Replicating objects created with server-side encryption (SSE-C, SSE-S3, SSE-KMS) - Amazon Simple Storage Service

Replicating objects created with server-side encryption (SSE-C, SSE-S3, SSE-KMS)

Replicating encrypted objects (SSE-C)

By using server-side encryption with customer-provided keys (SSE-C), you can manage proprietary keys. With SSE-C, you manage the keys while Amazon S3 manages the encryption and decryption process. You must provide an encryption key as part of your request, but you don't need to write any code to perform object encryption or decryption. When you upload an object, Amazon S3 encrypts the object by using the key that you provided. Amazon S3 then purges that key from memory. When you retrieve an object, you must provide the same encryption key as part of your request. For more information, see Using server-side encryption with customer-provided keys (SSE-C).

S3 Replication supports objects that are encrypted with SSE-C. You can configure SSE-C object replication in the Amazon S3 console or with the AWS SDKs, the same way that you configure replication for unencrypted objects. S3 Replication automatically replicates newly uploaded SSE-C encrypted objects if they are eligible, as per your S3 Replication configuration. For replicating existing objects in your buckets, use S3 Batch Replication. There aren't additional SSE-C permissions beyond what are currently required for replication. For more information about replicating objects, see Setting up replication and Replicating existing objects with S3 Batch Replication.

There are no additional charges for replicating SSE-C objects. For details about replication pricing, see the Amazon S3 pricing page.

Replicating encrypted objects (SSE-S3, SSE-KMS)

By default, Amazon S3 doesn't replicate objects that are stored at rest using server-side encryption with AWS KMS keys stored in AWS KMS. This section explains the additional configuration that you add to direct Amazon S3 to replicate these objects.

For an example with step-by-step instructions, see Replicating encrypted objects. For information about creating a replication configuration, see Replicating objects.

Specifying additional information in the replication configuration

In the replication configuration, you do the following:

  • In the Destination configuration, add the symmetric AWS KMS customer managed key that you want Amazon S3 to use to encrypt object replicas.

  • Explicitly opt in by enabling replication of objects encrypted by using KMS keys by adding the SourceSelectionCriteria element.

<ReplicationConfiguration> <Rule> ... <SourceSelectionCriteria> <SseKmsEncryptedObjects> <Status>Enabled</Status> </SseKmsEncryptedObjects> </SourceSelectionCriteria> <Destination> ... <EncryptionConfiguration> <ReplicaKmsKeyID>AWS KMS key ID for the AWS Region of the destination bucket.</ReplicaKmsKeyID> </EncryptionConfiguration> </Destination> ... </Rule> </ReplicationConfiguration>
Important

The KMS key must have been created in the same AWS Region as the destination buckets.

The KMS key must be valid. The PUT Bucket replication API operation doesn't check the validity of KMS keys. If you use a KMS key that isn't valid, you will receive the HTTP 200 OK status code in response, but replication fails.

The following example shows a replication configuration that includes optional configuration elements.

<?xml version="1.0" encoding="UTF-8"?> <ReplicationConfiguration> <Role>arn:aws:iam::account-id:role/role-name</Role> <Rule> <ID>Rule-1</ID> <Priority>1</Priority> <Status>Enabled</Status> <DeleteMarkerReplication> <Status>Disabled</Status> </DeleteMarkerReplication> <Filter> <Prefix>Tax</Prefix> </Filter> <Destination> <Bucket>arn:aws:s3:::destination-bucket</Bucket> <EncryptionConfiguration> <ReplicaKmsKeyID>The AWS KMS key ID for the AWS Region of the destination buckets. (S3 uses this key to encrypt object replicas.)</ReplicaKmsKeyID> </EncryptionConfiguration> </Destination> <SourceSelectionCriteria> <SseKmsEncryptedObjects> <Status>Enabled</Status> </SseKmsEncryptedObjects> </SourceSelectionCriteria> </Rule> </ReplicationConfiguration>

This replication configuration has one rule. The rule applies to objects with the Tax key prefix. Amazon S3 uses the AWS KMS key ID to encrypt these object replicas.

Granting additional permissions for the IAM role

To replicate objects that are encrypted at rest by using AWS KMS, grant the following additional permissions to the AWS Identity and Access Management (IAM) role that you specify in the replication configuration. You grant these permissions by updating the permissions policy that's associated with the IAM role.

  • s3:GetObjectVersionForReplication action for source objects – This action allows Amazon S3 to replicate both unencrypted objects and objects created with server-side encryption by using SSE-S3 keys or SSE-KMS.

    Note

    We recommend that you use the s3:GetObjectVersionForReplication action instead of the s3:GetObjectVersion action because s3:GetObjectVersionForReplication provides Amazon S3 with only the minimum permissions necessary for replication. In addition, the s3:GetObjectVersion action allows replication of unencrypted and SSE-S3-encrypted objects, but not of objects created by using SSE-KMS.

  • kms:Decrypt and kms:Encrypt AWS KMS actions for the KMS keys

    • You must grant kms:Decrypt permissions for the AWS KMS key that's used to decrypt the source object.

    • You must grant kms:Encrypt permissions for the AWS KMS key that's used to encrypt the object replica.

We recommend that you restrict these permissions only to the destination buckets and objects by using AWS KMS condition keys. The AWS account that owns the IAM role must have permissions for these AWS KMS actions (kms:Encrypt and kms:Decrypt) for the KMS keys that are listed in the policy. If the KMS keys are owned by another AWS account, the owner of the KMS keys must grant these permissions to the AWS account that owns the IAM role. For more information about managing access to these KMS keys, see Using IAM Policies with AWS KMS in the AWS Key Management Service Developer Guide.

