Re: [Ace] AD review of draft-ietf-ace-coap-est-12 part 2

Peter van der Stok <> Tue, 03 September 2019 12:18 UTC

Return-Path: <>
Received: from localhost (localhost []) by (Postfix) with ESMTP id 8A926120132; Tue, 3 Sep 2019 05:18:31 -0700 (PDT)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -1.997
X-Spam-Status: No, score=-1.997 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, HTML_MESSAGE=0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_NONE=0.001] autolearn=ham autolearn_force=no
Authentication-Results: (amavisd-new); dkim=pass (1024-bit key)
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id bgBoffUMBlxt; Tue, 3 Sep 2019 05:18:26 -0700 (PDT)
Received: from ( []) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by (Postfix) with ESMTPS id 5240312012C; Tue, 3 Sep 2019 05:18:26 -0700 (PDT)
Received: from ( []) by (Postfix) with ESMTP id B6CAE1822494D; Tue, 3 Sep 2019 12:18:24 +0000 (UTC)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;; h= mime-version:content-type:date:from:to:cc:subject:reply-to :in-reply-to:references:message-id; s=key; bh=iC1rDGiAcuku9/Fs7h fBdgMzYZF3YPNmgAU/GcxbQps=; b=SqzC+FqMB2lv4cyeyNfVecNsmlbuFTb8M/ mIVEbqyyS/OspJVH9QsCyOtP+Cuo5mAUCIRguqUk0q8NSndV2bSlqcY2wtMbgk6V R59NZVuunvggSkJguMlnSISwqg9tY/nP9lpM3wV1C1TG3g01GBTErFwdVeUaQbt8 13Fz02ZQg=
X-Session-Marker: 73746F6B636F6E73406262686D61696C2E6E6C
X-Spam-Summary: 10, 1, 0, , d41d8cd98f00b204,, :::::::::, RULES_HIT:152:355:379:582:599:960:962:967:968:973:988:989:1042:1152:1189:1221:1256:1260:1313:1314:1345:1359:1436:1437:1461:1516:1517:1518:1575:1588:1589:1592:1594:1605:1712:1730:1776:1792:1801:2194:2198:2199:2200:2540:2559:2562:2689:2692:2693:2731:2890:2892:2894:2895:2898:2903:2906:2911:2920:2922:2923:2924:2925:2926:3138:3139:3140:3141:3142:3622:3865:3866:3867:3868:3870:3871:3872:3873:3874:4250:4321:4362:4419:4425:4605:4641:4860:5007:6261:6298:6659:6678:6690:7774:7903:7974:8531:8603:8660:8784:8957:9010:9108:9121:10128:10559:10848:11233:11657:11914:12043:12109:12114:12219:12291:12295:12296:12438:12555:12663:12679:12683:12700:12737:12740:12895:12986:13141:13145:13148:13160:13161:13191:13192:13215:13229:13230:13870:13972:14110:14149:14161:14565:14799:21060:21063:21080:21094:21323:21324:21365:21433:21450:21451:21611:21625:21740:21772:21795:21796:21939:30030:30034:30036:30037:30041:30051:30054:30056:30062:30069:30070:3
X-HE-Tag: beast64_f14eede08b20
X-Filterd-Recvd-Size: 70376
Received: from (imap-ext []) (Authenticated sender: by (Postfix) with ESMTPA; Tue, 3 Sep 2019 12:18:23 +0000 (UTC)
MIME-Version: 1.0
Content-Type: multipart/alternative; boundary="=_1c65d4777981c3d61c556925d741d050"
Date: Tue, 03 Sep 2019 14:18:22 +0200
From: Peter van der Stok <>
To: Benjamin Kaduk <>
Cc: Jim Schaad <>,,,
Organization: vanderstok consultancy
In-Reply-To: <>
References: <> <027701d55ebf$994184b0$cbc48e10$> <> <> <>
Message-ID: <>
User-Agent: Roundcube Webmail/1.2.7
X-Originating-IP: []
Archived-At: <>
Subject: Re: [Ace] AD review of draft-ietf-ace-coap-est-12 part 2
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: "Authentication and Authorization for Constrained Environments \(ace\)" <>
List-Unsubscribe: <>, <>
List-Archive: <>
List-Post: <>
List-Help: <>
List-Subscribe: <>, <>
X-List-Received-Date: Tue, 03 Sep 2019 12:18:32 -0000

Hi Ben,

the last part of the responses to your thorough review.
Apart from nits you found some "nice" mistakes.

the openssl example make me worry a bit.

