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Hallow Quickstart

This guide is partially complete. If you are following this guide, please contribute information on any places where you've gotten stuck and how to work through that issue.

This document assumes some base level understanding of the moving AWS parts involved, as well as go. This also assumes hallow-cli has been installed, and can be run on the command line, as well as the ability for your local computer to talk to the AWS API.

Push Hallow deployment zip to S3

Pull the latest Hallow zip from GitHub Actions, or build your own zip using export GOARCH=amd64; export GOOS=linux ; make, and put that zip in an S3 bucket. When running Terraform, you will need the bucket name, as well as the name of the file (should be hallow.zip).

Create Hallow in your AWS Environment

First, we need to set up Hallow to run in your AWS environment. This will ask you where the bucket and file are, as well as which region you're in.

cd terraform
terraform apply

This works entirely by accident, for production deployments you'll probably want to instantiate this as a module.

In the output of terraform apply, you'll get a number of outputs, including the ARN of the KMS CA key, and the endpoint.

Testing hallow-cli locally.

Let's see if this all worked! First, take the API endpoint above, and export that into your environment.

# Change the following as required -- be sure us-east-1 is set to your region,
# and your endpoint is set to the right endpoint!

export AWS_REGION=us-east-1
export HALLOW_ENDPOINT=https://UNIQUE_ID.execute-api.REGION.amazonaws.com/prod/hallow

If you've never used ssh certificates before, there should be no keys when you run ssh-add -L | grep cert. If there are keys, you likely know how to debug the following steps on your own. If you don't feel OK debugging your ssh-agent, feel free to continue with the commands and if no breakage is apparent, assuming things are working until proven otherwise.

If this fails, you may not have Invoke permissions on the API Gateway. You may need to do debugging to figure out exactly what broke.

$ ssh-add -L | grep cert | wc -l
0
$ hallow-cli ssh-add
$ ssh-add -L | grep cert | wc -l
1

Great news! Hallow can issue you Certificates! Now let's try it on a spare computer!

Get your new CA's Public Key

In the step above, take your AWS KMS ARN (it starts with arn:aws:kms), and invoke hallow-cli.

$ hallow-cli get-pub-key arn:aws:kms:us-east-1:2........0:key/9fbb4f18-462e-11ea-a661-bfd5f224b840 | tee hallow-ca.pub

This will output something like:

ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBFvuBGdFLPNRg+xZkGfQ5u9V3FD6etx0cz0fx6HkjzAvZ0W/FF4HYZPsCkLpsJhjaRfF1Nm9mNXiyaHsrkfaKgQ=

That's your CA key! We'll be using that later, so keep that file handy!

Configure OpenSSH on a test server

Spin up a computer you feel comfortable testing with, and try to configure your new CA on that computer. Due to the fact we'll be playing with the ssh daemon configuration, it's very easy to lock yourself out of this computer, so please be sure it's not important!

Get our Principal Name

First, let's figure out who the heck we are. We'll ask AWS who they think we are, to figure out who Hallow will think we are. Keep a note of this ARN, this will be used to configure the SSH daemon.

$ aws sts get-caller-identity --query="Arn"
"arn:aws:iam::.......:root"

Remind ourselves of the SSH CA Public Key

We wrote this file out in the step above when we ran get-pub-key. Let's get it in our terminal for later.

$ cat hallow-ca.pub
ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBFvuBGdFLPNRg+xZkGfQ5u9V3FD6etx0cz0fx6HkjzAvZ0W/FF4HYZPsCkLpsJhjaRfF1Nm9mNXiyaHsrkfaKgQ=

SSH into the target machine

Let's edit the sshd_config.

$ sudo vim /etc/ssh/sshd_config

Append the following lines to the bottom of the sshd_config:

TrustedUserCAKeys=/etc/ssh/hallow_cas
AuthorizedPrincipalsFile=/etc/ssh/principals/%u

Write the key from hallow-ca.pub to /etc/ssh/hallow_cas on the remote machine.


[user@remote-computer]$ echo "ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBFvuBGdFLPNRg+xZkGfQ5u9V3FD6etx0cz0fx6HkjzAvZ0W/FF4HYZPsCkLpsJhjaRfF1Nm9mNXiyaHsrkfaKgQ=" | sudo tee /etc/ssh/hallow_cas

Now, let's write out the AWS ARNs as the authorized principals for any users we would like to grant access to:

[user@remote-computer]$ sudo mkdir /etc/ssh/principals/
[user@remote-computer]$ echo arn::aws::iam::..........:root | sudo tee /etc/ssh/principals/${USER}

Finally, let's reboot ssh, and keep this terminal open!. If something goes wrong, your open session can be used to help try and fix things. Open a new terminal if you can!

[user@remote-computer]$ sudo service ssh restart

Now, in a new terminal, try and ssh into the computer, just be sure the ssh-agent still knows about the certificate we just issued!

$ ssh -vvv user@remote-computer whoami 2>&1 | grep 'Server accepts key'
debug1: Server accepts key: paultag@nyx ECDSA-CERT SHA256:ISC1x8r1wXbiPDlIgIynjexLJhBdUSvfy/3HCLKAsYI agent

Great! The server likes our new CA!

Add Hallow to ssh/config

hallow-cli contains a mode that will allow it to refresh your key in your running ssh-agent when you remote into a computer that matches a rule.

Open ~/.ssh/config and add a few lines:

Match host remote-computer exec "hallow-cli ssh-add"

Host remote-computer
    HostName ...
    User ...
    ...

Now when you ssh into remote-computer, hallow-cli will refresh your Certificate if it's required!