[Cryptography] Comey: targeted ads => plaintext access

Benjamin Kreuter brk7bx at virginia.edu
Tue Sep 15 22:42:56 EDT 2015

On Sun, 2015-09-13 at 13:42 -0700, Henry Baker wrote:
> FYI -- Leaving aside Constitutional & political considerations, &
> focusing purely on technical issues, doesn't the FBI's Comey have a
> point?  If an email provider can target ads based upon keywords in the
> plaintext of your emails, why can't the FBI have access to the same
> plaintext?

Comey is conflating "encryption in transit" with end-to-end encryption,
so I do not think he has any point.  The point of end-to-end encryption
is that we do not trust mail servers with plaintext, regardless of what
they are doing with it.

> Obviously, any scheme that targets ads based upon the *unencrypted
> content* of an email must *leak a certain amount of information from
> that content* -- at least to the ad broker.

This is not necessarily true.  You can imagine a multiparty protocol
that targets ads based on email plaintexts without revealing information
about plaintexts to an ad broker, while still ensuring that payments
occur properly.  It is all theoretical for now and there are a lot of
complexities and subtle (and not so subtle) assumptions, but at least on
paper we could do it.

-- Ben
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