See below.


   When requesting server-side key generation, the client asks for the
   server or proxy to generate the private key and the certificate which
   are transferred back to the client in the server-side key generation
   response.  In all respects, the server SHOULD treat the CSR as it
   would treat any enroll or re-enroll CSR; the only distinction here is
   that the server MUST ignore the public key values and signature in
   the CSR.  These are included in the request only to allow re-use of
   existing codebases for generating and parsing such requests.

We need to reword this; the SHOULD is in conflict with the MUST. 


Removed the SHOULD -> "…the server treats the CSR …" 


   certificate and a private key.  The private key Content-Format
   requested by the client is depicted in the PKCS#10 CSR request.  If

nit: I suggest s/depicted/indicated/ 

<pvds>done </pvds>

   (Section 5.3) .  The two representations (each consisting of two CBOR
   array items) do not have to be in a particular order since each


s/do not have to be in a particular order since each representation is/ 


[side note: core-multipart-ct is looking to land on "multipart/mixed"
semantics to resolve my outstanding Discuss point; RFC 2046 is pretty
clear about the component parts "need[ing] to be in a particular order",
which this is in conflict with]

   representation is preceded by its Content-Format ID.  The private key
   can be in unprotected PKCS#8 [RFC5958] format (Content-Format 284) or
   protected inside of CMS SignedData (Content-Format 280).  The

Phrasing it like this makes it soun like the server can just
spontaneously decide that it wants to sign the key content, as opposed
to having it be dependant on the CSR's contents.  Also... 


/The private key/ 

Dependent on the contents of the CSR, the private key/ 


   SignedData is signed by the party that generated the private key,
   which may be the EST server or the EST CA.  The SignedData is further
   protected by placing it inside of a CMS EnvelopedData as explained in
   Section 4.4.2 of [RFC7030].  In summary, the symmetrically encrypted

.... if the SignedData is not the outermost container, then we don't
what the relevant Content-Format for it is; we only care about the
Content-Format for the EnvelopedData. 


s/ SignedData is signed/SignedData, placed in the outermost container,
is signed/ 

s/ The SignedData is further protected by placing it inside of a CMS

SignedData placed within the Enveloped Data does not need additional


Also, did we explicitly consider and reject AuthEnvelopedData? 


Not sure about this 


   key is included in the encryptedKey attribute in a KEKRecipientInfo
   structure.  In the case where the asymmetric encryption key is
   suitable for transport key operations the generated private key is
   encrypted with a symmetric key which is encrypted by the client
   defined (in the CSR) asymmetric public key and is carried in an

nit: hyphenate "client-defined" 

<pvds> done </pvds>

   encryptedKey attribute in a KeyTransRecipientInfo structure.
   Finally, if the asymmetric encryption key is suitable for key
   agreement, the generated private key is encrypted with a symmetric
   key which is encrypted by the client defined (in the CSR) asymmetric

In the key-agreement case, the symmetric key-encryption key is the
result of the key-agreement operation, no?  In which case it is not
itself encrypted, but rather the server's ephemeral public value is


In RFC7030 the text says: the EnvelopedData content is encrypted using a

generated symmetric encryption key (that means ephemeral I assume). The
cryptographic strength of 

the symmetric encryption key SHOULD be equivalent to the clientspecified

asymmetric key. 

However, I see no explicit relation with the ephemeral public value. 

