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Decrypts ciphertext and then reencrypts it entirely within 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 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 KMS. However, it cannot decrypt ciphertext produced by other
libraries, such as the Amazon
Web Services Encryption SDK or Amazon
S3 client-side encryption. These libraries return a ciphertext format that is
incompatible with 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. 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, 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.
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 KMS stores this information in the ciphertext blob. 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 KMS keys in the Key Management Service Developer Guide.
Cross-account use: Yes. The source KMS key and destination KMS key can be in different Amazon Web Services accounts. Either or both KMS keys can be in a different account than the caller. To specify a KMS key in a different account, you must use its key ARN or alias ARN.
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 KMS API follows an eventual consistency model. For more information, see KMS eventual consistency.
For .NET Core this operation is only available in asynchronous form. Please refer to ReEncryptAsync.
Namespace: Amazon.KeyManagementService
Assembly: AWSSDK.KeyManagementService.dll
Version: 3.x.y.z
public virtual ReEncryptResponse ReEncrypt( ReEncryptRequest request )
Container for the necessary parameters to execute the ReEncrypt service method.
| Exception | Condition |
|---|---|
| DependencyTimeoutException | The system timed out while trying to fulfill the request. You can retry the request. |
| DisabledException | The request was rejected because the specified KMS key is not enabled. |
| DryRunOperationException | The request was rejected because the DryRun parameter was specified. |
| IncorrectKeyException | The request was rejected because the specified KMS key cannot decrypt the data. The KeyId in a Decrypt request and the SourceKeyId in a ReEncrypt request must identify the same KMS key that was used to encrypt the ciphertext. |
| 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 KMS could not decrypt the encrypted (wrapped) key material. |
| InvalidGrantTokenException | The request was rejected because the specified grant token is not valid. |
| InvalidKeyUsageException | The request was rejected for one of the following reasons: The KeyUsage value of the KMS key 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 KMS key (KeySpec). For encrypting, decrypting, re-encrypting, and generating data keys, the KeyUsage must be ENCRYPT_DECRYPT. For signing and verifying messages, the KeyUsage must be SIGN_VERIFY. For generating and verifying message authentication codes (MACs), the KeyUsage must be GENERATE_VERIFY_MAC. To find the KeyUsage of a KMS key, use the DescribeKey operation. To find the encryption or signing algorithms supported for a particular KMS key, use the DescribeKey operation. |
| KeyUnavailableException | The request was rejected because the specified KMS key was not available. You can retry the request. |
| KMSInternalException | The request was rejected because an internal exception occurred. The request can be retried. |
| KMSInvalidStateException | The request was rejected because the state of the specified resource is not valid for this request. This exceptions means one of the following: The key state of the KMS key is not compatible with the operation. To find the key state, use the DescribeKey operation. For more information about which key states are compatible with each KMS operation, see Key states of KMS keys in the Key Management Service Developer Guide. For cryptographic operations on KMS keys in custom key stores, this exception represents a general failure with many possible causes. To identify the cause, see the error message that accompanies the exception. |
| NotFoundException | The request was rejected because the specified entity or resource could not be found. |
The following example reencrypts data with the specified KMS key.
var client = new AmazonKeyManagementServiceClient();
var response = client.ReEncrypt(new ReEncryptRequest
{
CiphertextBlob = new MemoryStream(<binary data>), // The data to reencrypt.
DestinationKeyId = "0987dcba-09fe-87dc-65ba-ab0987654321" // The identifier of the KMS key to use to reencrypt the data. You can use any valid key identifier.
});
MemoryStream ciphertextBlob = response.CiphertextBlob; // The reencrypted data.
string keyId = response.KeyId; // The ARN of the KMS key that was used to reencrypt the data.
string sourceKeyId = response.SourceKeyId; // The ARN of the KMS key that was originally used to encrypt the data.
.NET Framework:
Supported in: 4.5, 4.0, 3.5