Request Syntax Request Parameters Response Syntax Response Elements Errors Examples See Also

ReEncrypt

Decrypts ciphertext and then reencrypts it entirely within AWS KMS. You can use this operation to change the KMS key under which data is encrypted, such as when you manually rotate a KMS key or change the KMS key that protects a ciphertext. You can also use it to reencrypt ciphertext under the same KMS key, such as to change the encryption context of a ciphertext.

The ReEncrypt operation can decrypt ciphertext that was encrypted by using a KMS key in an AWS KMS operation, such as Encrypt or GenerateDataKey. It can also decrypt ciphertext that was encrypted by using the public key of an asymmetric KMS key outside of AWS KMS. However, it cannot decrypt ciphertext produced by other libraries, such as the AWS Encryption SDK or Amazon S3 client-side encryption. These libraries return a ciphertext format that is incompatible with AWS KMS.

When you use the ReEncrypt operation, you need to provide information for the decrypt operation and the subsequent encrypt operation.

If your ciphertext was encrypted under an asymmetric KMS key, you must use the SourceKeyId parameter to identify the KMS key that encrypted the ciphertext. You must also supply the encryption algorithm that was used. This information is required to decrypt the data.
If your ciphertext was encrypted under a symmetric encryption KMS key, the SourceKeyId parameter is optional. AWS KMS can get this information from metadata that it adds to the symmetric ciphertext blob. This feature adds durability to your implementation by ensuring that authorized users can decrypt ciphertext decades after it was encrypted, even if they've lost track of the key ID. However, specifying the source KMS key is always recommended as a best practice. When you use the SourceKeyId parameter to specify a KMS key, AWS KMS uses only the KMS key you specify. If the ciphertext was encrypted under a different KMS key, the ReEncrypt operation fails. This practice ensures that you use the KMS key that you intend.
To reencrypt the data, you must use the DestinationKeyId parameter to specify the KMS key that re-encrypts the data after it is decrypted. If the destination KMS key is an asymmetric KMS key, you must also provide the encryption algorithm. The algorithm that you choose must be compatible with the KMS key.

Important
When you use an asymmetric KMS key to encrypt or reencrypt data, be sure to record the KMS key and encryption algorithm that you choose. You will be required to provide the same KMS key and encryption algorithm when you decrypt the data. If the KMS key and algorithm do not match the values used to encrypt the data, the decrypt operation fails.
You are not required to supply the key ID and encryption algorithm when you decrypt with symmetric encryption KMS keys because AWS KMS stores this information in the ciphertext blob. AWS KMS cannot store metadata in ciphertext generated with asymmetric keys. The standard format for asymmetric key ciphertext does not include configurable fields.

The KMS key that you use for this operation must be in a compatible key state. For details, see Key states of AWS KMS keys in the AWS Key Management Service Developer Guide.

Note

When using grants with SourceArn constraints for ReEncrypt operations, the grants on both the source KMS key (for ReEncryptFrom) and the destination KMS key (for ReEncryptTo) must specify the same SourceArn value.

Cross-account use: Yes. The source KMS key and destination KMS key can be in different AWS accounts. Either or both KMS keys can be in a different account than the caller. To specify a KMS key in a different account, use the key ARN or alias ARN. A short key ID is also acceptable for the source key when decrypting symmetric ciphertexts, though using a full key ARN is recommended to be more explicit about the intended KMS key.

Required permissions:

kms:ReEncryptFrom permission on the source KMS key (key policy)
kms:ReEncryptTo permission on the destination KMS key (key policy)

To permit reencryption from or to a KMS key, include the "kms:ReEncrypt*" permission in your key policy. This permission is automatically included in the key policy when you use the console to create a KMS key. But you must include it manually when you create a KMS key programmatically or when you use the PutKeyPolicy operation to set a key policy.

Related operations:

Eventual consistency: The AWS KMS API follows an eventual consistency model. For more information, see AWS KMS eventual consistency.

Request Syntax


{
   "CiphertextBlob": blob,
   "DestinationEncryptionAlgorithm": "string",
   "DestinationEncryptionContext": { 
      "string" : "string" 
   },
   "DestinationKeyId": "string",
   "DryRun": boolean,
   "DryRunModifiers": [ "string" ],
   "GrantTokens": [ "string" ],
   "SourceEncryptionAlgorithm": "string",
   "SourceEncryptionContext": { 
      "string" : "string" 
   },
   "SourceKeyId": "string"
}

Request Parameters

For information about the parameters that are common to all actions, see Common Parameters.

The request accepts the following data in JSON format.

Note

In the following list, the required parameters are described first.

DestinationKeyId

A unique identifier for the KMS key that is used to reencrypt the data. Specify a symmetric encryption KMS key or an asymmetric KMS key with a KeyUsage value of ENCRYPT_DECRYPT. To find the KeyUsage value of a KMS key, use the DescribeKey operation.

To specify a KMS key, use its key ID, key ARN, alias name, or alias ARN. When using an alias name, prefix it with "alias/". To specify a KMS key in a different AWS account, you must use the key ARN or alias ARN.

For example:

Key ID: 1234abcd-12ab-34cd-56ef-1234567890ab
Key ARN: arn:aws:kms:us-east-2:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab
Alias name: alias/ExampleAlias
Alias ARN: arn:aws:kms:us-east-2:111122223333:alias/ExampleAlias

To get the key ID and key ARN for a KMS key, use ListKeys or DescribeKey. To get the alias name and alias ARN, use ListAliases.

Type: String

Length Constraints: Minimum length of 1. Maximum length of 2048.

Required: Yes

CiphertextBlob

Ciphertext of the data to reencrypt.

This parameter is required in all cases except when DryRun is true and DryRunModifiers is set to IGNORE_CIPHERTEXT.

Type: Base64-encoded binary data object

Length Constraints: Minimum length of 1. Maximum length of 6144.

Required: No

DestinationEncryptionAlgorithm

Specifies the encryption algorithm that AWS KMS will use to reecrypt the data after it has decrypted it. The default value, SYMMETRIC_DEFAULT, represents the encryption algorithm used for symmetric encryption KMS keys.

This parameter is required only when the destination KMS key is an asymmetric KMS key.

Type: String

Valid Values: SYMMETRIC_DEFAULT | RSAES_OAEP_SHA_1 | RSAES_OAEP_SHA_256 | SM2PKE

Required: No

DestinationEncryptionContext

Specifies that encryption context to use when the reencrypting the data.

Important

Do not include confidential or sensitive information in this field. This field may be displayed in plaintext in CloudTrail logs and other output.

A destination encryption context is valid only when the destination KMS key is a symmetric encryption KMS key. The standard ciphertext format for asymmetric KMS keys does not include fields for metadata.

An encryption context is a collection of non-secret key-value pairs that represent additional authenticated data. When you use an encryption context to encrypt data, you must specify the same (an exact case-sensitive match) encryption context to decrypt the data. An encryption context is supported only on operations with symmetric encryption KMS keys. On operations with symmetric encryption KMS keys, an encryption context is optional, but it is strongly recommended.

For more information, see Encryption context in the AWS Key Management Service Developer Guide.

Type: String to string map

Required: No