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Data Encryption

Encryption as a Service: Transit Secrets Engine

Vault's transit secrets engine handles cryptographic functions on data-in-transit. Vault doesn't store the data sent to the secrets engine, so it can also be viewed as encryption as a service.

Although the transit secrets engine provides additional features (sign and verify data, generate hashes and HMACs of data, and act as a source of random bytes), its primary use case is to encrypt data. This relieves the burden of proper encryption/decryption from application developers and pushes the burden onto the operators of Vault.

»Personas

The end-to-end scenario described in this guide involves two personas:

  • operator with privileged permissions to manage the encryption keys
  • app with un-privileged permissions encrypt/decrypt secrets via API

»Challenge

Think of the following scenario:

Example Inc. recently made headlines for a massive data breach which exposed millions of their users' payment card accounts online. When they tracked down the problem they found that a new HVAC system with management software had been put into their data centers and had created vulnerabilities in their networks and exposed ports and IPs to the databases publicly.

»Solutions

The transit secrets engine enables security teams to fortify data during transit and at rest. So even if an intrusion occurs, your data is encrypted with AES-GCM with a 256-bit AES key or other supported key types. Even if an attacker were able to access the raw data, they would only have encrypted bits. This means attackers would need to compromise multiple systems before exfiltrating data.

This guide demonstrates the basics of the transit secrets engine.

Encryption as a Service

»Prerequisites

To perform the tasks described in this guide, you need to have a Vault environment. Refer to the Getting Started guide to install Vault. Make sure that your Vault server has been initialized and unsealed.

NOTE: An interactive tutorial is also available if you do not have a Vault environment to perform the steps described in this guide. Click the Show Tutorial button to launch the tutorial.

»Policy requirements

To perform all tasks demonstrated in this guide, your policy must include the following permissions.

# Enable transit secrets engine
path "sys/mounts/transit" {
  capabilities = [ "create", "read", "update", "delete", "list" ]
}

# To read enabled secrets engines
path "sys/mounts" {
  capabilities = [ "read" ]
}

# Manage the transit secrets engine
path "transit/*" {
  capabilities = [ "create", "read", "update", "delete", "list" ]
}

If you are not familiar with policies, complete the policies guide.

»Step 1: Configure Transit Secrets Engine

(Persona: operator)

The transit secrets engine must be configured before it can perform its operations. This step is usually done by an operator or configuration management tool.

Enable the transit secrets engine by executing the following command.

$ vault secrets enable transit

By default, the secrets engine will mount at the name of the engine. If you wish to enable it at a different path, use the -path argument.

$ vault secrets enable -path=encryption transit

Now, create an encryption key ring named orders by executing the following command.

$ vault write -f transit/keys/orders

»Step 2: Encrypt Secrets

(Persona: operator)

Once the transit secrets engine has been configured, any client holding a valid token with the proper permissions can send data to encrypt.

Here, you are going to encrypt a plaintext credit card number (4111 1111 1111 1111).

To encrypt your secret, use the transit/encrypt endpoint.

$ vault write transit/encrypt/<key_ring_name>

Execute the following command to encrypt plaintext (using the shell to do the base64 encoding).

$ vault write transit/encrypt/orders plaintext=$(base64 <<< "4111 1111 1111 1111")

Key           Value
---           -----
ciphertext    vault:v1:cZNHVx+sxdMErXRSuDa1q/pz49fXTn1PScKfhf+PIZPvy8xKfkytpwKcbC0fF2U=

Notice that the ciphertext starts with vault:v1:. This prefix indicates that this value is wrapped by vault and the version of the orders encryption key used was v1. Therefore, when you decrypt this ciphertext, Vault knows to use v1 of the key. Later in Step 4, you are going to rotate the encryption key and learn how to re-wrap the ciphertext with the latest version of the encryption key.

»Step 3: Decrypt ciphertext

(Persona: operator)

Any client holding a valid token with proper permissions can decrypt ciphertext generated by Vault. To decrypt the ciphertext, invoke the transit/decrypt endpoint.

Execute the following command to decrypt the ciphertext emitted in Step 2.

$ vault write transit/decrypt/orders \
        ciphertext="vault:v1:cZNHVx+sxdMErXRSuDa1q/pz49fXTn1PScKfhf+PIZPvy8xKfkytpwKcbC0fF2U=" \

Key          Value
---          -----
plaintext    Y3JlZGl0LWNhcmQtbnVtYmVyCg==

The resulting data is base64-encoded and must be decoded to reveal the plaintext.

$ base64 --decode <<< "Y3JlZGl0LWNhcmQtbnVtYmVyCg=="
4111 1111 1111 1111

»Step 4: Rotate the Encryption Key

(Persona: operator)

One of the benefits of using the Vault transit secrets engine is its ability to easily rotate encryption keys. Keys can be rotated manually by a human or by an automated process which invokes the key rotation API endpoint through cron, a CI pipeline, a periodic Nomad batch job, Kubernetes Job, etc.

