ejson

ejson is a utility for managing a collection of secrets in source control. The secrets are encrypted using public key, elliptic curve cryptography (NaCl Box: Curve25519 + Salsa20 + Poly1305-AES). Secrets are collected in a JSON file, in which all the string values are encrypted. Public keys are embedded in the file, and the decrypter looks up the corresponding private key from its local filesystem.

The main benefits provided by ejson are:

• Secrets can be safely stored in a git repo.
• Changes to secrets are auditable on a line-by-line basis with git blame.
• Anyone with git commit access has access to write new secrets.
• Decryption access can easily be locked down to production servers only.
• Secrets change synchronously with application source (as opposed to secrets provisioned by Configuration Management).
• Simple, well-tested, easily-auditable source.

See the manpages for more technical documentation.

See ejson2env for a useful tool to help with exporting a portion of secrets as environment variables for environments/tools that require this pattern.

Installation

You can download the .deb package from Github Releases.

On development machines (64-bit linux or OS X), the recommended installation method is via Homebrew:

brew tap shopify/shopify
brew install ejson

Workflow

1: Create the Keydir

By default, EJSON looks for keys in /opt/ejson/keys. You can change this by setting EJSON_KEYDIR or passing the -keydir option.

$ mkdir -p /opt/ejson/keys

For Mac OS users. By default you won't have write permissions to /opt/ejson folder. Make sure to run the following command to grant these permissions:

sudo chown -R $(whoami) /opt/ejson

2: Generate a keypair

When called with -w, ejson keygen will write the keypair into the keydir and print the public key. Without -w, it will print both keys to stdout. This is useful if you have to distribute the key to multiple servers via configuration management, etc.

$ ejson keygen
Public Key:
63ccf05a9492e68e12eeb1c705888aebdcc0080af7e594fc402beb24cce9d14f
Private Key:
75b80b4a693156eb435f4ed2fe397e583f461f09fd99ec2bd1bdef0a56cf6e64

$ ejson keygen -w
53393332c6c7c474af603c078f5696c8fe16677a09a711bba299a6c1c1676a59
$ cat /opt/ejson/keys/5339*
888a4291bef9135729357b8c70e5a62b0bbe104a679d829cdbe56d46a4481aaf

3: Create an ejson file

The format is described in more detail later on. For now, create a file that looks something like this. Fill in the <key> with whatever you got back in step 2.

Create this file as test.ejson:

{
  "_public_key": "<key>",
  "_database_username": "1234username",
  "database_password": "1234password"
}

4: Encrypt the file

Running ejson encrypt test.ejson will encrypt any new plaintext keys in the file and leave any existing encrypted keys or keys with property names prefixed with _ untouched:

{
  "_public_key": "63ccf05a9492e68e12eeb1c705888aebdcc0080af7e594fc402beb24cce9d14f",
  "_database_username": "1234username",
  "database_password": "EJ[1:WGj2t4znULHT1IRveMEdvvNXqZzNBNMsJ5iZVy6Dvxs=:kA6ekF8ViYR5ZLeSmMXWsdLfWr7wn9qS:fcHQtdt6nqcNOXa97/M278RX6w==]"
}

Try adding another plaintext secret to the file and run ejson encrypt test.ejson again. The database_password field will not be changed, but the new secret will be encrypted.

5: Decrypt the file

To decrypt the file, you must have a file present in the keydir whose name is the 64-byte hex-encoded public key exactly as embedded in the ejson document. The contents of that file must be the similarly-encoded private key. If you used ejson keygen -w, you've already got this covered.

Unlike ejson encrypt, which overwrites the specified files, ejson decrypt only takes one file parameter, and prints the output to stdout:

$ ejson decrypt foo.ejson
{
  "_public_key": "63ccf05a9492e68e12eeb1c705888aebdcc0080af7e594fc402beb24cce9d14f",
  "_database_username": "1234username",
  "database_password": "1234password"
}

To write plaintext to a file instead of stdout, use ejson decrypt -o output.json foo.ejson. On Unix, new output files use mode 0600, further restricted by the process umask. Existing files are updated in place with their permissions and ownership unchanged, including files reached through symlinks or hard links. To share output with another user or group, create the destination with the intended ownership and permissions before decrypting.

Review existing output files before reuse: upgrading does not tighten their permissions. Use a trusted destination in a directory that untrusted users cannot write to. The CLI follows symlinks and does not revoke access from processes that already have the file open. Shell redirection (ejson decrypt foo.ejson > output.json) uses the shell's file-creation permissions, not the CLI's.

Format

The ejson document format is simple, but there are a few points to be aware of:

1. It's just JSON.
2. There must be a key at the top level named _public_key, whose value is a 32-byte hex-encoded (i.e. 64 ASCII byte) public key as generated by ejson keygen.
3. Any string literal that isn't an object key will be encrypted by default (ie. in {"a": "b"}, "b" will be encrypted, but "a" will not.
4. Numbers, booleans, and nulls aren't encrypted.
5. If a key begins with an underscore, its corresponding value will not be encrypted. This is used to prevent the _public_key field from being encrypted, and is useful for implementing metadata schemes.
6. Underscores do not propagate downward. For example, in {"_a": {"b": "c"}}, "c" will be encrypted.

See also

• If you use Capistrano for deployment you can use capistrano-ejson to automatically decrypt the secrets on deploy.
• If you use pre-commit, you can use it to automatically encrypt secrets on commit.