[Curdle] Alexey Melnikov's Discuss on draft-ietf-curdle-ssh-ext-info-12: (with DISCUSS and COMMENT)

[Alexey Melnikov <[e-mail]>]

Alexey Melnikov has entered the following ballot position for
draft-ietf-curdle-ssh-ext-info-12: Discuss

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DISCUSS:
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This is generally a good and useful document. I have some minor comments I
would like to discuss:

3.2.  "delay-compression"

  This extension MAY be sent by both parties as follows:

    string         "delay-compression"
    string:
      name-list    compression_algorithms_client_to_server
      name-list    compression_algorithms_server_to_client

It is not clear for me from the formatting whether the first name-list is sent
by the client and the second by the server, or both lists are always included
in the value. I suspect it is the former, but can you please clarify?


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COMMENT:
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1) Sentences like:
  Use of  Receivers MUST tolerate any sequence of bytes; including null bytes 
  at any position; in an unknown extension's extension-value.
or
 In particular, applications MUST  tolerate any sequence of bytes; including
 null bytes at any position;  in an unknown extension's extension-value.

Use of punctuation is not my strongest point, but I am reasonably certain that
use of ";" is not correct here. I think you should use (). Otherwise these
sentences are reading as a list of 3 things, yet in both cases the 3rd is a
continuation of the 1st.

2) In Section 2.5:

 The relative order in which extensions appear in an
  EXT_INFO message MUST be ignored by default; but an extension MAY
  specify that the order matters for that extension, in a specific way.

Can you provide an example of why depending on order would be useful? This
potentially makes it harder to implement.

In several places you use EXT_INFO instead of SSH_MSG_EXT_INFO. It would be
less confusing if you used the latter consistently everywhere.

3) In 3.1:

  This extension is sent by the server, and contains a list of public
  key algorithms that the server is able to process as part of a
  "publickey" authentication request. If a client sends this extension,
  the server MAY ignore it, and MAY disconnect.

Why would the client disconnect when seeing this extension? Does it mean it is
broken?

Also, as the client can always disconnect at any point, why mentioning this
here?

  If a server does not send this extension, a client MUST NOT make any
  assumptions about the server's public key algorithm support, and MAY
  proceed with authentication requests using trial and error. Note that
  implementations are known to exist that apply authentication penalties
  if the client attempts to use an unexpected public key algorithm.

Can you elaborate on what do you mean by "authentication penalties" in this
context?