Entries Tagged "encryption"

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The Logjam (and Another) Vulnerability against Diffie-Hellman Key Exchange

Logjam is a new attack against the Diffie-Hellman key-exchange protocol used in TLS. Basically:

The Logjam attack allows a man-in-the-middle attacker to downgrade vulnerable TLS connections to 512-bit export-grade cryptography. This allows the attacker to read and modify any data passed over the connection. The attack is reminiscent of the FREAK attack, but is due to a flaw in the TLS protocol rather than an implementation vulnerability, and attacks a Diffie-Hellman key exchange rather than an RSA key exchange. The attack affects any server that supports DHE_EXPORT ciphers, and affects all modern web browsers. 8.4% of the Top 1 Million domains were initially vulnerable.

Here’s the academic paper.

One of the problems with patching the vulnerability is that it breaks things:

On the plus side, the vulnerability has largely been patched thanks to consultation with tech companies like Google, and updates are available now or coming soon for Chrome, Firefox and other browsers. The bad news is that the fix rendered many sites unreachable, including the main website at the University of Michigan, which is home to many of the researchers that found the security hole.

This is a common problem with version downgrade attacks; patching them makes you incompatible with anyone who hasn’t patched. And it’s the vulnerability the media is focusing on.

Much more interesting is the other vulnerability that the researchers found:

Millions of HTTPS, SSH, and VPN servers all use the same prime numbers for Diffie-Hellman key exchange. Practitioners believed this was safe as long as new key exchange messages were generated for every connection. However, the first step in the number field sieve—the most efficient algorithm for breaking a Diffie-Hellman connection—is dependent only on this prime. After this first step, an attacker can quickly break individual connections.

The researchers believe the NSA has been using this attack:

We carried out this computation against the most common 512-bit prime used for TLS and demonstrate that the Logjam attack can be used to downgrade connections to 80% of TLS servers supporting DHE_EXPORT. We further estimate that an academic team can break a 768-bit prime and that a nation-state can break a 1024-bit prime. Breaking the single, most common 1024-bit prime used by web servers would allow passive eavesdropping on connections to 18% of the Top 1 Million HTTPS domains. A second prime would allow passive decryption of connections to 66% of VPN servers and 26% of SSH servers. A close reading of published NSA leaks shows that the agency’s attacks on VPNs are consistent with having achieved such a break.

Remember James Bamford’s 2012 comment about the NSA’s cryptanalytic capabilities:

According to another top official also involved with the program, the NSA made an enormous breakthrough several years ago in its ability to cryptanalyze, or break, unfathomably complex encryption systems employed by not only governments around the world but also many average computer users in the US. The upshot, according to this official: “Everybody’s a target; everybody with communication is a target.”

[…]

The breakthrough was enormous, says the former official, and soon afterward the agency pulled the shade down tight on the project, even within the intelligence community and Congress. “Only the chairman and vice chairman and the two staff directors of each intelligence committee were told about it,” he says. The reason? “They were thinking that this computing breakthrough was going to give them the ability to crack current public encryption.”

And remember Director of National Intelligence James Clapper’s introduction to the 2013 “Black Budget“:

Also, we are investing in groundbreaking cryptanalytic capabilities to defeat adversarial cryptography and exploit internet traffic.

It’s a reasonable guess that this is what both Bamford’s source and Clapper are talking about. It’s an attack that requires a lot of precomputation—just the sort of thing a national intelligence agency would go for.

But that requirement also speaks to its limitations. The NSA isn’t going to put this capability at collection points like Room 641A at AT&T’s San Francisco office: the precomputation table is too big, and the sensitivity of the capability is too high. More likely, an analyst identifies a target through some other means, and then looks for data by that target in databases like XKEYSCORE. Then he sends whatever ciphertext he finds to the Cryptanalysis and Exploitation Services (CES) group, which decrypts it if it can using this and other techniques.

