Services or capabilities described in Amazon Web Services documentation might vary by Region. To see the differences applicable to the China Regions, see Getting Started with Amazon Web Services in China (PDF).

How Amazon Simple Email Service (Amazon SES) uses Amazon KMS

You can use Amazon Simple Email Service (Amazon SES) to receive email, and (optionally) to encrypt the received email messages before storing them in an Amazon Simple Storage Service (Amazon S3) bucket that you choose. When you configure Amazon SES to encrypt email messages, you must choose the Amazon KMS Amazon KMS key under which Amazon SES encrypts the messages. You can choose the Amazon managed key for Amazon SES (its alias is aws/ses), or you can choose a symmetric customer managed key that you created in Amazon KMS.

For more information about receiving email using Amazon SES, go to Receiving Email with Amazon SES in the Amazon Simple Email Service Developer Guide.

Overview of Amazon SES encryption using Amazon KMS

When you configure Amazon SES to receive email and encrypt the email messages before saving them to your S3 bucket, the process works like this:

To accomplish Step 3 through Step 6, Amazon SES uses the Amazon–provided Amazon S3 encryption client. Use the same client to retrieve your encrypted email messages from Amazon S3 and decrypt them. For more information, see Getting and decrypting email messages.

Amazon SES encryption context

When Amazon SES requests a data key to encrypt your received email messages (Step 3 in the Overview of Amazon SES encryption using Amazon KMS), it includes an encryption context in the request. The encryption context provides additional authenticated data (AAD) that Amazon KMS uses to ensure data integrity. The encryption context is also written to your Amazon CloudTrail log files, which can help you understand why a given Amazon KMS key (KMS key) was used. Amazon SES uses the following encryption context:

The following example shows a JSON representation of the encryption context that Amazon SES uses:

{
  "aws:ses:source-account": "111122223333",
  "aws:ses:rule-name": "example-receipt-rule-name",
  "aws:ses:message-id": "d6iitobk75ur44p8kdnnp7g2n800"
}

Giving Amazon SES permission to use your Amazon KMS key

To encrypt your email messages, you can use the Amazon managed key in your account for Amazon SES (aws/ses), or you can use a customer managed key that you create. Amazon SES already has permission to use the Amazon managed key on your behalf. However, if you specify a customer managed key when you add the S3 action to your Amazon SES receipt rule, you must give Amazon SES permission to use the KMS key to encrypt your email messages.

To give Amazon SES permission to use your customer managed key, add the following statement to that KMS key's key policy:

{
  "Sid": "Allow SES to encrypt messages using this KMS key",
  "Effect": "Allow",
  "Principal": {"Service": "ses.amazonaws.com"},
  "Action": [
    "kms:Encrypt",
    "kms:GenerateDataKey*"
  ],
  "Resource": "*",
  "Condition": {
    "Null": {
      "kms:EncryptionContext:aws:ses:rule-name": false,
      "kms:EncryptionContext:aws:ses:message-id": false
    },
    "StringEquals": {"kms:EncryptionContext:aws:ses:source-account": "ACCOUNT-ID-WITHOUT-HYPHENS"}
  }
}

Replace ACCOUNT-ID-WITHOUT-HYPHENS with the 12-digit ID of the Amazon Web Services account where you've configured Amazon SES to receive email messages. This policy statement allows Amazon SES to encrypt data with this KMS key only under these conditions:

For more information about the encryption context that Amazon SES uses when encrypting your email messages, see Amazon SES encryption context. For general information about how Amazon KMS uses the encryption context, see encryption context.

Getting and decrypting email messages

Amazon SES does not have permission to decrypt your encrypted email messages and cannot decrypt them for you. You must write code to get your email messages from Amazon S3 and decrypt them. To make this easier, use the Amazon S3 encryption client. The following Amazon SDKs include the Amazon S3 encryption client:

The Amazon S3 encryption client simplifies the work of constructing the necessary requests to Amazon S3 to retrieve the encrypted email message and to Amazon KMS to decrypt the message's encrypted data key, and of decrypting the email message. For example, to successfully decrypt the encrypted data key you must pass the same encryption context that Amazon SES passed when requesting the data key from Amazon KMS (Step 3 in the Overview of Amazon SES encryption using Amazon KMS). The Amazon S3 encryption client handles this, and much of the other work, for you.

For sample code that uses the Amazon S3 encryption client in the Amazon SDK for Java to do client-side decryption, see the following: