Re: [lisp] AD Review of draft-ietf-lisp-sec-25

[Alvaro Retana <[e-mail]>]

Hi!

I'm just moving this message up in people's mailer to make sure everyone
saw it.

If you’re already working in it, sorry for the interruption.

Alvaro.

On April 21, 2022 at 3:27:18 PM, Alvaro Retana ([e-mail])
wrote:


Dear authors:

Thank you for the work on this document!

I put detailed comments inline below.

As we have a constrained timeline for this document, I would like to start
the IETF Last-Call in no more than a couple of weeks.  I don't think my
comments will be hard to address.  In fact, there are comments that I
repeat in different sections, and some overlap.

Please reply inline to this message to expedite my review of any updates.
Also, if you think talking would clear things up faster, feel free to find
time on my calendar:  https://doodle.com/mm/alvaroretana/book-a-time

Thanks!

Alvaro.


[Line numbers from idnits.]

...
15 Abstract

17   This memo specifies LISP-SEC, a set of security mechanisms that
18   provides origin authentication, integrity and anti-replay protection
19   to LISP's EID-to-RLOC mapping data conveyed via mapping lookup
20   process.  LISP-SEC also enables verification of authorization on EID-
21   prefix claims in Map-Reply messages.

[nit] s/via mapping lookup process/via the mapping lookup process/g


...
100 1.  Introduction
...
120   This memo specifies LISP-SEC, a set of security mechanisms that
121   provides origin authentication, integrity and anti-replay protection
122   to LISP's EID-to-RLOC mapping data conveyed via mapping lookup
123   process.  LISP-SEC also enables verification of authorization on EID-
124   prefix claims in Map-Reply messages, ensuring that the sender of a
125   Map-Reply that provides the location for a given EID-prefix is
126   entitled to do so according to the EID prefix registered in the
127   associated Map-Server.  Map-Register/Map-Notify security, including
128   the right for a LISP entity to register an EID-prefix or to claim
129   presence at an RLOC, is out of the scope of LISP-SEC as those
130   protocols are protected by the security mechanisms specified in
131   [I-D.ietf-lisp-rfc6833bis].  However, LISP-SEC extends the Map-
132   Register message to allow an ITR to securely downgrade to non LISP-
133   SEC Map-Requests.  Additional security considerations are described
134   in Section 6.

[major] "securely downgrade to non LISP-SEC Map-Requests"

To "securely downgrade" to no security doesn't sound right to me.  See more
comments in §6.7.


...
176 4.  LISP-SEC Threat Model

178   LISP-SEC addresses the control plane threats, described in section
179   3.7 and 3.8 of [RFC7835], that target EID-to-RLOC mappings, including
180   manipulations of Map-Request and Map-Reply messages, and malicious
181   ETR EID prefix overclaiming.  LISP-SEC makes two main assumptions:
182   (1) the LISP mapping system is expected to deliver a Map-Request
183   message to their intended destination ETR as identified by the EID,
184   and (2) no man-in-the-middle (MITM) attack can be mounted within the
185   LISP Mapping System.  How the Mapping System is protected from MITM
186   attacks depends from the particular Mapping System used, and is out
187   of the scope of this memo.  Furthermore, while LISP-SEC enables
188   detection of EID prefix overclaiming attacks, it assumes that Map-
189   Servers can verify the EID prefix authorization at registration time.

[] As part of the efforts to make the language in IETF documents more
inclusive, consider using "on-path attack" instead of MITM.  This term in
already in use in some parts of this document.

https://www.ietf.org/about/groups/iesg/statements/on-inclusive-language/


...
202 5.  Protocol Operations
...
210   LISP-SEC builds on top of the security mechanisms defined in
211   [I-D.ietf-lisp-rfc6833bis] to address the threats described in
212   Section 4 by leveraging the trust relationships existing among the
213   LISP entities participating to the exchange of the Map-Request/Map-
214   Reply messages.  Those trust relationships are used to securely
215   distribute, as described in Section 8.4, a per-message One-Time Key
216   (OTK) that provides origin authentication, integrity and anti-replay
217   protection to mapping data conveyed via the mapping lookup process,
218   and that effectively prevent overclaiming attacks.  The processing of
219   security parameters during the Map-Request/Map-Reply exchange is as
220   follows:

[nit] s/participating to/participating in


...
245   1.  The ITR, upon needing to transmit a Map-Request message,
246       generates and stores an OTK (ITR-OTK).  This ITR-OTK is included
247       into the Encapsulated Control Message (ECM) that contains the
248       Map-Request sent to the Map-Resolver.  ITR-OTK confidentiality
249       and integrity protection MUST be provided in the path between the
250       ITR and the Map-Resolver.  This can be achieved either by
251       encrypting the ITR-OTK with the pre-shared secret known to the
252       ITR and the Map-Resolver (as specified in Section 6.5), or by
253       enabling DTLS between the ITR and the Map-Resolver.

[major] "protection MUST be provided"

Please specify things only once.  In this case, because this section just
"describes the flow", there's no need to specify anything in it, or go into
some of the details.  The protection part is properly covered later in the
document and is not necessary to be called out at this point.


