Low-cost SSL proxy could bring cheaper, faster security; defeat threats like Firesheep

Researchers develop a less expensive way to efficiently split SSL processing between standard CPUs, GPUs

Researchers have found a cheaper, faster way to process SSL/TLS with off-the-shelf hardware, a development that could let more Web sites shut down cyber threats posed by the likes of the Firesheep hijacking tool.

The technology, dubbed SSLShading, shows how SSL proxies based on commodity hardware can protect Web servers without slowing down transactions, according to a presentation scheduled at the USENIX Symposium on Networked Design and Implementation in Boston March 30 through April 1.

SSL/TLS -- the cryptographic protocols used to protect online Web transactions -- encrypts traffic from visitors' machines all the way to Web servers. That makes it impossible to pick up data such as session cookies by preying on unencrypted wireless networks, which is what Firesheep does.

Based on an algorithm devised by researchers in Korea and the U.S., SSLShading is software that directs SSL traffic being proxied either to a CPU or a graphics processing unit (GPU), whichever is most appropriate to handle the current load. The researchers will discuss the algorithm in their paper "SSLShader: Cheap SSL Acceleration with Commodity Processors."

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"The key idea is to send all requests to CPU when the number of pending cryptographic operations is small enough to be handled by CPU," the research team says in an earlier paper. "If requests begin to pile up in the queue, then the algorithm offloads cryptographic operations to GPUs and benefits from parallel execution for high throughput."

SSL transactions per second (TPS) using just the CPU on the test servers totaled 3,632 in one experiment, the researchers stated. Using the proxy GPU and their algorithm yielded 18,482 TPS. The group used an Intel Xeon X5550 CPU ($260) with four cores and an NVIDIA GTX 480 graphic card with 480 cores.

SSLShader still has some shortcomings, the most notable of which is that he GPU processing works well for transactions under 1MB, but for larger transactions, the CPU works better because of the overhead of copying when the proxy is in place, according to the researcher's overview of SSLShader.

Another problem is that the Linux kernel used on the server has a networking stack that doesn't scale well to take advantage of multiple CPU cores, the researchers say.

The researchers say they plan to make their software available, but didn't say when. The team consists of Keon Jang, Sangjin Han, Sue Moon and KyoungSoo Park, all of KAIST in Korea, and Seungyeop Han of the University of Washington.

One of the traditional obstacles to using SSL to protect Web sites is the extra processing demand and its associated costs, says John Pironti, president of IP Architects, a security consulting firm, and the security track chairman for Interop. "The infrastructure costs to enable SSL can be challenging," he says, depending on the size and complexity of the deployment.

As processors get more powerful and less expensive per cycle, cost isn't as much of an issue, he says, if the SSL is designed into the infrastructure at the start. "It's less costly than adding it on later," he says.

There are barriers to implementing SSL on sites other than the hardware costs and performance, says PayPal CISO Michael Barrett. All of PayPal's site content is SSL-protected, and getting there involved more than just processing. "It can cause quite a bit of pain from an application perspective," he says.

For instance, if an application assumes it always operates under unsecured HTTP, it will try to redirect browsers to HTTP. In order to fix the problem, businesses may have to recode the offending applications, he says. That can lead to inefficiencies if HTTP requests are made, and the site reroutes them rerouted to make them HTTPS (SSL/TLS), requiring more round trip communications that introduce delay.

The PayPal site uses the proposed Internet standard HTTP Strict Transport Security (STS), which declares to browsers that Web servers are to be interacted with via HTTPS. The browser remembers so the next time a request is sent to the same URL -- even if it's typed in as HTTP -- it will be sent as HTTPS. So far versions of Firefox and Google Chrome browsers support HTTP STS, and it can be deployed without a negative impact on end users whose browsers don't support it.

Another barrier to SSL is the need to enlist a certificate authority to handle encryption key authentication and to manage the certificates, Barrett says.

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