hadoop-common-project/hadoop-kms/src/site/markdown/index.md.vm

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#set ( $H3 = '###' )
#set ( $H4 = '####' )
#set ( $H5 = '#####' )

Hadoop Key Management Server (KMS) - Documentation Sets
=======================================================

<!-- MACRO{toc|fromDepth=0|toDepth=3} -->

Hadoop KMS is a cryptographic key management server based on Hadoop's **KeyProvider** API.

It provides a client and a server components which communicate over HTTP using a REST API.

The client is a KeyProvider implementation interacts with the KMS using the KMS HTTP REST API.

KMS and its client have built-in security and they support HTTP SPNEGO Kerberos authentication and HTTPS secure transport.

KMS is a Java web-application and it runs using a pre-configured Tomcat bundled with the Hadoop distribution.

KMS Client Configuration
------------------------

The KMS client `KeyProvider` uses the **kms** scheme, and the embedded URL must be the URL of the KMS. For example, for a KMS running on `http://localhost:16000/kms`, the KeyProvider URI is `kms://http@localhost:16000/kms`. And, for a KMS running on `https://localhost:16000/kms`, the KeyProvider URI is `kms://https@localhost:16000/kms`

The following is an example to configure HDFS NameNode as a KMS client in
`core-site.xml`:

    <property>
      <name>hadoop.security.key.provider.path</name>
      <value>kms://http@localhost:9600/kms</value>
      <description>
        The KeyProvider to use when interacting with encryption keys used
        when reading and writing to an encryption zone.
      </description>
    </property>

KMS
---

$H3 KMS Configuration

Configure the KMS backing KeyProvider properties in the `etc/hadoop/kms-site.xml` configuration file:

```xml
  <property>
     <name>hadoop.kms.key.provider.uri</name>
     <value>jceks://file@/${user.home}/kms.keystore</value>
  </property>

  <property>
    <name>hadoop.security.keystore.java-keystore-provider.password-file</name>
    <value>kms.keystore.password</value>
  </property>
```

The password file is looked up in the Hadoop's configuration directory via the classpath.

NOTE: You need to restart the KMS for the configuration changes to take effect.

NOTE: The KMS server can choose any `KeyProvider` implementation as the backing provider. The example here uses a JavaKeyStoreProvider, which should only be used for experimental purposes and never be used in production. For detailed usage and caveats of JavaKeyStoreProvider, please see [Keystore Passwords section of the Credential Provider API](../hadoop-project-dist/hadoop-common/CredentialProviderAPI.html#Keystore_Passwords).

$H3 KMS Cache

KMS has two kinds of caching: a CachingKeyProvider for caching the encryption keys, and a KeyProvider for caching the EEKs.

$H4 CachingKeyProvider

KMS caches encryption keys for a short period of time to avoid excessive hits to the underlying KeyProvider.

This Cache is enabled by default (can be disabled by setting the `hadoop.kms.cache.enable` boolean property to false)

This cache is used with the following 3 methods only, `getCurrentKey()` and `getKeyVersion()` and `getMetadata()`.

For the `getCurrentKey()` method, cached entries are kept for a maximum of 30000 milliseconds regardless the number of times the key is being accessed (to avoid stale keys to be considered current).

For the `getKeyVersion()` method, cached entries are kept with a default inactivity timeout of 600000 milliseconds (10 mins).

These configurations can be changed via the following properties in the `etc/hadoop/kms-site.xml` configuration file:

```xml
   <property>
     <name>hadoop.kms.cache.enable</name>
     <value>true</value>
   </property>

   <property>
     <name>hadoop.kms.cache.timeout.ms</name>
     <value>600000</value>
   </property>

   <property>
     <name>hadoop.kms.current.key.cache.timeout.ms</name>
     <value>30000</value>
   </property>
```

$H4 KeyProvider

Architecturally, both server-side (e.g. KMS) and client-side (e.g. NameNode) have a cache for EEKs. The following are configurable on the cache:

* The size of the cache. This is the maximum number of EEKs that can be cached under each key name.
* A low watermark on the cache. For each key name, if after a get call, the number of cached EEKs are less than (size * low watermark), then the cache under this key name will be filled asynchronously. For each key name, only 1 thread could be running for the asynchronous filling.
* The maximum number of asynchronous threads overall, across key names, allowed to fill the queue in a cache.
* The cache expiry time, in milliseconds. Internally Guava cache is used as the cache implementation. The expiry approach is [expireAfterAccess](https://code.google.com/p/guava-libraries/wiki/CachesExplained).

