By Cory Doctorow
Dec 5, 2006
What if you could rig it so that competing with your flagship product
was against the law? Under 1998's Digital Millennium Copyright Act,
breaking an anti-copying system is illegal, even if you're breaking it
for a legal reason. For example, it's against the law to compete head-on
with the iPod by making a device that plays Apple's proprietary music,
or by making an iPod add-on that plays your own proprietary music. Nice
deal for Apple.
Microsoft gets the same deal, courtesy of something called "Information
Rights Management," a use-restriction system for Office files, such as
Word documents, PowerPoint presentations, and Excel spreadsheets.
We've had access control for documents for years, through traditional
cryptography. Using PGP or a similar product, you can encrypt your files
so that only people who have the keys can read them.
But Information Rights Management (IRM), first introduced in Office
2003, goes further -- it doesn't just control who can open the document,
it also controls what they can do with it afterwards. Crypto is like an
ATM that only lets you get money after you authenticate yourself with
your card and PIN. IRM is like some kind of nefarious goon hired by the
bank to follow you around after you get your money out, controlling how
you spend it.
With IRM, an Office user can specify whether her documents can be
printed, saved, edited, forwarded -- she can even revoke access to the
documents after sending them out, blocking leaks after they occur.
Documents travel with XML expressions explaining how they can and can't
Now, if anyone was allowed to make a document reader, it would be simple
to make a reader that ignores the rules. This is a perennial problem for
Adobe's password-restricted PDFs -- the only thing that distinguishes
them from normal PDFs is a bit that says, "I am a restricted PDF." Just
make a PDF reader that ignores the bit and you've defeated the
"security." It's about as secure as one of those bogus "Confidentiality
notices" that your mail-server pastes in at the bottom of every email
There are plenty of readers for Microsoft's Office formats these days.
Apple makes at least two -- Pages and TextEditor. Google and RIM both
have Office readers they use to convert Office documents to other
formats. And there's also free readers like OpenOffice.org, which are
open source and so can be modified by anyone with the interest to write
or commission new code for them.
But now that the format is well understood, Microsoft needs another way
to ensure that it only hands keys out to readers that can be trusted to
follow the rules that accompany them. Pages or OpenOffice.org can
request a set of document keys just as readily as Office can. Microsoft
can try to create secret handshakes to make sure it only gives out the
keys to authorized parties, but just as the document format can be
cracked, so can the handshaking.
IRM has an answer. Unlike a crippled PDF, a restricted Word file is
encrypted. Only authorized readers will get the keys. This technology
will return Office users to the days before the file format had been
reverse-engineered by competing products like WordPerfect, where reading
an Office file meant licensing the file-format from Microsoft.
If anyone makes a client that listens to its owner instead of Microsoft,
then the system collapses. No-print, no-forward, revoke and other flags
for the document can simply be ignored. Once Microsoft sends a
decryption key to an untrusted party, all bets are off -- Microsoft
loses its lock-in and you lose any notional security benefits from IRM.
This has been a purely theoretical problem until recently -- but the
advent of Vista and Trusted Computing should put it front-and-square on
Microsoft has an industrial-strength answer to the problem of figuring
out whether a remote client is authorized to request keys. Trusted
Computing. For years now, most PC manufacturers have been shipping
machines with an inactive "Trusted Computing Module" on the motherboard.
These modules can be used to sign the BIOS, bootloader, operating
system, and application, producing an "attestation" about the precise
configuration of a PC. If your PC doesn't pass muster -- because you're
running a third-party document reader, or a modified OS, or an OS inside
a virtual machine -- then you don't get any keys.
What this means is that Apple can make Pages, Google can make its
Doc-converter, and OpenOffice.org can make its interoperable products,
but none of these will be able to get the keys necessary to read
"protected" documents unless they're on the white-list of "trusted"
What's more, adding crypto to the mix takes us into another realm: the
realm of copyright law. The same copyright law that prohibits competing
head on with Apple also prohibits competing head-on with IRM. EDI and
other middleware companies built their fortunes on writing software that
unlocks your data from Vendor A's format so you can use it with Vendor
B's product. But once Vendor A's data-store is encrypted, you run afoul
of the law merely by figuring out how to read it without permission.
Vista is the first operating system to begin to use the features of the
Trusted Computing Module, though for now, Microsoft is eschewing the use
of "Remote Attestation" where software is verified over a network
(they've made no promise about doing this forever, of course). No
company has spent more time and money on preventing its competitors from
reading its documents: remember the fight at the Massachusetts
state-house over the proposal to require that government documents be
kept in open file-formats?
The deck is stacked against open file formats. Risk-averse enterprises
love the idea of revocable documents -- HIPPA compliance, for example,
is made infinitely simpler if any health record that leaks out of the
hospital can simply have its "read privileges" revoked. This won't keep
patients safer. As Don Marti says, "Bill Gates pitch[ed] DRM using the
example of an HIV test result, which is literally one bit of
information. If you hired someone untrustworthy enough to leak that but
unable to remember it, you don't need DRM, you need to fix your hiring
process." But it will go a long way towards satisfying picky compliance
officers. Look for mail-server advertising that implies that unless you
buy some fancy product that auto-converts plain Office documents to
"revocable" ones, you're being negligent.
No one ever opts for "less security." Naive users will pull the
"security" slider in Office all the way over the right. It's an
attractive nuisance, begging to be abused.
The Trusted Computing Module has sat silently on the motherboard for
years now. Adding Vista and IRM to it is takes it from egg to larva, and
turning on remote attestation in a year or two, once everyone is on
next-generation Office, will bring the larva to adulthood, complete with
Cory Doctorow is co-editor of the Boing Boing blog, as well as a
journalist, Internet activist, and science-fiction writer.
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