Exploring SSH Key Rotation with Thycotic Secret Server

Everyone knows and should be aware of the huge security issues there are surrounding the Windows administrator account, and there is a ton of guidance on how to properly secure that particular account, how to avoid password compromises, and how to use alternatives. But there seems to be much less intense focus on securing privileged accounts on Linux, and especially the idea that SSH keys are much like passwords in their absolute need to be protected at all costs.

SSH keys start out the security race ahead of passwords because they require two parts that do not exist in the same location all the time—a private key, which is often protected by a passphrase, is compared with a public key, and cryptographic analysis is carried out to determine if a user is authenticated to a system. This avoids the wholesale compromise of credentials just by gaining access to a system, since all that system would have is the public keys for authorized users. The other half of the puzzle, those users’ private keys, does not exist on the system anywhere.

Unfortunately, out of convenience or perhaps at the time, sheer necessity, the same private keys are re-used across multiple machines. This might be to make it easier for developers and testers to connect to a farm of Linux or Unix machines before they are moved collectively into production, or it may be that a single administrator is responsible for all of them and feels that he can properly secure that one single, well-formulated private key. It may even be an artifact of cloning a bunch of new virtual machines from an existing “template” image, or a relic of being able to easily automate a bunch of actions across a number of different machines using a single private key.

But of course, there is more to it than just one unique individual private key per user per machine. Those keys ought to be rotated and changed out, just like passwords should. This is for a variety of reasons: first, systems that contain private keys can be compromised, or the passphrases that protect the private keys can be compromised. Especially as news breaks today that the WPA2 wireless encryption technology has been broken and unprotected resources behind a vulnerable access point could be compromised, it is more important than ever to never fully trust a static key, password, phrase, or anything else, and make sure that secret is changed regularly.

The process of rotating keys is simple, but carrying it out is definitely not easy. Essentially it is a four-part process: you need to generate new keys, install that key into the authorized_keys file on all of your machines, test that new key, and then remove the stale key from that same authorized_keys file.

Brave folks use Ansible to take care of system administration tasks like these in an automated way, but then you need to spend time thinking about playbooks and plays and trying to make all of those pieces play together nicely. That all works well enough, and for the smallest deployments with the most limited of budgets it is a reasonable solution. But what about when the powers that be want proof your Linux or Unix endpoints are correctly protected this way? What if you need to easily control who can access those keys from an administrative staffing perspective? You need a stronger tool, and the folks at Thycotic have a proposition: why not use software designed from the start to automate the protection of our most sensitive privileged accounts and let it take care of the dirty work for you?

Thycotic Secret Server to the Rescue

Enter their Secret Server product and specifically the SSH Key Management function. This program will generate new keys and rotate them out either on demand or on a previously determined schedule, control via a role-based access control scheme and robust permissions which users have access to which keys, and provide a complete audit trail of which keys were sent where and when and who used them to access which systems on what date and time. Cobbling that together with Ansible would be a lot tougher and not nearly as seamless.

Thycotic asked me to spend some time evaluating this aspect of Secret Server and share my thoughts on the product.

My objective: get SSH key rotation going among 25 different Ubuntu virtual machines I have running in Amazon Web Services as part of another project. I installed a trial version of Secret Server on a Windows Server 2012 R2 box and added Microsoft SQL Server 2014 Express at the prompting of the installer. After completing the setup wizard, which was reasonably simple (although I did have to close and restart it due to an HTTPS binding issue which it automatically fixed), I went to the console and popped my license information in and enabled the Remote Password Changing settings. Then, I set out to create a new secret in Secret Server. Reading the Quick Start guide, I went with the Unix Account (SSH Key Rotation) template. On the template screen, I entered a friendly name for an account on one of those 25 machines as well as its username and password. I uploaded the private key file in .PEM format and entered its passphrase. I clicked the button and then watched for the Last Heartbeat field to say “Success” with an associated timestamp – that told me I was ready to go. I also liked I could just launch Putty and get signed in with one click – very convenient.

After that, I went to the Remote Password Changing tab and clicked Change Password Remotely. I generated a random password and then clicked Generate New SSH Key to get a new key. I also clicked the Generate button next to the Next Private Key Passphrase field to get a new protective passphrase. I clicked Change at the bottom and that was it. The key was rotated.

I went ahead and added a few of the other machines I was working with on that project and it all worked the same way as the previous one – add the secret, kick off the change, be done. It was a little work to get it set up but now I have a tool where with, what, three clicks? Four clicks? I can rotate keys all from a single point of management.

Pretty neat tool.

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