Re: secure sign & encrypt

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disastry wrote:
> fake pubkey encryption packets can be added
> by man in the middle so that recipient thinks that message was encrypted
> to him and to other preson.
> 
> I wrote about it here:
> http://lists.gnupg.org/pipermail/gnupg-devel/2001-August/006285.html

I think this can be solved by modifying
Sym. Encrypted Integrity Protected Data Packet (Tag 18).

Now it is:

version byte == 1
encrypted data

encrypted data consists of:
  encrypted iv
  encrypted plaintext
  encrypted Modification Detection Code Packet (Tag 19)

I suggest:

version byte == 2
encrypted data

encrypted data consists of:
  encrypted iv
  encrypted Recipients packet (Tag 20)
    (put it before plaintext - if it would be after it would
     be difficult to find where plaintext ends, when decrypting)
  encrypted plaintext
  encrypted Modification Detection Code Packet (Tag 19)

Recipients packet
  version byte == 1
  number of recipients, 2 bytes (should be enough..)
  number_of_recipients*20 byte list of fingerprints recipient keys
    (16 byte RSA v3 key fingerprints are appended with 4 zeros
     (or maybe with 4 lowest keyid bytes? I think, it's even better))


this ensures that recipient list is intact not only for signed & encrypted messages
but also for encrypted only messages.

__
Disastry  http://disastry.dhs.org/
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