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OpenSSH has come up with a new feature to avert Side-Channel attacks.
Memory side-channel flaws continue to loom modern processors, Spectre, and Meltdown, Rowhammer, and RAMBleed are just some samples.
Many specialists established alternatives of side-channel attacks against OpenSSH application connected on targeted systems. In the attack situation, a process owned by an poor attacker exploits memory read susceptibilities to snip secret SSH private keys from the memory of the target system.
That’s likely because OpenSSH has an agent that keeps a copy of your SSH key in the memory so that you don’t have to type your passphrase every time you want to connect to the same remote server.
To avert such kind of attacks, modern operating systems by evasion store sensitive data in the kernel memory that is not reachable by user-level privileged procedures.
Nevertheless, SSH keys are managed on the RAM or CPU memory in plaintext format, letting attackers access them with side channel attacks.
The latest version of the OpenSSH addresses this issue by executing the encryption of the private keys before storing them into the system memory.
“Add protection for private keys at rest in RAM against speculation and memory sidechannel attacks like Spectre, Meltdown, Rowhammer and Rambleed. This change encrypts private keys when they are not in use with a symmetic key that is derived from a relatively large “prekey” consisting of random data (currently 16KB). Attackers must recover the entire prekey with high accuracy before they can attempt to decrypt the shielded private key, but the current generation of attacks have bit error rates that, when applied cumulatively to the entire prekey, make this unlikely.” reads the security advisory published by OpenSSH developer Damien Miller.
“Implementation-wise, keys are encrypted “shielded” when loaded and then automatically and transparently unshielded when used for signatures or when being saved/serialised.”
Miller clarified that OpenSSH plans to eliminate this defense against side-channel attacks in a few years when computer architecture becomes less insecure.
