[144459] in cryptography@c2.net mail archive
Re: Warning! New cryptographic modes!
daemon@ATHENA.MIT.EDU (James A. Donald)
Thu May 21 17:24:59 2009
Date: Wed, 13 May 2009 09:19:32 +1000
From: "James A. Donald" <jamesd@echeque.com>
Reply-To: jamesd@echeque.com
To: Jerry Leichter <leichter@lrw.com>
CC: Victor Duchovni <Victor.Duchovni@morganstanley.com>,
Cryptography List <cryptography@metzdowd.com>
In-Reply-To: <16A8A985-33AC-47D8-A50D-1DCCA171A3B7@lrw.com>
Jerry Leichter wrote:
> Consider first just updates. Then you have exactly the same problem as
> for disk encryption: You want to limit the changes needed in the
> encrypted image to more or less the size of the change to the underlying
> data. Generally, we assume that the size of the encrypted change for a
> given contiguous range of changed underlying bytes is bounded roughly by
> rounding the size of the changed region up to a multiple of the
> blocksize. This does reveal a great deal of information, but there
> isn't any good alternative.
You specified a good alternative: Encrypted synchronization of a file
versioning system:
Git runs under SSH.
Suppose the files are represented as the original values of the files,
plus deltas. If the originals are encrypted, and the deltas encrypted,
no information is revealed other than the size of the change.
Git is scriptable, write a script to do the job.
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