I recently implemented some tests for renegotiation that turned up a
discrepancy between the way TLS and DTLS work.
If a server sends a HelloRequest to the client, then the client responds
by initiating a renegotiation handshake.
We support two forms of renegotiation handshake: normal and abbreviated.
The abbreviated form was added in OpenSSL 1.0.1. Basically the
difference is whether we can do session resumption in a reneg handshake
or not. With the normal form, we never do: with the abbreviated form we
will do if possible.
In TLS from 1.0.1, when a HelloRequest is received from the server, the
client will always attempt an abbreviated reneg handshake, i.e. it will
send through a session id in the ClientHello.
In DTLS (and TLS before 1.0.1) it never attempts an abbreviated reneg
handshake, i.e. it will always send through an empty session id in the
ClientHello.
This behaviour goes all the way back to when abbreviated reneg handshake
support was first added in this commit:
commit 48ae85b6ffe85e327f63c59d8de6a94a8b8f2d3b
Author: Dr. Stephen Henson <st...@openssl.org>
AuthorDate: Thu Aug 26 14:22:40 2010 +0000
Commit: Dr. Stephen Henson <st...@openssl.org>
CommitDate: Thu Aug 26 14:22:40 2010 +0000
PR: 1833
Submitted By: Robin Seggelmann <seggelm...@fh-muenster.de>
Support for abbreviated handshakes when renegotiating.
Looking at that commit, it appears to me that the intention was that the
"default" behaviour would remain unchanged. This was just a new feature
that you could use if you want. That would suggest that the DTLS
behaviour was what was intended to happen in this scenario, and the
change of default TLS behaviour was a bug. Reading through the original
RT ticket for this patch there is no suggestion that default behaviour
was going to change...it reads like this is optional new functionality.
The question is: what to do now?
The current behaviour is not *wrong* either for TLS or DTLS, but the
discrepancy is quite weird and confusing. Should we:
1) Change TLS to behave like it used to, and like DTLS still does
2) Change DTLS to be consistent with the TLS behaviour
3) Keep it as it is and retain the current inconsistency
And if we change things, should we just change it in the current dev
branch - or backport it as a bug fix?
Thoughts?
Matt
--
openssl-dev mailing list
To unsubscribe: https://mta.openssl.org/mailman/listinfo/openssl-dev
