Lessons About RSA Key Security

Spafford: Reviewing Systems Ensures Validity

By , March 22, 2012.
Lessons About RSA Key Security

A recently published research paper that raised questions about the efficacy of RSA public-private key cryptography shouldn't be too concerning for IT security practitioners, says Eugene Spafford of Purdue University. And although the research has since been disputed, Spafford explains why there's still value in such a discussion.

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The research paper, entitled Ron was Wrong, Whit was Right, concludes that the way the RSA algorithm generates random numbers to be used in encryption keys could, in rare instances, make a secret number public. And that could create a potential vulnerability that hackers might exploit, the researchers say.

Spafford says the exposed keys aren't the type that would be used by businesses such as financial institutions that conduct sensitive transactions on the Internet.

What apparently happened is that some smaller organizations created their own Secure-Socket-Layer public-private-key set using software to generate random numbers, Spafford says. The smaller organizations may have used a small set of seed values that would generate the same set of large prime numbers.

So what lessons can be learned from this? According to Spafford, one of the problems is with encryption, "the whole aspect of key generation and management, and that has been the case for a very long time."

He argues that although security practitioners can develop and use algorithms that are effectively unbreakable, if they're unable to generate truly random keys and keep them safe from prying eyes, "then it doesn't matter how strong the algorithms really are."

"There have been a number of systems that, going back in time, the generation of a key ... didn't use enough randomness and resulted in keys that were more trivially broken," Spafford says in an interview with Information Security Media Group's Eric Chabrow [transcript below].

Spafford says this kind of scrutiny and review of security systems is a necessary element in ensuring their validity. "It's important that we regularly verify our assumptions, verify that the systems we're using really work the way that they're supposed to work," he says.

In the interview, Spafford:

  • Summarizes the problem raised in the research paper;
  • Evaluates the response by RSA Chief Technologist Sam Curry to the paper;
  • Explains why such research into possible flaws of encryption and cryptographic solutions, even when disputed, is valuable.

Spafford also serves as executive director of the Purdue Center for Education and Research in Information Assurance and Security. Widely considered a leading expert in information security, Spafford has served on the Purdue computer science faculty since 1987. His research focuses on information security, computer crime investigation and information ethics.

RSA Public-Key Security Issue

ERIC CHABROW: Please take a few moments to summarize what you see as the problem the researchers raise in the paper entitled, "Ron was Wrong, Whit was Right," and the response by RSA Chief Technologist Sam Curry to the paper.

EUGENE SPAFFORD: What the researchers found is that by collecting a very large number of existing public keys and doing some analysis, they were able to find common factors that were used in generating those keys. This is a weakness that can be exploited because if one can find those factors, it's possible to find the private keys associated with them. The conclusion that they make in the paper is that this is a fundamental weakness in using the RSA algorithm, but in reality what it demonstrates is that there are weaknesses if a random number generation mechanism that's used to generate the keys isn't really truly random. It's not so much a flaw with RSA as it is with the implementation that has been used to generate many of the keys.

CHABROW: That sort of supports what RSA Chief Technologist Sam Curry said, that it's more of a process than it is actually the number generation itself?

SPAFFORD: I would say that's a reasonably accurate characterization.

Issues for Large Organizations

CHABROW: Okay, so I'm a CSO at a bank or a hospital or a government agency and our organization uses the RSA public-key cryptography. What should I do?

Follow Jeffrey Roman on Twitter: @gen_sec

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