255   2.  The Map-Resolver decapsulates the ECM message, decrypts the ITR-
256       OTK, if needed, and forwards through the Mapping System the
257       received Map-Request and the ITR-OTK, as part of a new ECM
258       message.  The LISP Mapping System delivers the ECM to the
259       appropriate Map-Server, as identified by the EID destination
260       address of the Map-Request.  As mentioned in Section 4, how the
261       Mapping System is protected from MITM attacks depends from the
262       particular Mapping Systems used, and is out of the scope of this
263       memo.

[minor] Anything "as mentioned in" can be left out of this description to
avoid duplication.


...
275   4.  The Map-Server derives a new OTK, the MS-OTK, by applying a Key
276       Derivation Function (KDF) to the ITR-OTK.  This MS-OTK is
277       included in the Encapsulated Control Message that the Map-Server
278       uses to forward the Map-Request to the ETR.  MS-OTK
279       confidentiality and integrity protection MUST be provided in the
280       path between the Map-Server and the ETR.  This can be achieved
281       either by encrypting the MS-OTK with the pre-shared secret known
282       to the Map-Server and the ETR (as specified in Section 6.5), or
283       by enabling DTLS between the Map-Server and the ETR.

[major] "protection MUST be provided":  Same comment as above: no need for
this part here.


...
303   8.  The ITR, upon receiving the Map-Reply, uses the locally stored
304       ITR-OTK to verify the integrity of the EID-prefix authorization
305       data included in the Map-Reply by the Map-Server.  The ITR
306       computes the MS-OTK by applying the same KDF (as specified in the
307       ECM encapsulated Map-Reply) used by the Map-Server, and verifies
308       the integrity of the Map-Reply.  If the integrity checks fail,
309       the Map-Reply MUST be discarded.  Also, if the EID-prefixes
310       claimed by the ETR in the Map-Reply are not equal or more
311       specific than the EID-prefix authorization data inserted by the
312       Map-Server, the ITR MUST discard the Map-Reply.

[major] "...MUST..."

These details are not needed here.


...
322 6.1.  Encapsulated Control Message LISP-SEC Extensions
...
358      V: Key Version bit.  This bit is toggled when the sender switches
359      to a new OTK wrapping key

[] I don't understand how this works.  If the OTK doesn't change then this
bit's value shouldn't change, is that it?

[major - If so..]  If so, what should a receiver do if the V bit didn't
change but the OTK did?  What if the OTK didn't change, but the V bit did?


...
363      Requested HMAC ID: The HMAC algorithm, that will be used to
364      protect the mappings, requested by the ITR.  See Section 6.4 for
365      details, and Section 8.3 for HMAC IDs that MUST be supported.

[major] §8.3 says this:

   AUTH-HMAC-SHA-1-96 MUST be supported, AUTH-HMAC-SHA-256-128 SHOULD be
   supported.

However, (1) it is not good practice to include specifications in the IANA
Considerations section (only instructions to IANA should be included
there), and, (2) the MUST/SHOULD combination doesn't match the MUST used
here.

Instead, please move the text (above + references to rfc2104/rfc6234) from
§8.3 to §6.4, and eliminate the reference to §8.3.

Note that similar text is used in multiple places.  Please update all.


...
377      OTK Wrapping ID: The identifier of the key derivation function and
378      of the key wrapping algorithm used to encrypt the One-Time-Key.
379      See Section 6.5 for more details, and Section 8.4 for Wrapping IDs
380      that MUST be supported.

[minor] The figure uses ("OTK Wrap. ID").  I know that's just an
abbreviation, but please include it here for completeness:

s/OTK Wrapping ID:/OTK Wrapping ID (OTK Wrap. ID):


[major] "and Section 8.4 for Wrapping IDs that MUST be supported."

Same comment as above: please move the text from §8.4 to §6.5.

BTW, §6.5 already has come text about requiring
 AES-KEY-WRAP-128+HKDF-SHA256, but not NULL-KEY-WRAP-128: this last
algorithm is mentioned, but the text doesn't require it.

Also, AES-KEY-WRAP-128 (without "+HKDF-SHA256") is mentioned separately,
but not listed in the table in §8.4.


382      One-Time-Key Preamble: set to 0 if the OTK is not encrypted.  When
383      the OTK is encrypted, this field MAY carry additional metadata
384      resulting from the key wrapping operation.  When a 128-bit OTK is
385      sent unencrypted by Map-Resolver, the OTK Preamble is set to
386      0x0000000000000000 (64 bits).  See Section 6.5.1 for details.

[nit] s/by Map-Resolver/by a Map-Resolver


...
391      EID-AD Length: length (in bytes) of the EID Authentication Data
392      (EID-AD).  The ITR MUST set EID-AD Length to 4 bytes, as it only
393      fills the KDF ID field, and all the remaining fields part of the
394      EID-AD are not present.  An EID-AD MAY contain multiple EID-
395      records.  Each EID-record is 4-byte long plus the length of the
396      AFI-encoded EID-prefix.

[nit] s/set EID-AD Length/set the EID-AD Length


[major] "ITR MUST set EID-AD Length to 4 bytes"

What should the receiver do if the length is set to anything else?

For messages not originated by the ITR, the length has to be more then 4.
In fact, it has to be 12 + the length of EID-prefix (multiple may be
present) + length of EID HMAC.  What should a receiver do if the length is
not appropriate?

I don't remember seeing anything in rfc6833bis about error handling or what
to do about mismatched lengths in general.  Did I miss it?


