Security services startup Sentrix mirrors customer Web sites in Amazon Web Services and Azure clouds in order to dynamically expand site resources during distributed denial of service attacks and keep the sites running until attackers exhaust their resources, give up or move on to easier targets.

The company, which was founded in 2010, just opened its U.S. headquarters and has already done a proof-of-concept trial with a U.S. bank that it hopes to land as a customer, says co-founder Israel Barak.

He says the Sentrix grid has withstood attacks of tens of thousands of gigabits per second approaching 100GBps launched against paying customers in Israel, where it serves banks, insurance companies and educational institutions.

The service defends not only against DDoS but also cross-site scripting, cross-site request forgery, SQL injection, zero-day and website defacement attacks, the company says. The company challenges on-premises Web firewalls such as those from F5, Imperva and Palo Alto Networks, as well as service providers Akamai,, Incapsula and Prolexic.

Adrian Lane, an analyst and CTO for Securosis, says the Sentrix approach is unique in that it looks at specific transactions on sites and focuses on those. Other engines block based on complex rule sets but don't necessarily respond well to new attacks not seen before. But they do reduce the noise surrounding network security events by blocking known threats. He says the Sentrix service could be seen as supplemental to other Web defenses.

Sentrix first analyzes customer websites and sorts their elements into two piles -- deterministic and business-logic. The deterministic elements are those that merely require being presented to the user, such as images and text, and represent about 80% of most Web sites.

The business-logic elements make up the other 20% and include search boxes and username fields -- components that need to actually reach the backend for processing.

Sentrix sets up mirror grids within AWS and Azure clouds to present the deterministic elements. Only legitimate business-logic requests are transmitted to customers' actual back-ends. That set of legitimate requests is finite and the grid is incapable of processing any others so illegitimate requests that might be sent by attackers are dropped.

When a customer site falls under DoS attack, the mirror grid expands to the point that it becomes too large for the attacker to swamp. If the volume of the attack increases, the grid expands more and so on until the attacker taps out its resources or decides to quit and look for an easier target.

The aim of DoS attackers is to take down sites as soon as possible and for as long as possible, so typically they hit with everything they have at the outset, Barak says. Sentrix responds by creating a larger mirror grid. If attackers have reserves and increase the bandwidth of the attack, the grid can respond by growing even larger. When an attack ceases, the grid shrinks.

A side benefit, the company says, is that Web sites work faster when they are not under attack than they would if they were delivered from in-house infrastructure.

The mirror grids are spread among worldwide cloud data centers run by AWS and Azure and load balanced between the two, Barak says.

The service is offered in two ways. The first is on-demand, so if an attack is succeeding against traditional defenses, customers can switch on a Sentrix mirror grid. The second is full-time use of a mirror grid. Customers pay a flat monthly fee determined by how large a Web site is and the amount of legitimate traffic it receives per month.

The company is using $6 million in venture capital funding from Magma Venture Partners and Cedar Fund to pay for its expansion into the U.S. The company was initially boot-strap funded so limited its reach to Israel where it started up its service in December 2011. It claims to have about 70 customers there, including four of the top banks and three of the top insurance companies.

Barak is a former red team member challenging network defenses for the Israeli Defense Force. Co-founder Nimrod Luria is CTO and a former leader of Microsoft Israel's ACE team. He founded several security startups, the latest being Q.rity, which was bought by Ness. CEO Ofer Wolf is a former Check Point executive and CEO of SterGen, which made 3D video conversion gear.