Page 8 of 22
Algebraic Eraser is a public-key key-agreement protocol that’s patented and being pushed by a company for the Internet of Things, primarily because it is efficient on small low-power devices. There’s a new cryptanalytic attack.
This is yet another demonstration of why you should not choose proprietary encryption over public algorithms and protocols. The good stuff is not patented.
News article.
The Internet is abuzz with this blog post and paper, speculating that the NSA is breaking the Diffie-Hellman key-exchange protocol in the wild through massive precomputation.
I wrote about this at length in May when this paper was first made public. (The reason it’s news again is that the paper was just presented at the ACM Computer and Communications Security conference.)
What’s newly being talked about his how this works inside the NSA surveillance architecture. Nicholas Weaver explains:
To decrypt IPsec, a large number of wiretaps monitor for IKE (Internet Key Exchange) handshakes, the protocol that sets up a new IPsec encrypted connection. The handshakes are forwarded to a decryption oracle, a black box system that performs the magic. While this happens, the wiretaps also record all traffic in the associated IPsec connections.
After a period of time, this oracle either returns the private keys or says “i give up”. If the oracle provides the keys, the wiretap decrypts all the stored traffic and continues to decrypt the connection going forward.
[…]
This would also better match the security implications: just the fact that the NSA can decrypt a particular flow is a critical secret. Forwarding a small number of potentially-crackable flows to a central point better matches what is needed to maintain such secrecy.
Thus by performing the decryption in bulk at the wiretaps, complete with hardware acceleration to keep up with the number of encrypted streams, this architecture directly implies that the NSA can break a massive amount of IPsec traffic, a degree of success which implies a cryptanalysis breakthrough.
That last paragraph is Weaver explaining how this attack matches the NSA rhetoric about capabilities in some of their secret documents.
Now that this is out, I’m sure there are a lot of really upset people inside the NSA.
EDITED TO ADD (11/15): How to protect yourself.
There’s a new cryptanalysis result against the hash function SHA-1:
Abstract: We present in this article a freestart collision example for SHA-1, i.e., a collision for its internal compression function. This is the first practical break of the full SHA-1, reaching all 80 out of 80 steps, while only 10 days of computation on a 64 GPU cluster were necessary to perform the attack. This work builds on a continuous series of cryptanalytic advancements on SHA-1 since the theoretical collision attack breakthrough in 2005. In particular, we extend the recent freestart collision work on reduced-round SHA-1 from CRYPTO 2015 that leverages the computational power of graphic cards and adapt it to allow the use of boomerang speed-up techniques. We also leverage the cryptanalytic techniques by Stevens from EUROCRYPT 2013 to obtain optimal attack conditions, which required further refinements for this work. Freestart collisions, like the one presented here, do not directly imply a collision for SHA-1.
However, this work is an important milestone towards an actual SHA-1 collision and it further shows how graphics cards can be used very efficiently for these kind of attacks. Based on the state-of-the-art collision attack on SHA-1 by Stevens from EUROCRYPT 2013, we are able to present new projections on the computational/financial cost required by a SHA-1 collision computation. These projections are significantly lower than previously anticipated by the industry, due to the use of the more cost efficient graphics cards compared to regular CPUs. We therefore recommend the industry, in particular Internet browser vendors and Certification Authorities, to retract SHA-1 soon. We hope the industry has learned from the events surrounding the cryptanalytic breaks of MD5 and will retract SHA-1 before example signature forgeries appear in the near future. With our new cost projections in mind, we strongly and urgently recommend against a recent proposal to extend the issuance of SHA-1 certificates by a year in the CAB/forum (the vote closes on October 16 2015 after a discussion period ending on October 9).
Especially note this bit: “Freestart collisions, like the one presented here, do not directly imply a collision for SHA-1. However, this work is an important milestone towards an actual SHA-1 collision and it further shows how graphics cards can be used very efficiently for these kind of attacks.” In other words: don’t panic, but prepare for a future panic.
This is not that unexpected. We’ve long known that SHA-1 is broken, at least theoretically. All the major browsers are planning to stop accepting SHA-1 signatures by 2017. Microsoft is retiring it on that same schedule. What’s news is that our previous estimates may be too conservative.
There’s a saying inside the NSA: “Attacks always get better; they never get worse.” This is obviously true, but it’s worth explaining why. Attacks get better for three reasons. One, Moore’s Law means that computers are always getting faster, which means that any cryptanalytic attack gets faster. Two, we’re forever making tweaks in existing attacks, which make them faster. (Note above: “…due to the use of the more cost efficient graphics cards compared to regular CPUs.”) And three, we regularly invent new cryptanalytic attacks. The first of those is generally predictable, the second is somewhat predictable, and the third is not at all predictable.
Way back in 2004, I wrote: “It’s time for us all to migrate away from SHA-1.” Since then, we have developed an excellent replacement: SHA-3 has been agreed on since 2012, and just became a standard.