Ross Anderson wrote about this earlier this month, almost certainly quoting Snowden:

As for crypto capabilities, a lot of stuff is decrypted automatically on ingest (e.g. using a “stolen cert”, presumably a private key obtained through hacking). Else the analyst sends the ciphertext to CES and they either decrypt it or say they can’t.

The analysts are instructed not to think about how this all works. This quote also applied to NSA employees:

Strict guidelines were laid down at the GCHQ complex in Cheltenham, Gloucestershire, on how to discuss projects relating to decryption. Analysts were instructed: “Do not ask about or speculate on sources or methods underpinning Bullrun.”

I remember the same instructions in documents I saw about the NSA’s CES.

Again, the NSA has put surveillance ahead of security. It never bothered to tell us that many of the “secure” encryption systems we were using were not secure. And we don’t know what other national intelligence agencies independently discovered and used this attack.

The good news is now that we know reusing prime numbers is a bad idea, we can stop doing it.

EDITED TO ADD: The DH precomputation easily lends itself to custom ASIC design, and is something that pipelines easily. Using BitCoin mining hardware as a rough comparison, this means a couple orders of magnitude speedup.

EDITED TO ADD (5/23): Good analysis of the cryptography.

EDITED TO ADD (5/24): Good explanation by Matthew Green.

Posted on May 21, 2015 at 6:30 AM • View Comments

Eighth Movie-Plot Threat Contest Semifinalists

On April 1, I announced the Eighth Movie Plot Threat Contest: demonstrate the evils of encryption.

Not a whole lot of good submissions this year. Possibly this contest has run its course, and there’s not a whole lot of interest left. On the other hand, it’s heartening to know that there aren’t a lot of encryption movie-plot threats out there.

Anyway, here are the semifinalists.

  1. Child pornographers.
  2. Bombing the NSA.
  3. Torture.
  4. Terrorists and a vaccine.
  5. Election systems.

Cast your vote by number here; voting closes at the end of the month.

Contest.

Previous contests.

Posted on May 14, 2015 at 11:26 PM • View Comments

More on the NSA's Capabilities

Ross Anderson summarizes a meeting in Princeton where Edward Snowden was “present.”

Third, the leaks give us a clear view of an intelligence analyst’s workflow. She will mainly look in Xkeyscore which is the Google of 5eyes comint; it’s a federated system hoovering up masses of stuff not just from 5eyes own assets but from other countries where the NSA cooperates or pays for access. Data are “ingested” into a vast rolling buffer; an analyst can run a federated search, using a selector (such as an IP address) or fingerprint (something that can be matched against the traffic). There are other such systems: “Dancing oasis” is the middle eastern version. Some xkeyscore assets are actually compromised third-party systems; there are multiple cases of rooted SMS servers that are queried in place and the results exfiltrated. Others involve vast infrastructure, like Tempora. If data in Xkeyscore are marked as of interest, they’re moved to Pinwale to be memorialised for 5+ years. This is one function of the MDRs (massive data repositories, now more tactfully renamed mission data repositories) like Utah. At present storage is behind ingestion. Xkeyscore buffer times just depend on volumes and what storage they managed to install, plus what they manage to filter out.

As for crypto capabilities, a lot of stuff is decrypted automatically on ingest (e.g. using a “stolen cert,” presumably a private key obtained through hacking). Else the analyst sends the ciphertext to CES and they either decrypt it or say they can’t. There’s no evidence of a “wow” cryptanalysis; it was key theft, or an implant, or a predicted RNG or supply-chain interference. Cryptanalysis has been seen of RC4, but not of elliptic curve crypto, and there’s no sign of exploits against other commonly used algorithms. Of course, the vendors of some products have been coopted, notably skype. Homegrown crypto is routinely problematic, but properly implemented crypto keeps the agency out; gpg ciphertexts with RSA 1024 were returned as fails.

[…]

What else might we learn from the disclosures when designing and implementing crypto? Well, read the disclosures and use your brain. Why did GCHQ bother stealing all the SIM card keys for Iceland from Gemalto, unless they have access to the local GSM radio links? Just look at the roof panels on US or UK embassies, that look like concrete but are actually transparent to RF. So when designing a protocol ask yourself whether a local listener is a serious consideration.

