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Crypto guru urges incentives for SSL cert recall

Come in MD5, your time is up

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An SSL security guru is urging incentives to promote website certificate upgrade in response to problems with a widely-used digital-signature algorithm.

Collisions in the MD5 hashing algorithm mean that two different inputs can produce the same output. Last year independent researchers showed how the cryptographic flaw might make it possible to forge counterfeit digital certificate credentials.

The trick might be used to set up phony websites with bogus certificates that, as far as a visiting surfer's browser is concerned, are indistinguishable from the real thing.

Dr Taher Elgamal, chief security officer at Axway, who is credited as the inventor of Secure Socket Layer (SSL) technology, told El Reg that solving the problem means moving onto digital certificates that use a more secure SHA-1 or SHA-2 hash function. However, progress has been far too slow, according to Elgamal. Although he didn't have figures the distinguished cryptographer was adamant that the digital certificate refresh process was p[proceeding only at snail's pace, and needed to be pushed along.

"Web servers need to discontinue MD5," Elgamal told El Reg. "VeriSign, which is fully aware of the problem, should offer discounted SHA-1 and SHA-2 certificates."

MD5 was fine in the past but is now simply not sophisticated enough. Indeed even SHA-1 is beginning to show itself as potentially vulnerable to the same sort of collision problems, albeit to a lesser extent than MD5.

"Algorithms don't stay secure forever, it's an issue of computing," Elgamal explained.

Much has been written, since the discovery of a serious vulnerability in the nets addressing system by Dan Kaminsky last year, about the need to move from DNS to a more secure version, DNSSec.

The SSL protocol, by contrast, remains robust and workable, according to Elgamal. "The protocol needs no big change, it's how it integrates with browser that needs to be improved," he explained.

For one thing, the trust model of browser makes it easy for consumers to add new trusted digital roots (Certificate Authorities). "Browser just randomly trust the root. There's not enough checking on the browser side."

Browser security came across as one of Elgamal's key concerns. He praised Google's developers for adopting a robust security model with Chrome, which used sandboxing to isolate any malware that does come through the browser from the rest of a system while adding that this is "the right model but it's not there yet". More generally, Elgamal said browser developers should "avoid trying to compete on trust", instead working more closely together on security.

Such co-operation is commonplace in cryptography but harder (though not impossible) to imagine between rival development teams at Microsoft, Google and Apple, of course.

Elgamal also said more needed to be done to address the potential danger of man-in-the middle attacks, where hackers sit in the middle of a conversation between a surfer and a bank, impersonating one to the other.

"This breaks the trust model, not the encryption, as such," Elgamal said. He added that two-factor authentication - while not complete - offered a way of mitigating risk. Two-factor authentication technology means, in practice, that users use a token that generates a variable electronic code in addition to their login credentials in order to gain access to an online banking site, for example. ®

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