open-vault/website/source/docs/secrets/transit/index.html.md

---
layout: "docs"
page_title: "Secret Backend: Transit"
sidebar_current: "docs-secrets-transit"
description: |-
  The transit secret backend for Vault encrypts/decrypts data in-transit. It doesn't store any secrets.
---

# Transit Secret Backend

Name: `transit`

The transit secret backend is used to encrypt/decrypt data in-transit. Vault
doesn't store the data sent to the backend. It can also be viewed as "encryption
as a service."

The primary use case for the transit backend is to encrypt data from
applications while still storing that encrypted data in some primary data
store. This relieves the burden of proper encryption/decryption from
application developers and pushes the burden onto the operators of Vault.
Operators of Vault generally include the security team at an organization,
which means they can ensure that data is encrypted/decrypted properly.

Additionally, since encrypt/decrypt operations must enter the audit log,
any decryption event is recorded.

Due to Vault's flexible ACLs, other interesting use-cases are possible. For
instance, one set of Internet-facing servers can be given permission to encrypt
with a named key but not decrypt with it; a separate set of servers not
directly connected to the Internet can then perform decryption, reducing the
data's attack surface.

As of Vault 0.2, the transit backend supports doing key derivation. This
allows data to be encrypted within a context such that the same context must be
used for decryption. This can be used to enable per-transaction unique keys which
further increase the security of data at rest.

As of Vault 0.3, the transit backend gained two new key features: key rotation
and datakey generation.

Key rotation allows a new version of the named key to be generated. All data
encrypted with the key will use the newest version of the key; previously
encrypted data can be decrypted using old versions of the key. Administrators
can control which previous versions of a key are available for decryption, to
prevent an attacker gaining an old copy of ciphertext to be able to successfully
decrypt it. At any time, a legitimate user can "rewrap" the data, providing an
old version of the ciphertext and receiving a new version encrypted with the
latest key. Because rewrapping does not expose the plaintext, using Vault's ACL
system, this can even be safely performed by unprivileged users or cron jobs.

Datakey generation allows processes to request a high-entropy key of a given
bit length be returned to them, encrypted with the named key. Normally this will
also return the key in plaintext to allow for immediate use, but this can be
disabled to accommodate auditing requirements.

N.B.: As part of adding rotation support, the initial version of a named key
now produces ciphertext starting with version 1, i.e. containing `:v1:`.
Existing keys, when rotated, will jump to version 2 despite their previous
ciphertext output containing `:v0:`. Decryption, however, treats version 0 and
version 1 the same, so old ciphertext will still work.

This page will show a quick start for this backend. For detailed documentation
on every path, use `vault path-help` after mounting the backend.

## Quick Start

The first step to using the transit backend is to mount it. Unlike the `generic`
backend, the `transit` backend is not mounted by default.

```
$ vault mount transit
Successfully mounted 'transit' at 'transit'!
```

The next step is to create a named encryption key. A named key is used so that
many different applications can use the transit backend with independent keys.
This is done by doing a write against the backend:

```
$ vault write -f transit/keys/foo
Success! Data written to: transit/keys/foo
```

This will create the "foo" named key in the transit backend. We can inspect
the settings of the "foo" key by reading it:

```
$ vault read transit/keys/foo
Key        	Value
name        foo
cipher_mode aes-gcm
derived     false
````

Now, if we wanted to encrypt a piece of plain text, we use the encrypt
endpoint using our named key:

```
$ echo -n "the quick brown fox" | base64 | vault write transit/encrypt/foo plaintext=-
Key       	Value
ciphertext	vault:v1:czEwyKqGZY/limnuzDCUUe5AK0tbBObWqeZgFqxCuIqq7A84SeiOq3sKD0Y/KUvv
```

The encryption endpoint expects the plaintext to be provided as a base64 encoded
strings, so we must first convert it. Vault does not store the plaintext or the
ciphertext, but only handles it _in transit_ for processing. The application
is free to store the ciphertext in a database or file at rest.

To decrypt, we simply use the decrypt endpoint using the same named key:

```
$ vault write transit/decrypt/foo ciphertext=vault:v1:czEwyKqGZY/limnuzDCUUe5AK0tbBObWqeZgFqxCuIqq7A84SeiOq3sKD0Y/KUvv
Key      	Value
plaintext	dGhlIHF1aWNrIGJyb3duIGZveAo=

$ echo "dGhlIHF1aWNrIGJyb3duIGZveAo=" | base64 -D
the quick brown fox
```

Using ACLs, it is possible to restrict using the transit backend such
that trusted operators can manage the named keys, and applications can
only encrypt or decrypt using the named keys they need access to.

## API

### /transit/keys/
#### POST

<dl class="api">
  <dt>Description</dt>
  <dd>
    Creates a new named encryption key. This is a root protected endpoint.
  </dd>

  <dt>Method</dt>
  <dd>POST</dd>

  <dt>URL</dt>
  <dd>`/transit/keys/<name>`</dd>

  <dt>Parameters</dt>
  <dd>
    <ul>
      <li>
        <span class="param">derived</span>
        <span class="param-flags">optional</span>
        Boolean flag indicating if key derivation MUST be used.
        If enabled, all encrypt/decrypt requests to this named key
        must provide a context which is used for key derivation.
        Defaults to false.
      </li>
    </ul>
  </dd>

  <dt>Returns</dt>
  <dd>
    A `204` response code.
  </dd>
</dl>

#### GET

<dl class="api">
  <dt>Description</dt>
  <dd>
    Returns information about a named encryption key. The `keys` object shows
    the creation time of each key version; the values are not the keys
    themselves. This is a root protected endpoint.
  </dd>

  <dt>Method</dt>
  <dd>GET</dd>

  <dt>URL</dt>
  <dd>`/transit/keys/<name>`</dd>

  <dt>Parameters</dt>
  <dd>
    None
  </dd>

  <dt>Returns</dt>
  <dd>

    ```javascript
    {
      "data": {
        "cipher_mode": "aes-gcm",
        "deletion_allowed": false,
        "derived": false,
        "keys": {
          "1": 1442851412
        },
        "min_decryption_version": 0,
        "name": "foo"
      }
    }
    ```

  </dd>
</dl>

#### DELETE

<dl class="api">
  <dt>Description</dt>
  <dd>
    Deletes a named encryption key. This is a root protected endpoint.
    It will no longer be possible to decrypt any data encrypted with the
    named key. Because this is a potentially catastrophic operation, the
    `deletion_allowed` tunable must be set in the key's `/config` endpoint.
  </dd>

  <dt>Method</dt>
  <dd>DELETE</dd>

  <dt>URL</dt>
  <dd>`/transit/keys/<name>`</dd>

  <dt>Parameters</dt>
  <dd>
    None
  </dd>

  <dt>Returns</dt>
  <dd>
    A `204` response code.
  </dd>
</dl>

### /transit/keys/config
#### POST

<dl class="api">
  <dt>Description</dt>
  <dd>
    Allows tuning configuration values for a given key. (These values are
    returned during a read operation on the named key.) This is a
    root-protected endpoint.
  </dd>

  <dt>Method</dt>
  <dd>POST</dd>

  <dt>URL</dt>
  <dd>`/transit/keys/<name>/config`</dd>

  <dt>Parameters</dt>
  <dd>
    <ul>
      <li>
        <span class="param">min_decryption_version</span>
        <span class="param-flags">optional</span>
        The minimum version of ciphertext allowed to be decrypted. Adjusting
        this as part of a key rotation policy can prevent old copies of
        ciphertext from being decrypted, should they fall into the wrong hands.
        Defaults to 0.
      </li>
      <li>
        <span class="param">deletion_allowed</span>
        <span class="param-flags">optional</span>
        When set, the key is allowed to be deleted. Defaults to false.
      </li>
    </ul>
  </dd>

  <dt>Returns</dt>
  <dd>
    A `204` response code.
  </dd>
</dl>

### /transit/keys/rotate/
#### POST

<dl class="api">
  <dt>Description</dt>
  <dd>
    Rotates the version of the named key. After rotation, new plaintext
    requests will be encrypted with the new version of the key. To upgrade
    ciphertext to be encrypted with the latest version of the key, use the
    `rewrap` endpoint. This is a root-protected endpoint.
  </dd>

  <dt>Method</dt>
  <dd>POST</dd>

  <dt>URL</dt>
  <dd>`/transit/keys/<name>/rotate`</dd>

  <dt>Parameters</dt>
  <dd>
    None
  </dd>

  <dt>Returns</dt>
  <dd>
    A `204` response code.
  </dd>
</dl>

### /transit/encrypt/
#### POST

<dl class="api">
  <dt>Description</dt>
  <dd>
    Encrypts the provided plaintext using the named key. If the named key
    does not already exist, it will be automatically generated for the given
    name with the default parameters.
  </dd>

