[Duplicity-talk] rdiff --encrypted

[Adam Megacz]

Currently, rdiff implements three operations:

  signature : old                 -> sig(old)
  delta     : sig(old), new       -> delta(old,new)
  patch     : old, delta(old,new) -> new

I would like to know if it is possible to extend this to operate
"through" some sort of encryption layer:

  signature : old                                 -> sig(old)
  delta     : sig(old), new                       -> delta(old,new)
  patch     : crypt1(old), crypt2(delta(old,new)) -> crypt1(new)

Assume you get to choose the crypt1() and crypt2() functions however
you like, so long as they provide appropriate privacy.  The crypt1()
and crypt2() functions might be the same, or they might be different
-- you might need to encrypt deltas differently from basefiles.

I believe that with such an extension to rdiff, it would be possible
to get duplicity-like security with all the advantages of
rdiff-backup's "full and backward diffs" format.

It ought to work for any cipher that has the property that inserting a
few bytes in the plaintext causes only "local" changes in the
ciphertext.  Unfortunately I am not sure if there are any sufficiently
strong ciphers that work this way.

  - a

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