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Here’s a physical attack against a credit card verification system. Basically, the attack disrupts the communications between the retail terminal and the system that identifies revoked credit cards. Since retailers generally default to accepting cards when the system doesn’t work, the attack is generally successful.
Last week, Ron Rivest gave a talk at MIT about Spritz, a new stream cipher by him and Jacob Schuldt. It’s basically a redesign of RC4, given current cryptographic tools and knowledge.
RC4 is an example of what I think of as a too-good-to-be-true cipher. It looks so simple. It is so simple. In classic cryptographic terms, it’s a single rotor machine. It’s a single self-modifying rotor, but it modifies itself very slowly. Even so, it’s very hard to cryptanalyze. Even though the single rotor leaks information about its internal state with every output byte, its self-modifying structure always seems to stay ahead of analysis. But RC4 been around for over 25 years, and the best attacks are at the edge of practicality. When I talk about what sorts of secret cryptographic advances the NSA might have, a practical RC4 attack is one of the possibilities.
Spritz is Rivest and Schuldt’s redesign of RC4. It retains all of the problems that RC4 had. It’s built on a 256-element array of bytes, making it less than ideal for modern 32-bit and 64-bit CPUs. It’s not very fast. (It’s 50% slower than RC4, which was already much slower than algorithms like AES and Threefish.) It has a long key setup. But it’s a very clever design.
Here are the cores of RC4 and Spritz:
RC4:
1: i = i + 1
2: j = j + S[i]
3: SWAP(S[i];S[j])
4: z = S[S[i] + S[j]]
5: Return zSpritz:
1: i = i + w
2: j = k + S[j + S[i]]
2a: k = i + k + S[j]
3: SWAP(S[i];S[j])
4: z = S[j + S[i + S[z + k]]]
5: Return z
S is an 8-bit permutation. In theory, it can be any size, which is nice for analysis, but in practice, it’s a 256-element array. RC4 has two pointers into the array: i and j. Spritz adds a third: k. The parameter w is basically a constant. It’s always 1 in RC4, but can be any odd number in Spritz (odd because that means it’s always relatively prime to 256). In both ciphers, i slowly walks around the array, and j—or j and k—bounce around wildly. Both have a single swap of two elements of the array. And both produce an output byte, z, a function of all the other parameters. In Spritz, the previous z is part of the calculation of the current z.
That’s the core. There are also functions for turning the key into the initial array permutation, using this as a stream cipher, using it as a hash function, and so on. It’s basically a sponge function, so it has a lot of applications.
What’s really interesting here is the way Rivest and Schuldt chose their various functions. They basically tried them all (given some constraints), and chose the ones with the best security properties. This is the sort of thing that can only be done with massive computing power.
I have always really liked RC4, and am happy to see a 21st-century redesign. I don’t know what kind of use it’ll get with its 8-bit word size, but surely there’s a niche for it somewhere.
A pair of Humboldt squids attacked a Greenpeace submarine. There’s video.
As usual, you can also use this squid post to talk about the security stories in the news that I haven’t covered.
Interesting paper: Maya Embar, Louis M. McHough IV, and William R. Wesselman, “Printer watermark obfuscation,” Proceeding
RIIT ’14: Proceedings of the 3rd annual conference on Research in information technology:
Abstract: Most color laser printers manufactured and sold today add “invisible” information to make it easier to determine when a particular document was printed and exactly which printer was used. Some manufacturers have acknowledged the existence of the tracking information in their documentation while others have not. None of them have explained exactly how it works or the scope of the information that is conveyed. There are no laws or regulations that require printer companies to track printer users this way, and none that prevent them from ceasing this practice or providing customers a means to opt out of being tracked. The tracking information is coded by patterns of yellow dots that the printers add to every page they print. The details of the patterns vary by manufacturer and printer model.
EDITED TO ADD (11/14): List of printers and whether or not they display tracking dots (may not be up to date).
Susan Landau has a new paper on the NSA’s increasing role in commercial cybersecurity. She argues that the NSA is the wrong organization to do this, and we need a more public and open government agency involved in commercial cybersecurity.
EDITED TO ADD (11/13): David Elliott Bell has a related paper. Also read this review of both papers.
Last week, Adi Shamir gave a presentation at Black Hat Europe on using all-in-one printers to control computers on the other side of air gaps. There’s no paper yet, but two publications reported on the talk:
Theoretically, if a malicious program is installed on an air-gapped computer by an unsuspecting user via, say, a USB thumb drive, attackers should have a hard time controlling the malicious program or stealing data through it because there is no Internet connection.