Vault maintains the versioned keyring and the operator can decide the minimum version allowed for decryption operations. When data is encrypted using Vault, the resulting ciphertext is prepended by the version of the key used to encrypt it.

To rotate the encryption key, invoke the transit/keys/<key_ring_name>/rotate endpoint.

$ vault write -f transit/keys/orders/rotate

Let's encrypt another data.

$ vault write transit/encrypt/orders plaintext=$(base64 <<< "4111 1111 1111 1111")

Key           Value
---           -----
ciphertext    vault:v2:45f9zW6cglbrzCjI0yCyC6DBYtSBSxnMgUn9B5aHcGEit71xefPEmmjMbrk3

Compare the ciphertexts from Step 2 as generated on your machine.

ciphertext    vault:v1:cZNHVx+sxdMErXRSuDa1q/pz49fXTn1PScKfhf+PIZPvy8xKfkytpwKcbC0fF2U=

Notice that the first ciphertext starts with "vault:v1:". After rotating the encryption key, the ciphertext starts with "vault:v2:". This indicates that the data is encrypted using the latest version of the key after the rotation.

Execute the following command to rewrap your ciphertext from Step 2 with the latest version of the encryption key.

$ vault write transit/rewrap/orders \
        ciphertext="vault:v1:cZNHVx+sxdMErXRSuDa1q/pz49fXTn1PScKfhf+PIZPvy8xKfkytpwKcbC0fF2U="

Key           Value
---           -----
ciphertext    vault:v2:kChHZ9w4ILRfw+DzO53IZ8m5PyB2yp2/tKbub34uB+iDqtDRB+NLCPrpzTtJHJ4=

Notice that the resulting ciphertext now starts with "vault:v2:".

This operation does not reveal the plaintext data. But Vault will decrypt the value using the appropriate key in the keyring and then encrypt the resulting plaintext with the newest key in the keyring.

»Step 5: Update Key Configuration

(Persona: operator)

Operators can update the encryption key configuration to specify the minimum version of ciphertext allowed to be decrypted, the minimum version of the key that can be used to encrypt the plaintext, the key is allowed to be deleted, etc.

This helps to further tighten the data encryption rule.

Execute the key rotation command a few times to generate multiple versions of the key.

$ vault write -f transit/keys/orders/rotate

Now, read the orders key information.

$ vault read transit/keys/orders

Key                       Value
---                       -----
...
keys                      map[6:1531439714 1:1531439594 2:1531439667 3:1531439714 4:1531439714 5:1531439714]
latest_version            6
min_decryption_version    1
min_encryption_version    0
...

In this example, the current version of the key is 6. However, there is no restriction about the minimum encryption key version, and any of the key versions can decrypt the data (min_decryption_version).

Run the following command to enforce the use of the encryption key at version 5 or later to decrypt the data.

$ vault write transit/keys/orders/config min_decryption_version=5

Now, verify the orders key configuration.

$ vault read transit/keys/orders

Key                       Value
---                       -----
allow_plaintext_backup    false
deletion_allowed          false
derived                   false
exportable                false
keys                      map[5:1531811719 6:1531811721]
latest_version            6
min_decryption_version    5
min_encryption_version    0
# ...snip...

»Step 6: Generate Data Key

(Persona: operator)

When you encrypt your data, the encryption key used to encrypt the plaintext is refer as a data key. This data key needs to be protected so that your encrypted data cannot be decrypted easily by an unauthorized party. In Step 2, you encrypted your data by specifying the key ring name (orders) and the actual data key used to encrypt the data was never presented to you.

In this step, you are going to use the transit/datakey endpoint which returns the plaintext of a named data key.

Why would I need the data key?

Think of a scenario where you have a 2GB base64 binary large object (blob) that needs to be encrypted. You probably don't want to send the 2GB over the network to Vault and receive the 2GB back. Instead, you can generate a data key and encrypt it locally and use the same data key to decrypt it locally when needed.

The idea with data keys is to allow applications to encrypt and decrypt data without round-tripping through Vault.

The data key is its own full key; you can't decrypt it with the transit key that it is wrapped with. However, because the data key is wrapped by a transit key, and thus protected, you can store it with the data. This way, you can control which Vault clients can decrypt the data through policies.

$ vault write -f transit/datakey/plaintext/orders

Key           Value
---           -----
ciphertext    vault:v1:Aj7SUcmCAEiBhNhYBZkXKzO4kuOIDCwDx6FXqpngC3WQeQ4Tw9JCRCXnsq7So+pBN0L6mt2GybRiaQvi
plaintext     uB8pBOQMqtAQUHtu6HpEsfOGWZ+KknaRUpDW1dtO6k0=

The response contains the plaintext of the data key as well as its ciphertext. Use the plaintext to encrypt your blob. Store the ciphertext of your data key wherever you want. You can even store it in the key/value secrets engine.

When you need to decrypt the blob, request Vault to decrypt the ciphertext of your data key (Step 3) so that you can get the plaintext back to decrypt the blob locally. In other words, once your blob is encrypted, you don't have to persist the data key. You only need to keep the ciphertext version of the data key.

»Help and Reference