Is SSL safe?

Two-thirds of servers vulnerable to new crypto attack, apparently

Czech security researchers this week claimed to have uncovered weaknesses in SSL that might permit crackers to decypher transmissions over supposedly secure links.

However, independent cryptography experts, who are studying a paper from Czech security outfit ICZ, are yet to verify the risk is real and as serious as ICZ suggests - so the research needs to be treated with caution.

A press release issued on behalf of Czech cryptologists Vlastimil Klíma and Tomá? Rosa, both of ICZ, and Ondrej Pokorný, paints a picture of severe problems with the SSL protocol. It states:

"The weakness identified by the cryptologists makes it possible to attack the SSL/TLS (Secure Sockets Layer and Transport Layer Security) protocols used as a cryptographic protection of a majority of electronic transactions, such as on-line purchases and e-banking, and, in some cases, a secured transmission of e-mails as well.

"An attack on these protocols, as described by the team of Czech cryptologists, can break through the protection completely and decrypt protected communication. This means for clients using applications relying on SSL/TLS protocols that an attacker is able to retrieve their credit card numbers, sensitive information about their bank accounts and misuse confidential data from their e-mails."

Lordy.

From the press release and an abstract of their paper we learn that the researchers have uncovered a possible means of obtaining cryptographic keys from a server and thereby unlocking the contents of a captured session. This side-channel attack, which builds on previous research, is explained in detail in the trio's paper, which you can read here (PDF).

The Czechs found "two thirds of randomly chosen Internet SSL/TLS servers were vulnerable" to the attack they document. Improvements to SSL are put forward in the paper, which, drawing as it does on complex mathematical analysis, doesn't lend itself to distillation into a news story.

So how great a risk does the attack present to e-commerce transactions?

To answer this question we contacted noted cryptographer Bruce Schneier, CTO of Counterpane Systems. Schneier wasn't available to provide an immediate response but told us he would be looking into the issue. We'll let you know what he comes up with.

A month ago Swiss security researchers discovered an attack against implementations of the ubiquitous SSL protocol that could potentially compromise email passwords, though not ecommerce transactions.

Writing about this attack in his Cryptogram newsletter, Schneier says users should be more concerned about their credit cards been lifted from insecure servers - rather than snapped up in transit, using either the Swiss or Czech attacks.

"The real risks to personal data are the large databases at the endpoints, not the communications between them. I wouldn't discard SSL as being irrelevant, but neither would I worry very much if it could be attacked. Security is only as strong as the weakest link, and SSL is nowhere close to being the weakest link," he writes. ®

Related Links

Attacking RSA-based Sessions in SSL/TLS - Czech it out...
Password Interception in a SSL/TLS Channel, paper by security researchers at (Swiss firm) Lasec

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