ReEncrypt - AWS Key Management Service

ReEncrypt

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

The ReEncrypt operation can decrypt ciphertext that was encrypted by using an AWS KMS CMK 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 CMK 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 CMK, you must identify the source CMK, that is, the CMK that encrypted the ciphertext. You must also supply the encryption algorithm that was used. This information is required to decrypt the data.

  • It is optional, but you can specify a source CMK even when the ciphertext was encrypted under a symmetric CMK. This ensures that the ciphertext is decrypted only by using a particular CMK. If the CMK that you specify cannot decrypt the ciphertext, the ReEncrypt operation fails.

  • To reencrypt the data, you must specify the destination CMK, that is, the CMK that re-encrypts the data after it is decrypted. You can select a symmetric or asymmetric CMK. If the destination CMK is an asymmetric CMK, you must also provide the encryption algorithm. The algorithm that you choose must be compatible with the CMK.

    Important

    When you use an asymmetric CMK to encrypt or reencrypt data, be sure to record the CMK and encryption algorithm that you choose. You will be required to provide the same CMK and encryption algorithm when you decrypt the data. If the CMK and algorithm do not match the values used to encrypt the data, the decrypt operation fails.

    You are not required to supply the CMK ID and encryption algorithm when you decrypt with symmetric CMKs 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.

Unlike other AWS KMS API operations, ReEncrypt callers must have two permissions:

  • kms:ReEncryptFrom permission on the source CMK

  • kms:ReEncryptTo permission on the destination CMK

To permit reencryption from or to a CMK, 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 CMK. But you must include it manually when you create a CMK programmatically or when you use the PutKeyPolicy operation to set a key policy.

The CMK that you use for this operation must be in a compatible key state. For details, see How Key State Affects Use of a Customer Master Key in the AWS Key Management Service Developer Guide.

Request Syntax

{ "CiphertextBlob": blob, "DestinationEncryptionAlgorithm": "string", "DestinationEncryptionContext": { "string" : "string" }, "DestinationKeyId": "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.

CiphertextBlob

Ciphertext of the data to reencrypt.

Type: Base64-encoded binary data object

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

Required: Yes

DestinationKeyId

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

To specify a CMK, use its key ID, Amazon Resource Name (ARN), alias name, or alias ARN. When using an alias name, prefix it with "alias/". To specify a CMK 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 CMK, 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

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 CMKs.

This parameter is required only when the destination CMK is an asymmetric CMK.

Type: String

Valid Values: SYMMETRIC_DEFAULT | RSAES_OAEP_SHA_1 | RSAES_OAEP_SHA_256

Required: No

DestinationEncryptionContext

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

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

An encryption context is a collection of non-secret key-value pairs that represents 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 optional when encrypting with a symmetric CMK, but it is highly recommended.

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

Type: String to string map

Required: No

GrantTokens

A list of grant tokens.

For more information, see Grant Tokens in the AWS Key Management Service Developer Guide.

Type: Array of strings

Array Members: Minimum number of 0 items. Maximum number of 10 items.

Length Constraints: Minimum length of 1. Maximum length of 8192.

Required: No

SourceEncryptionAlgorithm

Specifies the encryption algorithm that AWS KMS will use to decrypt the ciphertext before it is reencrypted. The default value, SYMMETRIC_DEFAULT, represents the algorithm used for symmetric CMKs.

Specify the same algorithm that was used to encrypt the ciphertext. If you specify a different algorithm, the decrypt attempt fails.

This parameter is required only when the ciphertext was encrypted under an asymmetric CMK.

Type: String

Valid Values: SYMMETRIC_DEFAULT | RSAES_OAEP_SHA_1 | RSAES_OAEP_SHA_256

Required: No

SourceEncryptionContext

Specifies the encryption context to use to decrypt the ciphertext. Enter the same encryption context that was used to encrypt the ciphertext.

An encryption context is a collection of non-secret key-value pairs that represents 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 optional when encrypting with a symmetric CMK, but it is highly recommended.

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

Type: String to string map

Required: No

SourceKeyId

A unique identifier for the CMK that is used to decrypt the ciphertext before it reencrypts it using the destination CMK.

This parameter is required only when the ciphertext was encrypted under an asymmetric CMK. Otherwise, AWS KMS uses the metadata that it adds to the ciphertext blob to determine which CMK was used to encrypt the ciphertext. However, you can use this parameter to ensure that a particular CMK (of any kind) is used to decrypt the ciphertext before it is reencrypted.

If you specify a KeyId value, the decrypt part of the ReEncrypt operation succeeds only if the specified CMK was used to encrypt the ciphertext.

To specify a CMK, use its key ID, Amazon Resource Name (ARN), alias name, or alias ARN. When using an alias name, prefix it with "alias/".

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 CMK, 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: No

Response Syntax

{ "CiphertextBlob": blob, "DestinationEncryptionAlgorithm": "string", "KeyId": "string", "SourceEncryptionAlgorithm": "string", "SourceKeyId": "string" }

Response Elements

If the action is successful, the service sends back an HTTP 200 response.

The following data is returned in JSON format by the service.

CiphertextBlob

The reencrypted data. When you use the HTTP API or the AWS CLI, the value is Base64-encoded. Otherwise, it is not Base64-encoded.

Type: Base64-encoded binary data object

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

DestinationEncryptionAlgorithm

The encryption algorithm that was used to reencrypt the data.

