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How to Keep Sensitive Information Secret

4.4 version
Maintained Unmaintained
5.0

How to Keep Sensitive Information Secret

New in version 4.4: The Secrets management was introduced in Symfony 4.4.

Environment variables are the best way to store configuration that depends on where the application is run - for example, some API key that might be set to one value while developing locally and another value on production.

When these values are sensitive and need to be kept private, you can safely store them by using Symfony’s secrets management system - sometimes called a “vault”.

Note

The Secrets system requires the sodium PHP extension that is bundled with PHP 7.2. If you’re using an earlier PHP version, you can install the libsodium PHP extension or use the paragonie/sodium_compat package.

Generate Cryptographic Keys

In order to encrypt and decrypt secrets, Symfony needs cryptographic keys. A pair of keys can be generated by running:

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$ php bin/console secrets:generate-keys

This will generate a pair of asymmetric cryptographic keys. Each environment has its own set of keys. Assuming you’re coding locally in the dev environment, this will create:

config/secrets/dev/dev.encrypt.public.php
Used to encrypt/add secrets to the vault. Can be safely committed.
config/secrets/dev/dev.decrypt.private.php
Used to decrypt/read secrets from the vault. The dev decryption key can be committed (assuming no highly-sensitive secrets are stored in the dev vault) but the prod decryption key should never be committed.

You can generate a pair of cryptographic keys for the prod environment by running:

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$ php bin/console secrets:generate-keys --env=prod

This will generate config/secrets/prod/prod.encrypt.public.php and config/secrets/prod/prod.decrypt.private.php.

Caution

The prod.decrypt.private.php file is highly sensitive. Your team of developers and even Continuous Integration services don’t need that key. If the decryption key has been exposed (ex-employee leaving for instance), you should consider generating a new one by running: secrets:generate-keys --rotate.

Create or Update Secrets

Suppose you want to store your database password as a secret. By using the secrets:set command, you should add this secret to both the dev and prod vaults:

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# the input is hidden as you type for security reasons

# set your default development value (can be overridden locally)
$ php bin/console secrets:set DATABASE_PASSWORD

# set your production value
$ php bin/console secrets:set DATABASE_PASSWORD --env=prod

This will create a new file for the secret in config/secrets/dev and another in config/secrets/prod. You can also set the secret in a few other ways:

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# provide a file where to read the secret from
$ php bin/console secrets:set DATABASE_PASSWORD ~/Download/password.json

# or contents passed to STDIN
$ echo -n "$DB_PASS" | php bin/console secrets:set DATABASE_PASSWORD -

# or let Symfony generate a random value for you
$ php bin/console secrets:set REMEMBER_ME --random

Referencing Secrets in Configuration Files

Secret values can be referenced in the same way as environment variables. Be careful that you don’t accidentally define a secret and an environment variable with the same name: environment variables override secrets.

If you stored a DATABASE_PASSWORD secret, you can reference it by:

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    # config/packages/doctrine.yaml
    doctrine:
        dbal:
            password: '%env(DATABASE_PASSWORD)%'
            # ...
        # ...
    
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    <!-- config/packages/doctrine.xml -->
    <?xml version="1.0" encoding="UTF-8" ?>
    <container xmlns="http://symfony.com/schema/dic/services"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xmlns:doctrine="http://symfony.com/schema/dic/doctrine"
        xsi:schemaLocation="http://symfony.com/schema/dic/services
            https://symfony.com/schema/dic/services/services-1.0.xsd
            http://symfony.com/schema/dic/doctrine
            https://symfony.com/schema/dic/doctrine/doctrine-1.0.xsd">
    
        <doctrine:config>
            <doctrine:dbal
                password="%env(DATABASE_PASSWORD)%"
            />
        </doctrine:config>
    
    </container>
    
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    // config/packages/doctrine.php
    $container->loadFromExtension('doctrine', [
        'dbal' => [
            'password' => '%env(DATABASE_PASSWORD)%',
        ]
    ]);
    

The actual value will be resolved at runtime: container compilation and cache warmup don’t need the decryption key.

List Existing Secrets

Everybody is allowed to list the secrets names with the command secrets:list. If you have the decryption key you can also reveal the secrets’ values by passing the --reveal option:

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$ php bin/console secrets:list --reveal

 ------------------- ------------ -------------
  Name                Value        Local Value
 ------------------- ------------ -------------
  DATABASE_PASSWORD   "my secret"
 ------------------- ------------ -------------

Remove Secrets

Symfony provides a convenient command to remove a Secret:

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$ php bin/console secrets:remove DATABASE_PASSWORD

Local secrets: Overriding Secrets Locally

The dev environment secrets should contain nice default values for development. But sometimes a developer still needs to override a secret value locally when developing.