I don't know what to do here; probably insert the 7030 text. 


   public key and is carried in an recipientEncryptedKeys attribute in a

   [RFC7030] recommends the use of additional encryption of the returned
   private key.  For the context of this specification, clients and
   servers that choose to support server-side key generation MUST
   support unprotected (PKCS#8) private keys (Content-Format 284).
   Symmetric or asymmetric encryption of the private key (CMS
   EnvelopedData, Content-Format 280) SHOULD be supported for
   deployments where end-to-end encryption needs to be provided between
   the client and a server.  Such cases could include architectures
   where an entity between the client and the CA terminates the DTLS
   connection (Registrar in Figure 4).

This carefully says nothing about recommendations for use, only for
software support.  Are we letting 7030's recommendation for use of
encryption stand?  It's probably worth being explicit, either way. 

<pvds> I did not find any recommendation for use in RFC7030 apart the
responsibility of the server for generating random numbers. The
recommendations at the top of section 5.8 of the draft seem adequate in
my opinion. The alternative is classifying the applications; unless you
see a better way to do this. 


Section 6

   The EST-coaps-to-HTTPS Registrar MUST terminate EST-coaps downstream
   and initiate EST connections over TLS upstream.  The Registrar MUST
   authenticate and OPTIONALLY authorize the clients and it MUST be 



s/ authenticate and OPTIONALLY authorize the clients and/ 

authenticate and authorize client request, while/ 


Why OPTIONAL?  (Also, nit: OPTIONALLY isn't a 2119 keyword; only

   client.  For example, it could be configured to accept POP linking
   information that does not match the current TLS session because the
   authenticated EST client Registrar has verified this information when
   acting as an EST server.

This is close enough to a literal quote that we might think about
actually quoting and using quotation marks.
nit: s/POP/PoP/ if we don't do the literal quote. 


Hope my co-authors will react to this 


   For some use cases, clients that leverage server-side key generation
   might prefer for the enrolled keys to be generated by the Registrar
   if the CA does not support server-side key generation.  Such
   Registrar is responsible for generating a new CSR signed by a new key
   which will be returned to the client along with the certificate from

nit: "Such a Registrar" 

<pvds> done </pvds>

   the CA.  In these cases, the Registrar MUST support random number
   generation using proper entropy.

Not just support -- use! 

<pvds>done </pvds>

   Additionally, a conversion from CBOR major type 2 to Base64 encoding
   MUST take place at the Registrar when server-side key generation is
   supported.  [...]

Not always? 

<pvds> IMO always; removed the when…. 


   key, the encrypted CMS EnvelopedData blob MUST be converted to binary
   in CBOR type 2 downstream to the client.

I think we should reword this -- my first reading of "downstream to the
client" is "after the client in the processing path", which doesn't
actually help the client.  Presumably we mean at the registrar, in the
downstream direction, towards the client. 


s/ MUST be converted to binary in CBOR type 2 downstream to the client./

MUST be converted at the Registrar to binary CBOR type 2 downstream to
the client./ 


   The EST-coaps-to-HTTP Registrar MUST support resource discovery
   according to the rules in Section 5.1.  Section 5.1. 


Second section 5.1 is removed 


Do we need to say anything about translation of discovered URIs? 

<pvds> I don't think so; 

The Registrar discovers the EST server, while the TLS client discovers
the registrar. I don't see the client discovering the EST server through
the Registrar 


Section 7

   This section addresses transmission parameters described in sections
   4.7 and 4.8 of [RFC7252].  EST does not impose any unique values on
   the CoAP parameters in [RFC7252], but the EST parameter values need
   to be tuned to the CoAP parameter values.

I don't understand what "but the EST parameter values need to be tuned
to the CoAP parameter values" means. 


s/ but the EST parameter values need to be tuned to the CoAP parameter

but the setting of the CoAP parameter values may have consequences for
the setting of the EST parameter values/ 


   It is recommended, based on experiments, to follow the default CoAP
   configuration parameters ([RFC7252]).  However, depending on the
   implementation scenario, retransmissions and timeouts can also occur
   on other networking layers, governed by other configuration
   parameters.  A change in a server parameter MUST ensure the adjusted
   value is also available to all the endpoints with which these
   adjusted values are to be used to communicate.

