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[TLS] Last Call for comments on modifications to section 7.4.1.4 of draft-ietf-tls-rfc4346-bis
This is a last call for comments on modifications to section 7.4.1.4 of
draft-ietf-tls-rfc4346-bis-10
(http://tools.ietf.org/html/draft-ietf-tls-rfc4346-bis-10), which is
currently in the RFC editor queue. The modifications are in response to
issues raised on the list with regard to missing text on hello
extensions and session resumption (see
http://www.ietf.org/mail-archive/web/tls/current/msg02645.html). The
modifications are attached below.
The last call will last for one week so please send your comments to the
list by May 22, 2008.
Thanks,
Joe
In 7.4.1.4, after "as described in Section 12" and before "There are
subtle":
An extension type MUST NOT appear in the ServerHello unless the
same extension type appeared in the corresponding ClientHello. If
a client receives an extension type in ServerHello that it did not
request in the associated ClientHello, it MUST abort the handshake
with an unsupported_extension fatal alert.
Nonetheless, "server-oriented" extensions may be provided in the
future within this framework. Such an extension (say, of type x)
would require the client to first send an extension of type x in
ClientHello with empty extension_data to indicate that it supports
the extension type. In this case, the client is offering the
capability to understand the extension type, and the server is
taking the client up on its offer.
When multiple extensions of different types are present in the
ClientHello or ServerHello messages, the extensions MAY appear in
any order. There MUST NOT be more than one extension of the same
type.
Finally, note that extensions can be sent both when starting a new
session and when requesting session resumption. Indeed, a client
that requests session resumption does not in general know whether
the server will accept this request, and therefore it SHOULD send
the same extensions as it would send if it were not attempting
resumption.
In general, the specification of each extension type needs to
describe the effect of the extension both during full handshake and
session resumption. Most current TLS extensions are relevant only
when a session is initiated: when an older session is resumed, the
server does not process these extensions in Client Hello, and does
not include them in Server Hello. However, some extensions may
specify different behavior during session resumption.
Also, we should add to end of Section 7.4.1.4.1:
When performing session resumption, this extension is not included
in Server Hello, and the server ignores the extension in Client
Hello (if present).
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