398      KDF ID: Identifier of the Key Derivation Function used to derive
399      the MS-OTK.  The ITR MAY use this field to indicate the
400      recommended KDF algorithm, according to local policy.  The Map-
401      Server can overwrite the KDF ID if it does not support the KDF ID
402      recommended by the ITR.  See Section 5.4 for more details, and
403      Section 8.5 for KDF IDs that MUST be supported.

[major] "Map-Server can overwrite the KDF ID if it does not support the KDF
ID recommended by the ITR"

Specify things only once.  The text in §6.7.1 is similar.  See comments
there.


[minor] s/5.4/6.4/g
§5.4 doesn't exist.


[major] "Section 8.5 for KDF IDs that MUST be supported"

Same comment as above: please move the text from §8.5 to §6.4.


405      Record Count: The number of records in this Map-Request message.
406      A record is comprised of the portion of the packet that is labeled
407      'Rec' above and occurs the number of times equal to Record Count.

[major] Should there at least be one, or is it ok if the value is 0?  If at
least one, what should a receiver do if no records are included?


409      E: ETR-Cant-Sign bit.  This bit is set to 1 to signal to the ITR
410      that at least one of the ETRs authoritative for the EID prefixes
411      of this Map-Reply has not enabled LISP-SEC.  This allows the ITR
412      to securely downgrade to non LISP-SEC requests, as specified in
413      Section 6.7, if so desired.

[major] If I understand correctly, this bit should only ever be set by a
Map-Server.  Are there other cases where setting it would be valid?

If this bit is set other than by a Map-Server, what should the receiver do.

Assuming my understanding is correct, please say something here about the
Map-Server being the only one that can set the bit.  §6.7 is about
Map-Server processing, but the fact that it can set the bit doesn't
explicitly preclude other from doing so.


[minor] s/This allows the ITR to securely downgrade to non LISP-SEC
requests, as specified in Section 6.7, if so desired./See Section 6.7 for
more details.


...
417      EID HMAC ID: Identifier of the HMAC algorithm used to protect the
418      integrity of the EID-AD.  This field is filled by Map-Server that
419      computed the EID-prefix HMAC.  See Section 5.4 for more details,
420      and Section 8.3 for HMAC IDs that MUST be supported.

[nit] s/by Map-Server/by the Map-Server


[major] "Section 8.3 for HMAC IDs that MUST be supported"

Same comment as above: please move the text from §8.3 to §6.4.


422      EID mask-len: Mask length for EID-prefix.

424      EID-AFI: Address family of EID-prefix according to [AFN].

426      EID-prefix: The Map-Server uses this field to specify the EID-
427      prefix that the destination ETR is authoritative for, and is the
428      longest match for the requested EID.

[major] These 3 fields, which are part of the "Rec", are the same as what
is specified in §5.2/rfc6833bis.  But the descriptions are different, and
the EID-AFI names doesn't match EID-Prefix-AFI.  Please point at the
definitions in rfc6833bis:

   EID mask-len: As defined in §5.2/rfc6833bis.
   ...


430      EID HMAC: HMAC of the EID-AD computed and inserted by Map-Server.
431      Before computing the HMAC operation the EID HMAC field MUST be set
432      to 0.  The HMAC MUST cover the entire EID-AD.

[major] s/by Map-Server/by a Map-Server


[major] "Before computing the HMAC operation the EID HMAC field MUST be set
to 0.  The HMAC MUST cover the entire EID-AD."

§6.7.1 describes the same operation, but without using Normative language:

   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.

Please specify things only once!  It seems to me that it may be more
appropriate to include the specification in §6.7.1 (Generating a LISP-SEC
Protected Encapsulated Map-Request).


434 6.2.  Map-Reply LISP-SEC Extensions
...
464      MR AD Type: 1 (LISP-SEC Authentication Data).  See Section 8.

[] Just wondering...  Why are separate registries used for ECM AD Type and
MR AD Type?  Are you expecting so many extensions that a single space won't
be enough?


466      EID-AD Length: length (in bytes) of the EID-AD.  An EID-AD MAY
467      contain multiple EID-records.  Each EID-record is 4-byte long plus
468      the length of the AFI-encoded EID-prefix.

[] It looks like you're mostly redefining the same fields as in the last
section, at least for the EID-AD and Rec.  Please point at the definitions
there instead of redefining again here.  If there are exceptions/variations
that are east to call out then just mention those here.

Otherwise, the comments from the last section apply here too.


470      KDF ID: Identifier of the Key Derivation Function used to derive
471      MS-OTK.  See Section 6.7 for more details, and Section 8.5 for KDF
472      IDs that MUST be supported.

[minor] §6.7 doesn't talk about the KFD ID.


...
480      EID HMAC ID: Identifier of the HMAC algorithm used to protect the
481      integrity of the EID-AD.  See Section 6.7 for more details, and
482      Section 8.3 for HMAC IDs that MUST be supported.

[minor] §6.7 doesn't talk about the EID HMAC ID.


484      EID mask-len: Mask length for EID-prefix.

486      EID-AFI: Address family of EID-prefix according to [RFC8060].

488      EID-prefix: This field contains an EID-prefix that the destination
489      ETR is authoritative for, and is the longest match for the
490      requested EID.

[major] Same comment as in §6.1: These 3 fields, which are part of the
"Rec", are the same as what is specified in §5.2/rfc6833bis.


...
499      PKT HMAC ID: Identifier of the HMAC algorithm used to protect the
500      integrity of the Map-Reply.  See Section 8.3 for HMAC IDs that
501      MUST be supported.

