[Standards] hash agility in file transfer

Dave Cridland dave at cridland.net
Thu Jun 16 08:31:52 UTC 2011


On Thu Jun 16 09:14:41 2011, Remko Tronçon wrote:
> > They're lowercase.
> > The usual way that IANA names differ from other names is that  
> IANA always
> > hash the hyphen in SHA names
> 
> Ok then, even better :)
> 
> One drawback of approach 2 and the agreement that all iana hash  
> names
> are ok as elements is the potential clash between hash names and
> element names in the namespace of the protocol using the hashes.  
> It's
> unlikely that Jingle will ever have an element 'sha-1', but still,
> theoretically ...

Hmmm... No. In the protocol, you can use a unified syntax, but in  
features you wouldn't. You'd add a hashing feature, and append the  
IANA names to that URI, perhaps using fragments (if they're legal in  
URNs).

So Jingle FT would still use:

<hash xmlns='urn:xmpp:crypto:hash' hash='sha-1'/>

(Presumably with the hash value somewhere)

There is a risk that IANA might register a hash name which is not a  
legal XML element, but the above copes with this.

I vaguely wonder whether we could use dynamically created namespaces  
and/or elements, but that seems to serve little purpose except to  
annoy purists.

(I'd personally enjoy the notion of a programmatically generated  
schema by processing an XSLT over the XML form of the IANA registry,  
but I can see the XML purists coming after me with troches and  
pitchforks).

Dave.
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