GoKawiilI’ve factored the RSA keys of a Certificate Authority...
… from the 90s.
I’ve been thinking about the security of RSA lately. RSA’s cryptography relies on the difficulty of factoring a large semiprime number, but what “large” means is an interesting question. The Web PKI deprecated 1024-bit RSA over a decade ago, and while I don’t know of anyone factoring a key of that size, it’s within the realm of possibility for a government or other organization with a large number of computers. Just a few days ago, someone factored the 862-bit RSA-260 key from the RSA factoring challenge. That’s the largest factorization I’m aware of. Today, the world uses RSA of at least 2048 bits, but even that will be deprecated soon with the risk of quantum computers in the future.
This led me to wonder: small RSA keys can be factored on even a modest desktop computer. And in the early days of the Web PKI, there were no standards, and no minimum requirements. Netscape shipped SSL support in 1994, and IE shortly afterwards. This was still the era of export restrictions on cryptography. Are there any keys small enough that I can factor? I don’t have any good reason to do that, but it seems like fun.
The spoiler is of course, yes, but first we need to find a key to crack.
Fortunately, root certificates were shipped with browser installers, and there are archives of both Internet Explorer and Netscape on archive.org. The archives aren’t comprehensive, but they should provide good coverage of old root CAs. I downloaded both collections and set Claude Code on extracting all the roots. I’ve hosted a Claude-generated webpage with all those old-timey, ancient roots. While I haven’t verified this LLM output is entirely trustworthy, it looks pretty plausible.
Using the filters on that site, we can find what small keys are trusted for SSL.
Aha! We have a target. Back in March 1999, Netscape 4.51 shipped a 512-bit RSA certificate authority trusted for SSL, and another for S/MIME. These two roots were both from the long-defunct Canadian certificate authority called E-Certify.
Later that year, the 512-bit RSA-155 was factored, so even in its era this was too weak and probably shouldn’t have shipped in the first place.
The E-Certify 512-bit roots were removed by Netscape in 2002. Unfortunately, Internet Explorer seems to have never shipped any 512-bit roots for SSL, so our fun will be limited to Netscape from a relatively small time frame.
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