Entries Tagged "encryption"

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Identifying Speakers in Encrypted Voice Communication

I’ve already written how it is possible to detect words and phrases in encrypted VoIP calls. Turns out it’s possible to detect speakers as well:

Abstract: Most of the voice over IP (VoIP) traffic is encrypted prior to its transmission over the Internet. This makes the identity tracing of perpetrators during forensic investigations a challenging task since conventional speaker recognition techniques are limited to unencrypted speech communications. In this paper, we propose techniques for speaker identification and verification from encrypted VoIP conversations. Our experimental results show that the proposed techniques can correctly identify the actual speaker for 70-75% of the time among a group of 10 potential suspects. We also achieve more than 10 fold improvement over random guessing in identifying a perpetrator in a group of 20 potential suspects. An equal error rate of 17% in case of speaker verification on the CSLU speaker recognition corpus is achieved.

Posted on September 16, 2011 at 12:31 PM • View Comments

New Attack on AES

“Biclique Cryptanalysis of the Full AES,” by Andrey Bogdanov, Dmitry Khovratovich, and Christian Rechberger.

Abstract. Since Rijndael was chosen as the Advanced Encryption Standard, improving upon 7-round attacks on the 128-bit key variant or upon 8-round attacks on the 192/256-bit key variants has been one of the most difficult challenges in the cryptanalysis of block ciphers for more than a decade. In this paper we present a novel technique of block cipher cryptanalysis with bicliques, which leads to the following results:

  • The first key recovery attack on the full AES-128 with computational complexity 2126.1.
  • The first key recovery attack on the full AES-192 with computational complexity 2189.7.
  • The first key recovery attack on the full AES-256 with computational complexity 2254.4.
  • Attacks with lower complexity on the reduced-round versions of AES not considered before, including an attack on 8-round AES-128 with complexity 2124.9.
  • Preimage attacks on compression functions based on the full AES versions.

In contrast to most shortcut attacks on AES variants, we do not need to assume related-keys. Most of our attacks only need a very small part of the codebook and have small memory requirements, and are practically verified to a large extent. As our attacks are of high computational complexity, they do not threaten the practical use of AES in any way.

This is what I wrote about AES in 2009. I still agree with my advice:

Cryptography is all about safety margins. If you can break n round of a cipher, you design it with 2n or 3n rounds. What we’re learning is that the safety margin of AES is much less than previously believed. And while there is no reason to scrap AES in favor of another algorithm, NST should increase the number of rounds of all three AES variants. At this point, I suggest AES-128 at 16 rounds, AES-192 at 20 rounds, and AES-256 at 28 rounds. Or maybe even more; we don’t want to be revising the standard again and again.

And for new applications I suggest that people don’t use AES-256. AES-128 provides more than enough security margin for the forseeable future. But if you’re already using AES-256, there’s no reason to change.

The advice about AES-256 was because of a 2009 attack, not this result.

Again, I repeat the saying I’ve heard came from inside the NSA: “Attacks always get better; they never get worse.”

Posted on August 18, 2011 at 6:12 AM • View Comments

Security Flaws in Encrypted Police Radios

“Why (Special Agent) Johnny (Still) Can’t Encrypt: A Security Analysis of the APCO Project 25 Two-Way Radio System,” by Sandy Clark, Travis Goodspeed, Perry Metzger, Zachary Wasserman, Kevin Xu, and Matt Blaze.

Abstract: APCO Project 25a (“P25”) is a suite of wireless communications protocols used in the US and elsewhere for public safety two-way (voice) radio systems. The protocols include security options in which voice and data traffic can be cryptographically protected from eavesdropping. This paper analyzes the security of P25 systems against both passive and active adversaries. We found a number of protocol, implementation, and user interface weaknesses that routinely leak information to a passive eavesdropper or that permit highly efficient and difficult to detect active attacks. We introduce new selective subframe jamming attacks against P25, in which an active attacker with very modest resources can prevent specific kinds of traffic (such as encrypted messages) from being received, while emitting only a small fraction of the aggregate power of the legitimate transmitter. We also found that even the passive attacks represent a serious practical threat. In a study we conducted over a two year period in several US metropolitan areas, we found that a significant fraction of the “encrypted” P25 tactical radio traffic sent by federal law enforcement surveillance operatives is actually sent in the clear, in spite of their users’ belief that they are encrypted, and often reveals such sensitive data as the such sensitive data as the names of informants in criminal investigations.

