Privacy Guru Locks Down VOIP

Eugen Leitl eugen at
Wed Jul 27 03:44:43 PDT 2005,1294,68306,00.html

Privacy Guru Locks Down VOIP
By Kim Zetter

Story location:,1282,68306,00.html

10:20 AM Jul. 26, 2005 PT

First there was PGP e-mail. Then there was PGPfone for modems. Now Phil
Zimmermann, creator of the wildly popular Pretty Good Privacy e-mail
encryption program, is debuting his new project, which he hopes will do for
internet phone calls what PGP did for e-mail.

Zimmermann has developed a prototype program for encrypting voice over
internet protocol, or VOIP, which he will announce at the BlackHat security
conference in Las Vegas this week.

Like PGP and PGPfone, which he created as human rights tools for people around
the world to communicate without fear of government eavesdropping, Zimmermann
hopes his new program will restore some of the civil liberties that have been
lost in recent years and help businesses shield themselves against corporate

VOIP, or internet telephony, allows people to speak to each other through
their computers using a microphone or phone. But because VOIP uses broadband
networks to transmit calls, conversations are vulnerable to eavesdropping in
the same way that e-mail and other internet traffic is open to snoops.
Attackers can also hijack calls and reroute them to a different number.

Few people consider these risks, however, when they switch to VOIP.

"Years ago, people kind of stumbled into e-mail without really thinking about
security," Zimmermann said. "I think that what's happening today with VOIP is
that we're kind of stumbling into it (as well) without thinking about
security." People don't think about it, he said, because they're used to phone
calls being secure on the regular phone system -- known as the Public Switched
Telephone Network.

"The PSTN is like a well-manicured neighborhood, (while) the internet is like
a crime-ridden slum," Zimmermann said. "To move all of our phone calls from
the PSTN to the internet seems foolish without protecting it."

Interest in VOIP is growing rapidly because the user pays less for the service
and pays no long-distance toll charges. Some services are free. According to
one recent survey, 11 million people worldwide use a subscription VOIP
service, compared to only 5 million in 2004, and at least another 35 million
use free VOIP services. That leaves a lot of people potentially open to

It's not as easy to eavesdrop on VOIP as it is to intercept and read e-mail.
Phone conversations aren't stored or backed up where an attacker can access
them, so the conversations have to be captured as they occur.

But a program available for free on the internet already allows intruders to
do just that. Using the tool, someone with access to a local VOIP network
could capture traffic, convert it to an audio file and replay the voice
conversation. The program is called Voice Over Misconfigured Internet
Telephones, a name clearly chosen for its catchy acronym -- VOMIT.

Bruce Schneier, chief technology officer of Counterpane Internet Security and
author of the Crypto-Gram newsletter, said that the need for VOIP encryption
is a given.

"If you're concerned about eavesdropping, then encryption is how you defend
against it," he said. "And it's not that hard to do. It's just a matter of
writing the code."

But David Endler, chairman of the VOIP Security Alliance industry group and
director of security research at TippingPoint, said a protocol for encrypting
and protecting VOIP data already exists and companies are starting to make
VOIP phones that support the protocol. But he said that people typically don't
enable the encryption option.

"Probably because we're not seeing attacks yet," he said.

He said most users are less concerned with eavesdropping than with having VOIP
service that provides the same quality and reliability that they expect from
regular phone service.

"Some people can see clearly that there's a need for this, and others wonder
if anyone cares about protecting phone calls," Zimmermann said. "But those are
the same people who wondered why anyone would want to protect e-mail. I think
as people gain experience with VOIP they're going to have a great appreciation
for the need to come up with extra measures to protect it."

Endler also said that companies using VOIP are reluctant to implement
encryption because of the overhead involved in managing the public key
infrastructure, or PKI.

"You have to be able to store a key on most of these end points," he said.

PKI requires two keys for encryption: a public key that a user gives to anyone
who wishes to communicate with him or her, and a private key, which decrypts
messages that the user receives.

That won't be a problem with Zimmermann's system, which doesn't use PKI.
Zimmermann said PKI is unnecessarily complex for VOIP.

"There's no need to centrally manage public key infrastructure to make a phone
call, in my view," he said.

He won't elaborate on how his system works but is preparing a protocol
document that will describe it in detail, which he'll post on the internet
when the program is ready.

The program is currently only a working prototype and still has non-security
bugs that need to be worked out. For example, sometimes the program fails to
hang up after a call, forcing the user to exit the program to end the call.

It's designed for a Mac, but will be adapted for PCs before Zimmermann makes
it available for download. He's looking for investors to back a startup
company that will support the product and oversee its distribution.

Zimmermann envisions it both as an add-on for manufacturers to put into VOIP
phones and as a software client that users can install on their laptop to use
when they don't have a VOIP phone with them. Both parties in a conversation
will need to have the software on their phone or computer. If only one person
has it, the call will still go through but it won't be encrypted.

It's been a while since Zimmermann came out with a new encryption product. He
released PGP in 1991; it was another five years before he released PGPfone to
encrypt data passing between modems.

Who could blame him for laying low for a while after the Justice Department
launched a three-year criminal investigation of him in 1993? Officials accused
him of violating a ban on exporting cryptography when he made PGP available
for download on the internet. The government finally dropped its investigation
in 1996.

The export laws were relaxed in 2000, so at least they're no longer a

"There's a lot more crypto in the computer industry now than there was in the
'90s," Zimmermann said. "And there's not much authorities can do about it now
because we went through this struggle with them in the '90s and we won."

Zimmermann isn't taking chances, however. He worked closely with a law firm
that specializes in export controls and filed the required paperwork with the
Commerce Department notifying the government that his product exists.

Still, he delayed producing VOIP encryption after the Sept. 11 terrorist
attacks, because the climate wasn't right.

"I was concerned that maybe this would attract some criticism," Zimmermann
said. "I just felt that maybe the government had their hands full with enough
problems, and I also needed to concentrate on other consulting projects to
make money."

Zimmermann received hate mail after 9/11 from people who accused him of aiding
the attackers by creating a program that allowed terrorists and criminals to
shield their correspondence from authorities.

The Washington Post erroneously reported shortly after the attacks that
Zimmermann was overwhelmed with guilt over the possibility that terrorists
might have used PGP to plan their attacks.

What he actually said was that he was sorry if al-Qaida used the program, but
that this was the trade-off for having a tool that could protect everyone's
privacy -- some people would use it with malicious intent. Overall, he said,
the world was better off with cryptography in the hands of the masses rather
than just in the hands of government.

Zimmermann is hoping people will accept his new program with the spirit in
which he created it.

"Because there are a lot of people who are concerned about the erosion of
civil liberties that the Patriot Act brought," Zimmermann said. "I'm hoping
that more people would approve of this project than disapprove."

Ultimately, however, he said that his encryption program was not about
politics, but about the need for protecting critical infrastructure.

Eugen* Leitl <a href="">leitl</a>
ICBM: 48.07100, 11.36820  
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