Note that due to the asynchronous filling mechanism, it is possible that after rollNewVersion(), the caller still gets the old EEKs. In the worst case, the caller may get up to (server-side cache size + client-side cache size) number of old EEKs, or until both caches expire. This behavior is a trade off to avoid locking on the cache, and is acceptable since the old version EEKs can still be used to decrypt.

Below are the configurations and their default values:

Server-side can be changed via the following properties in the `etc/hadoop/kms-site.xml` configuration file:

```xml
   <property>
     <name>hadoop.security.kms.encrypted.key.cache.size</name>
     <value>500</value>
   </property>

   <property>
     <name>hadoop.security.kms.encrypted.key.cache.low.watermark</name>
     <value>0.3</value>
   </property>

   <property>
     <name>hadoop.security.kms.encrypted.key.cache.num.fill.threads</name>
     <value>2</value>
   </property>

   <property>
     <name>hadoop.security.kms.encrypted.key.cache.expiry</name>
     <value>43200000</value>
   </property>
```

Client-side can be changed via the following properties in the `etc/hadoop/core-site.xml` configuration file:

```xml
   <property>
     <name>hadoop.security.kms.client.encrypted.key.cache.size</name>
     <value>500</value>
   </property>

   <property>
     <name>hadoop.security.kms.client.encrypted.key.cache.low-watermark</name>
     <value>0.3</value>
   </property>

   <property>
     <name>hadoop.security.kms.client.encrypted.key.cache.num.refill.threads</name>
     <value>2</value>
   </property>

   <property>
     <name>hadoop.security.kms.client.encrypted.key.cache.expiry</name>
     <value>43200000</value>
   </property>
```

$H3 KMS Aggregated Audit logs

Audit logs are aggregated for API accesses to the GET\_KEY\_VERSION, GET\_CURRENT\_KEY, DECRYPT\_EEK, GENERATE\_EEK operations.

Entries are grouped by the (user,key,operation) combined key for a configurable aggregation interval after which the number of accesses to the specified end-point by the user for a given key is flushed to the audit log.

The Aggregation interval is configured via the property :

      <property>
        <name>hadoop.kms.aggregation.delay.ms</name>
        <value>10000</value>
      </property>

$H3 Start/Stop the KMS

To start/stop KMS use KMS's bin/kms.sh script. For example:

    hadoop-${project.version} $ sbin/kms.sh start

NOTE: Invoking the script without any parameters list all possible parameters (start, stop, run, etc.). The `kms.sh` script is a wrapper for Tomcat's `catalina.sh` script that sets the environment variables and Java System properties required to run KMS.

$H3 Embedded Tomcat Configuration

To configure the embedded Tomcat go to the `share/hadoop/kms/tomcat/conf`.

KMS pre-configures the HTTP and Admin ports in Tomcat's `server.xml` to 16000 and 16001.

Tomcat logs are also preconfigured to go to Hadoop's `logs/` directory.

The following environment variables (which can be set in KMS's `etc/hadoop/kms-env.sh` script) can be used to alter those values:

* KMS_HTTP_PORT
* KMS_ADMIN_PORT
* KMS_PROTOCOL
* KMS_MAX_THREADS
* KMS_ACCEPT_COUNT
* KMS_ACCEPTOR_THREAD_COUNT
* KMS_MAX_HTTP_HEADER_SIZE
* KMS_LOG

NOTE: You need to restart the KMS for the configuration changes to take effect.

$H3 Loading native libraries

The following environment variable (which can be set in KMS's `etc/hadoop/kms-env.sh` script) can be used to specify the location of any required native libraries. For eg. Tomact native Apache Portable Runtime (APR) libraries:

* JAVA_LIBRARY_PATH

$H3 KMS Security Configuration

$H4 Enabling Kerberos HTTP SPNEGO Authentication

Configure the Kerberos `etc/krb5.conf` file with the information of your KDC server.

