SmartStore on S3 security strategies

SmartStore security strategies vary depending on the type of remote storage service. This topic covers security when using the Amazon Simple Storage Service (S3) as the remote storage service.

Authenticate with the remote storage service

How you authenticate into the remote storage service depends on the cloud infrastructure that your indexer or indexer cluster uses.

• If the indexer or indexer cluster runs on Amazon Elastic Compute Cloud (EC2), you can use the access and secret keys from its Identity and Access Management (IAM) role to authenticate.
• If the indexer or indexer cluster does not run on EC2, use hardcoded keys in indexes.conf. These are the relevant settings for hardcoding keys for S3:
  • remote.s3.access_key: The access key to use when authenticating with the remote storage system.
  • remote.s3.secret_key: The secret key to use when authenticating with the remote storage system.
  • remote.s3.endpoint: The URL of the remote storage system. This setting tells the indexer where to go for S3 authentication. Use the value for the S3 bucket region. For example, https://s3.us-west-2.amazonaws.com.

For more information on these settings, see the indexes.conf spec file.

The credentials that you use, whether from the IAM role or from indexes.conf, need permission to perform S3 operations. They also need permission to perform Amazon Key Management Service (KMS) operations if you are encrypting data-at-rest on the remote store.

IAM permissions required for SmartStore operations

The following permissions are needed for basic S3 operations:

• s3:ListBucket
• s3:PutObject
• s3:GetObject
• s3:DeleteObject

In addition, if using remote.s3.supports_versioning=true, the following permissions are required for bucket-freezing operations, in order to delete all versions of the files:

• s3:ListBucketVersions
• s3:DeleteObjectVersion

It is usually a better practice to set remote.s3.supports_versioning=false and instead use S3 lifecycle rules.

By default, s3:AbortMultipartUpload permission is already given to the S3 bucket owner and the initiator of the multipart upload, but it can be explicitly added if needed.

Manage SSL certifications for the remote store

The SSL certification settings vary according to the remote storage service type. This section provides information for managing SSL for an S3 remote store, using the settings provided in indexes.conf. For more details on any of these settings, as well as for information on additional S3-related SSL settings, see the indexes.conf spec file.

When you configure SSL settings for a remote volume, you must do so on a per-volume basis. This means you must specify SSL settings for each individual remote volume that you define in the indexes.conf file.

The S3 SSL settings are overlaid on the sslConfig stanza in the server.conf configuration file, with the following exceptions:

• sslVerifyServerCert
• sslAltNameToCheck
• sslCommonNameToCheck

If you run into problems with configuring SSL for S3 storage, consult the server.conf SSL settings in addition to the remote-storage-specific settings.

The following table includes common settings and their recommended values.

SSL setting	Description	Recommended value
remote.s3.sslVerifyServerCert	Specifies whether to check the server certificate provided by the S3 endpoint.	true
remote.s3.sslVersions	The SSL version to use.	tls1.2
remote.s3.sslAltNameToCheck	List of alternative names in the certificate presented by the server to match against. For example, s3.<region>.amazonaws.com.	N/A
remote.s3.sslRootCAPath	Absolute path to the Privacy Enhanced Mail (PEM) format file that contains the list of root certificates.	N/A
remote.s3.cipherSuite	Ciphers to use to connect with S3.	Check with your security experts. Here is an example of the type of value to enter for this setting: ECDHE-ECDSA-AES128-SHA256: ECDHE-ECDSA-AES256-SHA384: ECDHE-ECDSA-AES128-GCM-SHA256: ECDHE-ECDSA-AES256-GCM-SHA384: ECDHE-RSA-AES128-SHA:ECDHE-RSA-AES256-SHA: ECDHE-ECDSA-AES128-SHA: ECDHE-ECDSA-AES256-SHA: AES128-SHA256:AES256-SHA256: AES128-SHA:AES256-SHA: DHE-RSA-AES128-SHA: DHE-RSA-AES256-SHA: DHE-RSA-AES128-SHA256: DHE-RSA-AES256-SHA256
remote.s3.ecdhCurves	Elliptic Curve-Diffie Hellman (ECDH) curves to send.	Check with your security experts. Here is an example of the type of value to enter for this attribute: prime256v1, secp384r1, secp521r1

Encrypt the data on the remote store

SmartStore supports client- and server-side encryption of data at rest, or data which is neither in use nor in transit, on S3. SmartStore supports four encryption schemes through the remote.s3.encryption setting in the indexes.conf configuration file. You must use configuration files to encrypt data on S3 volumes, as there is no other method to perform this kind of configuration..

When you enable encryption, depending on the encryption method you use, the Splunk platform generates an encryption key and encrypts data that you upload to the target volume with this key. After a certain interval, the platform generates a new key.

With most encryption methods, the Splunk platform instance that does the encryption must maintain a connection to AWS or KMS. Failure to maintain this connection can cause problems with generating new keys for encryption.

The high-level procedure to encrypt data on a SmartStore volume on a single Splunk platform instance follows. If you want to encrypt data on a SmartStore volume on an indexer cluster, do not follow this procedure. Instead, see Update common peer configurations and apps. When you perform that procedure, supply the settings that appear in this procedure.

1. Choose the encryption method that you want to use on a SmartStore volume.
   

   Choosing the encryption method is a one-time decision. You cannot change the encryption method later.

2. On the Splunk platform instance where you want to encrypt data on a SmartStore volume, open the $SPLUNK_HOME/etc/system/local/indexes.conf for editing.
3. Specify the type of encryption method you want to apply to each SmartStore volume by using the remote.s3.encryption setting under the [volume:<volume_name>] stanza for that volume:

   [volume:myvolume]
   remote.s3.encryption = sse-s3 | sse-kms | sse-c | cse | none 
   

4. Depending on the type of encryption you use, specify additional settings that are required to interact with AWS or KMS to do the encryption. See the encryption examples later in this topic for information on the settings to use.
5. Save the indexes.conf file and close it,
6. Restart the Splunk platform.

Encryption occurs at the time of data upload to the volumes that you specify, and remains in effect until you change the encryption scheme again. When you configure encryption for the remote volume, you do not cause data that is already on the volume to be encrypted.

If you disable encryption, you do not cause existing encrypted data to be decrypted. Any encrypted data becomes unusable, because the Splunk platform cannot decrypt it.

If you do not already know which encryption scheme you want to use, the best choice for server-side encryption is sse-c (server-side encryption with customer keys). This method avoids running into potential throttling issues from KMS. For client-side encryption, cse is the best and only choice.

• For detailed information on the settings to use for encryption, see the indexes.conf spec file.
• For information on configuring server-side encryption in AWS, see the Amazon documentation.

Server-side encryption with customer-provided encryption keys (sse-c)

Here is an example of setting server-side encryption with customer keys. All of these settings go into the indexes.conf configuration file.

[volume:example_volume]
remote.s3.encryption = sse-c
remote.s3.encryption.sse-c.key_type = kms 
remote.s3.encryption.sse-c.key_refresh_interval = 86400
# 86400 equals 24 hours. This is the default and recommended value. 
# The minimum value is 3600. 
# Setting a very low value can degrade performance.
remote.s3.kms.auth_region = <aws_region>
remote.s3.kms.key_id = <kms_keyid> 
# The kms_keyid must be a unique key ID, the Amazon Resource Name (ARN) 
# of the CMK, or the name or ARN of an alias that points to the CMK. 

# SSL settings for KMS communication
remote.s3.kms.sslVerifyServerCert = true
remote.s3.kms.sslVersions = tls1.2
remote.s3.kms.sslAltNameToCheck = kms.<aws_region>.amazonaws.com
remote.s3.kms.sslRootCAPath = $SPLUNK_HOME/etc/auth/kms_rootcert.pem  
remote.s3.kms.cipherSuite = ECDHE-ECDSA-AES128-SHA256:ECDHE-ECDSA-AES256-SHA384:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES128-SHA:ECDHE-RSA-AES256-SHA:ECDHE-ECDSA-AES128-SHA:ECDHE-ECDSA-AES256-SHA:AES128-SHA256:AES256-SHA256:AES128-SHA:AES256-SHA:DHE-RSA-AES128-SHA:DHE-RSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES256-SHA256
remote.s3.kms.ecdhCurves = prime256v1, secp384r1, secp521r1

Server-side encryption with Amazon S3-managed encryption keys (sse-s3)

Here is an example of setting server-side encryption with AES256. All of these settings go into the indexes.conf configuration file.