I’ve heard Matt talk about this project several times. It’s great work, and a fascinating insight into the usability problems of encryption in the real world.

News article.

Posted on August 11, 2011 at 6:19 AM • View Comments

GPRS Hacked

Just announced:

Nohl’s group found a number of problems with GPRS. First, he says, lax authentication rules could allow an attacker to set up a fake cellular base station and eavesdrop on information transmitted by users passing by. In some countries, they found that GPRS communications weren’t encrypted at all. When they were encrypted, Nohl adds, the ciphers were often weak and could be either broken or decoded with relatively short keys that were easy to guess.

The group generated an optimized set of codes that an attacker could quickly use to find the key protecting a given communication. The attack the researchers designed against GPRS costs about 10 euros for radio equipment, Nohl says.

More articles.

Posted on August 10, 2011 at 4:11 PM • View Comments

Zodiac Cipher Cracked

I admit I don’t pay much attention to pencil-and-paper ciphers, so I knew nothing about the Zodiac cipher. Seems it has finally been broken:

The Zodiac Killer was a serial killer who preyed on couples in Northern California in the years between 1968 and 1970. Of his seven confirmed victims, five died. More victims and attacks are suspected.

The killer sent four messages to newspapers in California’s Bay Area, only one of which has ever been decrypted. This first message ­ split into three parts ­ claimed Zodiac wanted to kill victims so that they would become his slaves in the afterlife.

The 408-symbol cryptogram was cracked by Donald and Bettye Harden of Salinas, California.

Code and solution—with photos—here.

EDITED TO ADD (8/5): Solution seems to be a hoax.

Posted on August 5, 2011 at 12:25 PM • View Comments

New Information on the Inventor of the One-Time Pad

Seems that the one-time pad was not first invented by Vernam:

He could plainly see that the document described a technique called the one-time pad fully 35 years before its supposed invention during World War I by Gilbert Vernam, an AT&T engineer, and Joseph Mauborgne, later chief of the Army Signal Corps.

[…]

The 1882 monograph that Dr. Bellovin stumbled across in the Library of Congress was “Telegraphic Code to Insure Privacy and Secrecy in the Transmission of Telegrams,” by Frank Miller, a successful banker in Sacramento who later became a trustee of Stanford University. In Miller’s preface, the key points jumped off the page:

“A banker in the West should prepare a list of irregular numbers to be called ‘shift numbers,'” he wrote. “The difference between such numbers must not be regular. When a shift-number has been applied, or used, it must be erased from the list and not be used again.”

It seems that Vernam was not aware of Miller’s work, and independently invented the one-time pad.

Another article. And the paper.

Posted on August 3, 2011 at 12:57 PM • View Comments

Breaking the Xilinx Virtex-II FPGA Bitstream Encryption

It’s a power-analysis attack, which makes it much harder to defend against. And since the attack model is an engineer trying to reverse-engineer the chip, it’s a valid attack.

Abstract: Over the last two decades FPGAs have become central components for many advanced digital systems, e.g., video signal processing, network routers, data acquisition and military systems. In order to protect the intellectual property and to prevent fraud, e.g., by cloning an FPGA or manipulating its content, many current FPGAs employ a bitstream encryption feature. We develop a successful attack on the bitstream encryption engine integrated in the widespread Virtex-II Pro FPGAs from Xilinx, using side-channel analysis. After measuring the power consumption of a single power-up of the device and a modest amount of o-line computation, we are able to recover all three different keys used by its triple DES module. Our method allows extracting secret keys from any real-world device where the bitstream encryption feature of Virtex-II Pro is enabled. As a consequence, the target product can be cloned and manipulated at will of the attacker. Also, more advanced attacks such as reverse engineering or the introduction of hardware Trojans become potential threats. As part of the side-channel attack, we were able to deduce certain internals of the hardware encryption engine. To our knowledge, this is the first attack against the bitstream encryption of a commercial FPGA reported in the open literature.

