RE: Son of Ike status

[Charlie_Kaufman@notesdev.ibm.com]

> >My plan was to say that messages could be half-encrypted/half-plaintext
> >where the first half would always be plaintext and the second half
> >encrypted and integrity protected. The encryption syntax would be the
same
> >as before but would start not immediately after the header but rather
> >at the beginning of a particular playload type - that payload being
> >whatever
> >happened to appear first in the part of the message we wanted to
encrypt.
>
> An alternative is to have a payload called something like "Encrypted
> stuff" that contains other payloads. Recursion of this payload would
> be unneeded and should be prohibited.

I considered that, but judged it to be marginally more complicated.
Its advantage and its disadvantage is that it invites having more
than one encrypted block and having unencrypted information before
and after the encrypted information. It seemed like flexibility that we
didn't need but that people would have to code for.

> >I was planning to say that only message 3 in the exchange could be so
> >encoded... other messages had to be all cleartext or all plain.
>
> An advantage of having messages 3 and 4 have the same structure
> (clear payloads and one encrypted enclosing payload) is that the
> responder could send informational messages in the clear in message
> 4, such as "your key is in the wrong group and therefore I couldn't
> encrypt with it" or "your message 3 appears to be bogus, go away".

If we can encrypt any of message 4, we can encrypt all of it. In message
4 encryption is optional - certain errors would not be encrypted. But
I can't think of any reason message 4 would be partially encrypted.
Can you?

          --Charlie

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