I don't understand who this is a normative requirement upon.  Is it the
network operator's, to propagate configuration changes?  Or is there
supposed to be some automated protocol that makes adjusted values


It is meant as reminder to anyone doing the configuration of a given
installation; you want to suppress the text? 


   o  NSTART: A parameter that controls the number of simultaneous
      outstanding interactions that a client maintains to a given
      server.  An EST-coaps client is not expected to interact with more
      than one servers at the same time, which is the default NSTART
      value defined in [RFC7252].

nit: there's a mismatch between "to a given server" and "more than one
servers at the same time".  (Also, s/one servers/one server/.) 


s/ not expected to interact with more than one servers at the same time/

/is expected to control at most one interaction with a given server,/ 


   o  PROBING_RATE: A parameter which specifies the rate of re-sending
      non-confirmable messages.  The EST messages are defined to be sent
      as CoAP confirmable messages, hence this setting is not

Section 5.4 only has it as RECOMMENDED to send requests in CON messages,
so we should still say something here. 


s/ The EST messages are defined to be sent as CoAP confirmable messages,
hence this setting is not applicable./ 

In the rare situations that non-confirmable messages are used, the
default PROBING_RATE value defined in RFC7252 applies./ 


Section 9.1

I think we probably need this document as a reference for all the
allocations; as the document effectuating the registration, we are still
of interest even if most details of content encoding lie elsewhere.

Section 9.2

The grammar for these entries is a bit stilted, though the existing
registrations are not so far off.

nit: should ace.est.att include the word "get" like ace.est.crts does? 

<pvds> added get </pvds>

Section 10.1

   The security considerations of Section 6 of [RFC7030] are only
   partially valid for the purposes of this document.  As HTTP Basic
   Authentication is not supported, the considerations expressed for
   using passwords do not apply.

It may be worth explicitly stating that "the other portions of the
security considerations of RFC 7030 continue to apply". 

<pvds>added </pvds>

   Modern security protocols require random numbers to be available
   during the protocol run, for example for nonces, ephemeral (EC)
   Diffie-Hellman key generation.  This capability to generate random

nit: the comma expects a 3+ element list but we only have two elements.
Just "and" suffices? 

<pvds>absolutely right </pvds>

   Analysis SHOULD be done to establish whether server-side key
   generation increases or decreases the probability of digital identity

In the abstract sense, this seems like a non-normative "should".  But if
we make it apply specifically to those deploying server-side key
generation then it is appropriately normative. 


Preceded by: For those deploying server-side key generation, 


   It is important to note that sources contributing to the randomness
   pool used to generate random numbers on laptops or desktop PCs are
   not available on many constrained devices, such as mouse movement,
   timing of keystrokes, air turbulence on the movement of hard drive
   heads, as pointed out in [PsQs].  Other sources have to be used or

nit: need an "and" (or "or") to close the list. 

<pvds>repaired with or</pvds>

   It is also RECOMMENDED that the Implicit Trust Anchor database used
   for EST server authentication is carefully managed to reduce the
   chance of a third-party CA with poor certification practices
   jeopardizing authentication.  Disabling the Implicit Trust Anchor

We may want to call out that since the implicit database is used for the
initial /crts request, that single jeporadized exchange could cause all
subsequent exchanges from that client to be compromised as well. 

<pvds> before Disabling: 

"Remark that the initial /crts request uses the implicit database, and
that a compromised implicit database has as consequence that all
subsequent exchanges from that client are jeopardized." 


   database after successfully receiving the Distribution of CA
   certificates response (Section 4.1.3 of [RFC7030]) limits any risk to
   the first DTLS exchange.  Alternatively, in a case where a /sen
   request immediately follows a /crts, a client MAY choose to keep the
   connection authenticated by the Implicit TA open for efficiency
   reasons (Section 4).  A client that pipelines EST-coaps /crts request

nit: is "pipelines" the right word here, given that HTTP pipelining is a
thing and CoAP pipelining (probably?) isn't, and the former isn't what
we're doing anyway? 

