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73322Re: Encryption: Vim should use authenticated encryption mode

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  • Mosh
    Sep 22, 2013
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      I am happy to report that our vim encryption implementation is NOT affected
      by any of the weaknesses in the encryption algorithms and implementations in news recently, e.g.






      On Mon, Feb 18, 2013 at 10:05 PM, Ben Fritz <fritzophrenic@...> wrote:
      On Saturday, February 16, 2013 7:25:54 PM UTC-6, Ulrik wrote:
      > On 2013-02-16 18:16, Bram Moolenaar wrote:
      >
      > > The whole point of the encryption is to make the text unreadable.  It is
      >
      > > not a signature of any kind.  Signing files, encrypted or not, is a
      >
      > > totally different thing and there are plenty of tools for that.
      >
      > >
      >
      >
      >
      > The type of the attack is that if you XOR a value with the ciphertext,
      >
      > the same XOR difference shows in the decrypted text. Knowing a small
      >
      > part of the plaintext is not a big requirement on an attack as simple as
      >
      > this one.
      >
      >

      I still don't think preventing this kind of attack is within the scope of Vim's encryption.

      >
      > I understand that Vim only wants to provide confidentiality, not
      >
      > integrity, but taken together with the usability issue of not giving
      >
      > notice of a wrong password, I don't understand the choice. I don't enjoy
      >
      > the possibility given that I might absent-mindedly type :w when getting
      >
      > the garbage output after a mistyped password, destroying my data.
      >
      >

      But I think THIS is an excellent argument for your proposed feature. If we can easily protect the user from accidentally corrupting their important file, then it is a very good idea. There is already checksum code within Vim for the undo file...I think it uses some sort of SHA algorithm. I don't think this should be too hard to implement.

      I think :w! should force a write even though the checksum is wrong just in case somebody is doing something kooky intentionally, but :w with a mismatched checksum should give an error.

      As somebody mentioned, the encryption already stores a version flag in the file, so this should be a backwards compatible change.

      Should a file which was read without the checksum, also be written without one? I normally wouldn't think so, but perhaps it would be best to prevent that older Vims can't read the file after editing it in a newer Vim.

      A recent patch also added a vimscript function to get the checksum, I wonder if that could be used to do this as a plugin. I think it would be better built-in however.

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