[major] As mentioned before, please take Normative specifications out of
the IANA section and move it somewhere more appropriate.


503      PKT HMAC: HMAC of the whole Map-Reply packet, including the LISP-
504      SEC Authentication Data.  The scope of the authentication goes
505      from the Map-Reply Type field to the PKT HMAC field included.
506      Before computing the HMAC operation the PKT HMAC field MUST be set
507      to 0.  See Section 6.8 for more details.

[major] These two sentences don't seem to say the same thing:

   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.

Does it include the Map-Reply (first sentence) or just the data defined in
this document (second sentence)?  The description in §6.8 is slightly
clearer, but not by much:

   The PKT-AD contains the HMAC of the whole Map-Reply packet...
   The scope of the HMAC operation covers the entire PKT-AD, from the
   Map-Reply Type field to the PKT HMAC field...

It would be better if the specification was made only once.  A pointer to
§6.8 should be enough here.


[major] "Before computing the HMAC operation the PKT HMAC field MUST be set
to 0."

§6.8 describes the same operation, but without using Normative language:
"...to the PKT HMAC field, which must be set to 0 before the computation."

Please specify things only once!  It seems to me that it may be more
appropriate to include the specification in §6.8.


509 6.3.  Map-Register LISP-SEC Extentions

[] This section is not needed -- see below.

511   This memo is allocating one of the bits marked as Unassigned in the
512   Map-Register message defined in [I-D.ietf-lisp-rfc6833bis].  More
513   precisely, the second bit after the Type field in a Map-Register
514   message is allocated as the S bit.  The S bit indicates to the Map-
515   Server that the registering ETR is LISP-SEC enabled.  An ETR that
516   supports LISP-SEC MUST set the S bit in its Map-Register messages.

[major] The S-bit is already allocated and defined in rfc6833bis, so the
first two sentences are not needed.


[major] rfc6833bis is not as explicit as the last two sentences, but it
seems to me that it already covers them.  This is from §5.6/rfc6833bis
(Map-Register Message Format):

   S: This is the security-capable bit.  When set, the procedures from
      [I-D.ietf-lisp-sec] are supported.

This text doesn't explicitly require the ETR to set the bit.  If you want
to make that explicit, then we should update the text in rfc633bis.


518 6.4.  ITR Processing: Generating a Map-Request

520   Upon creating a Map-Request, the ITR generates a random ITR-OTK that
521   is stored locally (until the corresponding Map-Reply is received),
522   together with the nonce generated as specified in
523   [I-D.ietf-lisp-rfc6833bis].

[minor] "until the corresponding Map-Reply is received"

Please include a forward reference to §6.9.


...
531   The Map-Request MUST be encapsulated in an ECM, with the S-bit set to
532   1, to indicate the presence of Authentication Data.

[major] "Map-Request MUST be encapsulated in an ECM"

This part is confusing to me -- along with the many parts that talk about
an "encapsulated Map-Request".

What do you mean by an "encapsulated Map-Request"?  I see 3 options:

(1) The ECM Authentication Data (from Figure 1) carried in the ECM
(§5.8/rfc6833bis) with the S-bit set.  This is what I've been assuming
because §6.1 talks about it being a Map-Request when it describes the
Record Count.

If so, at minimum, the text is confusing because the content of the ECM
Authentication Data is different from the Map-Request from §5.2/rfc6833bis,
but the names are the same.  Also, the functionality from rfc6833bis is
different.


(2) A Map-Request (§5.2/rfc6833bis) encapsulated as the LCM in the ECM as
described in §5.8/rfc6833bis.  In this case, setting the S-bit, as required
above would indicate that the ECM Authentication Data (from Figure 1) would
also be there.

If so, this document is not clear about the interaction between the two
Map-Requests.  Should the Records match, what if they don't, etc..?


(3) A Map-Request (§5.2/rfc6833bis) encapsulated as the LCM in the ECM as
described in §5.8/rfc6833bis.  The S-bit is not set.

I don't think this interpretation makes sense because then it wouldn't be
protected at all.


Please clarify here, and update the descriptions elsewhere as needed.


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

[nit] s/ITR-OTK/The ITR-OTK


540   The Requested HMAC ID field contains the suggested HMAC algorithm to
541   be used by the Map-Server and the ETR to protect the integrity of the
542   ECM Authentication data and of the Map-Reply.  A HMAC ID Value of
543   NONE (0), MAY be used to specify that the ITR has no preferred HMAC
544   ID.

[nit] s/NONE (0), MAY/NONE (0) MAY


546   The KDF ID field specifies the suggested key derivation function to
547   be used by the Map-Server to derive the MS-OTK.  A KDF Value of NONE
548   (0), MAY be used to specify that the ITR has no preferred KDF ID.

[major] s/Value of NONE (0), MAY be used/Value of NONE (0) may be used

Even though it is optional to use 0, the optional use of the KDF ID field
by the ITR was already specified in §6.1, so this is just a statement of
fact.


...
554 6.4.1.  PITR Processing

[minor] Please expand PITR on first use.


556   The processing performed by a PITR is equivalent to the processing of
557   an ITR.  However, if the PITR is directly connected to a Mapping
558   System such as LISP+ALT [RFC6836], the PITR performs the functions of
559   both the ITR and the Map-Resolver forwarding the Map-Request
560   encapsulated in an ECM header that includes the Authentication Data
561   fields as described in Section 6.6.