  <dt>Method</dt>
  <dd>POST</dd>

  <dt>URL</dt>
  <dd>`/transit/encrypt/<name>`</dd>

  <dt>Parameters</dt>
  <dd>
    <ul>
      <li>
        <span class="param">plaintext</span>
        <span class="param-flags">required</span>
        The plaintext to encrypt, provided as base64 encoded.
      </li>
      <li>
        <span class="param">context</span>
        <span class="param-flags">optional</span>
        The key derivation context, provided as base64 encoded.
        Must be provided if derivation is enabled.
      </li>
    </ul>
  </dd>

  <dt>Returns</dt>
  <dd>

    ```javascript
    {
      "data": {
        "ciphertext": "vault:v1:abcdefgh"
      }
    }
    ```

  </dd>
</dl>

### /transit/decrypt/
#### POST

<dl class="api">
  <dt>Description</dt>
  <dd>
    Decrypts the provided ciphertext using the named key.
  </dd>

  <dt>Method</dt>
  <dd>POST</dd>

  <dt>URL</dt>
  <dd>`/transit/decrypt/<name>`</dd>

  <dt>Parameters</dt>
  <dd>
    <ul>
      <li>
        <span class="param">ciphertext</span>
        <span class="param-flags">required</span>
        The ciphertext to decrypt, provided as returned by encrypt.
      </li>
      <li>
        <span class="param">context</span>
        <span class="param-flags">optional</span>
        The key derivation context, provided as base64 encoded.
        Must be provided if derivation is enabled.
      </li>
    </ul>
  </dd>

  <dt>Returns</dt>
  <dd>

    ```javascript
    {
      "data": {
        "plaintext": "dGhlIHF1aWNrIGJyb3duIGZveAo="
      }
    }
    ```

  </dd>
</dl>

### /transit/rewrap/
#### POST

<dl class="api">
  <dt>Description</dt>
  <dd>
    Rewrap the provided ciphertext using the latest version of the named key.
    Because this never returns plaintext, it is possible to delegate this
    functionality to untrusted users or scripts.
  </dd>

  <dt>Method</dt>
  <dd>POST</dd>

  <dt>URL</dt>
  <dd>`/transit/rewrap/<name>`</dd>

  <dt>Parameters</dt>
  <dd>
    <ul>
      <li>
        <span class="param">ciphertext</span>
        <span class="param-flags">required</span>
        The ciphertext to decrypt, provided as returned by encrypt.
      </li>
      <li>
        <span class="param">context</span>
        <span class="param-flags">optional</span>
        The key derivation context, provided as base64 encoded.
        Must be provided if derivation is enabled.
      </li>
    </ul>
  </dd>

  <dt>Returns</dt>
  <dd>

    ```javascript
    {
      "data": {
        "ciphertext": "vault:v2:abcdefgh"
      }
    }
    ```

  </dd>
</dl>

### /transit/datakey/
#### POST

<dl class="api">
  <dt>Description</dt>
  <dd>
    Generate a new high-entropy key and the valued encrypted with the named
    key. Optionally return the plaintext of the key as well. Whether plaintext
    is returned depends on the path; as a result, you can use Vault ACL
    policies to control whether a user is allowed to retrieve the plaintext
    value of a key. This is useful if you want an untrusted user or operation
    to generate keys that are then made available to trusted users.
  </dd>

  <dt>Method</dt>
  <dd>POST</dd>

  <dt>URL</dt>
  <dd>`/transit/datakey/<plaintext|wrapped>/<name>`</dd>

  <dt>Parameters</dt>
  <dd>
    <ul>
      <li>
        <span class="param">plaintext|wrapped (path parameter)</span>
        <span class="param-flags">required</span>
        If `plaintext`, the plaintext key will be returned along with the
        ciphertext. If `wrapped`, only the ciphertext value will be returned.
      </li>
      <li>
        <span class="param">context</span>
        <span class="param-flags">optional</span>
        The key derivation context, provided as base64 encoded.
        Must be provided if derivation is enabled.
      </li>
      <li>
        <span class="param">bits</span>
        <span class="param-flags">optional</span>
        The number of bits in the desired key. Can be 128, 256, or 512; if not
        given, defaults to 256.
      </li>
    </ul>
  </dd>

  <dt>Returns</dt>
  <dd>

    ```javascript
    {
      "data": {
        "plaintext": "dGhlIHF1aWNrIGJyb3duIGZveAo=",
        "ciphertext": "vault:v1:abcdefgh"
      }
    }
    ```

  </dd>
</dl>