A commit for the OpenSSH project adds protection for private keys stored in memory when they are not in use. The change is intended for the long term but the goal is not to become permanent. It makes attacks like Spectre, Meltdown, Rowhammer and RAMBleed more difficult for an adversary to extract them through side-channel attacks leveraging hardware vulnerabilities. Attackers must recover the entire prekey with high accuracy before they can attempt to decrypt the shielded private key, developer Damien Miller says.
Source: https://www.bleepingcomputer.com/news/security/openssh-to-keep-private-keys-encrypted-at-rest-in-ram/