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 • 40 Comments