On 25/09/13 13:25, Adam Back wrote:
On Wed, Sep 25, 2013 at 11:59:50PM +1200, Peter Gutmann wrote:
Something that can sign a new RSA-2048 sub-certificate is called a
CA. For
a browser, it'll have to be a trusted CA. What I was asking you to
explain is
how the browsers are going to deal with over half a billion (source:
Netcraft
web server survey) new CAs in the ecosystem when websites sign a new
RSA-2048
sub-certificate.
This is all ugly stuff, and probably 3072 bit RSA/DH keys should be
deprecated in any new standard, but for the legacy work-around senario to
try to improve things while that is happening:
Is there a possibility with RSA-RSA ciphersuite to have a certified RSA
signing key, but that key is used to sign an RS key negotiation?
At least that was how the export ciphersuites worked (1024+ bit RSA auth,
512-bit export-grade key negotation). And that could even be weakly
forward
secret in that the 512bit RSA key could be per session. I imagine that
ciphersuite is widely disabled at this point.
But wasnt there also a step-up certificate that allowed stronger keys if
the
right certificate bits were set (for approved export use like banking.)
Would setting that bit in all certificates allow some legacy
server/browsers
to get forward secrecy via large, temporary key negotiation only RSA keys?
(You have to wonder if the 1024-bit max DH standard and code limits was bit
of earlier sabotage in itself.)
A couple of points: all the big CAs will give you a new certificate with
a new key for free (but revocation is your baby) - while it isn't
something they do, can't they issue say two years worth of one-day certs
for perhaps a little more than the price of a two-year cert?
In the UK we have a law called RIPA, part of which allows Plod to demand
keys. They can demand keys used for encryption and for key setup - but
they can't demand keys used only for authentication. I don't think they
routinely demand keys from TLS/SSL webservers.
The point is that in an ordinary TLS session the RSA key is used for
both secrecy and authentication - in any future TLS these functions
should be split.
Also, Dan Boneh was talking at this years RSA cryptographers track about
putting some sort of quantum-computer-resistant PK into browsers - maybe
something like that should go into TLS2 as well?
You need to get the browser makers - Apple, Google, Microsoft, Mozilla -
and the webservers - Apache, Microsoft, nginx - together and get them to
agree we must all implement this before writing the RFC.
-- Peter Fairbrother
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