Re: A patch to loop.c for better cryption support

From: Ingo Rohloff (
Date: Sat Oct 14 2000 - 10:21:09 EST

Reed Petty wrote:
> Caution is advised when depending upon crypto systems that use relative
> block numbers as IV. The security may not be a strong as hoped.
> There are some who believe that "not unique" IVs (across multiple
> filesystems) facilitates some methods of cryptanalysis.
Ahh that explains it...

> Perhaps losetup can allow the user to specify a "IVseed" value
> and then pass to the transfer modules IVseed + relative block.
> This would also allow existing absolute block based encrypted file
> systems to be relocated (IVseed = absolute # of 1st block), satisfy
> those among us who demand unique IVs, and allow those who prefer
> operational convenience at the cost of weaker security to do so.
An IVseed is a good idea.

What would you think of using a secure hash function on the key
as IVseed ?
This should ensure almost unique IVs and you don't need a
second parameter two encrypt/decrypt a file.
(On the other hand this scheme is of course weaker than
 your approach...)

so long

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