This is a fork of credstash, to add
some utilities I find useful, see HISTORY.md for details.
pip install credsmash[yaml, templates]- Set up a key called
credsmashin KMS - Make sure you have AWS creds in a place that boto/botocore can read
them (eg, Use environment
AWS_CONFIG_FILE) credsmash setup-dynamodb
Software systems often need access to some shared credential. For example, your web application needs access to a database password, or an API key for some third party service.
Some organizations build complete credential-management systems, but for most of us,
managing these credentials is usually an afterthought. In the best case, people use
systems like ansible-vault, which does a pretty good job, but leads to other management
issues (like where/how to store the master key). A lot of credential management schemes
amount to just SCP'ing a secrets file out to the fleet, or in the worst case, burning
secrets into the SCM (do a github search on password).
CredSmash is a very simple, easy to use credential management and distribution system that uses AWS Key Management Service (KMS) for key wrapping and master-key storage, and DynamoDB for credential storage and sharing.
After you complete the steps in the Setup section, you will have an encryption key
in KMS (in this README, we will refer to that key as the master key), and a credential
storage table in DDB.
Whenever you want to store/share a credential, such as a database password, you simply
run echo [credential-value] | credsmash put [credential-name] -.
For example, echo 'supersecretpassword1234' | credsmash put myapp.db.prod -. credsmash will
go to the KMS and generate a unique data encryption key, which itself is encrypted by the
master key (this is called key wrapping). credsmash will use the data encryption key to
encrypt the credential value. It will then store the encrypted credential, along with the
wrapped (encrypted) data encryption key in the credential store in DynamoDB.
When you want to fetch the credential, for example as part of the bootstrap process on
your web-server, you simply do credsmash get [credential-name]. For example,
export DB_PASSWORD=$(credsmash get myapp.db.prod). When you run get,
credsmash will go and fetch the encrypted credential and the wrapped encryption
key from the credential store (DynamoDB). It will then send the wrapped encryption key to
KMS, where it is decrypted with the master key. credsmash then uses the decrypted data
encryption key to decrypt the credential. The credential is printed to stdout, so you
can use it in scripts or assign it to environment variables.
Optionally, you can include any number of Encryption Context
key value pairs to associate with the credential. The exact set of encryption context
key value pairs that were associated with the credential when it was put in DynamoDB
must be provided in the get request to successfully decrypt the credential. These
encryption context key value pairs are useful to provide auditing context to the encryption
and decryption operations in your CloudTrail logs. They are also useful for constraining
access to a given credsmash stored credential by using KMS Key Policy conditions and KMS
Grant conditions. Doing so allows you to, for example, make sure that your database servers
and web-servers can read the web-server DB user password but your database servers can not
read your web-servers TLS/SSL certificate's private key. A put request with encryption
context would look like
echo 'supersecretpassword1234' | credsmash put myapp.db.prod - --context app.tier db --context environment prod.
In order for your web-servers to read that same credential they would execute a get call
like export DB_PASSWORD=$(credsmash get myapp.db.prod --context environment prod --context app.tier db)
Credentials stored in the credential-store are versioned and immutable. That is, if
you put a credential called foo with a version of 1 and a value of bar,
then foo version 1 will always have a value of bar, and there is no way in credsmash to
change its value (although you could go fiddle with the bits in DDB, but you shouldn't do that).
Credential rotation is handed through versions. Suppose you do echo 'bar' | credsmash put foo -, and
then decide later to rotate foo, you can put version 2 of foo by doing
echo 'baz' | credsmash put foo - -v 2 .
The next time you do credsmash get foo, it will return baz. You can get specific credential versions
as well (with the same -v flag). You can fetch a list of all credentials in the
credential-store and their versions with the list command.
If you use incrementing integer version numbers (for example, [1, 2, 3, ...]), then you can
simply skip the -v flag with the put command to automatically increment the version number.
