Factoring RSA Keys in the IoT Era

RSA keys are at risk of compromise when using improper random number generation. Many weak keys can efficiently be discovered and subsequently compromised by finding reused prime factors in a large data set. We collect and analyze 75 million RSA certificates from the Internet, and find that 1 in 172 keys share a factor with another. In contrast, only 5 of 100 million certificates found in a sample from Certificate Transparency logs are compromised by the same technique. The discrepancy in rates of compromise is overwhelmingly due to IoT devices exposed to the Internet, which may be subject to design constraints and limited entropy. The widespread susceptibility of these IoT devices poses a potential risk to the public due to their presence in sensitive settings. We conclude that device manufacturers must ensure their devices have access to sufficient entropy and adhere to best practices in cryptography to protect consumers.