Entries Tagged "keys"

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More on Heartbleed

This is an update to my earlier post.

Cloudflare is reporting that it’s very difficult, if not practically impossible, to steal SSL private keys with this attack.

Here’s the good news: after extensive testing on our software stack, we have been unable to successfully use Heartbleed on a vulnerable server to retrieve any private key data. Note that is not the same as saying it is impossible to use Heartbleed to get private keys. We do not yet feel comfortable saying that. However, if it is possible, it is at a minimum very hard. And, we have reason to believe based on the data structures used by OpenSSL and the modified version of NGINX that we use, that it may in fact be impossible.

The reasoning is complicated, and I suggest people read the post. What I have heard from people who actually ran the attack against a various servers is that what you get is a huge variety of cruft, ranging from indecipherable binary to useless log messages to peoples’ passwords. The variability is huge.

This xkcd comic is a very good explanation of how the vulnerability works. And this post by Dan Kaminsky is worth reading.

I have a lot to say about the human aspects of this: auditing of open-source code, how the responsible disclosure process worked in this case, the ease with which anyone could weaponize this with just a few lines of script, how we explain vulnerabilities to the public — and the role that impressive logo played in the process — and our certificate issuance and revocation process. This may be a massive computer vulnerability, but all of the interesting aspects of it are human.

EDITED TO ADD (4/12): We have one example of someone successfully retrieving an SSL private key using Heartbleed. So it’s possible, but it seems to be much harder than we originally thought.

And we have a story where two anonymous sources have claimed that the NSA has been exploiting Heartbleed for two years.

EDITED TO ADD (4/12): Hijacking user sessions with Heartbleed. And a nice essay on the marketing and communications around the vulnerability

EDITED TO ADD (4/13): The US intelligence community has denied prior knowledge of Heatbleed. The statement is word-game free:

NSA was not aware of the recently identified vulnerability in OpenSSL, the so-called Heartbleed vulnerability, until it was made public in a private sector cybersecurity report. Reports that say otherwise are wrong.

The statement also says:

Unless there is a clear national security or law enforcement need, this process is biased toward responsibly disclosing such vulnerabilities.

Since when is “law enforcement need” included in that decision process? This national security exception to law and process is extending much too far into normal police work.

Another point. According to the original Bloomberg article:

http://www.bloomberg.com/news/2014-04-11/nsa-said-to-have-used-heartbleed-bug-exposing-consumers.html

Certainly a plausible statement. But if those millions didn’t discover something obvious like Heartbleed, shouldn’t we investigate them for incompetence?

Finally — not related to the NSA — this is good information on which sites are still vulnerable, including historical data.

Posted on April 11, 2014 at 1:10 PMView Comments

Heartbleed

Heartbleed is a catastrophic bug in OpenSSL:

“The Heartbleed bug allows anyone on the Internet to read the memory of the systems protected by the vulnerable versions of the OpenSSL software. This compromises the secret keys used to identify the service providers and to encrypt the traffic, the names and passwords of the users and the actual content. This allows attackers to eavesdrop communications, steal data directly from the services and users and to impersonate services and users.

Basically, an attacker can grab 64K of memory from a server. The attack leaves no trace, and can be done multiple times to grab a different random 64K of memory. This means that anything in memory — SSL private keys, user keys, anything — is vulnerable. And you have to assume that it is all compromised. All of it.

“Catastrophic” is the right word. On the scale of 1 to 10, this is an 11.

Half a million sites are vulnerable, including my own. Test your vulnerability here.

The bug has been patched. After you patch your systems, you have to get a new public/private key pair, update your SSL certificate, and then change every password that could potentially be affected.

At this point, the probability is close to one that every target has had its private keys extracted by multiple intelligence agencies. The real question is whether or not someone deliberately inserted this bug into OpenSSL, and has had two years of unfettered access to everything. My guess is accident, but I have no proof.

This article is worth reading. Hacker News thread is filled with commentary. XKCD cartoon.

EDITED TO ADD (4/9): Has anyone looked at all the low-margin non-upgradable embedded systems that use OpenSSL? An upgrade path that involves the trash, a visit to Best Buy, and a credit card isn’t going to be fun for anyone.

EDITED TO ADD (4/10): I’m hearing that the CAs are completely clogged, trying to reissue so many new certificates. And I’m not sure we have anything close to the infrastructure necessary to revoke half a million certificates.

Possible evidence that Heartbleed was exploited last year.

EDITED TO ADD (4/10): I wonder if there is going to be some backlash from the mainstream press and the public. If nothing really bad happens — if this turns out to be something like the Y2K bug — then we are going to face criticisms of crying wolf.

EDITED TO ADD (4/11): Brian Krebs and Ed Felten on how to protect yourself from Heartbleed.

Posted on April 9, 2014 at 5:03 AMView Comments

"Unbreakable" Encryption Almost Certainly Isn't

This headline is provocative: “Human biology inspires ‘unbreakable’ encryption.”

The article is similarly nonsensical:

Researchers at Lancaster University, UK have taken a hint from the way the human lungs and heart constantly communicate with each other, to devise an innovative, highly flexible encryption algorithm that they claim can’t be broken using the traditional methods of cyberattack.

Information can be encrypted with an array of different algorithms, but the question of which method is the most secure is far from trivial. Such algorithms need a “key” to encrypt and decrypt information; the algorithms typically generate their keys using a well-known set of rules that can only admit a very large, but nonetheless finite number of possible keys. This means that in principle, given enough time and computing power, prying eyes can always break the code eventually.

The researchers, led by Dr. Tomislav Stankovski, created an encryption mechanism that can generate a truly unlimited number of keys, which they say vastly increases the security of the communication. To do so, they took inspiration from the anatomy of the human body.

Regularly, someone from outside cryptography — who has no idea how crypto works — pops up and says “hey, I can solve their problems.” Invariably, they make some trivial encryption scheme because they don’t know better.

Remember: anyone can create a cryptosystem that he himself cannot break. And this advice from 15 years ago is still relevant.

Another article, and the paper.

Posted on April 8, 2014 at 6:16 AMView Comments

Tor Appliance

Safeplug is an easy-to-use Tor appliance. I like that it can also act as a Tor exit node.

EDITED TO ADD: I know nothing about this appliance, nor do I endorse it. In fact, I would like it to be independently audited before we start trusting it. But it’s a fascinating proof-of-concept of encapsulating security so that normal Internet users can use it.

Posted on November 27, 2013 at 6:28 AMView Comments

Defending Against Crypto Backdoors

We already know the NSA wants to eavesdrop on the Internet. It has secret agreements with telcos to get direct access to bulk Internet traffic. It has massive systems like TUMULT, TURMOIL, and TURBULENCE to sift through it all. And it can identify ciphertext — encrypted information — and figure out which programs could have created it.

But what the NSA wants is to be able to read that encrypted information in as close to real-time as possible. It wants backdoors, just like the cybercriminals and less benevolent governments do.

And we have to figure out how to make it harder for them, or anyone else, to insert those backdoors.

How the NSA Gets Its Backdoors

The FBI tried to get backdoor access embedded in an AT&T secure telephone system in the mid-1990s. The Clipper Chip included something called a LEAF: a Law Enforcement Access Field. It was the key used to encrypt the phone conversation, itself encrypted in a special key known to the FBI, and it was transmitted along with the phone conversation. An FBI eavesdropper could intercept the LEAF and decrypt it, then use the data to eavesdrop on the phone call.

But the Clipper Chip faced severe backlash, and became defunct a few years after being announced.

Having lost that public battle, the NSA decided to get its backdoors through subterfuge: by asking nicely, pressuring, threatening, bribing, or mandating through secret order. The general name for this program is BULLRUN.

Defending against these attacks is difficult. We know from subliminal channel and kleptography research that it’s pretty much impossible to guarantee that a complex piece of software isn’t leaking secret information. We know from Ken Thompson’s famous talk on “trusting trust” (first delivered in the ACM Turing Award Lectures) that you can never be totally sure if there’s a security flaw in your software.

Since BULLRUN became public last month, the security community has been examining security flaws discovered over the past several years, looking for signs of deliberate tampering. The Debian random number flaw was probably not deliberate, but the 2003 Linux security vulnerability probably was. The DUAL_EC_DRBG random number generator may or may not have been a backdoor. The SSL 2.0 flaw was probably an honest mistake. The GSM A5/1 encryption algorithm was almost certainly deliberately weakened. All the common RSA moduli out there in the wild: we don’t know. Microsoft’s _NSAKEY looks like a smoking gun, but honestly, we don’t know.

How the NSA Designs Backdoors

While a separate program that sends our data to some IP address somewhere is certainly how any hacker — from the lowliest script kiddie up to the NSA — spies on our computers, it’s too labor-intensive to work in the general case.

For government eavesdroppers like the NSA, subtlety is critical. In particular, three characteristics are important:

  • Low discoverability. The less the backdoor affects the normal operations of the program, the better. Ideally, it shouldn’t affect functionality at all. The smaller the backdoor is, the better. Ideally, it should just look like normal functional code. As a blatant example, an email encryption backdoor that appends a plaintext copy to the encrypted copy is much less desirable than a backdoor that reuses most of the key bits in a public IV (initialization vector).
  • High deniability. If discovered, the backdoor should look like a mistake. It could be a single opcode change. Or maybe a “mistyped” constant. Or “accidentally” reusing a single-use key multiple times. This is the main reason I am skeptical about _NSAKEY as a deliberate backdoor, and why so many people don’t believe the DUAL_EC_DRBG backdoor is real: they’re both too obvious.
  • Minimal conspiracy. The more people who know about the backdoor, the more likely the secret is to get out. So any good backdoor should be known to very few people. That’s why the recently described potential vulnerability in Intel’s random number generator worries me so much; one person could make this change during mask generation, and no one else would know.

These characteristics imply several things:

  • A closed-source system is safer to subvert, because an open-source system comes with a greater risk of that subversion being discovered. On the other hand, a big open-source system with a lot of developers and sloppy version control is easier to subvert.
  • If a software system only has to interoperate with itself, then it is easier to subvert. For example, a closed VPN encryption system only has to interoperate with other instances of that same proprietary system. This is easier to subvert than an industry-wide VPN standard that has to interoperate with equipment from other vendors.
  • A commercial software system is easier to subvert, because the profit motive provides a strong incentive for the company to go along with the NSA’s requests.
  • Protocols developed by large open standards bodies are harder to influence, because a lot of eyes are paying attention. Systems designed by closed standards bodies are easier to influence, especially if the people involved in the standards don’t really understand security.
  • Systems that send seemingly random information in the clear are easier to subvert. One of the most effective ways of subverting a system is by leaking key information — recall the LEAF — and modifying random nonces or header information is the easiest way to do that.

Design Strategies for Defending against Backdoors

With these principles in mind, we can list design strategies. None of them is foolproof, but they are all useful. I’m sure there’s more; this list isn’t meant to be exhaustive, nor the final word on the topic. It’s simply a starting place for discussion. But it won’t work unless customers start demanding software with this sort of transparency.

  • Vendors should make their encryption code public, including the protocol specifications. This will allow others to examine the code for vulnerabilities. It’s true we won’t know for sure if the code we’re seeing is the code that’s actually used in the application, but surreptitious substitution is hard to do, forces the company to outright lie, and increases the number of people required for the conspiracy to work.
  • The community should create independent compatible versions of encryption systems, to verify they are operating properly. I envision companies paying for these independent versions, and universities accepting this sort of work as good practice for their students. And yes, I know this can be very hard in practice.
  • There should be no master secrets. These are just too vulnerable.
  • All random number generators should conform to published and accepted standards. Breaking the random number generator is the easiest difficult-to-detect method of subverting an encryption system. A corollary: we need better published and accepted RNG standards.
  • Encryption protocols should be designed so as not to leak any random information. Nonces should be considered part of the key or public predictable counters if possible. Again, the goal is to make it harder to subtly leak key bits in this information.

This is a hard problem. We don’t have any technical controls that protect users from the authors of their software.

And the current state of software makes the problem even harder: Modern apps chatter endlessly on the Internet, providing noise and cover for covert communications. Feature bloat provides a greater “attack surface” for anyone wanting to install a backdoor.

In general, what we need is assurance: methodologies for ensuring that a piece of software does what it’s supposed to do and nothing more. Unfortunately, we’re terrible at this. Even worse, there’s not a lot of practical research in this area — and it’s hurting us badly right now.

Yes, we need legal prohibitions against the NSA trying to subvert authors and deliberately weaken cryptography. But this isn’t just about the NSA, and legal controls won’t protect against those who don’t follow the law and ignore international agreements. We need to make their job harder by increasing their risk of discovery. Against a risk-averse adversary, it might be good enough.

This essay previously appeared on Wired.com.

EDITED TO ADD: I am looking for other examples of known or plausible instances of intentional vulnerabilities for a paper I am writing on this topic. If you can think of an example, please post a description and reference in the comments below. Please explain why you think the vulnerability could be intentional. Thank you.

Posted on October 22, 2013 at 6:15 AMView Comments

Twitter's Two-Factor Authentication System

Twitter just rolled out a pretty nice two-factor authentication system using your smart phone as the second factor:

The new two-factor system works like this. A user enrolls using the mobile app, which generates a 2048-bit RSA keypair. The private key lives on the phone itself, and the public key is uploaded to Twitter’s server.

When Twitter receives a new login request with a username and password, the server sends a challenge based on a 190-bit, 32 character random nonce, to the mobile app — along with a notification that gives the user the time, location, and browser information associated with the login request. The user can then opt to approve or deny this login request. If approved, the app replies to a challenge with its private key, relays that information back to the server. The server compares that challenge with a request ID, and if it authenticates, the user is automatically logged in.

On the user end, this means there’s no string of numbers to enter, nor do you have to swap to a third party authentication app or carrier. You just use the Twitter client itself. It means that the system isn’t vulnerable to a compromised SMS delivery channel, and moreover, it’s easy.

Posted on August 8, 2013 at 12:20 PMView Comments

Scientists Banned from Revealing Details of Car-Security Hack

The UK has banned researchers from revealing details of security vulnerabilities in car locks. In 2008, Phillips brought a similar suit against researchers who broke the Mifare chip. That time, they lost. This time, Volkswagen sued and won.

This is bad news for security researchers. (Remember back in 2001 when security researcher Ed Felten sued the RIAA in the US to be able to publish his research results?) We’re not going to improve security unless we’re allowed to publish our results. And we can’t start suppressing scientific results, just because a big corporation doesn’t like what it does to their reputation.

EDITED TO ADD (8/14): Here’s the ruling.

Posted on August 1, 2013 at 6:37 AMView Comments

Bluetooth-Controlled Door Lock

Here is a new lock that you can control via Bluetooth and an iPhone app.

That’s pretty cool, and I can imagine all sorts of reasons to get one of those. But I’m sure there are all sorts of unforeseen security vulnerabilities in this system. And even worse, a single vulnerability can affect all the locks. Remember that vulnerability found last year in hotel electronic locks?

Anyone care to guess how long before some researcher finds a way to hack this one? And how well the maker anticipated the need to update the firmware to fix the vulnerability once someone finds it?

I’m not saying that you shouldn’t use this lock, only that you understand that new technology brings new security risks, and electronic technology brings new kinds of security risks. Security is a trade-off, and the trade-off is particularly stark in this case.

Posted on May 16, 2013 at 8:45 AMView Comments

Stealing VM Keys from the Hardware Cache

Research into one VM stealing crypto keys from another VM running on the same hardware.

ABSTRACT: This paper details the construction of an access-driven side-channel attack by which a malicious virtual machine (VM) extracts fine-grained information from a victim VM running on the same physical computer. This attack is the first such attack demonstrated on a symmetric multiprocessing system virtualized using a modern VMM (Xen). Such systems are very common today, ranging from desktops that use virtualization to sandbox application or OS compromises, to clouds that co-locate the workloads of mutually distrustful customers. Constructing such a side-channel requires overcoming challenges including core migration, numerous sources of channel noise, and the difficulty of preempting the victim with sufficient frequency to extract fine-grained information from it. This paper addresses these challenges and demonstrates the attack in a lab setting by extracting an ElGamal decryption key from a victim using the most recent version of the libgcrypt cryptographic library.

Two articles.

Posted on November 16, 2012 at 6:13 AMView Comments

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Sidebar photo of Bruce Schneier by Joe MacInnis.