasman Drive
>    San Jose, California  95134
>    USA
> 
>    Email: [e-mail]
> 
> 
>    Albert Cabellos
>    Technical University of Catalonia
>    c/ Jordi Girona s/n
>    Barcelona  08034
>    Spain
> 
>    Email: [e-mail]
> 
> 
>    Damien Saucez
>    INRIA
>    2004 route des Lucioles - BP 93
>    Sophia Antipolis
>    France
> 
>    Email: [e-mail]
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
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> 
> 
>