This new result is important right now:
Thursday’s research showing SHA1 is weaker than previously thought comes as browser developers and certificate authorities are considering a proposal that would extend the permitted issuance of the SHA1-based HTTPS certificates by 12 months, that is through the end of 2016 rather than no later than January of that year. The proposal argued that some large organizations currently find it hard to move to a more secure hashing algorithm for their digital certificates and need the additional year to make the transition.
As the papers’ authors note, approving this proposal is a bad idea.
More on the paper here.
Quantum computing is a novel way to build computers—one that takes advantage of the quantum properties of particles to perform operations on data in a very different way than traditional computers. In some cases, the algorithm speedups are extraordinary.
Specifically, a quantum computer using something called Shor’s algorithm can efficiently factor numbers, breaking RSA. A variant can break Diffie-Hellman and other discrete log-based cryptosystems, including those that use elliptic curves. This could potentially render all modern public-key algorithms insecure. Before you panic, note that the largest number to date that has been factored by a quantum computer is 143. So while a practical quantum computer is still science fiction, it’s not stupid science fiction.
(Note that this is completely different from quantum cryptography, which is a way of passing bits between two parties that relies on physical quantum properties for security. The only thing quantum computation and quantum cryptography have to do with each other is their first words. It is also completely different from the NSA’s QUANTUM program, which is its code name for a packet-injection system that works directly in the Internet backbone.)
Practical quantum computation doesn’t mean the end of cryptography. There are lesser-known public-key algorithms such as McEliece and lattice-based algorithms that, while less efficient than the ones we use, are currently secure against a quantum computer. And quantum computation only speeds up a brute-force keysearch by a factor of a square root, so any symmetric algorithm can be made secure against a quantum computer by doubling the key length.
We know from the Snowden documents that the NSA is conducting research on both quantum computation and quantum cryptography. It’s not a lot of money, and few believe that the NSA has made any real advances in theoretical or applied physics in this area. My guess has been that we’ll see a practical quantum computer within 30 to 40 years, but not much sooner than that.
This all means that now is the time to think about what living in a post-quantum world would be like. NIST is doing its part, having hosted a conference on the topic earlier this year. And the NSA announced that it is moving towards quantum-resistant algorithms.
Earlier this week, the NSA’s Information Assurance Directorate updated its list of Suite B cryptographic algorithms. It explicitly talked about the threat of quantum computers:
IAD will initiate a transition to quantum resistant algorithms in the not too distant future. Based on experience in deploying Suite B, we have determined to start planning and communicating early about the upcoming transition to quantum resistant algorithms. Our ultimate goal is to provide cost effective security against a potential quantum computer. We are working with partners across the USG, vendors, and standards bodies to ensure there is a clear plan for getting a new suite of algorithms that are developed in an open and transparent manner that will form the foundation of our next Suite of cryptographic algorithms.
Until this new suite is developed and products are available implementing the quantum resistant suite, we will rely on current algorithms. For those partners and vendors that have not yet made the transition to Suite B elliptic curve algorithms, we recommend not making a significant expenditure to do so at this point but instead to prepare for the upcoming quantum resistant algorithm transition.
Suite B is a family of cryptographic algorithms approved by the NSA. It’s all part of the NSA’s Cryptographic Modernization Program. Traditionally, NSA algorithms were classified and could only be used in specially built hardware modules. Suite B algorithms are public, and can be used in anything. This is not to say that Suite B algorithms are second class, or breakable by the NSA. They’re being used to protect US secrets: “Suite A will be used in applications where Suite B may not be appropriate. Both Suite A and Suite B can be used to protect foreign releasable information, US-Only information, and Sensitive Compartmented Information (SCI).”
The NSA is worried enough about advances in the technology to start transitioning away from algorithms that are vulnerable to a quantum computer. Does this mean that the agency is close to a working prototype in their own classified labs? Unlikely. Does this mean that they envision practical quantum computers sooner than my 30-to-40-year estimate? Certainly.
Unlike most personal and corporate applications, the NSA routinely deals with information it wants kept secret for decades. Even so, we should all follow the NSA’s lead and transition our own systems to quantum-resistant algorithms over the next decade or so—possibly even sooner.
The essay previously appeared on Lawfare.
EDITED TO ADD: The computation that factored 143 also accidentally “factored much larger numbers such as 3599, 11663, and 56153, without the awareness of the authors of that work,” which shows how weird this all is.
EDITED TO ADD: Seems that I need to be clearer: I do not stand by my 30-40-year prediction. The NSA is acting like practical quantum computers will exist long before then, and I am deferring to their expertise.
