Re: [TLS] New draft: draft-solinas-tls-additional-prf-input-00.txt
Simon Josefsson <simon@josefsson.org> Tue, 06 October 2009 13:32 UTC
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From: Simon Josefsson <simon@josefsson.org>
To: Paul Hoffman <paul.hoffman@vpnc.org>
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Date: Tue, 06 Oct 2009 15:34:04 +0200
In-Reply-To: <p0624087dc6efe84bcc54@[10.20.30.163]> (Paul Hoffman's message of "Mon\, 5 Oct 2009 11\:17\:58 -0700")
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Cc: tls@ietf.org
Subject: Re: [TLS] New draft: draft-solinas-tls-additional-prf-input-00.txt
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Paul Hoffman <paul.hoffman@vpnc.org> writes: >>http://www.ietf.org/internet-drafts/draft-solinas-tls-additional-prf-input-00.txt > > Greetings again. We would like to hear input on this draft from the > TLS community. The basic idea is an extension that would allow the two > parties to give additional information that is directly mixed into the > master secret through the PRF. The document seems fine to me. As far as I can tell, any implementation (including mine) of draft-rescorla-tls-opaque-prf-input-00.txt would be compatible with draft-solinas-tls-additional-prf-input-00.txt, and that is good. The two last examples in section 1.1 doesn't appear fully baked to me. Quoting: TLS servers may arrange for their clients to provide authentication data early in the protocol (such as an HMAC value computed over a fresh random value using a shared secret as the key) in order to authenticate the client as a member of a private network or as an additional means of mitigating the impact of a denial-of-service attack. Implementors may want to provide a mechanism for relaying identity and version information similar to the "Vendor ID Payload" used in ISAKMP [RFC2408]. If these use-cases are intended to be realistic use-cases of the extension (which doesn't seem clear to me), I believe the document needs more work: it should suggest a structure of the PRF data so that servers will understand what type of data the client sent. Compare for example how RFC 5077 suggests a format. The document could even go further and mandate a particular format, which would make the use-cases more likely to interoperate, such as: enum { entropy(0), (65535) } AdditionalPRFInputType; struct { AdditionalPRFInputType type; opaque value<0..2^16-1>; } AdditionalPRFInput; AdditionalPRFInput prfinputs<2..2^16-2>; The AdditionalPRFInputType could be a FCFS registry. The intention with the "entropy" field is that it should contain random data with no intended meaning, which appears to be the typical use-case. Other types can be allocated to signal the two use-cases in the example if/when needed. Alternatively, and considering the complexities in my proposed change, I would suggest that you remove other use cases than the one to provide additional entropy to the MS key computation and say that there is only one intended use-case for this extension. If other use-cases of the extension are important, they can be described in separate documents. Thanks, /Simon
- [TLS] New draft: draft-solinas-tls-additional-prf… Paul Hoffman
- Re: [TLS] New draft: draft-solinas-tls-additional… Simon Josefsson
- Re: [TLS] New draft: draft-solinas-tls-additional… Michael Gray
- Re: [TLS] New draft: draft-solinas-tls-additional… Nicolas Williams
- Re: [TLS] New draft: draft-solinas-tls-additional… Paul Hoffman
- Re: [TLS] New draft: draft-solinas-tls-additional… Michael Gray
- Re: [TLS] New draft: draft-solinas-tls-additional… Paul Hoffman
- Re: [TLS] New draft: draft-solinas-tls-additional… Michael Gray
- Re: [TLS] New draft: draft-solinas-tls-additional… Pasi.Eronen
- Re: [TLS] New draft: draft-solinas-tls-additional… Michael D'Errico
- Re: [TLS] New draft: draft-solinas-tls-additional… Russ Housley
- Re: [TLS] New draft: draft-solinas-tls-additional… Paul Hoffman
- Re: [TLS] New draft: draft-solinas-tls-additional… Nicolas Williams
- Re: [TLS] New draft: draft-solinas-tls-additional… Pasi.Eronen