Create a service principal and its keytab for the KMS, it must be an `HTTP` service principal.

Configure KMS `etc/hadoop/kms-site.xml` with the correct security values, for example:

```xml
   <property>
     <name>hadoop.kms.authentication.type</name>
     <value>kerberos</value>
   </property>

   <property>
     <name>hadoop.kms.authentication.kerberos.keytab</name>
     <value>${user.home}/kms.keytab</value>
   </property>

   <property>
     <name>hadoop.kms.authentication.kerberos.principal</name>
     <value>HTTP/localhost</value>
   </property>

   <property>
     <name>hadoop.kms.authentication.kerberos.name.rules</name>
     <value>DEFAULT</value>
   </property>
```

NOTE: You need to restart the KMS for the configuration changes to take effect.

$H4 KMS Proxyuser Configuration

Each proxyuser must be configured in `etc/hadoop/kms-site.xml` using the following properties:

```xml
  <property>
    <name>hadoop.kms.proxyuser.#USER#.users</name>
    <value>*</value>
  </property>

  <property>
    <name>hadoop.kms.proxyuser.#USER#.groups</name>
    <value>*</value>
  </property>

  <property>
    <name>hadoop.kms.proxyuser.#USER#.hosts</name>
    <value>*</value>
  </property>
```

`#USER#` is the username of the proxyuser to configure.

The `users` property indicates the users that can be impersonated.

The `groups` property indicates the groups users being impersonated must belong to.

At least one of the `users` or `groups` properties must be defined. If both are specified, then the configured proxyuser will be able to impersonate and user in the `users` list and any user belonging to one of the groups in the `groups` list.

The `hosts` property indicates from which host the proxyuser can make impersonation requests.

If `users`, `groups` or `hosts` has a `*`, it means there are no restrictions for the proxyuser regarding users, groups or hosts.

$H4 KMS over HTTPS (SSL)

To configure KMS to work over HTTPS the following 2 properties must be set in the `etc/hadoop/kms_env.sh` script (shown with default values):

* KMS_SSL_KEYSTORE_FILE=$HOME/.keystore
* KMS_SSL_KEYSTORE_PASS=password

In the KMS `tomcat/conf` directory, replace the `server.xml` file with the provided `ssl-server.xml` file.

You need to create an SSL certificate for the KMS. As the `kms` Unix user, using the Java `keytool` command to create the SSL certificate:

    $ keytool -genkey -alias tomcat -keyalg RSA

You will be asked a series of questions in an interactive prompt. It will create the keystore file, which will be named **.keystore** and located in the `kms` user home directory.

The password you enter for "keystore password" must match the value of the `KMS_SSL_KEYSTORE_PASS` environment variable set in the `kms-env.sh` script in the configuration directory.

The answer to "What is your first and last name?" (i.e. "CN") must be the hostname of the machine where the KMS will be running.

NOTE: You need to restart the KMS for the configuration changes to take effect.


Set environment variable `KMS_SSL_CLIENT_AUTH` to change client
authentication. The default is `false`. See `clientAuth` in
[Tomcat 6.0 SSL Support](https://tomcat.apache.org/tomcat-6.0-doc/config/http.html#SSL_Support).

Set environment variable `KMS_SSL_ENABLED_PROTOCOLS` to specify a list of
enabled SSL protocols. The default list includes `TLSv1`, `TLSv1.1`,
`TLSv1.2`, and `SSLv2Hello`. See `sslEnabledProtocols` in
[Tomcat 6.0 SSL Support](https://tomcat.apache.org/tomcat-6.0-doc/config/http.html#SSL_Support).

In order to support some old SSL clients, the default encryption ciphers
include a few relatively weaker ciphers. Set environment variable
`KMS_SSL_CIPHERS` to override. The value is a comma separated list of ciphers
documented in [Tomcat Wiki](https://wiki.apache.org/tomcat/Security/Ciphers).

$H4 ACLs (Access Control Lists)

KMS supports ACLs (Access Control Lists) for fine-grained permission control.

