"RSA-260" finally solved. Posting a "130-digit number" on X attracts attention around the world. Musk says, "I'm glad they increased the number of characters."

A post dated September 3, in which he succeeded in factoring ``RSA-260'', which had been unsolved for 35 years, with only a 130-digit number and the words ``divides RSA-260'' (divides RSA-260), is attracting attention from all over the world.

The fact that X's work was published in a form that could be verified by a third party, rather than in a paper or a press conference, was praised from all over the world. X owner Elon Musk responded, ``I'm glad they increased the character limit (for X).''

The person who posted it was Eric Lu (@penlume), an engineer at the American AI company Cognition. Although they do not mention the method used to solve the problem or the computational resources, there have been a number of posts from cryptography researchers pointing out that ``quantum computers are not involved.''

"RSA-260" is one of the standards for measuring the strength of RSA encryption. RSA encryption, which supports internet security, maintains security because it has the property that ``multiplying two large prime numbers is easy, but it is extremely difficult to calculate backwards the original two prime numbers from the multiplication result.''

``RSA-260'' is one of the ``RSA Factoring Challenge'' tests that only reveal a 260-digit number multiplied by two large prime numbers, and test your ability to guess the two original prime numbers. It was released in 1991 by the US RSA Data Security (at the time). Although the RSA Factoring Challenge itself ended in 2007, challenges to unsolved problems have continued.

Mr. Lu's post is

43973286548448269237950681025058725717218835265533496595612569245 05973939597593482272505698004801207988043088656411102133523080581 divides RSA-260

That's what it means.

This number is one of the two prime numbers that make up RSA-260; dividing RSA-260 by this number yields another 130-digit prime number, and multiplying the two together to get back to RSA-260.

RSA-260 has 260 digits (862 bits), surpassing "RSA-250" (250 digits, 829 bits), which was factorized in 2020, and became the largest prime factorization record in the history of the challenge.

RSA keys commonly used today are over 2048 bits, which is more than twice as long as RSA-260. This result does not mean that the current RSA encryption has been broken.