However, because of the lexicographical sorting in DynamoDB, credsmash will left-pad
the version representation with zeros (for example, [001, 025, 103, ...], except to 19 characters,
enough to handle sys.maxint on 64-bit systems).
credsmash uses the following AWS services:
- AWS Key Management Service (KMS) - for master key management and key wrapping
- AWS Identity and Access Management - for access control
- Amazon DynamoDB - for credential storage
- Set up a key called
credsmashin KMS pip install credsmash- Make sure you have AWS creds in a place that boto/botocore can read them
- Run
credsmash setup-dynamodb
credsmash will not currently set up your KMS master key. To create a KMS master key,
- Go to the AWS console
- Go to the IAM console/tab
- Click "Encryption Keys" in the left
- Click "Create Key". For alias, put "credsmash". If you want to use a different name, be sure to pass it to credsmash with the
-kflag - Decide what IAM principals you want to be able to manage the key
- On the "Key Usage Permissions" screen, pick the IAM users/roles that will be using credsmash (you can change your mind later)
- Done!
The easiest thing to do is to just run pip install credsmash. That will download and install credsmash and its dependencies (boto and PyCypto).
The second easiest thing to do is to do python setup.py install in the credsmash directory.
The python dependencies for credsmash are in the requirements.txt file. You can install them with pip install -r requirements.txt.
In all cases, you will need a C compiler for building PyCrypto (you can install gcc by doing apt-get install gcc or yum install gcc).
You will need to have AWS credentials accessible to boto/botocore. The easiest thing to do is to run credsmash on an EC2 instance with an IAM role. Alternatively, you can put AWS credentials in the AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY environment variables. Or, you can put them in a file (see http://boto.readthedocs.org/en/latest/boto_config_tut.html).
You can specify the region in which credsmash should operate by using the -r flag, or by setting the AWS_DEFAULT_REGION environment variable. Note that the command line flag takes precedence over the environment variable. If you set neither, then credsmash will operate against us-east-1.
Once credentials are in place, run credsmash setup-dynamodb. This will create the DDB table needed for credential storage.
If you need to work with multiple AWS accounts, an easy thing to do is to set up multiple profiles in
your ~/.aws/credentials file. For example,
[dev]
aws_access_key_id = AKIDEXAMPLEASDFASDF
aws_secret_access_key = SKIDEXAMPLE2103429812039423
[prod]
aws_access_key_id= AKIDEXAMPLEASDFASDF
aws_secret_access_key= SKIDEXAMPLE2103429812039423
Then, by setting the AWS_PROFILE environment variable to the name of the profile, (dev or prod, in this case),
you can point credsmash at the appropriate account.
See https://blogs.aws.amazon.com/security/post/Tx3D6U6WSFGOK2H/A-New-and-Standardized-Way-to-Manage-Credentials-in-the-AWS-SDKs for more information.
Usage: credsmash [OPTIONS] COMMAND [ARGS]...
Options:
-c, --config PATH
-t, --table-name TEXT DynamoDB table to use for credential storage
-k, --key-id TEXT the KMS key-id of the master key to use. See the
README for more information. Defaults to
alias/credsmash
--context <TEXT TEXT>... the KMS encryption context to use.Only works if
--key-id is passed.
--help Show this message and exit.
Commands:
delete Delete every version of a single secret
delete-many Delete every version of all matching secrets
find-many Find all secrets matching <pattern>
find-one Find exactly one secret matching <pattern>
get Fetch the latest, or a specific version of a...
get-all Fetch the latest version of all secrets
list List all secrets & their versions.
prune Delete all but the latest version of a single...
prune-many Delete all but the latest version of all...
put Store a secret
put-many Store many secrets
render-template Render a configuration template....
render-templates Render multiple configuration templates -...
setup-dynamodb Setup the credential table in AWS DynamoDB
You can put or write secrets to credsmash by either using KMS Key Grants, KMS Key Policies, or IAM Policies. If you are using IAM Policies, the following IAM permissions are the minimum required to be able to put or write secrets:
{
"Version": "2012-10-17",
"Statement": [
{
"Action": [
"kms:GenerateDataKey"
],
"Effect": "Allow",
"Resource": "arn:aws:kms:us-east-1:AWSACCOUNTID:key/KEY-GUID"
},
{
"Action": [
"dynamodb:PutItem"
],
"Effect": "Allow",
"Resource": "arn:aws:dynamodb:us-east-1:AWSACCOUNTID:table/credential-store"
}
]
}
If you are using Key Policies or Grants, then the kms:GenerateDataKey is not required in the policy for the
IAM user/group/role. Replace AWSACCOUNTID with the account ID for your table, and replace the KEY-GUID with the
identifier for your KMS key (which you can find in the KMS console).