[…]

On the policy front, one of the eye-openers was the scale of intelligence sharing—it’s not just 5 eyes, but 15 or 35 or even 65 once you count all the countries sharing stuff with the NSA. So how does governance work? Quite simply, the NSA doesn’t care about policy. Their OGC has 100 lawyers whose job is to “enable the mission”; to figure out loopholes or new interpretations of the law that let stuff get done. How do you restrain this? Could you use courts in other countries, that have stronger human-rights law? The precedents are not encouraging. New Zealand’s GCSB was sharing intel with Bangladesh agencies while the NZ government was investigating them for human-rights abuses. Ramstein in Germany is involved in all the drone killings, as fibre is needed to keep latency down low enough for remote vehicle pilots. The problem is that the intelligence agencies figure out ways to shield the authorities from culpability, and this should not happen.

[…]

The spooks’ lawyers play games saying for example that they dumped content, but if you know IP address and file size you often have it; and IP address is a good enough pseudonym for most intel / LE use. They deny that they outsource to do legal arbitrage (e.g. NSA spies on Brits and GCHQ returns the favour by spying on Americans). Are they telling the truth? In theory there will be an MOU between NSA and the partner agency stipulating respect for each others’ laws, but there can be caveats, such as a classified version which says “this is not a binding legal document.” The sad fact is that law and legislators are losing the capability to hold people in the intelligence world to account, and also losing the appetite for it.

Worth reading in full.

Posted on May 11, 2015 at 6:26 AM •

The Further Democratization of QUANTUM

From my book Data and Goliath:

…when I was working with the Guardian on the Snowden documents, the one top-secret program the NSA desperately did not want us to expose was QUANTUM. This is the NSA’s program for what is called packet injection­—basically, a technology that allows the agency to hack into computers. Turns out, though, that the NSA was not alone in its use of this technology. The Chinese government uses packet injection to attack computers. The cyberweapons manufacturer Hacking Team sells packet injection technology to any government willing to pay for it. Criminals use it. And there are hacker tools that give the capability to individuals as well. All of these existed before I wrote about QUANTUM. By using its knowledge to attack others rather than to build up the Internet’s defenses, the NSA has worked to ensure that anyone can use packet injection to hack into computers.

And that’s true. China’s Great Cannon uses QUANTUM. The ability to inject packets into the backbone is a powerful attack technology, and one that is increasingly being used by different attackers.

I continued:

Even when technologies are developed inside the NSA, they don’t remain exclusive for long. Today’s top-secret programs become tomorrow’s PhD theses and the next day’s hacker tools.

I could have continued with “and the next day’s homework assignment,” because Michalis Polychronakis at Stony Book University has just assigned building a rudimentary QUANTUM tool as a homework assignment. It’s basically sniff, regexp match, swap sip/sport/dip/dport/syn/ack, set ack and push flags, and add the payload to create the malicious reply. Shouldn’t take more than a few hours to get it working. Of course, it would take a lot more to make it as sophisticated and robust as what the NSA and China have at their disposal, but the moral is that the tool is now in the hands of anyone who wants it. We need to make the Internet secure against this kind of attack instead of pretending that only the “good guys” can use it effectively.

End-to-end encryption is the solution. Nicholas Weaver wrote:

The only self defense from all of the above is universal encryption. Universal encryption is difficult and expensive, but unfortunately necessary.

Encryption doesn’t just keep our traffic safe from eavesdroppers, it protects us from attack. DNSSEC validation protects DNS from tampering, while SSL armors both email and web traffic.

There are many engineering and logistic difficulties involved in encrypting all traffic on the internet, but its one we must overcome if we are to defend ourselves from the entities that have weaponized the backbone.

Yes.

And this is true in general. We have one network in the world today. Either we build our communications infrastructure for surveillance, or we build it for security. Either everyone gets to spy, or no one gets to spy. That’s our choice, with the Internet, with cell phone networks, with everything.