Two levels of ACLs exist in KMS: KMS ACLs and Key ACLs. KMS ACLs control access at KMS operation level, and precede Key ACLs. In particular, only if permission is granted at KMS ACLs level, shall the permission check against Key ACLs be performed.

The configuration and usage of KMS ACLs and Key ACLs are described in the sections below.

$H5 KMS ACLs

KMS ACLs configuration are defined in the KMS `etc/hadoop/kms-acls.xml` configuration file. This file is hot-reloaded when it changes.

KMS supports both fine grained access control as well as blacklist for kms operations via a set ACL configuration properties.

A user accessing KMS is first checked for inclusion in the Access Control List for the requested operation and then checked for exclusion in the Black list for the operation before access is granted.

```xml
<configuration>
  <property>
    <name>hadoop.kms.acl.CREATE</name>
    <value>*</value>
    <description>
          ACL for create-key operations.
          If the user is not in the GET ACL, the key material is not returned
          as part of the response.
    </description>
  </property>

  <property>
    <name>hadoop.kms.blacklist.CREATE</name>
    <value>hdfs,foo</value>
    <description>
          Blacklist for create-key operations.
          If the user is in the Blacklist, the key material is not returned
          as part of the response.
    </description>
  </property>

  <property>
    <name>hadoop.kms.acl.DELETE</name>
    <value>*</value>
    <description>
          ACL for delete-key operations.
    </description>
  </property>

  <property>
    <name>hadoop.kms.blacklist.DELETE</name>
    <value>hdfs,foo</value>
    <description>
          Blacklist for delete-key operations.
    </description>
  </property>

  <property>
    <name>hadoop.kms.acl.ROLLOVER</name>
    <value>*</value>
    <description>
          ACL for rollover-key operations.
          If the user is not in the GET ACL, the key material is not returned
          as part of the response.
    </description>
  </property>

  <property>
    <name>hadoop.kms.blacklist.ROLLOVER</name>
    <value>hdfs,foo</value>
    <description>
          Blacklist for rollover-key operations.
    </description>
  </property>

  <property>
    <name>hadoop.kms.acl.GET</name>
    <value>*</value>
    <description>
          ACL for get-key-version and get-current-key operations.
    </description>
  </property>

  <property>
    <name>hadoop.kms.blacklist.GET</name>
    <value>hdfs,foo</value>
    <description>
          ACL for get-key-version and get-current-key operations.
    </description>
  </property>

  <property>
    <name>hadoop.kms.acl.GET_KEYS</name>
    <value>*</value>
    <description>
         ACL for get-keys operation.
    </description>
  </property>

  <property>
    <name>hadoop.kms.blacklist.GET_KEYS</name>
    <value>hdfs,foo</value>
    <description>
          Blacklist for get-keys operation.
    </description>
  </property>

  <property>
    <name>hadoop.kms.acl.GET_METADATA</name>
    <value>*</value>
    <description>
        ACL for get-key-metadata and get-keys-metadata operations.
    </description>
  </property>

  <property>
    <name>hadoop.kms.blacklist.GET_METADATA</name>
    <value>hdfs,foo</value>
    <description>
         Blacklist for get-key-metadata and get-keys-metadata operations.
    </description>
  </property>

  <property>
    <name>hadoop.kms.acl.SET_KEY_MATERIAL</name>
    <value>*</value>
    <description>
            Complimentary ACL for CREATE and ROLLOVER operation to allow the client
            to provide the key material when creating or rolling a key.
    </description>
  </property>

  <property>
    <name>hadoop.kms.blacklist.SET_KEY_MATERIAL</name>
    <value>hdfs,foo</value>
    <description>
            Complimentary Blacklist for CREATE and ROLLOVER operation to allow the client
            to provide the key material when creating or rolling a key.
    </description>
  </property>

  <property>
    <name>hadoop.kms.acl.GENERATE_EEK</name>
    <value>*</value>
    <description>
          ACL for generateEncryptedKey
          CryptoExtension operations
    </description>
  </property>

  <property>
    <name>hadoop.kms.blacklist.GENERATE_EEK</name>
    <value>hdfs,foo</value>
    <description>
          Blacklist for generateEncryptedKey
          CryptoExtension operations
    </description>
  </property>

  <property>
    <name>hadoop.kms.acl.DECRYPT_EEK</name>
    <value>*</value>
    <description>
          ACL for decrypt EncryptedKey
          CryptoExtension operations
    </description>
  </property>

  <property>
    <name>hadoop.kms.blacklist.DECRYPT_EEK</name>
    <value>hdfs,foo</value>
    <description>
          Blacklist for decrypt EncryptedKey
          CryptoExtension operations
    </description>
  </property>
</configuration>
```

$H5 Key ACLs

KMS supports access control for all non-read operations at the Key level. All Key Access operations are classified as :

* MANAGEMENT - createKey, deleteKey, rolloverNewVersion
* GENERATE_EEK - generateEncryptedKey, warmUpEncryptedKeys
* DECRYPT_EEK - decryptEncryptedKey
* READ - getKeyVersion, getKeyVersions, getMetadata, getKeysMetadata, getCurrentKey
* ALL - all of the above

These can be defined in the KMS `etc/hadoop/kms-acls.xml` as follows

For all keys for which a key access has not been explicitly configured, It is possible to configure a default key access control for a subset of the operation types.

It is also possible to configure a "whitelist" key ACL for a subset of the operation types. The whitelist key ACL grants access to the key, in addition to the explicit or default per-key ACL. That is, if no per-key ACL is explicitly set, a user will be granted access if they are present in the default per-key ACL or the whitelist key ACL. If a per-key ACL is explicitly set, a user will be granted access if they are present in the per-key ACL or the whitelist key ACL.

If no ACL is configured for a specific key AND no default ACL is configured AND no whitelist key ACL is configured for the requested operation, then access will be DENIED.

**NOTE:** The default and whitelist key ACL does not support `ALL` operation qualifier.

```xml
  <property>
    <name>key.acl.testKey1.MANAGEMENT</name>
    <value>*</value>
    <description>
      ACL for create-key, deleteKey and rolloverNewVersion operations.
    </description>
  </property>

  <property>
    <name>key.acl.testKey2.GENERATE_EEK</name>
    <value>*</value>
    <description>
      ACL for generateEncryptedKey operations.
    </description>
  </property>

  <property>
    <name>key.acl.testKey3.DECRYPT_EEK</name>
    <value>admink3</value>
    <description>
      ACL for decryptEncryptedKey operations.
    </description>
  </property>

  <property>
    <name>key.acl.testKey4.READ</name>
    <value>*</value>
    <description>
      ACL for getKeyVersion, getKeyVersions, getMetadata, getKeysMetadata,
      getCurrentKey operations
    </description>
  </property>

  <property>
    <name>key.acl.testKey5.ALL</name>
    <value>*</value>
    <description>
      ACL for ALL operations.
    </description>
  </property>

  <property>
    <name>whitelist.key.acl.MANAGEMENT</name>
    <value>admin1</value>
    <description>
      whitelist ACL for MANAGEMENT operations for all keys.
    </description>
  </property>

  <!--
  'testKey3' key ACL is defined. Since a 'whitelist'
  key is also defined for DECRYPT_EEK, in addition to
  admink3, admin1 can also perform DECRYPT_EEK operations
  on 'testKey3'
-->
  <property>
    <name>whitelist.key.acl.DECRYPT_EEK</name>
    <value>admin1</value>
    <description>
      whitelist ACL for DECRYPT_EEK operations for all keys.
    </description>
  </property>

  <property>
    <name>default.key.acl.MANAGEMENT</name>
    <value>user1,user2</value>
    <description>
      default ACL for MANAGEMENT operations for all keys that are not
      explicitly defined.
    </description>
  </property>

  <property>
    <name>default.key.acl.GENERATE_EEK</name>
    <value>user1,user2</value>
    <description>
      default ACL for GENERATE_EEK operations for all keys that are not
      explicitly defined.
    </description>
  </property>

  <property>
    <name>default.key.acl.DECRYPT_EEK</name>
    <value>user1,user2</value>
    <description>
      default ACL for DECRYPT_EEK operations for all keys that are not
      explicitly defined.
    </description>
  </property>

  <property>
    <name>default.key.acl.READ</name>
    <value>user1,user2</value>
    <description>
      default ACL for READ operations for all keys that are not
      explicitly defined.
    </description>
  </property>
```

$H3 KMS Delegation Token Configuration

KMS supports delegation tokens to authenticate to the key providers from processes without Kerberos credentials.

KMS delegation token authentication extends the default Hadoop authentication. Same as Hadoop authentication, KMS delegation tokens must not be fetched or renewed using delegation token authentication. See [Hadoop Auth](../hadoop-auth/index.html) page for more details.

Additionally, KMS delegation token secret manager can be configured with the following properties:

```xml
  <property>
    <name>hadoop.kms.authentication.delegation-token.update-interval.sec</name>
    <value>86400</value>
    <description>
      How often the master key is rotated, in seconds. Default value 1 day.
    </description>
  </property>

  <property>
    <name>hadoop.kms.authentication.delegation-token.max-lifetime.sec</name>
    <value>604800</value>
    <description>
      Maximum lifetime of a delegation token, in seconds. Default value 7 days.
    </description>
  </property>

  <property>
    <name>hadoop.kms.authentication.delegation-token.renew-interval.sec</name>
    <value>86400</value>
    <description>
      Renewal interval of a delegation token, in seconds. Default value 1 day.
    </description>
  </property>

  <property>
    <name>hadoop.kms.authentication.delegation-token.removal-scan-interval.sec</name>
    <value>3600</value>
    <description>
      Scan interval to remove expired delegation tokens.
    </description>
  </property>
```

$H3 High Availability

Multiple KMS instances may be used to provide high availability and scalability.
Currently there are two approaches to supporting multiple KMS instances:
running KMS instances behind a load-balancer/VIP,
or using LoadBalancingKMSClientProvider.

In both approaches, KMS instances must be specially configured to work properly
as a single logical service, because requests from the same client may be
handled by different KMS instances. In particular,
Kerberos Principals Configuration, HTTP Authentication Signature and Delegation
Tokens require special attention.

$H4 Behind a Load-Balancer or VIP

Because KMS clients and servers communicate via a REST API over HTTP,
Load-balancer or VIP may be used to distribute incoming traffic to achieve
scalability and HA. In this mode, clients are unaware of multiple KMS instances
at the server-side.

$H4 Using LoadBalancingKMSClientProvider

An alternative to running multiple KMS instances behind a load-balancer or VIP,
is to use LoadBalancingKMSClientProvider. Using this approach, a KMS client
(for example, a HDFS NameNode) is aware of multiple KMS instances, and it sends
requests to them in a round-robin fashion. LoadBalancingKMSClientProvider is
implicitly used when more than one URI is specified in
`hadoop.security.key.provider.path`.

The following example in `core-site.xml` configures two KMS
instances, `kms01.example.com` and `kms02.example.com`.
The hostnames are separated by semi-colons, and all KMS instances must run
on the same port.

    <property>
      <name>hadoop.security.key.provider.path</name>
      <value>kms://https@kms01.example.com;kms02.example.com:9600/kms</value>
      <description>
        The KeyProvider to use when interacting with encryption keys used
        when reading and writing to an encryption zone.
      </description>
    </property>

If a request to a KMS instance fails, clients retry with the next instance. The
request is returned as failure only if all instances fail.

$H4 HTTP Kerberos Principals Configuration

When KMS instances are behind a load-balancer or VIP, clients will use the hostname of the VIP. For Kerberos SPNEGO authentication, the hostname of the URL is used to construct the Kerberos service name of the server, `HTTP/#HOSTNAME#`. This means that all KMS instances must have a Kerberos service name with the load-balancer or VIP hostname.

In order to be able to access directly a specific KMS instance, the KMS instance must also have Keberos service name with its own hostname. This is required for monitoring and admin purposes.

