[ntpwg] [ntp:hackers] Handling authentication extensions (was MS-SNTP)

[Danny Mayer]

David L. Mills wrote:
> Danny,
> 
> I'm baffled by your comments. The current NTPv4 spec says nothing about 
> Autokey and makes no interpretation about the type field. The parser can 
> and does step through the extension fields without knowing anything 
> about the contents in order to find the MAC. The MAC can't be in an 
> extension field without violating backwards compatibility with 
> symmetric-key NTPv3 and NTPv4.
> 
> The current extension field design evolved from 1996 and was first 
> formally proposed in 2000. It has been through two Autokey versions, 
> both with the same extension field format. The point being that it is a 
> little late to change it. The further point being that, without breaking 
> backwards compatibility, it is easy to add new tenants of the extension 
> fields. Break the version field into class/version nibbles. This 
> requires no change to the existing Autokey implmentation, as it ignores 
> other than class 0, version 2..
> 
> Dave

No, versioning does not belong in that field. It belongs in the 
extension itself. If need be we can take a bit in the extension field 
(or reduce the length field by one bit to accommodate a way to signal 
the type of extension, 0 for current behavior and 1 for new behavior. We 
are unlikely to use 32535 bytes for this information anyway so we don't 
really lose anything by doing this.

Danny