Subject: [Isms] Comments about draft-ietf-isms-secshell-13, Section 5

From: <[email-masked]>
Date: Thu, 27 Nov 2008 13:56:55 +0200

Comments about draft-ietf-isms-secshell-13, Section 5:

Overall: I think we're *almost* done -- I think we need to fill in
some minor details, but those shouldn't affect the overall processing.

- The distinction between tmStateReference cache and LCD is a bit
unclear -- do these actually mean the same thing? For example, Section
5.3 talks about creating an LCD entry when the SSH client has
established a connection (step 7), and Section 5.2 checks if the LCD
entry exists (step 2).

But there's no text saying that the SSH server ever creates any LCD
entries -- so step 2 of Section 5.2 would always fail when
e.g. sending command responses. That's clearly not the intention.
Section 5.1 does talk about creating a tmStateReference cache --
perhaps it should talk about creating a LCD cache entry? Or perhaps
Sections 5.2/5.3 should talk about tmStateReference cache? Or perhaps 
we need to describe opening a session also from SSH server's point 
of view? (Section 5.3 talks only about what the SSH client does, and 
says basically nothing about what the server does.)

- Section 5.2 (step 2) says the LCD entry is indexed by
(destTransportAddress,tmSecurityName) but 5.3 (step 7) says it's
(destTransportAddress,tmStateReference). Probably the former is
correct? (but in that case, there's no need to store tmSecurityName 
in the entry itself, so step 7 of 5.3 may need some editing)

- Section 5.3, step 1: it would be *really* useful to add a note 
that to authenticate the server, the client usually stores
(destTransportAddress, server host public key) pairs in
implementation-dependent manner.  (Otherwise, this text gets difficult
to understand.)

- Section 5.1: we shouldneed a better description of how tmSecurityName
works on the SSH client side; IMHO the current behavior isn't quite
right: Suppose a command generator sends a command with
tmSecurityName="alice" and
destTransportAddress="[email-masked]:1234". An SSH
connection is opened and so on. When the command response is received,
the current text in Section 5.1 would lead to having
tmSecurityName="ahopkins" in the response -- a slightly unexpected
response.  Would it be better to extract the tmSecurityName from the
"LCD cache entry" (or whatever is the right term) that was created
when the client first established the session?

- Section 5.1, on related note, on SSH client side, the
tmTransportAddress in incoming messages should probably also be
extracted from the "LCD cache entry", so that it's exactly the same as
was used for the outgoing message (that triggered creating the SSH
connection).

- Section 5.1, we should say what the tmTransportAddress for incoming
messages looks on the SSH server side: it's "address:port" form (not
user@address:port).

- Typos:
Section 5.3, "tmSecurtityName"
Section 5.4, "sever"
Several sections (including the MIB): "sshtmSessionUnavaliableSubsystems"

Best regards,
Pasi
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From: "tom.petch" <[email-masked]>
Date: Fri, 28 Nov 2008 14:22:56 +0100

On LCD, this is architected in RFC3411.

The LCD is defined as sets of configuration information needed by models and
applications (s3.4.2).

The cache is introduced so that if the LCD is changed, then the same security
information is still available for a Response as was used in the Request (s
A.1.5).

So no, the (securityStateReference at least) cache is quite separate from the
LCD.  tmsm likens the tmStateReference to the existing RFC3411 cache so by
implication, it too should be distinct from the LCD.

Tom Petch