<pvds> suggestion: 



   What's more, POP linking uses tls-unique as it is defined in
   [RFC5929].  The 3SHAKE attack [tripleshake] poses a risk by allowing

nit: "such POP linking" or "the CMC POP linking" 

<pvds>CMC POP </pvds>

   a man-in-the-middle to leverage session resumption and renegotiation
   to inject himself between a client and server even when channel
   binding is in use.  The attack was possible because of certain (D)TLS
   implementation imperfections.  In the context of this specification,

I don't think we can solely blame the attacks on implementation
imperfections (though they were certainly compounding factors).  Does
this sentence really add any value to the current document? 


Leave this to my co-authors 


   binding mechanism.  Such a mechanism could include an updated tls-
   unique value generation like the tls-unique-prf defined in
   [I-D.josefsson-sasl-tls-cb] by using a TLS exporter [RFC5705] in TLS
   1.2 or TLS 1.3's updated exporter (Section 7.5 of [RFC8446]).  Such
   mechanism has not been standardized yet.  Adopting a channel binding

We probably should be explicit about "using a TLS Exporter value in
place of the tls-unique value in the CSR", just from a writing clarity


Leave to my co-authors from here to section 10.2 


It might be worth splitting the triple-handshake bits (including open
question) into a separate subsection so that we can make a forward
reference to it from earlier in the document.

   value generated from an exporter would break backwards compatibility.
   Thus, in this specification we still depend on the tls-unique
   mechanism defined in [RFC5929], especially since a 3SHAKE attack does
   not expose messages exchanged with EST-coaps.

I suppose that new endpoint names would be one way to work through the
backwards-compatibility break, though it's not entirely clear that we
need to say so in this document.  We probably do want to say that even
though EST-coaps looks like a new protocol that could get away with
changing the default, we want to preserve the ability for the RA to
proxy through to a "classic" EST HTTPS server, so we are in fact
constrained to use the compatible choice.

   Regarding the Certificate Signing Request (CSR), an EST-coaps server
   is expected to be able to recover from improper CSR requests.

What does "recover" mean?  Is it just "not crash" or is it expected to
somehow still be able to issue a certificate?  (If the former, that
might be implicit in an RFC 3552 threat model, though saying it
explicitly probably doesn't hurt.)

Section 10.2

   The Registrar proposed in Section 6 must be deployed with care, and
   only when the recommended connections are impossible.  When POP

Do we actually explicitly say that the direct connection is recommended
anywhere?  If not, we should. 


Added at the end of the first paragraph of section 6: 

When not explicitly needed, it is RECOMMENDED to use direct connections
between EST server and client 


   linking is used the Registrar terminating the TLS connection
   establishes a new one with the upstream CA.  Thus, it is impossible

I think technically it terminates DTLS and esablishes a new TLS


s/ terminating the TLS connection establishes a new one/ 

terminating the DTLS connection establishes a new TLS connection/ 


   for POP linking to be enforced end-to-end for the EST transaction.
   The EST server could be configured to accept POP linking information
   that does not match the current TLS session because the authenticated
   EST Registrar client has verified this information when acting as an
   EST server.

I think we need to say that the EST server "assumes" or "trusts" that
the registrar has verified this information -- it is to some extent a
leap of faith. 

<pvds> Suggestion: 

s/ client has verified this information when acting as an EST server / 

acting as an EST-server, assumes that the client has verified this


   The introduction of an EST-coaps-to-HTTP Registrar assumes the client
   can trust the registrar using its implicit or explicit TA database.

I'm not entirely sold on "trust" as the best word here (vs., e.g.,
validate), but don't object to it.