Type: String

Valid Values: SYMMETRIC_DEFAULT | RSAES_OAEP_SHA_1 | RSAES_OAEP_SHA_256

KeyId

The Amazon Resource Name (key ARN) of the CMK that was used to reencrypt the data.

Type: String

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

SourceEncryptionAlgorithm

The encryption algorithm that was used to decrypt the ciphertext before it was reencrypted.

Type: String

Valid Values: SYMMETRIC_DEFAULT | RSAES_OAEP_SHA_1 | RSAES_OAEP_SHA_256

SourceKeyId

Unique identifier of the CMK used to originally encrypt the data.

Type: String

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

Errors

For information about the errors that are common to all actions, see Common Errors.

DependencyTimeoutException

The system timed out while trying to fulfill the request. The request can be retried.

HTTP Status Code: 500

DisabledException

The request was rejected because the specified CMK is not enabled.

HTTP Status Code: 400

IncorrectKeyException

The request was rejected because the specified CMK cannot decrypt the data. The KeyId in a Decrypt request and the SourceKeyId in a ReEncrypt request must identify the same CMK that was used to encrypt the ciphertext.

HTTP Status Code: 400

InvalidCiphertextException

From the Decrypt or ReEncrypt operation, the request was rejected because the specified ciphertext, or additional authenticated data incorporated into the ciphertext, such as the encryption context, is corrupted, missing, or otherwise invalid.

From the ImportKeyMaterial operation, the request was rejected because AWS KMS could not decrypt the encrypted (wrapped) key material.

HTTP Status Code: 400

InvalidGrantTokenException

The request was rejected because the specified grant token is not valid.

HTTP Status Code: 400

InvalidKeyUsageException

The request was rejected for one of the following reasons:

  • The KeyUsage value of the CMK is incompatible with the API operation.

  • The encryption algorithm or signing algorithm specified for the operation is incompatible with the type of key material in the CMK (CustomerMasterKeySpec).

For encrypting, decrypting, re-encrypting, and generating data keys, the KeyUsage must be ENCRYPT_DECRYPT. For signing and verifying, the KeyUsage must be SIGN_VERIFY. To find the KeyUsage of a CMK, use the DescribeKey operation.

To find the encryption or signing algorithms supported for a particular CMK, use the DescribeKey operation.

HTTP Status Code: 400

KeyUnavailableException

The request was rejected because the specified CMK was not available. You can retry the request.

HTTP Status Code: 500

KMSInternalException

The request was rejected because an internal exception occurred. The request can be retried.

HTTP Status Code: 500

KMSInvalidStateException

The request was rejected because the state of the specified resource is not valid for this request.

For more information about how key state affects the use of a CMK, see How Key State Affects Use of a Customer Master Key in the AWS Key Management Service Developer Guide .

HTTP Status Code: 400

NotFoundException

The request was rejected because the specified entity or resource could not be found.

HTTP Status Code: 400

Examples

The following examples are formatted for legibility.

Example Request

POST / HTTP/1.1 Host: kms.us-east-2.amazonaws.com Content-Length: 306 X-Amz-Target: TrentService.ReEncrypt X-Amz-Date: 20161207T225816Z Content-Type: application/x-amz-json-1.1 Authorization: AWS4-HMAC-SHA256\ Credential=AKIAI44QH8DHBEXAMPLE/20161207/us-east-2/kms/aws4_request,\ SignedHeaders=content-type;host;x-amz-date;x-amz-target,\ Signature=7afd339e2a680e0726592ddf687aabe48e1d8a7933a60ebbdc0154b8e2936ef2 { "SourceKeyId": "arn:aws:kms:us-east-2:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab", "DestinationKeyId": "0987dcba-09fe-87dc-65ba-ab0987654321", "CiphertextBlob": "AQECAHj/M9MyvNsMT8kW+K5DVkMfunTHr0w6V6crnuAGw80uRwAAAH0wewYJKoZIhvcNAQcGoG4wbAIBADBnBgkqhkiG9w0BBwEwHgYJYIZIAWUDBAEuMBEEDPXExREUtnnGy1wC3wIBEIA6LvpU7BRMW+FSkUmNmmE0H0aHHRYRD6XqUnaCNnzAuhhq4VTGBfii6oWtjVU83pGmradvUawxE/tbCg==" }

Example Response

HTTP/1.1 200 OK Server: Server Date: Wed, 07 Dec 2016 22:58:17 GMT Content-Type: application/x-amz-json-1.1 Content-Length: 423 Connection: keep-alive x-amzn-RequestId: a434eca2-bcd0-11e6-b60b-ffb5eb2d1d15 { "CiphertextBlob": "AQECAHjRYf5WytIc0C857tFSnBaPn2F8DgfmThbJlGfR8P3WlwAAAH0wewYJKoZIhvcNAQcGoG4wbAIBADBnBgkqhkiG9w0BBwEwHgYJYIZIAWUDBAEuMBEEDIwicafp/vwjXjPBhQIBEIA6wjfzufQPhuU+nVqa3Kj4nqSTdhDw1PTkImKCUEuvQDui6qsooyB4Qxe8OOBqciRNC7ENQN8lKaEijg==", "KeyId": "arn:aws:kms:us-east-2:111122223333:key/0987dcba-09fe-87dc-65ba-ab0987654321", "SourceKeyId": "arn:aws:kms:us-east-2:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab", "SourceEncryptionAlgorithm": "SYMMETRIC_DEFAULT", "DestinationEncryptionAlgorithm": "SYMMETRIC_DEFAULT" }

See Also

For more information about using this API in one of the language-specific AWS SDKs, see the following: