keymaker 0.5.0

Lightweight SSH key management on AWS EC2

Keymaker is the missing link between SSH and IAM accounts on Amazon AWS. It’s a stateless synchronization engine that securely manages the process of SSH public key sharing and verification, user and group synchronization, and home directory sharing (via optional EFS integration). You, the AWS account administrator, define or import user and group identities in IAM, and instances in your account dynamically retrieve and use those identities to authenticate your users. Keymaker is the modern, minimalistic alternative to LDAP or Active Directory authentication.

Installation

Run pip install keymaker.

On instances that accept SSH logins:

• Run keymaker install.

• Ensure processes launched by sshd have the IAM permissions iam:GetSSHPublicKey, iam:ListSSHPublicKeys, iam:GetUser, iam:ListGroups, and iam:ListGroupsForUser. The easiest way to do this is to use an Instance Profile and corresponding IAM role that has a policy attached enumerating these permissions. (You can also attach the IAMReadOnlyAccess managed policy.)

Keymaker requires OpenSSH v6.2+, provided by Ubuntu 14.04+ and RHEL7+.

Usage

Run keymaker with no arguments to get usage information. In client mode (running on a computer that you will connect from), you can run keymaker <subcommand>, where subcommand is:

upload_key          Upload public SSH key for a user. Run this command for each user who will be accessing EC2 hosts.
list_keys           Get public SSH keys for a given or current IAM/SSH user.
disable_key         Disable a given public SSH key for a given or current IAM/SSH user.
enable_key          Enable a given public SSH key for a given or current IAM/SSH user.
delete_key          Delete a given public SSH key for a given or current IAM/SSH user.

Principle of operation

Amazon Web Services IAM user accounts provide the ability to add SSH public keys to their metadata (up to 5 keys can be added; individual keys can be disabled). Keymaker uses this metadata to authenticate SSH logins. Keymaker provides an integrated way for a user to upload their public SSH key to their IAM account with keymaker upload_key.

Run keymaker install on instances that you want your users to connect to. This installs three components:

• An AuthorizedKeysCommand sshd configuration directive, which acts as a login event hook and dynamically retrieves public SSH keys from IAM for the user logging in, using the default boto3 credentials (which default to the instance’s IAM role credentials).

• A pam_exec PAM configuration directive, which causes sshd to call keymaker-create-account-for-iam-user early in the login process. This script detects if a Linux user account does not exist for the authenticating principal but an authorized IAM account exists with the same name, and creates the account on demand.

• A cron job that runs on your instance once an hour and synchronizes IAM group membership information. Only IAM groups whose names start with a configurable prefix (by default, keymaker_*) are synchronized as Linux groups.

As a result, users who connect to your instances over SSH are given access based on information centralized in your AWS account. Users must have an active IAM account with active matching SSH public keys in order for authentication to succeed. Users’ UIDs and group memberships are also synchronized across your instances, so any UID-based checks or group-based privileges remain current as well.

Security considerations

Integrating IAM user identities with Unix user identities has implications for your security threat model. With Keymaker, a principal with the ability to set SSH public keys on an IAM user account can impersonate that user when logging in to an EC2 instance. As an example, this can expand the scope of a compromised AWS secret key. You can mitigate this threat with an IAM policy restricting access to the UploadSSHPublicKey method.

EFS integration

Email [e-mail] for details on the EFS integration.

Authors

• Andrey Kislyuk

Links

• Project home page (GitHub)

• Documentation (Read the Docs)

• Package distribution (PyPI)

Bugs

Please report bugs, issues, feature requests, etc. on GitHub.

License

Licensed under the terms of the Apache License, Version 2.0.