key-switcheroo: SSH key rotator toolkit

Table of Contents

1. What is it?
2. Features
   1. Publisher
   2. Retriever
   3. Key Rotation
3. Where to get it
4. How to use
   1. Publisher
   2. Retriever
   3. AWS Profile Management
5. Dependencies
6. Configuring your SSHD
7. Contributing

What is it?

key-switcheroo is a Python package that provides tools for easy :smile:, reliable :white_check_mark:, and secure :lock: SSH key management. The package contains tools to allow users to generate SSH public/private key pairs and securely store the public key either on AWS S3 or locally based on user preferences. The package also contains a tool used by the server host to retrieve and match the public keys with the corresponding private key during SSH connection attempts. Additionally, the package supports a feature for periodic rotation and swapping of public keys to enhance security. Click here for the video presentation.

Features

Publisher

The publisher tool offers a user-friendly interface to securely generate SSH public/private key pairs. It allows users to specify the storage location for the public key, either on AWS S3 or on their local machine. The generated private key is stored securely and can be used for SSH authentication.

Retriever

The retriever tool is designed to be used by server hosts for retrieving the public keys stored by the publisher. When an SSH connection attempt is made, the retriever fetches the corresponding public key associated with the private key used in the connection attempt. The tool compares the retrieved public key with the provided public key, ensuring a secure and authenticated connection.

Key rotation

To enhance security, key-switcheroo supports a key rotation feature. The user simply needs to call the publisher script again with the same credentials and the program will swap and rotate the stored public keys. This process helps mitigate the risks associated with long-term key exposure and strengthens the overall security posture.

Where to get it

The source code is currently hosted on GitHub at: https://github.com/SSH-key-rotation-AWS/key-switcheroo

Binary installer for the latest released version is available at the Python Package Index (PyPI).

pip install key-switcheroo

How to use

Once the package is installed, commands can be called from the user's CLI for both the publisher and retriever using different optional arguments.

For help with command-line arguments,

switcheroo_publish --help or switcheroo_publish -h

switcheroo_retrieve --help or switcheroo_retrieve -h

AWS Profile Management

Switcheroo uses its own AWS profile management system. This can be accessed by the base command switcheroo_configure. Run switcheroo_configure -h to get help.

The following command is used to create a profile, which is automatically used:

switcheroo_configure add --access-key [access key] --secret-access-key [secret access key] --region [region]

If multiple profiles are added, you can select which one to use with switcheroo_configure select, delete one with switcheroo_configure delete, and view your profiles with switcheroo_configure view.

Publisher

When using the publisher for creating and publishing new SSH keys, the user has a couple of different optional arguments, in addition to the required arguments.

Required Arguments:

1. hostname - host server. This is the return value of socket.getfqdn().
2. user - username of the connecting client

Optional Arguments:

• --datastore local or -ds local
  • Stores the public key on the local file system
• --datastore s3 or -ds s3
  • Stores the public key in an S3 bucket
  • If s3 is selected, the user MUST also input --bucket, followed by a name for their S3 bucket
  • If no --datastore is selected, the program will default to s3
• --sshdir path/to/key/dir
  • Input the absolute path to your directory that stores the local keys (private key for S3 publisher)
  • Defaults to local .ssh home directory
• --metric aws or -m aws
  • Opt to have metrics published to AWS cloudwatch (time to generate keys and key count)
• --metric file or -m file
  • Opt to have metrics published to the local file system (time to generate keys and key count)
  • If file is selected, the user CAN also input --metricpath, followed by path to a directory to store the metrics in (default is {user's home}/switcheroo_app_data/metrics)

Example

switcheroo_publish 127.0.0.1 johndoe -ds s3 --bucket mybucket --sshdir home/johndoe/.ssh -m aws

switcheroo_publish 127.0.0.1 johndoe --datastore local --metric file --metricpath home/switcheroo/metrics

Retriever

When using the retriever for fetching the public SSH keys, the user has a couple of different optional arguments, in addition to the required arguments.

Required Arguments:

1. user - username of the client whose key is being fetched

The hostname is assumed to be that of the executing computer, as retrieved by socket.getfqdn().

Optional Arguments:

• --datastore local or -ds local
  • Retrieves the public key from the local file system
• --datastore s3 or -ds s3
  • Retrieves the public key from the S3 bucket
  • If s3 is selected, the user MUST also input --bucket, followed by their S3 bucket name
  • If no --datastore is selected, the program will default to s3
• --sshdir path/to/key/dir
  • The absolute path to your directory that stores the local keys (private key for S3 publisher)
  • Defaults to local .ssh home directory

Example

switcheroo_retrieve johndoe --datastore s3 --bucket mybucket

switcheroo_retrieve johndoe -ds local --sshdir /home/johndoe/.ssh/keys

Configuring Your SSHD

If you want to configure your SSHD to use key-switcheroo for SSH connections, follow the following steps:

1. pip install key-switcheroo. Note that installing packages onto the system may cause issues, and should be done with care. You may want to consider using pipx to isolate the installation in a virtual environment.

2. This installs 3 binaries - switcheroo_configure,switcheroo_retrieve and switcheroo_publish. The exact location of these binaries depends on your OS and if you used a tool like pipx to install them

3. Configure an AWS profile using switcheroo_configure add. Note that the user that configures this profile will be the user retrieving keys - SSH reccomends having a separate user to do this, such as aws_user.

4. Open your sshd_config, or create a *.conf file in sshd_config.d.

5. In the config, add the following two lines:

   AuthorizedKeysCommand /path/to/switcheroo_retrieve -ds s3 --bucket [your-bucket] %u

   AuthorizedKeysCommandUser [your user configured in step 2]

6. Restart sshd/the system.

That's it! Now, if a public key is published to the bucket, your server will use it for SSH authentication.

Dependencies

• boto3 - Adds support for publishing public SSH keys to S3 using the AWS SDK for Python
• pycryptodome - Provides tools for generating secure public/private SSH key pairs

Contributing to key-switcheroo

Contributions to key-switcheroo are welcome! If you encounter any issues, have suggestions, or would like to add new features, please feel free to open an issue or submit a pull request on the GitHub repository.