Posted on April 24, 2015 at 8:55 AM • View Comments

Can the NSA Break Microsoft's BitLocker?

The Intercept has a new story on the CIA’s—yes, the CIA, not the NSA—efforts to break encryption. These are from the Snowden documents, and talk about a conference called the Trusted Computing Base Jamboree. There are some interesting documents associated with the article, but not a lot of hard information.

There’s a paragraph about Microsoft’s BitLocker, the encryption system used to protect MS Windows computers:

Also presented at the Jamboree were successes in the targeting of Microsoft’s disk encryption technology, and the TPM chips that are used to store its encryption keys. Researchers at the CIA conference in 2010 boasted about the ability to extract the encryption keys used by BitLocker and thus decrypt private data stored on the computer. Because the TPM chip is used to protect the system from untrusted software, attacking it could allow the covert installation of malware onto the computer, which could be used to access otherwise encrypted communications and files of consumers. Microsoft declined to comment for this story.

This implies that the US intelligence community—I’m guessing the NSA here—can break BitLocker. The source document, though, is much less definitive about it.

Power analysis, a side-channel attack, can be used against secure devices to non-invasively extract protected cryptographic information such as implementation details or secret keys. We have employed a number of publically known attacks against the RSA cryptography found in TPMs from five different manufacturers. We will discuss the details of these attacks and provide insight into how private TPM key information can be obtained with power analysis. In addition to conventional wired power analysis, we will present results for extracting the key by measuring electromagnetic signals emanating from the TPM while it remains on the motherboard. We will also describe and present results for an entirely new unpublished attack against a Chinese Remainder Theorem (CRT) implementation of RSA that will yield private key information in a single trace.

The ability to obtain a private TPM key not only provides access to TPM-encrypted data, but also enables us to circumvent the root-of-trust system by modifying expected digest values in sealed data. We will describe a case study in which modifications to Microsoft’s Bitlocker encrypted metadata prevents software-level detection of changes to the BIOS.

Differential power analysis is a powerful cryptanalytic attack. Basically, it examines a chip’s power consumption while it performs encryption and decryption operations and uses that information to recover the key. What’s important here is that this is an attack to extract key information from a chip while it is running. If the chip is powered down, or if it doesn’t have the key inside, there’s no attack.

I don’t take this to mean that the NSA can take a BitLocker-encrypted hard drive and recover the key. I do take it to mean that the NSA can perform a bunch of clever hacks on a BitLocker-encrypted hard drive while it is running. So I don’t think this means that BitLocker is broken.

But who knows? We do know that the FBI pressured Microsoft to add a backdoor to BitLocker in 2005. I believe that was unsuccessful.

More than that, we don’t know.

EDITED TO ADD (3/12): Starting with Windows 8, Microsoft removed the Elephant Diffuser from BitLocker. I see no reason to remove it other than to make the encryption weaker.

Posted on March 10, 2015 at 2:34 PM • View Comments

FREAK: Security Rollback Attack Against SSL

This week, we learned about an attack called “FREAK”—”Factoring Attack on RSA-EXPORT Keys”—that can break the encryption of many websites. Basically, some sites’ implementations of secure sockets layer technology, or SSL, contain both strong encryption algorithms and weak encryption algorithms. Connections are supposed to use the strong algorithms, but in many cases an attacker can force the website to use the weaker encryption algorithms and then decrypt the traffic. From Ars Technica:

In recent days, a scan of more than 14 million websites that support the secure sockets layer or transport layer security protocols found that more than 36 percent of them were vulnerable to the decryption attacks. The exploit takes about seven hours to carry out and costs as little as $100 per site.

This is a general class of attack I call “security rollback” attacks. Basically, the attacker forces the system users to revert to a less secure version of their protocol. Think about the last time you used your credit card. The verification procedure involved the retailer’s computer connecting with the credit card company. What if you snuck around to the back of the building and severed the retailer’s phone lines? Most likely, the retailer would have still accepted your card, but defaulted to making a manual impression of it and maybe looking at your signature. The result: you’ll have a much easier time using a stolen card.

