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Re: Students' Project seeks help

From: Jan Peters <peters.jan.r_at_googlemail.com>
Date: Mon, 01 Aug 2011 12:09:11 +0200

Hi Everybody,
thanks for all the quick repsonses. I myself wasn't able to answer until
now since we wanted to discuss things in our group.

We plan to integrate this so that a compromised server does not allow
the attacker to read data, even if he has got access to the
repositories, no matter how he got it. The "Professor" who gave this
task to us, is willing to accept the loss in performance for the
enhanced security.

Tom Widmer, Peter Samuelson, Markus Schaber:
We are allowed a loss in performance, and more explicitly the
delta-functionality. But as Peter Samuelson pointed out delta
transmission might still work on a block-basis with block-ciphers and
this is what we hope for. Unfortunately this would require us to make
sure that plain-text blocks' borders aren't moved, when data is inserted
or removed.

We know that, since we do not want attackers to analyze the data by
assuming that the first x byte are some kind of constant header (pdf,
html , etc) - thus having plain-text-cypher pairs - we do need to mask
those parts. But this could be aranged by simply adding some random
number to the plaintext (224 bit plaintext 32 random or something like
that) which is only changed when the plaintext-block is changed. This
way we wouldn't have full feedback encryption, which reduces security,
because it is easier to find pairs, but we would still allow the delta
handler to at least work on "blocks".

Philip Martin

You might like to look atsvn:eol-style=native on Windows

We are going to check that out. Regarding the checksums: We aren't
storing the checksums for the encrypted data yet, since we only started
trying to understand the SVN library. But we'll keep that in mind for
the future. We assumed that transmitting those checksums would be
necessary for the server to accept the file.

Markus Schaber
Concerning the RA solution: Our task is to integrate the client-side
encryption into Tortoise. But we figured that a general solution, which
worked on all clients would be the best way to handle this. Having an RA
solution for every RA solution currently in existence didn't seem feasible.

Thanks for the replies.

Next we are going to follow Philip Martin's idea and have a look at
those line-ending-conversions. But other ideas how and where to
manipulate data, directly after it is received when updating are welcome
and gladly received.

Best regards
Jan Peters
Received on 2011-08-01 12:09:53 CEST

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