Jefferson's Wheel

In light of our recent results showing the security vulnerabilities in the Mifare Classic chip used in the London Transport Oyster card (and many other systems), this article about how the police use data collected from Oyster card users raises some interesting evidence and privacy concerns:
Police make 3,000 requests for data from Oyster cards, The Evening Standard, 21 February 2008.

Information obtained today by consumer magazine Which? shows that Transport for London received more than 3,100 requests from the police for passenger journey data between January and October last year.

Oyster cards were introduced five years ago and account for millions of journeys each day.

Which? today raised concerns about the apparent failure of Transport for London to make clear to passengers that their travel data will be stored for eight weeks at a time. It claims this is in breach of the Data Protection Act.

TfL says the information is required if journeys have to be refunded.

According to Which?, passengers signing up for an Oyster card are told their personal information is used for “the purposes of administration, customerservices and research”. However-there is no explanation that their bus, Tube and train journeys will be logged for up to two months.

Which? editor Neil Fowler said: “Which? is concerned that some private companies aren’t complying with the Data Protection Act and we urge them to tighten up their processes, so that consumers can be reassured that their data is in safe hands.”

Liberal Democrat mayoral candidate Brian Paddick said: “Companies increasingly have access to more and more of people’s personal details – and the public expect that data to be protected. It’s extremely worrying that every journey you make using Oystercard is recorded on TfL’s computer.

This article in The Register describes Karsten Nohl’s work on the Mifare cryptanalysis:
Microscope-wielding boffins crack Tube smartcard: The keys to London Underground, and plenty more. (12 March 2008)

For non-British readers, here’s how Wikipedia defines a “boffin”:

In the slang of the United Kingdom, Australia, New Zealand and South Africa, boffins are scientists, engineers, and other people who are stereotypically seen as engaged in technical or scientific research. The word conjures up an image of men in thick spectacles and white lab coats, obsessively working with complicated apparatus. Portrayals of boffins emphasize both their eccentric genius and their naive ineptitude in social interaction. They are, in that respect, closer to the “absent-minded professor” stereotype than to the classic mad scientist.

(For the record, Karsten doesn’t usually wear white coats.)

It’s nice to see our research being cited in so many places. Most of the news coverage is accurate and resonates our call for better security through open designs.

We would still like to clarify a few facts and address some points of critique: The focus of our research was on Mifare Classic RFID tags. While these are by far the most popular contactless smart cards, there are plenty of others that may or may not be secure. Using a proprietary cipher is usually evidence of bad design and only cards with standard ciphers such as 3-DES, AES, and ECC should be considered for security applications.

Our results do not apply to contactless credit cards since these do not encrypt data.

The manufacturer of the Mifare cards has repeatedly claimed that we have only broken one layer of security, which is true when looking at systems as a whole. Cryptography can only ever provide one layer of protection, two of the others being automated fraud detection and law enforcement. Computerized systems tend to rely on the cryptography, however, and are much more vulnerable to attacks once this layer of security is lost.

We believe in the potential of RFIDs to improve security in many domains. The current discussion will hopefully provide guidance in building more open, more secure systems.

PC World has an article about Karsten Nohl’s RFID cryptanalysis work: Hackers Find a Way to Crack Popular Smartcard in Minutes: Security on RFID-enabled smartcards is easily broken by young hackers. March 7, 2008.

The team used an inexpensive RFID reader to collect encrypted data, and then reverse-engineered the chip to figure out the encryption key to decipher that data. They examined the chip under an optical microscope and used micro-polishing sandpaper to remove a few microns of the surface at time, photographing each of the five layers of circuitry. Nohl wrote his own optical recognition software to refine and clarify the images, and then patiently worked through the arrangement of the logic gates to deduce the encryption algorithm, a task made possible by the fact that the Mifare Classic relies on a secret key of no more than 48 bits.

“Regardless of the cryptographic strength of the cipher, the small key space therefore permits counterfeiting of any card that is read wirelessly,” the team wrote in a follow-up statement issued on Jan. 8. “Knowing the details of the cipher would permit anyone to try all possible keys in a matter of days,” the researchers noted. “Given basic knowledge of cryptographic trade-offs and sufficient storage, the secret keys of cards can be found in a matter of minutes.”

[Added 12 March] PCWorld has a second article on this: RFID-Hack Hits 1 Billion Digital Access Cards Worldwide: A warning is issued that some security access cards that use RFID technology are vulenarble to hack attacks, 12 March, 2008.

The Boston Herald also has a story: Research: CharlieCard is far from hack-proof, March 6, 2008.

The Boston Globe has a story about Karsten Nohl’s work on cryptanalyzing the Mifare Classic: T card has security flaw, says researcher: Cracked code could lead to counterfeits, study team warns.

A computer science student at the University of Virginia asserts that he has found a security flaw in the technology behind the Massachusetts Bay Transportation Authority’s CharlieCard system.

German-born graduate student Karsten Nohl specializes in computer security. Nohl and two fellow security researchers in Germany say they’ve cracked the encryption scheme that protects the data on the card. The team warns that their breakthrough could be used to make counterfeit copies of the cards, which are used by commuters to pay for MBTA bus and subway rides.