<pvds> leave as is, have no better word </pvds> 

   generating the key.  In such cases, the existence of a Registrar
   requires the client to put its trust on the registrar doing the right
   thing if it is generating the private key.

This is true, though it (probably correctly, for our purposes) does not
give any indication of what "the right thing" is intended to be :) 


Remove: "doing the right thing" 



Section 11.2

I think draft-ietf-lamps-rfc5751-bis, RFC 5958, RFC 8075, and RFC 8422
should be normative references. 

<pvds>done; </pvds>

If we're going to say that this spec requires conformance to RFC 7925's
DTLS profile (which we currently don't, but I suggest above that we do),
it will need to be a normative reference as well. 


In section 4, 

/fits into/conforms to/ 


I don't understand why RFC 7231 is in the 'reference' column for
application/csrattrs in Table 4; its presence there would normally
suggest that it should be a normative reference.  


Removed RFC7231, it is not mentioned in RFC7030 


RFC 5929 is interesting, as it is of course a normative reference for
RFC 7030, which we use normatively, but we may not need to cite it
directly as a normative reference from this document. 


Continue to do so 


It may be worth citing RFC 7525 as BCP 195 where it appears. 

<pvds>To be done </pvds>

Appendix A

   transported in hex, but in binary.  The payloads are shown
   unencrypted.  In practice the message content would be transferred
   over an encrypted DTLS tunnel.

I expect a tsvart reviewer to complain about the use of the word
"tunnel" here, and suggest "channel" as an alternative. 

<pvds>done </pvds>

   The certificate responses included in the examples contain Content-
   Format 281 (application/pkcs7).  If the client had requested Content-
   Format TBD287 (application/pkix-cert) by querying /est/skc, the
   server would respond with a single DER binary certificate.

Just to check my own understanding: this will always appear within a
multipart-core container, right? 


Added: in the multipart-core container 


Appendix A.1

     Option (Uri-Port)
        Option Delta = 0x4  (option# 3+4=7)
        Option Length = 0x4
        Option Value = 9085
      Option (Uri-Path)
        Option Delta = 0x4   (option# 7+4=11)
        Option Length = 0x5
        Option Value = "est"

This is more for my own edification than the document's sake, so thank
you for your time, but what accounts for the "extra" length here?  The
"est" is three bytes, and what makes up for the other two?  Also, I
assume that the port value of 9805 is the decimal value, which gets
CBOR encoded into two bytes  of integer encoding plus the byte with
additional information 25 to indicate the two-byte integer, and another
byte that I need help accounting for. 


Many thanks; an old misreading of an example in 7252. 

For the option length of URI-Path we included the quotations as well;
That is WRONG. 

Repaired it everywhere. 

Options are not CBOR encoded. 


Appendix A.2

Do we want to say anything about the IDevID in the CSR/cert?
I note that the breakdown in Appendix C.2 (looks like openssl output)
does not decode the otherName (though asn1parse can be convinced to do


What do you suggest for IDevID? 

Actually openssl was used extensively for generating the examples. 

Will be happy to learn about otherName 


Appendix A.3

I'm having trouble validating the private key in the PKCS#8 component:
asn1parse says: 


As input I used recently a hex dump of Wt1234.key.der: 


I used openssl pkey -in Wt1234.key.der -text -noout -inform der\ 

-passin pass:watnietweet 

The password is may be prohibitive? 