[?] This description of a PITR having multiple colocated functionality is
not specific to the PITR, right?  Also, the description is not specific to
LISP+ALT, the same would happen with any Mapping System, right?   It seems
to me that this section is not needed.


563 6.5.  Encrypting and Decrypting an OTK
...
594   Implementations of this specification MUST support OTK Wrapping ID
595   AES-KEY-WRAP-128+HKDF-SHA256 that specifies the use of the HKDF-
596   SHA256 Key Derivation Function specified in[RFC4868] to derive a per-
597   message encryption key (per-msg-key), as well as the AES-KEY-WRAP-128
598   Key Wrap algorithm used to encrypt a 128-bit OTK, according to
599   [RFC3394].

[nit] s/in[RFC4868]/in [RFC4868]


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

604   1.  The KDF algorithm is identified by the field 'OTK Wrapping ID'
605       according to the table in Section 8.4.

607   2.  The Key Wrap algorithm is identified by the field 'OTK Wrapping
608       ID' according to the table in Section 8.4.

[minor] Can we merge these two steps?  Also, given that other algorithms
may be defined later, let's separate the process from the table itself.

Suggestion>
   The KDF and Key Wrap algorithms are identified by the value of
   the 'OTK Wrapping ID' field.  The initial values are documented
   in Table #x.


610   3.  If the NULL-KEY-WRAP-128 algorithm (defined in (Section 8.4)) is
611       selected and DTLS is not enabled, the Map-Request MUST be dropped
612       and an appropriate log action SHOULD be taken.

[minor] s/8.4/6.5


...
640 6.5.1.  Unencrypted OTK

642   MS-OTK confidentiality and integrity protection MUST be provided in
643   the path between the Map-Server and the ETR.  Similarly, ITR-OTK
644   confidentiality and integrity protection MUST be provided in the path
645   between the ITR and the Map-Resolver.

[major] This same specification is also present in §6.5.  Please specify
the bahavior only once.


...
676 6.7.  Map-Server Processing

678   Upon receiving an ECM encapsulated Map-Request with the S-bit set to
679   1, the Map-Server process the Map-Request according to the value of
680   the security-capable S-bit and of the proxy map-reply P-bit contained
681   in the Map-Register sent by the ETRs authoritative for that prefix
682   during registration.

[minor] This is a long sentence...my first read got me confused about what
was meant by "the value of the security-capable S-bit" if it had just been
pointed that it is set to 1.

Please come up with a shortcut for "ECM encapsulated Map-Request with the
S-bit set to 1".  Refer back to the comments on §6.4.  Suggestion: "secure
Map-Request".

Suggestion>
   Upon receiving a "secure Map-Request", the Map-Server precesses
   it according to the setting of the S and P-bits in the Map-Register
   received from the authoritative ETRs for the corresponding prefix,
   as described below.


...
731   In this way the ITR that sent a LISP-SEC protected Map-Request always
732   receives a LISP-SEC protected Map-Reply.  However, the ETR-Cant-Sign
733   E-bit set to 1 specifies that a non LISP-SEC Map-Request might reach
734   additional ETRs that have LISP-SEC disabled.  This mechanism allows
735   the ITR to securely downgrade to non LISP-SEC requests, if so
736   desired.

[major] "This mechanism allows the ITR to securely downgrade to non
LISP-SEC requests, if so desired."

Besides the fact that "securely downgrade to non LISP-SEC" sounds like a
contradiction, the "if so desired" part leaves the operation up in the
air.  When/why would an ITR desire to disable security?  What are the use
cases where it may be ok?  What are the risks that should be considered?

As I see it, downgrading is risky because it can open the door to
overclaiming, which list-sec closes (rfc6833bis).  IOW, a rogue ETR can
decide not to set the S-bit (even if it did support lisp-sec) and eliminate
its benefits.  rfc6833bis also says this:

   3.  LISP-SEC [I-D.ietf-lisp-sec] MUST be implemented.  Network
       operators should carefully weight 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.


Please add a "Deployment/Operational Considerations" section to help
operators in making the decision above, particularly about when an ITR may
desire to downgrade.  Please include (as appropriate) information as
described in §2/rfc5706.

FWIW, I see the E-bit as useful as a transition mechanism: while not all
the ETRs may have been upgraded then it seems ok to downgrade to maintain
the operation of the network.  However, I'm having a hard time seeing the
value afterwards.


738 6.7.1.  Generating a LISP-SEC Protected Encapsulated Map-Request
...
745   The Map-Server updates the OTK-AD by deriving a new OTK (MS-OTK) from
746   the ITR-OTK received with the Map-Request.  MS-OTK is derived
747   applying the key derivation function specified in the KDF ID field.
748   If the algorithm specified in the KDF ID field is not supported, the
749   Map-Server uses a different algorithm to derive the key and updates
750   the KDF ID field accordingly.

[major]

   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.

See the comment below (after line 775) about the future existence of
multiple required/recommended algorithms.


752   MS-OTK confidentiality and integrity protection MUST be provided in
753   the path between the Map-Server and the ETR.  This can be achieved
754   either by enabling DTLS between the Map-Server and the ETR, or by
755   encrypting the MS-OTK with the pre-shared secret known to the Map-
756   Server and the ETR.

[major] This is specified in §6.5.  Please specify behaviors only once.


