COMMAND

    MS Access 'known database attack'

SYSTEMS AFFECTED

    Win running MS Access 2.0 (others?)

PROBLEM

    Mark Rosen has  examined the encryption  on MS Access  (v 2.0) and
    found that  it was  really easy  to break  without ever  having to
    determine the key.   It is RC4 based.   During examination of  it,
    he  found  it  behaved  as  a  stream  cipher where the stream was
    XORed  with  the  database.   MS  Access  databases  grow  in   2K
    increments, so  it makes  since that  everything is  done the  way
    described below.

    However, encrypting with MS Access  has a major flaw: It  does not
    ask you for a password!  You might expect that, like almost  every
    other thing with encryption, you would be prompted for a password.
    In effect the same key is used for encryption and decryption.

    The method to break:
        - Create a known  database which is at  least as large as  the
          database you are trying to break.
        - Encrypt it.
        - Find the XOR between the known database and its  encryption.
          This is the key stream.
        - XOR  the  key  stream  against  the target database you  are
          trying to break.

    So there  is no  need for  a brute  force attack.   MS can  use  a
    900,000+ bit key and it won't matter.

SOLUTION

    Microsoft Access versions 1.0, 1.1, 2.0, 7.0 have same  encryption
    so there is potentional danger.   Anyway, nothing you can do  here
    more.  Leave it MS.