Both Kerberos service principal credentials (for the load-balancer/VIP hostname and for the actual KMS instance hostname) must be in the keytab file configured for authentication. And the principal name specified in the configuration must be '\*'. For example:

```xml
  <property>
    <name>hadoop.kms.authentication.kerberos.principal</name>
    <value>*</value>
  </property>
```

**NOTE:** If using HTTPS, the SSL certificate used by the KMS instance must be configured to support multiple hostnames (see Java 7 `keytool` SAN extension support for details on how to do this).

$H4 HTTP Authentication Signature

KMS uses Hadoop Authentication for HTTP authentication. Hadoop Authentication issues a signed HTTP Cookie once the client has authenticated successfully. This HTTP Cookie has an expiration time, after which it will trigger a new authentication sequence. This is done to avoid triggering the authentication on every HTTP request of a client.

A KMS instance must verify the HTTP Cookie signatures signed by other KMS instances. To do this, all KMS instances must share the signing secret. Please see [SignerSecretProvider Configuration](../hadoop-auth/Configuration.html#SignerSecretProvider_Configuration) for detailed description and configuration examples. Note that KMS configurations need to be prefixed with `hadoop.kms.authentication`, as shown in the example below.

This secret sharing can be done using a Zookeeper service which is configured in KMS with the following properties in the `kms-site.xml`:

```xml
  <property>
    <name>hadoop.kms.authentication.signer.secret.provider</name>
    <value>zookeeper</value>
    <description>
      Indicates how the secret to sign the authentication cookies will be
      stored. Options are 'random' (default), 'file' and 'zookeeper'.
      If using a setup with multiple KMS instances, 'zookeeper' should be used.
      If using file, signature.secret.file should be configured and point to the secret file.
    </description>
  </property>
  <property>
    <name>hadoop.kms.authentication.signer.secret.provider.zookeeper.path</name>
    <value>/hadoop-kms/hadoop-auth-signature-secret</value>
    <description>
      The Zookeeper ZNode path where the KMS instances will store and retrieve
      the secret from. All KMS instances that need to coordinate should point to the same path.
    </description>
  </property>
  <property>
    <name>hadoop.kms.authentication.signer.secret.provider.zookeeper.connection.string</name>
    <value>#HOSTNAME#:#PORT#,...</value>
    <description>
      The Zookeeper connection string, a list of hostnames and port comma
      separated.
    </description>
  </property>
  <property>
    <name>hadoop.kms.authentication.signer.secret.provider.zookeeper.auth.type</name>
    <value>sasl</value>
    <description>
      The Zookeeper authentication type, 'none' (default) or 'sasl' (Kerberos).
    </description>
  </property>
  <property>
    <name>hadoop.kms.authentication.signer.secret.provider.zookeeper.kerberos.keytab</name>
    <value>/etc/hadoop/conf/kms.keytab</value>
    <description>
      The absolute path for the Kerberos keytab with the credentials to
      connect to Zookeeper.
    </description>
  </property>
  <property>
    <name>hadoop.kms.authentication.signer.secret.provider.zookeeper.kerberos.principal</name>
    <value>kms/#HOSTNAME#</value>
    <description>
      The Kerberos service principal used to connect to Zookeeper.
    </description>
  </property>
```

$H4 Delegation Tokens

Similar to HTTP authentication, KMS uses Hadoop Authentication for delegation tokens too.

Under HA, A KMS instance must verify the delegation token given by another KMS instance, by checking the shared secret used to sign the delegation token. To do this, all KMS instances must be able to retrieve the shared secret from ZooKeeper.

Please see the examples given in HTTP Authentication section to configure ZooKeeper for secret sharing.

$H3 KMS HTTP REST API

$H4 Create a Key

*REQUEST:*

    POST http://HOST:PORT/kms/v1/keys
    Content-Type: application/json

    {
      "name"        : "<key-name>",
      "cipher"      : "<cipher>",
      "length"      : <length>,        //int
      "material"    : "<material>",    //base64
      "description" : "<description>"
    }

*RESPONSE:*

    201 CREATED
    LOCATION: http://HOST:PORT/kms/v1/key/<key-name>
    Content-Type: application/json

    {
      "name"        : "versionName",
      "material"    : "<material>",    //base64, not present without GET ACL
    }

