Re: [TLS] PR #604 Change "supported_groups" to "supported_kems"

Sean Turner <sean@sn3rd.com> Tue, 13 September 2016 17:19 UTC

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From: Sean Turner <sean@sn3rd.com>
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Date: Tue, 13 Sep 2016 13:19:51 -0400
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To: Zhenfei Zhang <zzhang@securityinnovation.com>, "<tls@ietf.org>" <tls@ietf.org>
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Subject: Re: [TLS] PR #604 Change "supported_groups" to "supported_kems"
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There appears to be no consensus to adopt the change proposed by this PR.

The small condolence here is that the name+semantics for this extension has been changed once before and if the extension really needs to be renamed in 5-7 years we’ve got precedence for doing so.

spt

> On Aug 29, 2016, at 15:52, Zhenfei Zhang <zzhang@securityinnovation.com> wrote:
> 
> Hi list,
> 
> 
> 
> I have created a pull request
> 
> https://github.com/tlswg/tls13-spec/pull/604
> 
> 
> 
> I would like to suggest that we change the terminology "NamedGroup" to "KeyExchangeMethod".
> 
> 
> 
> In [1], it is suggested that we redefine the syntax, which leads to the separation of public key crypto 
> 
> and symmetric crypto during a handshake. Because of this separation, new terminology was defined
> 
> for key exchange algorithms and authentication algorithms for public key crypto in the key exchange 
> 
> extension. "NamedGroup" was used to refer the underlying key exchange parameters, which comes 
> 
> from the "Supported Elliptic Curves" in previous versions.
> 
> 
> 
> The use of "NamedGroup" implicitly requests the key exchange algorithm to be Deffie-Hellman type. 
> 
> While it is safe for now, it would be nice to have some crypto agility, and future proof. It would make 
> 
> the transition to other key exchange primitives (such as lattice based key exchange) or methods 
> 
> (such as key encapsulation mechanism) easier in the future, if we do not restrict the key exchange
> 
> by certain "Group".
> 
> 
> 
> Knowing that NIST has planned to standardize quantum-safe cryptography within 7 years of time 
> 
> (which can and should be accelerated), and those algorithms cannot be described in terms of "group",
> 
> the current terminology will due for a redesign by then. So I would suggest to change the 
> 
> "NamedGroup" now rather than later.
> 
> 
> 
> 
> Overall, this will have the following impact
> 
> 
> 
> 1. HelloRetryRequest
> 
> 
> 
> Change HelloRetryRequest structure to
> 
> 
> 
> struct {
> 
> ProtocolVersion server_version;
> 
> KeyExchangeMethod selected_kem;
> 
> Extension extensions<0..2^16-1>;
> 
> } HelloRetryRequest;
> 
> 
> 
> 2. Negotiated Groups
> 
> 
> 
> Throughout, change "supported_groups" to "supported_kems"; change "NamedGroupList" to 
> "KeyExchangeMethodList"; change "named_group_list" to "kem_list"; change NamedGroup to
> 
> KeyExchangeMethod
> 
> 
> 
> 3. Key Share:
> 
> Change KeyShareEntry structure to
> 
> 
> 
> struct {
> 
> KeyExchangeMethod kem;
> 
> opaque key_exchange<1..2^16-1>;
> 
> } KeyShareEntry;
> 
> 
> [1] https://github.com/ekr/tls13-spec/blob/15126cf5a08c445aeed97c0c25c4f10c2c1b8f26/draft-ietf-tls-tls13.md
> 
> 
> 
> Thanks for your time.
> 
> 
> 
> Zhenfei Zhang
> 
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