… Nohl said that his team needed only about $1,000 worth of equipment to dismantle the chip and crack the code.

Nohl said that the RFID chip they compromised, the MiFare Classic by NXP Semiconductors of the Netherlands, is the one used in London’s subway system and in the MBTA CharlieCard. But MBTA spokesman Joe Pesaturo refused to confirm or deny this. “It’s MBTA policy not to discuss security measures around its smart card technology,” he said.

A 2004 policy analysis of the CharlieCard system produced by the Massachusetts Institute of Technology said that it would be based on MiFare technology.

NXP Semiconductors issued a statement saying that Nohl’s team breached only one of several security features built into the MiFare Classic chip. “This does not breach the security of the overall system,” the company said. “Even if one layer were to be compromised, other layers will stop the misuse.”

Evans said it might be hard to solve the issue. “There are chips that have a much higher security level available,” he said. “They cost more and it is not a trivial matter to upgrade the system.”

Ari Juels, chief scientist and director of computer security company RSA Laboratories in Bedford, said that Nohl’s research illustrates that there are serious security flaws in many smartcard applications. “The vulnerability is most certainly for real,” Juels said.

I’d be very curious to hear about those mysterious “other layers” the NXP spokesperson is talking about. Perhaps they are using the same amazing “extensive security mechanisms operating behind the scenes” that Facebook’s chief privacy officer was talking about here.

The Daily Press (Hampton Roads, Virginia) has a story about Karsten Nohl’s cryptanalysis work: U.Va. student, hackers crack credit card security code, March 1, 2008. It is currently #7 on their list of most popular stories (but I doubt it will overtake this story: Here’s a guy who takes his beer seriously).

[Added 2 March] Also reported by WTOP (Washington DC), Examiner.com (Norfolk, Virginia), Richmond Times-Dispatch, WVEC-TV (ABC in Norfolk), The Washington Times, WAVY-TV, WSLS (Roanoke), Culpeper Star Exponent, and WVIR NBC-29 (Charlottesville).

The Daily Progress has an article about Karsten Nohl’s work on analyzing RFID tag security: Security code easy hacking for UVa student, 28 February 2008.

… Projects such as hacking the security code of a RFID chip is the “evil twin” of Nohl’s regular research, he said, which focuses on the development of cryptographic algorithms for computer security.
…
Nohl said that a more secure option for RFID security codes would be to rely on publicly known and time-tested security algorithms. NXP’s secret code, he said, is an example of “security by obscurity,” or the practice of keeping the code private and hoping hackers do not figure it out. Private algorithms, Nohl said, are more likely to have flaws and vulnerabilities.

“We found significant vulnerabilities in their algorithm,” he said. “By keeping it secret, they hurt themselves in the end.”

[Added 1 March] The story also appears in The Danville Register (Hackers claim they broke key security code). Blog reports include PogoWasRight and LiquidMatrix Security Digest.

[Added 2 March]: More reports: Xenophilia, WAVY-TV.

UVaToday has an article about Karsten Nohl’s work on reverse engineering the cryptographic algorithms on the Mifare Classic RFID tag:

… The idea of keeping secret the design of a security system is known in the trade as “security by obscurity.” It almost never works; the secret invariably leaks out and then the security is gone, Evans and Nohl said.

As a result, most security professionals espouse Kerckhoffs Principle — first published by the Dutch cryptographer Auguste Kerckhoffs in 1883 — the idea that the design of all security systems should be fully public, with the security dependent only on a secret key. Public review of security designs also tends to catch flaws during the design process, rather than after the flaws are inherent in expensive systems, such as in the Netherlands transit system, noted Nohl and Evans.

… If more consumers understand the fundamental flaw of “proprietary security algorithms” and other marketing-speak that touts what amounts to security by obscurity, then manufacturers may start opening up more of their security designs to the light of public scrutiny, which will ultimately result in better security in our digital age.

Full article: Group Demonstrates Security Hole in World’s Most Popular Smartcard, UVaToday, February 26, 2008.

Karsten Nohl, in collaboration with Starbug and Henryk Plötz, has reverse-engineered the encryption algorithm used in Mifare Classic RFID tags, and identified several serious weaknesses in the ciper design and the way it generated random numbers. Mifare tags are used in several large public transportation systems including London Transport’s Oyster cards, and the Dutch government was planning to used them for the nationwide OV-Chipkaart system, but is reconsidering this in light of the revealed security weaknesses. The work involved reverse engineering the cipher from images of its hardware implementation.

The results were announced at the Chaos Communication Congress (December 28). Here’s Karsten’s talk (including a link to a video): Mifare: Little Security, Despite Obscurity.

Some posts about this work include:

• Schneier on Security (Bruce Schneier), Dutch RFID Transit Card Hacked
• Freedom to Tinker (Ed Felten), New $2B Dutch Transport Card is Insecure.
• Andy Tanenbaum, Dutch Public Transit Card Broken (includes links to many Dutch newspaper articles).

Karsten will also be giving a talk about this work at the RFID Security Workshop at Johns Hopkins University, January 23-24.