$H4 Rollover Key

*REQUEST:*

    POST http://HOST:PORT/kms/v1/key/<key-name>
    Content-Type: application/json

    {
      "material"    : "<material>",
    }

*RESPONSE:*

    200 OK
    Content-Type: application/json

    {
      "name"        : "versionName",
      "material"    : "<material>",    //base64, not present without GET ACL
    }

$H4 Delete Key

*REQUEST:*

    DELETE http://HOST:PORT/kms/v1/key/<key-name>

*RESPONSE:*

    200 OK

$H4 Get Key Metadata

*REQUEST:*

    GET http://HOST:PORT/kms/v1/key/<key-name>/_metadata

*RESPONSE:*

    200 OK
    Content-Type: application/json

    {
      "name"        : "<key-name>",
      "cipher"      : "<cipher>",
      "length"      : <length>,        //int
      "description" : "<description>",
      "created"     : <millis-epoc>,   //long
      "versions"    : <versions>       //int
    }

$H4 Get Current Key

*REQUEST:*

    GET http://HOST:PORT/kms/v1/key/<key-name>/_currentversion

*RESPONSE:*

    200 OK
    Content-Type: application/json

    {
      "name"        : "versionName",
      "material"    : "<material>",    //base64
    }

$H4 Generate Encrypted Key for Current KeyVersion

*REQUEST:*

    GET http://HOST:PORT/kms/v1/key/<key-name>/_eek?eek_op=generate&num_keys=<number-of-keys-to-generate>

*RESPONSE:*

    200 OK
    Content-Type: application/json
    [
      {
        "versionName"         : "encryptionVersionName",
        "iv"                  : "<iv>",          //base64
        "encryptedKeyVersion" : {
            "versionName"       : "EEK",
            "material"          : "<material>",    //base64
        }
      },
      {
        "versionName"         : "encryptionVersionName",
        "iv"                  : "<iv>",          //base64
        "encryptedKeyVersion" : {
            "versionName"       : "EEK",
            "material"          : "<material>",    //base64
        }
      },
      ...
    ]

$H4 Decrypt Encrypted Key

*REQUEST:*

    POST http://HOST:PORT/kms/v1/keyversion/<version-name>/_eek?ee_op=decrypt
    Content-Type: application/json

    {
      "name"        : "<key-name>",
      "iv"          : "<iv>",          //base64
      "material"    : "<material>",    //base64
    }

*RESPONSE:*

    200 OK
    Content-Type: application/json

    {
      "name"        : "EK",
      "material"    : "<material>",    //base64
    }

$H4 Get Key Version

*REQUEST:*

    GET http://HOST:PORT/kms/v1/keyversion/<version-name>

*RESPONSE:*

    200 OK
    Content-Type: application/json

    {
      "name"        : "versionName",
      "material"    : "<material>",    //base64
    }

$H4 Get Key Versions

*REQUEST:*

    GET http://HOST:PORT/kms/v1/key/<key-name>/_versions

*RESPONSE:*

    200 OK
    Content-Type: application/json

    [
      {
        "name"        : "versionName",
        "material"    : "<material>",    //base64
      },
      {
        "name"        : "versionName",
        "material"    : "<material>",    //base64
      },
      ...
    ]

$H4 Get Key Names

*REQUEST:*

    GET http://HOST:PORT/kms/v1/keys/names

*RESPONSE:*

    200 OK
    Content-Type: application/json

    [
      "<key-name>",
      "<key-name>",
      ...
    ]

$H4 Get Keys Metadata

    GET http://HOST:PORT/kms/v1/keys/metadata?key=<key-name>&key=<key-name>,...

*RESPONSE:*

    200 OK
    Content-Type: application/json

    [
      {
        "name"        : "<key-name>",
        "cipher"      : "<cipher>",
        "length"      : <length>,        //int
        "description" : "<description>",
        "created"     : <millis-epoc>,   //long
        "versions"    : <versions>       //int
      },
      {
        "name"        : "<key-name>",
        "cipher"      : "<cipher>",
        "length"      : <length>,        //int
        "description" : "<description>",
        "created"     : <millis-epoc>,   //long
        "versions"    : <versions>       //int
      },
      ...
    ]