...
767   The Map-Server includes in the EID-AD the longest match registered
768   EID-prefix for the destination EID, and an HMAC of this EID-prefix.
769   The HMAC is keyed with the ITR-OTK contained in the received ECM
770   Authentication Data, and the HMAC algorithm is chosen according to
771   the Requested HMAC ID field.  If the Map-Server does not support this
772   algorithm, the Map-Server uses a different algorithm and specifies it
773   in the EID HMAC ID field.  The scope of the HMAC operation covers the
774   entire EID-AD, from the EID-AD Length field to the EID HMAC field,
775   which must be set to 0 before the computation.

[major]

   ...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.

This document defines one required and one recommended algorithms.  The
logic above then works.  What happens when other algorithms are added --
but are only recommended?  It seems to me that if the ITR requests one of
the recommended algorithms, and the Map-Server doesn't support it then
another recommended algorithm, in this case not supported by the ITR, might
be selected.

How do the different LISP nodes know/learn what is supported by the other
nodes?  If the "uses a different algorithm" part results in a required
algorithm then we should be ok as long as future documents Update the set
of required and recommended algorithms in the future.


[major] "does not support this algorithm"

It's possible for the ITR to set the value to 0.  That case needs to be
covered here too.


[] See the related comment about the last sentence in §6.1.


...
782 6.7.2.  Generating a Proxy Map-Reply

784   LISP-SEC proxy Map-Reply are generated according to
785   [I-D.ietf-lisp-rfc6833bis], with the Map-Reply S-bit set to 1.  The
786   Map-Reply includes the Authentication Data that contains the EID-AD,
787   computed as specified in Section 6.7.1, as well as the PKT-AD
788   computed as specified in Section 6.8.

[major] "Map-Reply...as specified in Section 6.7.1"

§6.7.1 talks about Map-Requests, not Map-Replies.  It looks like theres a
section missing.


790 6.8.  ETR Processing
...
802   The EID-AD is copied from the Authentication Data of the received
803   encapsulated Map-Request.

[major] The KFD ID may have to be updated so the EID-AD can't simply be
copied.  And the EID HMAC needs to be recalculated.

Note that §6.1 says that the EID HMAC is "computed and inserted by
Map-Server."  IOW, it doesn't take into account that it may have to be
updated.


805   The PKT-AD contains the HMAC of the whole Map-Reply packet, keyed
806   with the MS-OTK and computed using the HMAC algorithm specified in
807   the Requested HMAC ID field of the received encapsulated Map-Request.
808   If the ETR does not support the Requested HMAC ID, it uses a
809   different algorithm and updates the PKT HMAC ID field accordingly.
810   The scope of the HMAC operation covers the entire PKT-AD, from the
811   Map-Reply Type field to the PKT HMAC field, which must be set to 0
812   before the computation.

[] See the related comment in §6.2.


...
817 6.9.  ITR Processing: Receiving a Map-Reply

819   In response to an encapsulated Map-Request that has the S-bit set, an
820   ITR MUST receive a Map-Reply with the S-bit set, that includes an
821   EID-AD and a PKT-AD.  If the Map-Reply does not include both ADs, the
822   ITR MUST discard it.  In response to an encapsulated Map-Request with
823   S-bit set to 0, the ITR expects a Map-Reply with S-bit set to 0, and
824   the ITR SHOULD discard the Map-Reply if the S-bit is set.

[major] "ITR MUST receive a Map-Reply with the S-bit set"

The style of the second part of the paragraph is clearer on what the action
is.

OLD>
   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.

NEW>
   In response to a "secure 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.


[major] "ITR SHOULD discard the Map-Reply if the S-bit is set"

When is it ok for the the ITR not to discard the Map-Reply?  Why is this a
recommendation and not a requirement?


...
831   The integrity of the EID-AD is verified using the ITR-OTK (stored
832   locally for the duration of this exchange) to re-compute the HMAC of
833   the EID-AD using the algorithm specified in the EID HMAC ID field.
834   If the EID HMAC ID field does not match the Requested HMAC ID the ITR
835   SHOULD discard the Map-Reply and send, at the first opportunity it
836   needs to, a new Map-Request with a different Requested HMAC ID field,
837   according to ITR's local policy.  The scope of the HMAC operation
838   covers the entire EID-AD, from the EID-AD Length field to the EID
839   HMAC field.

[major] "If the EID HMAC ID field does not match the Requested HMAC ID the
ITR SHOULD discard the Map-Reply and send, at the first opportunity it
needs to, a new Map-Request with a different Requested HMAC ID field,
according to ITR's local policy.

§6.8 says that the ETR can use a different algorithm.

When is ok for the ITR to not discard the Map-Reply?  Why is this a
recommendation and not a requirement?


...
843   To verify the integrity of the PKT-AD, first the MS-OTK is derived
844   from the locally stored ITR-OTK using the algorithm specified in the
845   KDF ID field.  This is because the PKT-AD is generated by the ETR
846   using the MS-OTK.  If the KDF ID in the Map-Reply does not match the
847   KDF ID requested in the Map-Request, the ITR SHOULD discard the Map-
848   Reply and send, at the first opportunity it needs to, a new Map-
849   Request with a different KDF ID, according to ITR's local policy.
850   Without consistent configuration of involved entities, extra delays
851   may be experienced.  However, since HKDF-SHA1-128 is specified as
852   mandatory to implement in Section 8.5, the process will eventually
853   converge.