[volume:example_volume]
remote.s3.encryption = sse-s3 

Server-side encryption with customer master keys stored in AWS KMS (sse-kms)

Here is an example of setting server-side encryption with KMS-managed keys. All of these settings go into the indexes.conf configuration file.

[volume:example_volume]
remote.s3.encryption = sse-kms
remote.s3.kms.key_id = <kms_keyid> 

Client-side encryption (cse)

Client side encryption of data ensures that the cloud service provider (CSP) cannot read the encrypted data in any way.

SmartStore contacts the AWS KMS service on an interval that you specify. It uses KMS to generate data encryption keys (DEKs) based on the Customer Master Key (CMK) that KMS stores. When you upload data after you enable CSE, SmartStore stores the data encryption keys with the uploaded data buckets.

There is no support for key revocation of any kind in the software. You are responsible for managing the customer master key and any DEKs. Also, you cannot encrypt data that has already been encrypted with a new DEK. You must decrypt the data first, then have the platform generate a new DEK before uploading the data again.

You must use AWS KMS to take advantage of this feature. It does not work with any other type of key management service.

There are some caveats to enabling client-side encryption on an index in SmartStore:

• Performance can degrade up to 20% due to the data encryption.
• There are limitations to some of the remote file system CLI commands that you can run on a SmartStore volume for maintenance or troubleshooting purposes:
  • The splunk cmd splunkd rfs getF command only lets you upload the receipt.json file, and CSE does not encrypt this file on upload.
  • The splunk cmd splunkd rfs putF command only lets you download the receipt.json file, and assumes the file has not been encrypted.
  • The splunk cmd splunkd rfs get command must include receipt.json as an argument, otherwise it fails.

Here is an example of setting client-side encryption. All of these settings go into the indexes.conf configuration file.

# The volume stanza and path specify the name of the remote volume. 
# This is the volume that the index that will store the encrypted data uses.
# The Splunk platform expects the path to be in the remote storage format.
[volume:<VOLUME_NAME>]
path = <S3_BUCKET_PATH>
storageType = remote

# The following settings facilitate interaction with AWS KMS. You need
# KMS to generate the client-side encryption key. The settings
# set the the KMS endpoint and authentication region, 
#
# You must configure one of the following two settings
# If you configure neither setting, the Splunk platform attempts
# to use the 'remote.s3.endpoint' and 'remote.s3.auth_region' settings
# before it fails to start.
remote.s3.kms.endpoint = <KMS_ENDPOINT>
remote.s3.kms.auth_region = <KMS_AUTH_REGION>

# The unique ID or Amazon Resource Name (ARN) of the 
# customer master key to use, or the alias name or ARN
# of the alias that refers to this key. 
remote.s3.kms.key_id = <KEY_ID>

# The signature version to use when authenticating the remote storage
# system supporting the S3 API. Since CSE uses KMS to manage encryption
# keys, you must set this to "v4".
remote.s3.signature_version = v4

# Enable client-side encryption on the remote volume.
remote.s3.encryption = cse

# The bucket encryption algorithm to use for CSE.
# Currently, "aes-256-gcm" is the only acceptable value.
remote.s3.encryption.cse.algorithm = aes-256-gcm

# How long to wait, in seconds, between generation of
# keys to encrypt data that is uploaded to S3 when CSE
# is active.
remote.s3.encryption.cse.key_refresh_interval = 86400

# The key mechanism to use for CSE. Currently, "kms"
# is the only acceptable value. You must configure this
# setting for the Splunk platform to start.
remote.s3.encryption.cse.key_type = kms


[INDEX_NAME]
# The index you specify for CSE of data. When the Splunk
# platform adds data to this index, it encrypts the data with
# the key that you provide. The index references
# the remote S3 storage volume.
homePath = $SPLUNK_DB/<INDEX_NAME>/db
coldPath = $SPLUNK_DB/<INDEX_NAME>/colddb
thawedPath = $SPLUNK_DB/<INDEX_NAME>/thaweddb
remotePath = volume:<VOLUME_NAME>/$_index_name