OpenSSH Now Encrypts Secret Keys in Memory Against Side-Channel Attacks

Did you ever notice that they all had at least one thing in
common?

That’s OpenSSH.

As a proof-of-concept, many researchers demonstrated their
side-channel attacks against OpenSSH application installed on a
targeted computer, where an unprivileged attacker-owned process
exploits memory read vulnerabilities to steal secret SSH private
keys from the restricted memory regions of the system.

That’s possible 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.

However, modern operating systems by default store sensitive
data, including encryption keys and passwords, in the kernel memory
which can not be accessed by user-level privileged processes.

But since these SSH keys live on the RAM or CPU memory in
plaintext format, the feature is susceptible to hacking attempts
when the attacks involve memory read vulnerabilities.

OpenSSH Now Stores Only Encrypted Keys in the Memory

Here’s good news — it’s not the case anymore.

The latest update from the OpenSSH developers resolves this
issue by introducing a new security feature that encrypts private
keys before storing them into the system memory, protecting it
against almost all types of side-channel attacks.

According to OpenSSH developer Damien Miller, a new patch to
OpenSSH^[1] now “encrypts
private keys when they are not in use with a symmetric key that is
derived from a relatively large “prekey” consisting of random data
(currently 16KB).”