In this case, the security flaw was designed in deliberately. Matthew Green writes:

Back in the early 1990s when SSL was first invented at Netscape Corporation, the United States maintained a rigorous regime of export controls for encryption systems. In order to distribute crypto outside of the U.S., companies were required to deliberately “weaken” the strength of encryption keys. For RSA encryption, this implied a maximum allowed key length of 512 bits.

The 512-bit export grade encryption was a compromise between dumb and dumber. In theory it was designed to ensure that the NSA would have the ability to “access” communications, while allegedly providing crypto that was still “good enough” for commercial use. Or if you prefer modern terms, think of it as the original “golden master key.”

The need to support export-grade ciphers led to some technical challenges. Since U.S. servers needed to support both strong and weak crypto, the SSL designers used a “cipher suite” negotiation mechanism to identify the best cipher both parties could support. In theory this would allow “strong” clients to negotiate “strong” ciphersuites with servers that supported them, while still providing compatibility to the broken foreign clients.

And that’s the problem. The weak algorithms are still there, and can be exploited by attackers.

Fixes are coming. Companies like Apple are quickly rolling out patches. But the vulnerability has been around for over a decade, and almost has certainly used by national intelligence agencies and criminals alike.

This is the generic problem with government-mandated backdoors, key escrow, “golden keys,” or whatever you want to call them. We don’t know how to design a third-party access system that checks for morality; once we build in such access, we then have to ensure that only the good guys can do it. And we can’t. Or, to quote the Economist: “…mathematics applies to just and unjust alike; a flaw that can be exploited by Western governments is vulnerable to anyone who finds it.”

This essay previously appeared on the Lawfare blog.

EDITED TO ADD: Microsoft Windows is vulnerable.

Posted on March 6, 2015 at 10:46 AM • View Comments

IRS Encourages Poor Cryptography

I’m not sure what to make of this, or even what it means. The IRS has a standard called IDES: International Data Exchange Service: “The International Data Exchange Service (IDES) is an electronic delivery point where Financial Institutions (FI) and Host Country Tax Authorities (HCTA) can transmit and exchange FATCA data with the United States.” It’s like IRS data submission, but for other governments and foreign banks.

Buried in one of the documents are the rules for encryption:

While performing AES encryption, there are several settings and options depending on the tool used to perform encryption. IRS recommended settings should be used to maintain compatibility:

  • Cipher Mode: ECB (Electronic Code Book).
  • Salt: No salt value
  • Initialization Vector: No Initialization Vector (IV). If an IV is present, set to all zeros to avoid affecting the encryption.
  • Key Size: 256 bits / 32 bytes ­ Key size should be verified and moving the key across operating systems can affect the key size.
  • Encoding: There can be no special encoding. The file will contain only the raw encrypted bytes.
  • Padding: PKCS#7 or PKCS#5.

ECB? Are they serious?

Posted on February 18, 2015 at 6:42 AM • View Comments

Cryptography for Kids

Interesting National Science Foundation award:

In the proposed “CryptoClub” afterschool program, middle-grade students will explore cryptography while applying mathematics to make and break secret codes. The playfulness and mystery of the subject will be engaging to students, and the afterschool environment will allow them to learn at their own pace. Some activities will involve moving around, for example following a trail of encrypted clues to find a hidden treasure, or running back and forth in a relay race, competing to be the first to gather and decrypt the parts of a secret message. Other activities will involve sitting more quietly and thinking deeply about patterns that might help break a code. On the other hand, in the proposed CryptoClub Online approach, the CryptoClub Website will provide additional opportunities for applying and learning cryptography in a playful way. It currently includes cipher tools for encrypting and decrypting, message and joke boards where users decrypt messages or submit their own encrypted messages, historical comics about cryptography, and adventure games that involve secret messages.

Posted on February 13, 2015 at 1:13 PM • View Comments

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Sidebar photo of Bruce Schneier by Joe MacInnis.