Deniability

[Jerome Baum]

Hi all,

I  am looking  into the  "plausible  deniability" issue  again that  was
discussed here in the past. My problem definition:

    Configure gpg  in such a way  that when I  encrypt a file, be  it to
    someone else or  to myself, the recipient(s) can  deny being able to
    decrypt the file in question.  An adversary should also be unable to
    derive information about the  recipient(s) -- including their number
    -- from  the encrypted  message. Assume  I like  encrypt-to-self and
    have it enabled.

The obvious way to start is with throw-keyids. Problems:

1. The number of recipients is revealed.

2. If I encrypt to only myself, this is revealed.

I could generate some bogus  keys and throw out the secrets, effectively
making them "encryption-only" keys. Then  to solve #2, I just encrypt to
such a  bogus key in  addition to  my actual key.  I could also  set the
encrypt-to option  for several bogus  keys to make the  adversary's life
more difficult in determining the number of recipients.

After seeing a number of encrypted messages, the adversary will know for
how many bogus keys I have  encrypt-to set. #1 appears again. This could
be solved by randomly picking a  subset of the bogus keys, possibly as a
wrapper around gpg.  So, both problems can be  solved this way, although
it would be annoying  to have to put randomly-pick-some-bogus-keys.sh in
place.

I can imagine  there are going to be  some relatively simple statistical
attacks on  this scheme (by looking  at algorithms and  key-sizes of the
recipients). What  do you  guys think? What  problems and  solutions are
there?

-- 
Jerome Baum <jerome at jeromebaum.com> 0xC58C753A
Key fingerprint = A0E4 B2D4 94E6 20EE 85BA  E45B 63E4 2BD8 C58C 753A
Jerome Baum 0x215236DA
Key fingerprint = 2C23 EBFF DF1A 840D 2351  F5F5 F25B A03F 2152 36DA
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