Most of the secrets commands - including secrets:set - have a --local option that stores the “secret” in the .env.{env}.local file as a standard environment variable. To override the DATABASE_PASSWORD secret locally, run:

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$ php bin/console secrets:set DATABASE_PASSWORD --local

If you entered root, you will now see this in your .env.dev.local file:

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DATABASE_PASSWORD=root

This will override the DATABASE_PASSWORD secret because environment variables always take precedence over secrets.

Listing the secrets will now also display the local variable:

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$ php bin/console secrets:list --reveal
 ------------------- ------------- -------------
  Name                Value         Local Value
 ------------------- ------------- -------------
  DATABASE_PASSWORD   "dev value"   "root"
 ------------------- ------------- -------------

Symfony also provides the secrets:decrypt-to-local command to decrypts all secrets and stores them in the local vault and secrets:encrypt-from-local to encrypt all local secrets to the vault.

Secrets in the test Environment

If you add a secret in the dev and prod environments, it will be missing from the test environment. You could create a “vault” for the test environment and define the secrets there. But an easier way is to set the test values via the .env.test file:

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# .env.test
DATABASE_PASSWORD="testing"

Deploy Secrets to Production

Due to the fact that decryption keys should never be committed, you will need to manually store this file somewhere and deploy it. There are 2 ways to do that:

  1. Uploading the file:

The first option is to copy the production decryption key - config/secrets/prod/prod.decrypt.private.php to your server.

  1. Using an Environment Variable

The second way is to set the SYMFONY_DECRYPTION_SECRET environment variable to the base64 encoded value of the production decryption key. A fancy way to fetch the value of the key is:

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# this command only gets the value of the key; you must also set an env var
# in your system with this value (e.g. `export SYMFONY_DECRYPTION_SECRET=...`)
$ php -r 'echo base64_encode(require "config/secrets/prod/prod.decrypt.private.php");'

To improve performance (i.e. avoid decrypting secrets at runtime), you can decrypt your secrets during deployment to the “local” vault:

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$ php bin/console secrets:decrypt-to-local --force --env=prod

This will write all the decrypted secrets into the .env.prod.local file. After doing this, the decryption key does not need to remain on the server(s).

Rotating Secrets

The secrets:generate-keys command provides a --rotate option to regenerate the cryptographic keys. Symfony will decrypt existing secrets with the old key, generate new cryptographic keys and re-encrypt secrets with the new key. In order to decrypt previous secrets, the developer must have the decryption key.

Configuration

The secrets system is enabled by default and some of its behavior can be configured:

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    # config/packages/framework.yaml
    framework:
        secrets:
            #vault_directory: '%kernel.project_dir%/config/secrets/%kernel.environment%'
            #local_dotenv_file: '%kernel.project_dir%/.env.%kernel.environment%.local'
            #decryption_env_var: 'base64:default::SYMFONY_DECRYPTION_SECRET'
    
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    <!-- config/packages/framework.xml -->
    <?xml version="1.0" encoding="UTF-8" ?>
    <container xmlns="http://symfony.com/schema/dic/services"
        xmlns:framework="http://symfony.com/schema/dic/framework"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation="http://symfony.com/schema/dic/services https://symfony.com/schema/dic/services/services-1.0.xsd
            http://symfony.com/schema/dic/framework https://symfony.com/schema/dic/framework/framework-1.0.xsd"
    >
        <framework:config secret="%env(APP_SECRET)%">
            <framework:secrets
                vault_directory="%kernel.project_dir%/config/secrets/%kernel.environment%"
                local_dotenv_file="%kernel.project_dir%/.env.%kernel.environment%.local"
                decryption_env_var="base64:default::SYMFONY_DECRYPTION_SECRET"
            />
        </framework:config>
    </container>
    
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    // config/packages/framework.php
    $container->loadFromExtension('framework', [
        'secrets' => [
            // 'vault_directory' => '%kernel.project_dir%/config/secrets/%kernel.environment%',
            // 'local_dotenv_file' => '%kernel.project_dir%/.env.%kernel.environment%.local',
            // 'decryption_env_var' => 'base64:default::SYMFONY_DECRYPTION_SECRET',
        ],
    ]);
    

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.