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14 September 2018

Week 6, Building Key Rotation

The short version:

This week we:

Please give us feedback on key rotation

Last week Ian teased that Fluidkeys 0.2 will do key rotation for you. This week, we came up with a draft design and started implementing this.

But your feedback would be incredibly helpful!

Here’s the technical detail of what we’re thinking:

There’s a couple of things to point out with this scheme:

Rotation doesn’t affect your primary key

We’re actually trying to move away from long lived keys, but if you do have a well-known key, and perhaps you’ve published your fingerprint far and wide (like me), that’s fine.

In this scheme, it’s only the encryption subkey that’s affected.

Short-lived keys sidestep the painful revocation process

Revocation — when you announce that a key is no longer valid — has proven to be a bit of a nightmare in practice. It’s tricky to generate a revocation message, especially if you’ve lost your key, and it’s tricky to reliably ensure everyone sees it. Because revocation is not practised often, it’s not reliable at the time when you do try to use it.

Short-lived keys sidestep the difficulties of revocation. Instead of a long-lived key with a possible revocation notice, use a short-lived key and constantly refresh it.

The refresh message is a bit like a heartbeat — “this key’s still OK! I haven’t lost it!”

Team members will rotate keys around the same time

By triggering rotation on the 1st of the month, all team members will be in sync which we think helps with team members supporting each other.

Provided we make it incredibly quick and easy, I think it could be a bit of a ceremony … that security thing we do each month.

Also, because all your keys (if you have more than one) trigger on the same day, you only need to rotate every month as a maximum.

Key rotation relies on a solid method for updating keys

Rotating your keys regularly is a really powerful feature for security.

For members of your team, Fluidkeys will take care of distributing your updated key to everyone else, and vice versa.

People outside the team, whose software you don’t control, may have difficulty if their software doesn’t automatically update your key. We’re still thinking about this, and would value your input.

What do you think?

I’d love to hear your thoughts on the key rotation strategy I’ve just described.

Do please send us an email to hello@fluidkeys.com. Thank you!

Now you can actually list your keys!

Most of the work we did this week was displaying back the keys you’ve created or linked from GnuPG. Here’s how we’re looking:

a table with three columns displaying keys

The status column is starting to shape up… that’s where we’re starting to surface issues with the key, and below the table we’ll put simple, plain-English instructions on how to fix the issue.

We submitted another fix to golang/x/crypto

We’ve got all-too-familiar with Go’s crypto/openpgp library. This week we bumped into a known bug relating to subkeys. The way I’ve used my key in the past is to repeatedly extend the expiry date of my subkeys. Unfortunately crypto/openpgp couldn’t handle that case, taking only the first subkey binding signature, rather than the most recent.

We made a working patch on our fork and submitted a pull request to Google.

As ever, thanks for reading, and your feedback is greatly appreciated.

— Paul

All feedback is welcome, pop us an email to hello@fluidkeys.com

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