From: Martin Minow <minow@apple.com>
Date: Sun, 17 Nov 1996 17:38:46 -0800 (PST)
To: Hal Finney <hal@rain.org>
Subject: Re: Computer CPU chips with built-in crypto?
In-Reply-To: <199611172105.NAA04230@crypt.hfinney.com>
Message-ID: <v03007803aeb55bc5644c@[17.219.103.245]>
MIME-Version: 1.0
Content-Type: text/plain


Hal Finney writes:

>Another possible application for the built in encryption is software
>piracy protection.  ...  In these days of razor thin profit
>margins in the PC business it is hard to see how this will sell.
>

Let me offer a possible scenario: we're entering an era when
there is much more chip real-estate than "consumer-grade" PC's
can use. Adding an encryption engine to the instruction stream
could be as simple as adding a series of barrel shifters between
(or inside) the processor cache and the instruction decoder.
(Imagine blowfish or DES -- or something as simple as RC4).

If encryption is turned off, the chip would be bug-for-bug
compatible with the existing PC. The vendor would put the
chip into the ordinary production cycle and, in two to
three years, it would be on the target audience's desktops.
(Remember, it would run existing and new, non-encrypted,
software without change.)

Encryption would be turned on on a module-by-module basis by
operating system "loader" code that would detect a "key required"
cookie in the executable file (or the Open Doc file, or
the Java class file). Before starting the module, the
o.s. loader would lookup the cookie and load the decryption
key into the chip. The customer would purchase a key by
giving a magic number from the software and a magic number
(processor serial number) to the vendor. This could be
done automatically over the network.

Now, a software vendor could provide the latest software for
free from a public FTP site, and could offer a variety of
decryption keys (30 day free trial, one-time-use micropayment,
etc.) at a variety of prices. This could also be integrated
into multiple site-license managers such as KeyServer.
As with KeyServer, key management could be done "invisibly"
over the Internet.

Note that the chip does not offer end users any encryption
or decryption capabilities -- the decrypted instruction
stream cannot be directly examined by end users. On the
other hand, if the encryption key generator was available
to "anybody," it would be trivial to construct secret
messages by generating programs that, when run, constructed
the desired message. For that reason, I suspect that
keys will be limited to a length that "national interests"
are comfortable with.

Martin Minow
minow@apple.com