Amazon S3 Bucket Keys and replication

To use replication with an S3 Bucket Key, the AWS KMS key policy for the KMS key that's used to encrypt the object replica must include kms:Decrypt permissions for the calling principal. The call to kms:Decrypt verifies the integrity of the S3 Bucket Key before using it. For more information, see Using an S3 Bucket Key with replication.

When an S3 Bucket Key is enabled for the source or destination bucket, the encryption context will be the bucket Amazon Resource Name (ARN), not the object ARN (for example, arn:aws:s3:::bucket_ARN). You must update your IAM policies to use the bucket ARN for the encryption context:

"kms:EncryptionContext:aws:s3:arn": [ "arn:aws:s3:::bucket_ARN" ]

For more information, see Encryption context (x-amz-server-side-encryption-context) and Changes to note before enabling an S3 Bucket Key.

Example policies – Using SSE-S3 and SSE-KMS with replication

The following example IAM policies show statements for using SSE-S3 and SSE-KMS with replication.

Example : Using SSE-KMS – separate destination buckets

The following example policy shows statements for using SSE-KMS with separate destination buckets.

{ "Action": ["kms:Decrypt"], "Effect": "Allow", "Condition": { "StringLike": { "kms:ViaService": "s3.source-bucket-region.amazonaws.com", "kms:EncryptionContext:aws:s3:arn": [ "arn:aws:s3:::source-bucket-name/key-prefix1*", ] } }, "Resource": [ "List of AWS KMS key ARNs used to encrypt source objects.", ] }, { "Action": ["kms:Encrypt"], "Effect": "Allow", "Condition": { "StringLike": { "kms:ViaService": "s3.destination-bucket-1-region.amazonaws.com", "kms:EncryptionContext:aws:s3:arn": [ "arn:aws:s3:::destination-bucket-name-1/key-prefix1*", ] } }, "Resource": [ "AWS KMS key ARNs (for the AWS Region of the destination bucket 1). Used to encrypt object replicas created in destination bucket 1.", ] }, { "Action": ["kms:Encrypt"], "Effect": "Allow", "Condition": { "StringLike": { "kms:ViaService": "s3.destination-bucket-2-region.amazonaws.com", "kms:EncryptionContext:aws:s3:arn": [ "arn:aws:s3:::destination-bucket-2-name/key-prefix1*", ] } }, "Resource": [ "AWS KMS key ARNs (for the AWS Region of destination bucket 2). Used to encrypt object replicas created in destination bucket 2.", ] }

Example : Replicating objects created with SSE-S3 and SSE-KMS

The following is a complete IAM policy that grants the necessary permissions to replicate unencrypted objects, objects created with SSE-S3, and objects created with SSE-KMS.

{ "Version":"2012-10-17", "Statement":[ { "Effect":"Allow", "Action":[ "s3:GetReplicationConfiguration", "s3:ListBucket" ], "Resource":[ "arn:aws:s3:::source-bucket" ] }, { "Effect":"Allow", "Action":[ "s3:GetObjectVersionForReplication", "s3:GetObjectVersionAcl" ], "Resource":[ "arn:aws:s3:::source-bucket/key-prefix1*" ] }, { "Effect":"Allow", "Action":[ "s3:ReplicateObject", "s3:ReplicateDelete" ], "Resource":"arn:aws:s3:::destination-bucket/key-prefix1*" }, { "Action":[ "kms:Decrypt" ], "Effect":"Allow", "Condition":{ "StringLike":{ "kms:ViaService":"s3.source-bucket-region.amazonaws.com", "kms:EncryptionContext:aws:s3:arn":[ "arn:aws:s3:::source-bucket-name/key-prefix1*" ] } }, "Resource":[ "List of AWS KMS key ARNs used to encrypt source objects." ] }, { "Action":[ "kms:Encrypt" ], "Effect":"Allow", "Condition":{ "StringLike":{ "kms:ViaService":"s3.destination-bucket-region.amazonaws.com", "kms:EncryptionContext:aws:s3:arn":[ "arn:aws:s3:::destination-bucket-name/prefix1*" ] } }, "Resource":[ "AWS KMS key ARNs (for the AWS Region of the destination buckets) to use for encrypting object replicas" ] } ] }

Granting additional permissions for cross-account scenarios

In a cross-account scenario, where the source and destination buckets are owned by different AWS accounts, you can use a KMS key to encrypt object replicas. However, the KMS key owner must grant the source bucket owner permission to use the KMS key.

To grant the source bucket owner permission to use the KMS key (AWS KMSconsole)

  1. Sign in to the AWS Management Console and open the AWS KMS console at https://console.aws.amazon.com/kms.

  2. To change the AWS Region, use the Region selector in the upper-right corner of the page.

  3. To view the keys in your account that you create and manage, in the navigation pane choose Customer managed keys.

  4. Choose the KMS key.

  5. Under General configuration, choose the Key policy tab.

  6. Scroll down to Other AWS accounts.

  7. Choose Add other AWS accounts.

  8. arn:aws:iam::, enter the source bucket account ID.

  9. Choose Save.

To grant the source bucket owner permission to use the KMS key (AWS CLI)

AWS KMS transaction quota considerations

When you add many new objects with AWS KMS encryption after enabling Cross-Region Replication (CRR), you might experience throttling (HTTP 503 Service Unavailable errors). Throttling occurs when the number of AWS KMS transactions per second exceeds the current quota. For more information, see Quotas in the AWS Key Management Service Developer Guide.

To request a quota increase, use Service Quotas. For more information, see Amazon Web Services Quotas. If Service Quotas isn't supported in your Region, open an AWS Support case.