December 4, 2022

TECHNICALME

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Researcher uses 379-year-old algorithm to crack crypto keys found in the wild

3 min read
Researcher uses 379-year-old algorithm to crack crypto keys found in the wild


Stylistic illustration of key.

Cryptographic keys generated from outdated software owned by technology company Rambus are so weak that they can be instantly broken using commodity hardware, a researcher reported on Monday. The revelation is part of an investigation that has also uncovered some vulnerable keys in the wild.

The software comes from an original version of the SafeZone crypto library, which was developed by a company called Inside Secure and acquired by Rambus as part of it. 2019 Acquisitions of Verimetrics, said a Rambus representative. That version was dropped prior to the acquisition and is distinct from a FIPS-certified version that the company now sells under the Rambus FIPS Security Toolkit brand.

Keep track of your Ps and Qs

researcher Hanno Boki Said that the insecure SafeZone library does not sufficiently randomize the two prime numbers used to generate the RSA key. (These keys can be used to secure web traffic, shells, and other online connections.) Instead, after a prime number is selected by the SafeZone tool, it uses one as the second required to generate the key. Picks the prime number in the proximity.

“The problem is that both primes are very similar,” Bock said in an interview. “So the difference between two primes is really small.” The SafeZone vulnerability is tracked as CVE-2022-26320.

Cryptographers have long known that RSAs generated with keys that are too close together can be trivially broken. Fermat’s Multiplication Method, French mathematician Pierre de Fermata This method was first described in 1643.,

Fermat’s algorithm was based on the fact that any odd number could be expressed as the difference between two squares. When the factors are close to the root of the number, they can be calculated easily and quickly. This method is not feasible when the factors are truly random and therefore very far apart.

The security of RSA keys depends on the difficulty of factoring a large complex number of keys (usually denoted as N) to obtain its two factors (usually denoted as P and Q). When P and Q are made publicly known, the key they create is broken, meaning that anyone can decrypt the data protected by the key or use the key to authenticate messages. Is.

So far, Bock has identified only a handful of keys in the wild that are vulnerable to causal attack. Some keys are from printers from two manufacturers, Canon and Fujifilm (originally branded as Fuji Xerox). Printer users can use the keys to generate certificate signing requests. All vulnerable keys had a manufacturing date of 2020 or later. Weak Canon keys are tracked as CVE-2022-26351.

Bock also found four weak PGP keys on the SKS PGP key server, which are commonly used to encrypt email. A user ID tied to the keys means they were created for testing, so they don’t believe they are in active use.

Bock said he believed all keys he found were generated using software or methods that were not linked to the SafeZone library. If true, other software that generates the key can be easily broken using the Fermat algorithm. It is plausible that the keys were generated manually, “presumably by people aware of this attack to create test data,” Bock said.

The researcher found the keys by searching the billions of public keys he had access to. They also looked at keys that were shared with them by other researchers and keys that were available through certificate transparency programs.



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