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https://github.com/Netflix/bless

Repository for BLESS, an SSH Certificate Authority that runs as a AWS Lambda function
https://github.com/Netflix/bless

aws bastion lambda python security serverless ssh ssh-certificates

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Repository for BLESS, an SSH Certificate Authority that runs as a AWS Lambda function

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README 

        
# Archived

With the existence of more SSH certificate tools since the release of BLESS, and better SSH access management from AWS, we're moving BLESS to the archived OSS project state. This means we no longer plan to maintain the project, but will be keeping it public for others who may still use it.



![alt text](bless_logo.png "BLESS")

# BLESS - Bastion's Lambda Ephemeral SSH Service

[![Build Status](https://travis-ci.org/Netflix/bless.svg?branch=master)](https://travis-ci.org/Netflix/bless) [![Test coverage](https://coveralls.io/repos/github/Netflix/bless/badge.svg?branch=master)](https://coveralls.io/github/Netflix/bless) [![Join the chat at https://gitter.im/Netflix/bless](https://badges.gitter.im/Netflix/bless.svg)](https://gitter.im/Netflix/bless?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge) [![NetflixOSS Lifecycle](https://img.shields.io/osslifecycle/Netflix/bless.svg)]()



BLESS is an SSH Certificate Authority that runs as an AWS Lambda function and is used to sign SSH

public keys.



SSH Certificates are an excellent way to authorize users to access a particular SSH host,

as they can be restricted for a single use case, and can be short lived.  Instead of managing the

authorized_keys of a host, or controlling who has access to SSH Private Keys, hosts just

need to be configured to trust an SSH CA.



BLESS should be run as an AWS Lambda in an isolated AWS account.  Because BLESS needs access to a

private key which is trusted by your hosts, an isolated AWS account helps restrict who can access

that private key, or modify the BLESS code you are running.



AWS Lambda functions can use an AWS IAM Policy to limit which IAM Roles can invoke the Lambda

Function.  If properly configured, you can restrict which IAM Roles can request SSH Certificates.

For example, your SSH Bastion (aka SSH Jump Host) can run with the only IAM Role with access to

invoke a BLESS Lambda Function configured with the SSH CA key trusted by the instances accessible

to that SSH Bastion.



## Getting Started

These instructions are to get BLESS up and running in your local development environment.

### Installation Instructions

Clone the repo:



    $ git clone [email protected]:Netflix/bless.git



Cd to the bless repo:



    $ cd bless



Create a virtualenv if you haven't already:



    $ python3.8 -m venv venv



Activate the venv:



    $ source venv/bin/activate



Install package and test dependencies:



    (venv) $ make develop



Run the tests:



    (venv) $ make test



## Deployment

To deploy an AWS Lambda Function, you need to provide a .zip with the code and all dependencies.

The .zip must contain your lambda code and configurations at the top level of the .zip.  The BLESS

Makefile includes a publish target to package up everything into a deploy-able .zip if they are in

the expected locations.  You will need to setup your own Python 3.7 lambda to deploy the .zip to.



Previously the AWS Lambda Handler needed to be set to `bless_lambda.lambda_handler`, and this would generate a user 

cert.  `bless_lambda.lambda_handler` still works for user certs.  `bless_lambda_user.lambda_handler_user` is a handler 

that can also be used to issue user certificates.



A new handler `bless_lambda_host.lambda_handler_host` has been created to allow for the creation of host SSH certs.



All three handlers exist in the published .zip.



### Compiling BLESS Lambda Dependencies

To deploy code as a Lambda Function, you need to package up all of the dependencies.  You will need to

compile and include your dependencies before you can publish a working AWS Lambda.



BLESS uses a docker container running [Amazon Linux 2](https://hub.docker.com/_/amazonlinux) to package everything up:

- Execute ```make lambda-deps``` and this will run a container and save all the dependencies in ./aws_lambda_libs



### Protecting the CA Private Key

- Generate a password protected RSA Private Key in the PEM format:

```

$ ssh-keygen -t rsa -b 4096 -m PEM -f bless-ca- -C "SSH CA Key"

```

- **Note:** OpenSSH Private Key format is not supported.

- Use KMS to encrypt your password.  You will need a KMS key per region, and you will need to

encrypt your password for each region.  You can use the AWS Console to paste in a simple lambda

function like this:

```

import boto3

import base64

import os



def lambda_handler(event, context):

    region = os.environ['AWS_REGION']

    client = boto3.client('kms', region_name=region)

    response = client.encrypt(

    KeyId='alias/your_kms_key',

    Plaintext='Do not forget to delete the real plain text when done'

    )



    ciphertext = response['CiphertextBlob']

    return base64.b64encode(ciphertext)

```



- Manage your Private Keys .pem files and passwords outside of this repo.