[major] "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."

§6.1 says that the ETR can use a different algorithm.

When is ok for the ITR to not discard the Map-Reply?  Why is this a
recommendation and not a requirement?


[minor] s/Section 8.5/Section 6.4


855   The derived MS-OTK is then used to re-compute the HMAC of the PKT-AD
856   using the Algorithm specified in the PKT HMAC ID field.  If the PKT
857   HMAC ID field does not match the Requested HMAC ID the ITR SHOULD
858   discard the Map-Reply and send, at the first opportunity it needs to,
859   a new Map-Request with a different Requested HMAC ID according to
860   ITR's local policy or until all HMAC IDs supported by the ITR have
861   been attempted.

[major] "If the PKT HMAC ID field does not match the Requested HMAC ID the
ITR SHOULD discard the Map-Reply..."

Same comments as above...


...
873   [I-D.ietf-lisp-rfc6833bis] allows ITRs to send solicited Map-Requests
874   directly to the ETRs that send the SMR message in the first place.
875   However, in order to receive a secure Map-Reply, ITRs SHOULD send SMR
876   triggered Map-Requests over the mapping system using the
877   specifications of this memo.  If an ITR accepts piggybacked Map-
878   Replies, it SHOULD also send a Map-Request over the mapping system in
879   order to verify the piggybacked Map-Reply with a secure Map-Reply.

[minor] Expand SMR on first use.


[major] "in order to receive a secure Map-Reply, ITRs SHOULD
send...Map-Requests...using the specifications of this memo."

The only way to receive a secure Map-Reply is to use this specification, so
the "SHOULD" seems out of place because it is a statement of fact.

Note however that rfc6833bis already requires the behavior (from §6.1):

   An SMR message is simply a bit set in a Map-Request message.  An ITR
   or PITR will send a Map-Request (SMR-invoked Map-Request) when they
   receive an SMR message.  While the SMR message is sent through the
   data-plane, the SMR-invoked Map-Request MUST be sent through the
   Mapping System (not directly).

IOW, the sentence is not needed.  Specify things only once.


[major] What are "piggybacked Map-Replies"?  Where are they specified?
When is it ok for the ITR to not verify the information?  Why is it a
recommendation and not a requirement?


881 6.9.1.  Map-Reply Record Validation
...
917   The EID-record with EID-prefix 2001:db8:102::/48 is not eligible to
918   be used by the ITR since it is not included in any of the EID-ADs
919   signed by the Map-Server.  A log action MUST be taken.

[major] "A log action MUST be taken."

This action is specified as part of an example.  Please generalize the
specification, include the text before the example, and don't use normative
language in an example.

Suggestion>
   If any EID-prefix in the payload of the Map-Reply is not
   included in the EID-AD signed by the Map-Server a log action
   MUST be taken.


...
925   The EID-record with EID-prefix 2001:db8:200::/40 is not eligible to
926   be used by the ITR since it is not included in any of the EID-ADs
927   signed by the Map-Server.  A log action MUST be taken.  In this last
928   example the ETR is trying to over claim the EID-prefix
929   2001:db8:200::/40, but the Map-Server authorized only
930   2001:db8:203::/48, hence the EID-record is discarded.

[major] "A log action MUST be taken."  See comment above.


...
934 7.1.  Mapping System Security

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

[minor] "eventually" ??  Maybe that word is not needed.


...
949 7.2.  Random Number Generation

951   The ITR-OTK MUST be generated by a properly seeded pseudo-random (or
952   strong random) source.  See [RFC4086] for advice on generating
953   security-sensitive random data

[nit] s/data/data.


...
963 7.4.  Deploying LISP-SEC

965   This memo is written according to [RFC2119].  Specifically, the use
966   of the key word SHOULD "or the adjective 'RECOMMENDED', mean that
967   there may exist valid reasons in particular circumstances to ignore a
968   particular item, but the full implications must be understood and
969   carefully weighed before choosing a different course".

[major] §2 already includes the rfc2119/rfc8174 template.  There's no need
to include this text here, or the last paragraph.

I wonder the intent of putting it in this section: there are no SHOULDs in
it.  Should there be any? [I don't think so.]

Also, I expect the specification to call out some of the considerations to
be taken into account -- and not just mention that considerations may
exist.  [I made sure to ask about the SHOULDs in other parts of the text.]


...
977   As an example, in certain closed and controlled deployments, it is
978   possible that the threat associated with a MITM between the xTR and
979   the Mapping System is very low, and after carfeul consideration it
980   may be decided to allow a NULL key wrapping algorithm while carrying
981   the OTKs between the xTR and the Mapping System.

[nit] s/carfeul/careful


...
992 7.5.  Shared Keys Provisioning

994   Provisioning of the keys shared between the ITR and the Map-Resolver
995   as well as between the ETR and the Map-Server should be performed via
996   an orchestration infrastructure and it is out of the scope of this
997   memo.  It is recommended that both shared keys are refreshed at
998   periodical intervals to address key aging or attackers gaining
999   unauthorized access to the shared keys.  Shared keys should be
1000   unpredictable random values.

[] You will be asked about LISP management and the YANG model in
particular.  It is up to you whether or not you want to include an
Informative reference to draft-ietf-lisp-yang.


