Re: [TLS] security levels for TLS
Nicolas Williams <Nicolas.Williams@sun.com> Fri, 12 October 2007 22:00 UTC
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Date: Fri, 12 Oct 2007 16:59:01 -0500
From: Nicolas Williams <Nicolas.Williams@sun.com>
To: Mike <mike-list@pobox.com>
Subject: Re: [TLS] security levels for TLS
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On Fri, Oct 12, 2007 at 02:41:51PM -0700, Mike wrote: > >>How long do you think it would take > >>to add this extension to a TLS toolkit? In my own code, I could > >>probably do it in less than a day, with time left over to get in a > >>round of 18 holes. > > > >No doubt. Of what positive and negative value would such code be? > > Positives: > > - this would allow a server to maintain multiple sets of keys > and certificate chains of varying cryptographic strength; > clients with differing requirements could ask for the level > they desire, instead of being stuck with the lowest common > denominator It can do things like this today. > - knowing exactly what the client is looking for helps the > server select the appropriate cipher suite without the need > for the client to renegotiate the connection; for example, > if the server only supports 1024-bit DH parameters, and the > client asks for 1536-bit, the server can skip past the DHE_* > cipher suites and select maybe an RSA-based cipher suite > that the client would accept The server and client already know how to negotiate properly. > - this mechanism would give power to the client that it > currently doesn't have, to directly influence the crypto- > graphic strength of the connection beyond simply listing > acceptable cipher suites The client already can negotiate from what it's willing to accept, and that's sufficient. > - hash agility (or now signature algorithm agility) is being > added to TLS; this is cryptographic strength agility You're ignoring everything we've been telling you about why absolute security measurements of ciphersuites are not a good idea. > - a client is free to develop its own security profiles; no > "standard" profiles would be defined The client and server are already free to do so. > - a server can keep statistics on the values it receives, > allowing an administrator to know when it would make sense > to add support for longer keys, based on actual demand The server can already do this. > Negatives: > > - effort is needed to write a specification and approve it > - a server may not support the extension, so a client may > have to implement an inefficient renegotiation scheme in > addition anyway > - Eric doesn't like it ;-) > - Others? This is not about personal preferences. We're telling you this is not needed and that fixed absolute cryptographic strength numbers are neither feasible nor a good idea. > >Confusing and/or giving users false senses of security are definitely > >negative. > > Fully agreed. I don't see how this would be confusing or give > a false sense of security. The client still has to check that > the requested key lengths (and other parameters it cares about) > are satisfied in the negotiated session. Eric points out that local policy is sufficient to achieve what you want. I do think that a standard way to describe security policies for TLS and other protocols might be useful for distributing policy, but at the end of the day that'd still be _local_ policy, with no changes to TLS being required. Nico -- _______________________________________________ TLS mailing list TLS@lists.ietf.org https://www1.ietf.org/mailman/listinfo/tls
- [TLS] security levels for TLS Nikos Mavrogiannopoulos
- Re: [TLS] security levels for TLS Eric Rescorla
- Re: [TLS] security levels for TLS Nikos Mavrogiannopoulos
- Re: [TLS] security levels for TLS Eric Rescorla
- Re: [TLS] security levels for TLS Yngve Nysaeter Pettersen
- Re: [TLS] security levels for TLS Paul Hoffman
- RE: [TLS] security levels for TLS Kemp, David P.
- Re: [TLS] security levels for TLS Mike
- Re: [TLS] security levels for TLS Eric Rescorla
- Re: [TLS] security levels for TLS Mike
- Re: [TLS] security levels for TLS Eric Rescorla
- Re: [TLS] security levels for TLS Nicolas Williams
- Re: [TLS] security levels for TLS Eric Rescorla
- Re: [TLS] security levels for TLS Steven M. Bellovin
- Re: [TLS] security levels for TLS Nicolas Williams
- Re: [TLS] security levels for TLS Mike
- Re: [TLS] security levels for TLS Eric Rescorla
- Re: [TLS] security levels for TLS Mike
- Re: [TLS] security levels for TLS Eric Rescorla
- Re: [TLS] security levels for TLS Mike
- Re: [TLS] security levels for TLS Paul Hoffman
- Re: [TLS] security levels for TLS Nikos Mavrogiannopoulos
- Re: [TLS] security levels for TLS Eric Rescorla
- Re: [TLS] security levels for TLS Eric Rescorla
- Re: [TLS] security levels for TLS Nicolas Williams
- Re: [TLS] security levels for TLS Nicolas Williams
- Re: [TLS] security levels for TLS Mike
- Re: [TLS] security levels for TLS Mike
- Re: [TLS] security levels for TLS Nicolas Williams
- Re: [TLS] security levels for TLS Mike
- Re: [TLS] security levels for TLS Eric Rescorla
- Re: [TLS] security levels for TLS Eric Rescorla
- Re: [TLS] security levels for TLS Mike
- Re: [TLS] security levels for TLS Mike
- Re: [TLS] security levels for TLS Eric Rescorla
- Re: [TLS] security levels for TLS Mike
- Re: [TLS] security levels for TLS Mike
- Re: [TLS] security levels for TLS Eric Rescorla
- Re: [TLS] security levels for TLS Eric Rescorla
- Re: [TLS] security levels for TLS Eric Rescorla
- Re: [TLS] security levels for TLS Paul Hoffman