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 use the
SourceKeyId
parameter to identify the CMK 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 CMK, 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 CMK ID. However, specifying the source CMK is always recommended as a best practice. When you use theSourceKeyId
parameter to specify a CMK, AWS KMS uses only the CMK you specify. If the ciphertext was encrypted under a different CMK, theReEncrypt
operation fails. This practice ensures that you use the CMK that you intend. -
To reencrypt the data, you must use the
DestinationKeyId
parameter specify 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.
The CMK that you use for this operation must be in a compatible key state. For details, see Key state: Effect on your CMK in the AWS Key Management Service Developer Guide.
Cross-account use: Yes. The source CMK and destination CMK can be in different AWS accounts. Either or both CMKs can be in a different account than the caller.
Required permissions:
-
kms:ReEncryptFrom permission on the source CMK (key policy)
-
kms:ReEncryptTo permission on the destination CMK (key policy)
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.
Related operations:
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.
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 ofENCRYPT_DECRYPT
. To find theKeyUsage
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.
Use a grant token when your permission to call this operation comes from a new grant that has not yet achieved eventual consistency. For more information, see Grant token 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
-
Specifies the customer master key (CMK) that AWS KMS will use to decrypt the ciphertext before it is re-encrypted. Enter a key ID of the CMK that was used to encrypt the ciphertext.
This parameter is required only when the ciphertext was encrypted under an asymmetric CMK. If you used a symmetric CMK, AWS KMS can get the CMK from metadata that it adds to the symmetric ciphertext blob. However, it is always recommended as a best practice. This practice ensures that you use the CMK that you intend.
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: 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 theSourceKeyId
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 beENCRYPT_DECRYPT
. For signing and verifying, theKeyUsage
must beSIGN_VERIFY
. To find theKeyUsage
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
This example illustrates one usage of ReEncrypt.
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* ReEncrypt 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
This example illustrates one usage of ReEncrypt.
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: