The Privacy BlogPrivacy, Security, Cryptography, and Anonymity

CAT | Cryptography

Yesterday Google announced that it was updating its certificates to use 2048 bit public key encryption, replacing the previous 1024 bit RSA keys.

I have always found the short keys used by websites somewhat shocking. I recall back in the early 1990’s discussion about whether 1024 bits was good enough for PGP keys. Personally, I liked to go to 4096 bits although it was not really officially supported.

The fact that, 20 years later, only a fraction of websites have moved up to 2048 bits is incredible to me.

Just as a note, you often see key strengths described in bit length with RSA being 1024 or 2048 bits, and AES being 128 or 256 bits.

This might lead one to assume that RSA is much stronger that AES, but the opposite is true (at these key lengths). The problem is that the two systems are attacked in very different ways. AES is attacked by a brute force search through all possible keys until the right one is found. If the key is 256 bits long, then you need to try, on average, half of the 2^256 keys. That is about 10^77 keys (a whole lot). This attack is basically impossible for any computer that we can imagine being built, in any amount of time relevant to the human species (let alone any individual human).

By comparison, RSA is broken by factoring a 1024 or 2048 bit number in the key into its two prime factors. While very hard, it is not like brute force. It is generally thought that 1024 bit RSA is about as hard to crack as 80 bit symmetric encryption. Not all that hard. 

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The Register has an article on Firefox black listing an SSL Certificate authority.

Certificates and certificate authorities are the underpinnings of our secure web infrastructure.

When you see the lock on your browser, it means that the session is encrypted and the site has presented a valid site certificate (so it is who it claims to be).

That site certificate is signed by one of many certificate authorities.

I see 86 certificate issuing authorities in my Firefox now.

Many of those certificate authorities have multiple signing certificates.

Additionally the certificate authorities can delegate to subordinate certificate authorities to sign site certificates.

Any certificate signed by any of these authorities or subordinate authorities is recognized as valid.

These entities are located all over the world, many under the control of oppressive governments (however you define that).

Certificate authorities can create certificates to enable man in the middle attacks, by signing keys purporting to be for a given website, but actually created and held by some other entity.

There are plugins like certificate patrol for Firefox that will tell you when a site you have visited before changes certificates or certificate authorities. Unfortunately this happens fairly frequently for legitimate reasons, such as when renewing certificates every year or few years.

Some certificate authorities are known or suspected to be working with various law enforcement entities to create false certificate for surveillance.

Here is how it works:

The government has certificate authority create a new certificate for a website.

The government then intercepts all sessions to that site with a server (at national level routers for example).

The server uses real site certificate to communicate with the real website securely.

The server uses the new fake certificate to communicate with user securely.

The server then has access to everything in the clear as it shuttles data between the two secure connections..

It can read and/or modify anything in the data stream.

 

Firefox is removing TeliaSonera’s certificate authority from the list in Firefox for this reason. Going forward no certificate issued by them will be recognized as valid. This will impact a large number of legitimate websites that have contracted with TeliaSonera, as well as preventing the fake certificates.

There is a lot of controversy about this. What is appropriate cooperation with law enforcement vs. supporting and enabling dictators.

In any case, this is a failure of the protocol. If the browser shows a certificate as valid when it has not come from the real website, then there has been a security failure.

The SSL key infrastructure is showing its age. It was “good enough” when there were only one or two certificate authorities and the certificates were not actually protecting anything of great importance. Now everyone relies heavily on the security of the web. Unfortunately, while it is broken, it is very hard to replace.

In the short term, installing a certificate checker like certificate patrol is probably a good idea, despite the number of false positives you will see.

In the longer term, there is a really hard problem to solve.


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Gigaom reports on a major security issue at Nokia, first announced in the “Treasure Hunt” blog.

Their Asha and Lumia phones come with something they call the “Xpress Browser”. To improve the browser experience, the web traffic is proxies and cached. That is a fairly common and accepted practice.

Where Nokia has stepped into questionable territory is when it does this for secure web traffic (URLs starting with HTTPS://). Ordinarily it is impossible to cache secure web pages because the encryption key is unique and used only for a single session, and is negotiated directly between the browser and the target website. If it was cached no one would be able to read the cached data.

Nokia is doing a “man in the middle attack” on the user’s secure browser traffic. Nokia does this by having all web traffic sent to their proxy servers. The proxy then impersonate the intended website to the phone, and set up a new secure connection between the proxy and the real website.

Ordinarily this would generate security alerts because the proxy would not have the real website’s cryptographic Certificate. Nokia gets around this by creating new certificates which are signed by a certificate authority they control and which is pre-installed and automatically trusted by the phone.

So, you try to go to Gmail. The proxy intercepts that connection, and gives you a fake Gmail certificate signed by the Nokia certificate authority. Your phone trusts that so everything goes smoothly. The proxy then securely connects to Gmail using the real certificate. Nokia can cache the data, and the user gets a faster experience.

All good right?

The fly in the ointment is that Nokia now has access to all of your secure browser traffic in the clear, including email, banking, etc.

They claim that they don’t look at this information, and I think that is probably true. The problem is that you can’t really rely on that. What if Nokia gets a subpoena? What about hackers? What about accidental storage or logging?

This is a significant breaking of the HTTPS security model without any warning to end users.

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The FBI in conjunction with the Bureau of Justice Assistance and Joint Regional Intelligence Center have produced a number of fliers to help the public identify possible terrorists. While some of the points have merit, it is very likely that this will generate an extremely high proportion of false alerts based on perfectly reasonable and legal behaviors.

A big red flag for me were the fliers for cyber cafes and electronics stores. These suggest that the use of privacy protecting services, like Anonymizer, should be deemed suspicious. They also call out Encryption, VoIP, and communicating through video games.

In almost all of the fliers they suggest that wanting to pay cash (legal tender for all debts public and private) is suspicious.

Thanks to Public Intelligence for pulling together PDFs of the documents.

Internet Cafe flier.

Electronics Store flier.

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Matt Blaze analyzes why the widespread use of cryptography has had almsost no impact on our practical ability to do wiretaps and gather information under legitimate court orders. Not too technical and absolutely worth a read.

Matt Blaze: Wiretapping and Cryptography Today:

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The EFF has an excellent article on eight reasons why government regulation of cryptography is a bad idea.

The short answer is: the bad guys can easily get it and use it anyway, and it will make security for the rest of us much worse (not including the big brother surveillance  and constitutional issues).

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This NYTimes article discusses a bill which the Obama administration is proposing to submit to congress. The general background of the bill is that evolving technology has made it more difficult for law enforcement to conduct effective wiretaps and other intercepts because much of the targeted communication now takes place on the Internet and is often encrypted.

The actual text of the proposed bill does not appear to be available, but the article lists the following likely requirements.

  1. Communications services that encrypt messages must have a way to unscramble them.
  2. Foreign-based providers that do business inside the United States must install a domestic office capable of performing intercepts.
  3. Developers of software that enables peer-to-peer communication must redesign their service to allow interception.

The first of these is similar to the CALEA law which requires telecommunications carriers to design their services to enable automated real time intercepts. While this generally sounds reasonable when “we” say it, the idea is more ominous when coming from some other governments.

The second of these feels uncomfortably familiar. See my past blog posts (and here)on the attempts of privacy hostile countries to require similar concessions from RIM.

The third proposal is completely outrageous. In effect it says that I may not speak in a way which is unintelligible to the wire tappers. As a colleague quipped “I am hiring Navajo code talkers.” This would require a back door be inserted in to cryptography tools. Experience shows that any crypto system with such a back door will be breached and then left vulnerable to the enormous number of criminal hackers on the Internet today.

In 1993 the US Government proposed a system called the “Clipper Chip” which would provide all encryption for personal computers, but to which the US Government would have back door access. This was a terrible idea then, it was widely ridiculed, and suffered a well justified death by 1996. This third proposal would be much worse. It is asking huge numbers of non-crypto experts to build back doors in to their systems. Frankly, the cryptography in most software is already badly broken in many cases. Something as subtle and complex as a secure and effective law enforcement back door would be far beyond their abilities and render currently poor security completely untrustworthy.

All this is not to mention the potential abuse by oppressive regimes, who will pounce on the capability to further crush dissent within their countries. Finally, it will be largely ineffective against serious threats. Very strong and easy to use cryptography is already available world wide, for free (GPG, ZPhone, TrueCrypt, etc.). This is a classic case of damaging the innocent while leaving the guilty and dangerous unaffected.

It seems to me that there is a pendulum swing to these things. Technology cuts both ways. Some times it favors the interceptor and some times it favors the communicator. In most ways the Internet has been a fantastic boon to law enforcement. Cloud computing, email hosts, social networking, open WiFi, and huge hard drive that encourage people to save everything all provide law enforcement with enormous amounts of information they could never have collected in the past.

It may not be shocking to anyone that there is no federal push to make that more difficult to access while pushing to enhance their ability to intercept encrypted communications.

All this is argument about a bill we have not seen yet. Let us hope that the furor that has swirled around it will cause it to be retraced or modified significantly before it is actually delivered to congress.

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In a recent post on Privacy Digest, and an article in the NYTimes, there is a discussion of some major and well known vulnerabilities in the global public key infrastructure (PKI) and some examples of exploitations of that vulnerability.

The issue is with the proliferation of certificate authorities on the Internet, and the low level of oversight on their policies.

Using the web as an example, here is how it works. Embedded in every browser is a list of “certificate authorities”. These are companies that are deemed trustworthy to issue and sign website certificates. Website certificates are what allows websites to be authenticated by your browser and enables SSL based secure connections (e.g. to your bank).

These certificate authorities may also be able to delegate their certificate signing authorities to other secondary certificate authority organizations. The list of primary certificate authorities in your browser is long (I count 43 in my copy of Firefox), and who knows how many secondary certificate authorities may be out there. These certificate authorities exist all over the world, and any of them can issue a certificate that your browser will accept as valid.

A malevolent certificate authority could issue certificates to allow them to impersonate any secure website.

The articles talk specifically about a secondary certificate authority called Etisalat, located in the UAE. They created a certificate which allowed them to sign code which would be accepted as valid and authorized by BlackBerry cell phones. They then created and distributed software to about 100,000 users which enabled government surveillance of the devices. RIM, the maker of BlackBerry, was able to detect and patch this introduced back door.

Etisalat could create certificates to allow the UAE to intercept and read all secure web traffic traveling over networks within that country.

It is likely that there are many other certificate authorities that are similarly willing to compromise the security of the PKI for various ends. To date, no action has been taken against Etisalat. The EFF is calling for Verizon to revoke Etisalat’s ability to issue certificates (Verizon is the primary authority that delegated to Etisalat as the secondary).

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There has been a lot of media coverage of the threats of Saudi Arabia and the UAE to shut down BlackBerry connectivity in their countries unless RIM (the maker of BlackBerry) introduces a back door so they can monitor communications.

I have been following this story closely, but wanted to wait until I had all the facts before blogging about it. At this point I don’t think I am going to get the whole story. The statements I am seeing are absolutely contradictory and the whole thing is getting really fishy.

UAE/SA say that they need to be able to access BlackBerry communications, but they can’t.

RIM says that their technology makes interception impossible because the communications are encrypted end to end between the BES server (located at the users place of business) and the handset. RIM claims not to have access to the decryption keys.

Third parties claim that RIM has arrangements with other countries (including the US and Russia) which allows such access.

RIM responds that this is false and that they don’t have this ability.

It looks like RIM and UAE/SA will come to an agreement while both continue to claim that they have not compromised their positions.

The moral of this story is that you should not trust security you can not fully analyze yourself. Anonymizer Universal uses strongly encrypted L2TP VPN technology to secure your information so even if your telecommunications provider is cooperating with surveillance they still can’t read the contents of your messages.

Unfortunately Anonymizer Universal does not support BlackBerry yet, but iPhone, Windows, and Mac users are protected.

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This year the “Computers Freedom and Privacy” (CFP) conference is taking place in San Jose from June 15-18. This year is the 20th anniversary of the conference which helped shape my thinking about Internet Privacy and introduced me to many of the key players in this space.

Around the same time in 1992 an email mailing list started called “Cypherpunks”. Members were devoted discussions of Internet freedom and to creating and distributing privacy and security tools. Best known of these are the various flavors of Anonymous Remailers following the original anon.penen.fi.

This seems like a good time to stop and take stock of what has been achieved, lost, and abandoned in the evolution of privacy and anonymity on the Internet. I have organized a panel at CFP of some of the key Cypherpunks from the early days to talk about those early days, and share their vision and insight about where we are and where we should / are likely to end up.

I hope I will see many of you there.

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