1002 7.6.  Replay Attacks
...
1010   In case of replayed Map-Request, the Map-Server, Map-Resolver and
ETR
1011   will have to do a LISP-SEC computation.  This is equivalent to a
1012   valid LISP-SEC computation and an attacker does not obtain any
1013   benefit.

[major] You mean "equivalent to a valid LISP-SEC computation" in terms of
resources, right?

It might be a good idea to indicate why "an attacker does not obtain any
benefit".  Is it because the Map-Request will be discarded?  Why?

There's some text in the Security Considerations of rfc6833bis about this
topic and rate limiting.  It might be worth referencing it.

BTW, please include a paragraph at the start of this section (before §7.1)
that explicitly says that the Security Considerations of rfc6833bis apply
to this document too.


1015 7.7.  Message Privacy

1017   DTLS [RFC6347] SHOULD be used to provide communication privacy and
to
1018   prevent eavesdropping, tampering, or message forgery to the messages
1019   exchanged between the ITR, Map-Resolver, Map-Server, and ETR.

[major] "DTLS [RFC6347] SHOULD be used"

When is it ok to not use DTLS?  Why is this a recommendation and not a
requirement?

There are many places in this document that say this:

   ...confidentiality and integrity protection MUST be provided
   in the path between [A] and [B].  This can be achieved either
   by enabling DTLS between [A] and [B], or by encrypting...

I can see how enabling DLTS is not required if the *-OTK is encrypted.  Is
this the conditioning statement that leads to a SHOULD?  Please write it
out here.


...
1030 8.  IANA Considerations

[] The comments in §8.1 apply to all the sections.


1032 8.1.  ECM AD Type Registry

1034   IANA is requested to create the "ECM Authentication Data Type"
1035   registry with values 0-255, for use in the ECM LISP-SEC Extensions
1036   Section 6.1.  The registry MUST be initially populated with the
1037   following values:

[major] Where should this registry be located?  I assume you would want it
to be a sub-registry of the "Locator/ID Separation Protocol (LISP)
Parameters" registry.  (
https://www.iana.org/assignments/lisp-parameters/lisp-parameters.xhtml)


[major] "registry MUST be initially populated"

Normative keywords should only be used for interoperability reasons, not to
give instructions to IANA:

Suggestion>
   Table x shows the initial allocations made to this new registry.


1039             Name                     Value        Defined In
1040             -------------------------------------------------
1041             Reserved                 0             This memo
1042             LISP-SEC-ECM-EXT         1             This memo

[minor] Please add a table number -- to all the tables in this section.


1044   Values 2-255 are unassigned.  They are to be assigned according to
1045   the "Specification Required" policy defined in [RFC8126].

[major] The Specification Required policy requires the review of a
Designated Expert.  Please provide instructions for the experts?  What
factors should they take into account when approving a new value?


...
1126 10.1.  Normative References
...
1141   [RFC4086]  Eastlake 3rd, D., Schiller, J., and S. Crocker,
1142              "Randomness Requirements for Security", BCP 106, RFC
4086,
1143              DOI 10.17487/RFC4086, June 2005,
1144              <https://www.rfc-editor.org/info/rfc4086>.

[minor] This reference can be Informative.


...
1164 10.2.  Informational References
...
1170   [I-D.ietf-lisp-rfc6830bis]
1171              Farinacci, D., Fuller, V., Meyer, D., Lewis, D., and A.
1172              Cabellos, "The Locator/ID Separation Protocol (LISP)",
1173              Work in Progress, Internet-Draft, draft-ietf-lisp-
1174              rfc6830bis-36, 18 November 2020,
1175              <https://www.ietf.org/archive/id/draft-ietf-lisp-
1176              rfc6830bis-36.txt>.

[major] This reference must be Normative.


1178   [RFC2104]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
1179              Hashing for Message Authentication", RFC 2104,
1180              DOI 10.17487/RFC2104, February 1997,
1181              <https://www.rfc-editor.org/info/rfc2104>.

[major] This reference must be Normative.


1183   [RFC3394]  Schaad, J. and R. Housley, "Advanced Encryption Standard
1184              (AES) Key Wrap Algorithm", RFC 3394, DOI
10.17487/RFC3394,
1185              September 2002, <https://www.rfc-editor.org/info/rfc3394>.


[major] This reference must be Normative.


1187   [RFC5869]  Krawczyk, H. and P. Eronen, "HMAC-based
Extract-and-Expand
1188              Key Derivation Function (HKDF)", RFC 5869,
1189              DOI 10.17487/RFC5869, May 2010,
1190              <https://www.rfc-editor.org/info/rfc5869>.

[major] This reference must be Normative.


1192   [RFC6234]  Eastlake 3rd, D. and T. Hansen, "US Secure Hash
Algorithms
1193              (SHA and SHA-based HMAC and HKDF)", RFC 6234,
1194              DOI 10.17487/RFC6234, May 2011,
1195              <https://www.rfc-editor.org/info/rfc6234>.

[major] This reference must be Normative.


...
1202   [RFC7835]  Saucez, D., Iannone, L., and O. Bonaventure, "Locator/ID
1203              Separation Protocol (LISP) Threat Analysis", RFC 7835,
1204              DOI 10.17487/RFC7835, April 2016,
1205              <https://www.rfc-editor.org/info/rfc7835>.

[major] This reference must be Normative as "LISP-SEC addresses the control
plane threats, described in 3.7 and 3.8 of [RFC7835]".

[EoR -25]