- Update your bless_deploy.cfg with your Private Key's filename and encrypted passwords.

- Provide your desired ./lambda_configs/ca_key_name.pem prior to Publishing a new Lambda .zip

- Set the permissions of ./lambda_configs/ca_key_name.pem to 444.



You can now provide your private key and/or encrypted private key password via the lambda environment or config file.

In the `[Bless CA]` section, you can set `ca_private_key` instead of the `ca_private_key_file` with a base64 encoded

version of your .pem (e.g. `cat key.pem | base64` ).



Because every config file option is supported in the environment, you can also just set `bless_ca_default_password`

and/or `bless_ca_ca_private_key`.  Due to limits on AWS Lambda environment variables, you'll need to compress RSA 4096

private keys, which you can now do by setting `bless_ca_ca_private_key_compression`. For example, set 

`bless_ca_ca_private_key_compression = bz2` and `bless_ca_ca_private_key` to the output of 

`cat ca-key.pem | bzip2 | base64`.



### BLESS Config File

- Refer to the the [Example BLESS Config File](bless/config/bless_deploy_example.cfg) and its

included documentation.

- Manage your bless_deploy.cfg files outside of this repo.

- Provide your desired ./lambda_configs/bless_deploy.cfg prior to Publishing a new Lambda .zip

- The required [Bless CA] option values must be set for your environment.

- Every option can be changed in the environment. The environment variable name is constructed

as section_name_option_name (all lowercase, spaces replaced with underscores).



### Publish Lambda .zip

- Provide your desired ./lambda_configs/ca_key_name.pem prior to Publishing

- Provide your desired [BLESS Config File](bless/config/bless_deploy_example.cfg) at

./lambda_configs/bless_deploy.cfg prior to Publishing

- Provide the [compiled dependencies](#compiling-bless-lambda-dependencies) at ./aws_lambda_libs

- run:

```

(venv) $ make publish

```



- deploy ./publish/bless_lambda.zip to AWS via the AWS Console,

[AWS SDK](http://boto3.readthedocs.io/en/latest/reference/services/lambda.html), or

[S3](https://aws.amazon.com/blogs/compute/new-deployment-options-for-aws-lambda/)

- remember to deploy it to all regions.



### Lambda Requirements

You should deploy this function into its own AWS account to limit who has access to modify the

code, configs, or IAM Policies.  An isolated account also limits who has access to the KMS keys

used to protect the SSH CA Key.



The BLESS Lambda function should run as its own IAM Role and will need access to an AWS KMS Key in

each region where the function is deployed.  The BLESS IAMRole will also need permissions to obtain

random from kms (kms:GenerateRandom) and permissions for logging to CloudWatch Logs

(logs:CreateLogGroup,logs:CreateLogStream,logs:PutLogEvents).



## Using BLESS

After you have [deployed BLESS](#deployment) you can run the sample [BLESS Client](bless_client/bless_client.py)

from a system with access to the required [AWS Credentials](http://boto3.readthedocs.io/en/latest/guide/configuration.html).

This client is really just a proof of concept to validate that you have a functional lambda being called with valid

IAM credentials. 



    (venv) $ ./bless_client.py region lambda_function_name bastion_user bastion_user_ip remote_usernames bastion_source_ip bastion_command  



## Verifying Certificates

You can inspect the contents of a certificate with ssh-keygen directly:



    $ ssh-keygen -L -f your-cert.pub



## Enabling BLESS Certificates On Servers

Add the following line to `/etc/ssh/sshd_config`:



    TrustedUserCAKeys /etc/ssh/cas.pub



Add a new file, owned by and only writable by root, at `/etc/ssh/cas.pub` with the contents:



    ssh-rsa AAAAB3NzaC1yc2EAAAADAQ…  #id_rsa.pub of an SSH CA

    ssh-rsa AAAAB3NzaC1yc2EAAAADAQ…  #id_rsa.pub of an offline SSH CA

    ssh-rsa AAAAB3NzaC1yc2EAAAADAQ…  #id_rsa.pub of an offline SSH CA 2



To simplify SSH CA Key rotation you should provision multiple CA Keys, and leave them offline until

you are ready to rotate them.



Additional information about the TrustedUserCAKeys file is [here](https://www.freebsd.org/cgi/man.cgi?sshd_config(5))



## Project resources

- Source code 

- Issue tracker