Encryption at rest
Data delivered to general-purpose S3 buckets is encrypted at rest using the destination bucket's default encryption settings:
SSE-S3 (Amazon S3 managed keys) — default.
SSE-KMS (AWS KMS managed keys) — specify your KMS key.
If you use SSE-KMS, the Channel service role must have kms:GenerateDataKey and kms:Decrypt permissions on the specified key. Scope the KMS permission with the kms:ViaService and kms:EncryptionContext:aws:s3:arn conditions shown in IAM permissions.
You can also set a customer-managed KMS key at the Channel level when you create the Channel, using the encryptionConfiguration.kmsKeyArn field.