Resulting in:
Private-Key: (256 bit)
ASN1 OID: prime256v1

$ unhex|openssl asn1parse -inform der
    0:d=0  hl=3 l= 135 cons: SEQUENCE          
    3:d=1  hl=2 l=   1 prim: INTEGER           :00
    6:d=1  hl=2 l=  19 cons: SEQUENCE          
    8:d=2  hl=2 l=   7 prim: OBJECT            :id-ecPublicKey
   17:d=2  hl=2 l=   8 prim: OBJECT            :prime256v1
   27:d=1  hl=2 l= 109 prim: OCTET STRING      [HEX

which doesn't look like an RFC5208 PrivateKeyInfo:

      PrivateKeyInfo ::= SEQUENCE {
        version                   Version,
        privateKeyAlgorithm       PrivateKeyAlgorithmIdentifier,
        privateKey                PrivateKey,
        attributes           [0]  IMPLICIT Attributes OPTIONAL }

      Version ::= INTEGER

      PrivateKeyAlgorithmIdentifier ::= AlgorithmIdentifier

      PrivateKey ::= OCTET STRING

      Attributes ::= SET OF Attribute

due to the lack of OID for privateKeyAlgorithm, etc.
(`openssl pkcs8` also chokes on it, but I don't have a working example
can't rule out user error there.)

Even that giant OCTET STRING 27 bytes in doesn't seem to match a

$ unhex|openssl asn1parse -inform der -strparse 27
    0:d=0  hl=2 l= 107 cons: SEQUENCE          
    2:d=1  hl=2 l=   1 prim: INTEGER           :01
    5:d=1  hl=2 l=  32 prim: OCTET STRING      [HEX
   39:d=1  hl=2 l=  68 cons: cont [ 1 ]        
   41:d=2  hl=2 l=  66 prim: BIT STRING        

though the OCTET STRING does have the private key and the BIT STRING has
the public key's contents as depicted in C.3 (details of that too boring
to show).

So I have to wonder if I'm messing something up, somewhere.

Section A.4

I'm not sure how useful repeating the RFC 7030 csrattrs is: do we expect
(e.g.) brainpoolP384r1 to be relevant for our readers? 


It was added for completeness sake; nothing more. 

Suppressing it may provoke other questions like: Why is it not there? 


Appendix B.1

   and BLOCK option Block2.  The minimum PMTU is 1280 bytes, which is
   the example value assumed for the DTLS datagram size.  The example

I'm not seeing how this relates to the rest of the section. 


I see. We do not use it anymore.; suppressed it. 


                                  The CoAP message adds around 10 bytes,
   the DTLS record 29 bytes.  To avoid IP fragmentation, the CoAP Block

The DTLS overhead can also vary based on cipher suite, padding, etc., so
a bit more qualification ("we assume", "around", etc.) might be in


Added: "in this example" 


   tenth packet of 63 bytes.  The client sends an IPv6 packet containing
   the UDP datagram with the DTLS record that encapsulates the CoAP
   request 10 times.  The server returns an IPv6 packet containing the
   UDP datagram with the DTLS record that encapsulates the CoAP
   response.  The CoAP request-response exchange with block option is

The definite vs. indefinite articles here don't seem quite right, and
each of the 10 datagrams do not encapsulate the entire CoAP request. 


I don't understand your meaning. 


   with exponent (2**(SZX+4)) separated by slashes.  The Length 64 is
   used with SZX=2 to avoid IP fragmentation.  The CoAP Request is sent

We just said "to avoid IP fragmentation" ten lines ago.




Should we be using the same Token value in two different exchanges in
this document? 


No opinion 


Appendix B.2

   In this example, the requested Block2 size of 256 bytes, required by
   the client, is transferred to the server in the very first request
   message.  The block size 256=(2**(SZX+4)) which gives SZX=4.  The

I don't see a Block2 size in the first request message, just Block1: 


Thanks. Block1 it is 


   POST [2001:db8::2:321]:61616/est/sen (CON)(1:0/1/256) {CSR req} -->
          <-- (ACK) (1:0/1/256) (2.31 Continue)

Also, we seem to have stopped using the "{CSR req frag#2}" notation that
we had in the main body text. 

<pvds>That is an oversight; adapted 


Appendix C.2

[I mentioned otherName's non-decoding earlier]

Appendix C.3

I find it kind of amusing that we have a "Netscape Comment" in the
generated cert :) 


This was the result of a lengthy openssl struggle. 

Any suggestions for improvement are very welcome indeed.