improving encryption performance

[Tom M. <tme...@vl...>]

Could rsyncrypto improve its encryption performance by incorporating the 
rsync algorithm?

Instead of re-encrypting the entire file each time a change occurs, it 
could use an rsync-like algorithm to determine which blocks of a file 
need to be re-encrypted.

If I remember the details of the rsync algorithm correctly, you probably 
couldn't literally use the rsync algorithm, as you can't re-encrypt some 
arbitrary size block in the middle of a file. You'd have to stick with 
fixed blocks.

For this to work, you'd need to have the prior version of a changed file 
on hand to compare against. Or to avoid keeping local copies of the 
prior version you could "index" the files, storing a series of block 
offsets and SHA or MD5 digests. Then only the indexes would need to be kept.

Either way I guess you wouldn't end up with a very robust algorithm, as 
something as simple as adding text to the top of a file would cause the 
entire file to appear changed. I'd be curious to know if your block 
encryption approach suffers from that same problem.

  -Tom

-- 
Tom Metro
Venture Logic, Newton, MA, USA
"Enterprise solutions through open source."
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