On 2011-10-04 at 14:22:49, Manger, James H wrote:
> > di:sha-128:B_K97zTtFuOhug27fke4_Q?enc=aes-cbc:Fw3x20nEKfq6FDGzq7ttIQ
> 
> Instead if defining new names for truncated digests, why not simply 
> include a truncated digest with the existing algorithm name? You can 
> determine the truncation (in bytes) from the length of the base64url- 
> encoding so there is no ambiguity.

You would have to specify that the truncation is by the byte, rather than by 
6-bit slices.  I see that you carefully used 'Bw' instead of 'B_' :)

I'll note that base16 avoids that particular problem.

> The only downside I see is the risk of bad implementations accepting
> a digest truncated to, say, 1 byte (eg di:sha-256:Bw) instead of
> enforcing a minimum security level.

It might be enough to say that truncation is possible, though it increases the 
chances of collision.  ...and that you should care about that.

--Martin

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