Posted on August 1, 2011 at 12:29 PM • View Comments

Cryptography and Wiretapping

Matt Blaze analyzes the 2010 U.S. Wiretap Report.

In 2000, government policy finally reversed course, acknowledging that encryption needed to become a critical part of security in modern networks, something that deserved to be encouraged, even if it might occasionally cause some trouble for law enforcement wiretappers. And since that time the transparent use of cryptography by everyday people (and criminals) has, in fact, exploded. Crypto software and algorithms, once categorized for arms control purposes as a “munition” alongside rocket launchers and nuclear triggers, can now be openly discussed, improved and incorporated into products and services without the end user even knowing that it’s there. Virtually every cellular telephone call is today encrypted and effectively impervious to unauthorized over-the-air eavesdropping. Web transactions, for everything from commerce to social networking, are now routinely encrypted end-to-end. (A few applications, particularly email and wireline telephony, remain stubbornly unencrypted, but they are increasingly the exception rather than the rule.)

So, with this increasing proliferation of eavesdrop-thwarting encryption built in to our infrastructure, we might expect law enforcement wiretap rooms to have become quiet, lonely places.

But not so fast: the latest wiretap report identifies a total of just six (out of 3194) cases in which encryption was encountered, and that prevented recovery of evidence a grand total of … (drumroll) … zero times. Not once. Previous wiretap reports have indicated similarly minuscule numbers.

I second Matt’s recommendation of Susan Landau’s book: Surveillance or Security: The Risks Posed by New Wiretapping Technologies (MIT Press, 2011). It’s an excellent discussion of the security and politics of wiretapping.

Posted on July 27, 2011 at 2:10 PM • View Comments

Telex Anti-Censorship System

This is really clever:

Many anticensorship systems work by making an encrypted connection (called a “tunnel”) from the user’s computer to a trusted proxy server located outside the censor’s network. This server relays requests to censored websites and returns the responses to the user over the encrypted tunnel. This approach leads to a cat-and-mouse game, where the censor attempts to discover and block the proxy servers. Users need to learn the address and login information for a proxy server somehow, and it’s very difficult to broadcast this information to a large number of users without the censor also learning it.

Telex turns this approach on its head to create what is essentially a proxy server without an IP address. In fact, users don’t need to know any secrets to connect. The user installs a Telex client app (perhaps by downloading it from an intermittently available website or by making a copy from a friend). When the user wants to visit a blacklisted site, the client establishes an encrypted HTTPS connection to a non-blacklisted web server outside the censor’s network, which could be a normal site that the user regularly visits. Since the connection looks normal, the censor allows it, but this connection is only a decoy.

The client secretly marks the connection as a Telex request by inserting a cryptographic tag into the headers. We construct this tag using a mechanism called public-key steganography. This means anyone can tag a connection using only publicly available information, but only the Telex service (using a private key) can recognize that a connection has been tagged.

As the connection travels over the Internet en route to the non-blacklisted site, it passes through routers at various ISPs in the core of the network. We envision that some of these ISPs would deploy equipment we call Telex stations. These devices hold a private key that lets them recognize tagged connections from Telex clients and decrypt these HTTPS connections. The stations then divert the connections to anti­censorship services, such as proxy servers or Tor entry points, which clients can use to access blocked sites. This creates an encrypted tunnel between the Telex user and Telex station at the ISP, redirecting connections to any site on the Internet.

EDITED TO ADD (8/1): Another article.

EDITED TO ADD (8/13): Another article.

Posted on July 19, 2011 at 9:59 AM • View Comments

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Sidebar photo of Bruce Schneier by Joe MacInnis.