New research: “All Your Biases Belong To Us: Breaking RC4 in WPA-TKIP and TLS,” by Mathy Vanhoef and Frank Piessens:
Abstract: We present new biases in RC4, break the Wi-Fi Protected Access Temporal Key Integrity Protocol (WPA-TKIP), and design a practical plaintext recovery attack against the Transport Layer Security (TLS) protocol. To empirically find new biases in the RC4 keystream we use statistical hypothesis tests. This reveals many new biases in the initial keystream bytes, as well as several new long-term biases. Our fixed-plaintext recovery algorithms are capable of using multiple types of biases, and return a list of plaintext candidates in decreasing likelihood.
To break WPA-TKIP we introduce a method to generate a large number of identical packets. This packet is decrypted by generating its plaintext candidate list, and using redundant packet structure to prune bad candidates. From the decrypted packet we derive the TKIP MIC key, which can be used to inject and decrypt packets. In practice the attack can be executed within an hour. We also attack TLS as used by HTTPS, where we show how to decrypt a secure cookie with a success rate of 94% using 9*227 ciphertexts. This is done by injecting known data around the cookie, abusing this using Mantin’s ABSAB bias, and brute-forcing the cookie by traversing the plaintext candidates. Using our traffic generation technique, we are able to execute the attack in merely 75 hours.
We need to deprecate the algorithm already.
There’s a new paper on a low-cost TEMPEST attack against PC cryptography:
We demonstrate the extraction of secret decryption keys from laptop computers, by nonintrusively measuring electromagnetic emanations for a few seconds from a distance of 50 cm. The attack can be executed using cheap and readily-available equipment: a consumer-grade radio receiver or a Software Defined Radio USB dongle. The setup is compact and can operate untethered; it can be easily concealed, e.g., inside pita bread. Common laptops, and popular implementations of RSA and ElGamal encryptions, are vulnerable to this attack, including those that implement the decryption using modern exponentiation algorithms such as sliding-window, or even its side-channel resistant variant, fixed-window (m-ary) exponentiation.
We successfully extracted keys from laptops of various models running GnuPG (popular open source encryption software, implementing the OpenPGP standard), within a few seconds. The attack sends a few carefully-crafted ciphertexts, and when these are decrypted by the target computer, they trigger the occurrence of specially-structured values inside the decryption software. These special values cause observable fluctuations in the electromagnetic field surrounding the laptop, in a way that depends on the pattern of key bits (specifically, the key-bits window in the exponentiation routine). The secret key can be deduced from these fluctuations, through signal processing and cryptanalysis.
From Wired:
Researchers at Tel Aviv University and Israel’s Technion research institute have developed a new palm-sized device that can wirelessly steal data from a nearby laptop based on the radio waves leaked by its processor’s power use. Their spy bug, built for less than $300, is designed to allow anyone to “listen” to the accidental radio emanations of a computer’s electronics from 19 inches away and derive the user’s secret decryption keys, enabling the attacker to read their encrypted communications. And that device, described in a paper they’re presenting at the Workshop on Cryptographic Hardware and Embedded Systems in September, is both cheaper and more compact than similar attacks from the past—so small, in fact, that the Israeli researchers demonstrated it can fit inside a piece of pita bread.
Another article. NSA article from 1972 on TEMPEST. Hacker News thread. Reddit thread.
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.
This 1947 document describes a German machine to cryptanalyze the American
EDITED TO ADD (5/14): German attacks on the M-209.
Anyone can design a cipher that he himself cannot break. This is why you should uniformly distrust amateur cryptography, and why you should only use published algorithms that have withstood broad cryptanalysis. All cryptographers know this, but non-cryptographers do not. And this is why we repeatedly see bad amateur cryptography in fielded systems.
The latest is the cryptography in the Open Smart Grid Protocol, which is so bad as to be laughable. From the paper:
Dumb Crypto in Smart Grids: Practical Cryptanalysis of the Open Smart Grid Protocol
Philipp Jovanovic and Samuel Neves
Abstract: This paper analyses the cryptography used in the Open Smart Grid Protocol (OSGP). The authenticated encryption (AE) scheme deployed by OSGP is a non-standard composition of RC4 and a home-brewed MAC, the “OMA digest’.”
We present several practical key-recovery attacks against the OMA digest. The first and basic variant can achieve this with a mere 13 queries to an OMA digest oracle and negligible time complexity. A more sophisticated version breaks the OMA digest with only 4 queries and a time complexity of about 2^25 simple operations. A different approach only requires one arbitrary valid plaintext-tag pair, and recovers the key in an average of 144 message verification queries, or one ciphertext-tag pair and 168 ciphertext verification queries.
Since the encryption key is derived from the key used by the OMA digest, our attacks break both confidentiality and authenticity of OSGP.
My still-relevant 1998 essay: “Memo to the Amateur Cipher Designer.” And my 1999 essay on cryptographic snake oil.
ThreatPost article. BoingBoing post.
Note: That first sentence has been called “Schneier’s Law,” although the sentiment is much older.
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.
Sidebar photo of Bruce Schneier by Joe MacInnis.