But the researchers found that if a multifunction printer is attached to such a computer, attackers could issue commands to a malicious program running on it by flashing visible or infrared light at the scanner lid when open.
[…]
The researchers observed that if a source of light is pointed repeatedly at the white coating on the inside of the scanner’s lid during a scanning operation, the resulting image will have a series of white lines on darker background. Those lines correspond to the pulses of light hitting the lid and their thickness depends on the duration of the pulses, Shamir explained.
Using this observation the researchers developed Morse code that can be used to send pulses of light at different intervals and interpret the resulting lines as binary data1s and 0s. Malware running on an air-gapped system could be programmed to initiate a scanning operation at a certain time—for example, during the night—and then interpret the commands sent by attackers using the technique from far away.
Shamir estimated that several hundred bits of data can be sent during a single scan. That’s enough to send small commands that can activate various functionality built into the malware.
This technique can be used to send commands into an air-gapped computer network, and to exfiltrate data from that network.
Interesting essay on the sorts of things you can learn from anonymized taxi passenger and fare data.
The Guardian has reported that the app Whisper tracks users, and then published a second article explaining what it knows after Whisper denied the story. Here’s Whisper’s denial; be sure to also read the first comment from Moxie Marlinspike.
Slashdot thread. Hacker News thread.
EDITED TO ADD (10/22): Another Whisper explanation, and another Guardian article. An analysis.
FBI Director James Comey again called for an end to secure encryption by putting in a backdoor. Here’s his speech:
There is a misconception that building a lawful intercept solution into a system requires a so-called “back door,” one that foreign adversaries and hackers may try to exploit.
But that isn’t true. We aren’t seeking a back-door approach. We want to use the front door, with clarity and transparency, and with clear guidance provided by law. We are completely comfortable with court orders and legal process—front doors that provide the evidence and information we need to investigate crime and prevent terrorist attacks.
Cyber adversaries will exploit any vulnerability they find. But it makes more sense to address any security risks by developing intercept solutions during the design phase, rather than resorting to a patchwork solution when law enforcement comes knocking after the fact. And with sophisticated encryption, there might be no solution, leaving the government at a dead end—all in the name of privacy and network security.
I’m not sure why he believes he can have a technological means of access that somehow only works for people of the correct morality with the proper legal documents, but he seems to believe that’s possible. As Jeffrey Vagle and Matt Blaze point out, there’s no technical difference between Comey’s “front door” and a “back door.”
As in all of these sorts of speeches, Comey gave examples of crimes that could have been solved had only the police been able to decrypt the defendant’s phone. Unfortunately, none of the three stories is true. The Intercept tracked down each story, and none of them is actually a case where encryption foiled an investigation, arrest, or conviction:
In the most dramatic case that Comey invoked—the death of a 2-year-old Los Angeles girl—not only was cellphone data a non-issue, but records show the girl’s death could actually have been avoided had government agencies involved in overseeing her and her parents acted on the extensive record they already had before them.
In another case, of a Louisiana sex offender who enticed and then killed a 12-year-old boy, the big break had nothing to do with a phone: The murderer left behind his keys and a trail of muddy footprints, and was stopped nearby after his car ran out of gas.
And in the case of a Sacramento hit-and-run that killed a man and his girlfriend’s four dogs, the driver was arrested in a traffic stop because his car was smashed up, and immediately confessed to involvement in the incident.
[…]
His poor examples, however, were reminiscent of one cited by Ronald T. Hosko, a former assistant director of the FBI’s Criminal Investigative Division, in a widely cited—and thoroughly debunked—Washington Post opinion piece last month.
In that case, the Post was eventually forced to have Hosko rewrite the piece, with the following caveat appended:
Editors note: This story incorrectly stated that Apple and Google’s new encryption rules would have hindered law enforcement’s ability to rescue the kidnap victim in Wake Forest, N.C. This is not the case. The piece has been corrected.
Hadn’t Comey found anything better since then? In a question-and-answer session after his speech, Comey both denied trying to use scare stories to make his point—and admitted that he had launched a nationwide search for better ones, to no avail.
This is important. All the FBI talk about “going dark” and losing the ability to solve crimes is absolute bullshit. There is absolutely no evidence, either statistically or even anecdotally, that criminals are going free because of encryption.
So why are we even discussing the possibility to forcing companies to provide insecure encryption to their users and customers?
The EFF points out that companies are protected by law from being required to provide insecure security to make the FBI happy.
Sadly, I don’t think this is going to go away anytime soon.
My first post on these new Crypto Wars is here.
Sidebar photo of Bruce Schneier by Joe MacInnis.