You can read secrets from credsmash with the get or getall actions by either using KMS Key Grants, KMS Key Policies, or IAM Policies. If you are using IAM Policies, the following IAM permissions are the minimum required to be able to get or read secrets:
{
"Version": "2012-10-17",
"Statement": [
{
"Action": [
"kms:Decrypt"
],
"Effect": "Allow",
"Resource": "arn:aws:kms:us-east-1:AWSACCOUNTID:key/KEY-GUID"
},
{
"Action": [
"dynamodb:GetItem",
"dynamodb:Query",
"dynamodb:Scan"
],
"Effect": "Allow",
"Resource": "arn:aws:dynamodb:us-east-1:AWSACCOUNTID:table/credential-store"
}
]
}
If you are using Key Policies or Grants, then the kms:Decrypt is not required in the policy for
the IAM user/group/role. Replace AWSACCOUNTID with the account ID for your table, and replace
the KEY-GUID with the identifier for your KMS key (which you can find in the KMS console). Note
that the dynamodb:Scan permission is not required if you do not use wildcards in your gets.
Any IAM principal who can get items from the credential store DDB table, and can call KMS.Decrypt, can read stored credentials.
The target deployment-story for credsmash is an EC2 instance running with an IAM role that has
permissions to read the credential store and use the master key. Since IAM role credentials are
vended by the instance metadata service, by default, any user on the system can fetch creds and
use them to retrieve credentials. That means that by default, the instance boundary is the security
boundary for this system. If you are worried about unauthorized users on your instance, you should
take steps to secure access to the Instance Metadata Service (for example, use iptables to block
connections to 169.254.169.254 except for privileged users). Also, because credsmash is written in
python, if an attacker can dump the memory of the credsmash process, they may be able to recover
credentials. This is a known issue, but again, in the target deployment case, the security boundary
is assumed to be the instance boundary.
The master key is stored in AWS Key Management Service (KMS), where it is stored in secure HSM-backed storage. The Master Key never leaves the KMS service.
Every credential in the store has a version number. Whenever you want to a credential to a new
value, you have to do a put with a new credential version. For example, if you have foo
version 1 in the database, then to update foo, you can put version 2. You can either specify
the version manually (i.e. echo 'bar' | credsmash put foo - -v 2), or you can omit the -v flag,
which will attempt to autoincrement the version number (for example, echo 'baz' | credsmash put foo -).
Whenever you do a get operation, credsmash will fetch the most recent (highest version) version of that
credential. So, to do credential rotation, simply put a new version of the credential, and clients fetching
the credential will get the new version.
tl;dr: If you are using less than 25 reads/sec and 25 writes per second on DDB today, it will cost ~$1/month to use credsmash.
The master key in KMS costs $1 per month.
The credential store DDB table uses 1 provisioned read and 1 provisioned write throughput, along with a small amount of actual storage. This falls well below the free tier for DDB (25 reads and 25 writes per second). If you are already a heavy DDB user and exceed the free tier, the credential store table will cost about $0.53 per month (mostly from the write throughput).
If you are using credsmash heavily and need to increase the provisioned reads/writes, you may incur additional charges. You can estimate your bill using the AWS Simple Monthly Calculator (http://calculator.s3.amazonaws.com/index.html#s=DYNAMODB).
DDB fits the application really well. Having very low latency fetches are really nice if credsmash is in the critical path of spinning up an application. Being able to turn throughput up or down based on load and requirements are also great things to have in a config management tool. Also, as credsmash gets into more complex credential management functions, the query capabilities of DDB get super handy.
That said, S3 support may happen someday.
Check out this blog post: http://blog.fugue.it/2015-04-21-aws-kms-secrets.html