[tahoe-dev] UEB hash size

[Shawn Willden]

Hi guys,

What's the rationale for including the full 256-bit UEB hash in the CHK URI?  
Those URIs could be shortened considerably by truncating it to, say, 128 
bits.

How difficult would it be to allow Tahoe to operate with either full UEB 
hashes or abbreviated hashes?  I'm thinking I could shorten my read cap index 
entries significantly if I could store only half of the UEB hash.  Along 
those lines in the context of small, trusted grids, it might even be 
reasonable to omit the UEB hash entirely (in my case I have a separate 
content hash, and it should also be possible to hash the retrieved and 
decrypted file to regenerate the read key and check integrity that way, 
assuming an unchanged convergence secret).

What is the bare minimum data needed to retrieve, reassemble and decrypt an 
immutable file?  Just the AES read key?

The web API doesn't like CHK URIs that conform to the full specification, but 
I'm sure that could be changed easily enough, if it made sense.

	Shawn.