Gutmann cites Fermat checks for RSA keys with close primes
Original title: Re: eMudhra Intermediates Compromise
On the eMudhra intermediates thread, he says Let's Encrypt rejects public keys whose primes are too close.
Peter Gutmann replied on the oss-security thread about the eMudhra intermediates compromise. He says Let's Encrypt has long applied Fermat's factorisation method to public keys to detect unsuitable RSA keys whose primes p and q are too close. He notes his own code does the same check.
Unconfirmed: Gutmann says he thinks the Fermat check was Let's Encrypt's but is not certain.
- The note is a reply, not a description of the eMudhra compromise itself.
- The check targets RSA public keys with p and q too close.
- Gutmann says he found the method while checking his own code.
- Organizations
- Let's EncrypteMudhra
From the original article
Posted by Peter Gutmann on Oct 21 Solar Designer writes: Let's Encrypt has done this, at least for public keys, for awhile now, for example they apply Fermat's factorisation method to detect unsuitable keys with too-close p+q (I think it was L-E anyway, I found it when I was checking my own code which does the same thing). Peter.
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