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

Decrypt

Decrypts ciphertext that was encrypted by a KMS key using any of the following operations:

You can use this operation to decrypt ciphertext that was encrypted under a symmetric encryption KMS key or an asymmetric encryption KMS key. When the KMS key is asymmetric, you must specify the KMS key and the encryption algorithm that was used to encrypt the ciphertext. For information about asymmetric KMS keys, see Asymmetric KMS keys in the AWS Key Management Service Developer Guide.

The Decrypt operation also decrypts ciphertext that was encrypted outside of AWS KMS by the public key in an AWS KMS asymmetric KMS key. However, it cannot decrypt symmetric 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.

If the ciphertext was encrypted under a symmetric encryption KMS key, the KeyId 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 KMS key is always recommended as a best practice. When you use the KeyId parameter to specify a KMS key, AWS KMS only uses the KMS key you specify. If the ciphertext was encrypted under a different KMS key, the Decrypt operation fails. This practice ensures that you use the KMS key that you intend.

Whenever possible, use key policies to give users permission to call the Decrypt operation on a particular KMS key, instead of using IAM policies. Otherwise, you might create an IAM policy that gives the user Decrypt permission on all KMS keys. This user could decrypt ciphertext that was encrypted by KMS keys in other accounts if the key policy for the cross-account KMS key permits it. If you must use an IAM policy for Decrypt permissions, limit the user to particular KMS keys or particular trusted accounts. For details, see Best practices for IAM policies in the AWS Key Management Service Developer Guide.

Decrypt also supports AWS Nitro Enclaves, which provide an isolated compute environment in Amazon EC2. To call Decrypt for a Nitro enclave, use the AWS Nitro Enclaves SDK or any AWS SDK. Use the Recipient parameter to provide the attestation document for the enclave. Instead of the plaintext data, the response includes the plaintext data encrypted with the public key from the attestation document (CiphertextForRecipient). For information about the interaction between AWS KMS and AWS Nitro Enclaves, see How AWS Nitro Enclaves uses AWS KMS in the AWS Key Management Service Developer Guide.

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.

Cross-account use: Yes. If you use the KeyId parameter to identify a KMS key in a different AWS account, specify the key ARN or the alias ARN of the KMS key.

Required permissions: kms:Decrypt (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,
   "DryRun": boolean,
   "EncryptionAlgorithm": "string",
   "EncryptionContext": { 
      "string" : "string" 
   },
   "GrantTokens": [ "string" ],
   "KeyId": "string",
   "Recipient": { 
      "AttestationDocument": blob,
      "KeyEncryptionAlgorithm": "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 to be decrypted. The blob includes metadata.

Type: Base64-encoded binary data object

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

Required: Yes

DryRun

Checks if your request will succeed. DryRun is an optional parameter.

To learn more about how to use this parameter, see Testing your permissions in the AWS Key Management Service Developer Guide.

Type: Boolean

Required: No

EncryptionAlgorithm

Specifies the encryption algorithm that will be used to decrypt the ciphertext. Specify the same algorithm that was used to encrypt the data. If you specify a different algorithm, the Decrypt operation fails.

This parameter is required only when the ciphertext was encrypted under an asymmetric KMS key. The default value, SYMMETRIC_DEFAULT, represents the only supported algorithm that is valid for symmetric encryption KMS keys.

Type: String

Valid Values: SYMMETRIC_DEFAULT | RSAES_OAEP_SHA_1 | RSAES_OAEP_SHA_256 | SM2PKE

Required: No

EncryptionContext

Specifies the encryption context to use when decrypting the data. An encryption context is valid only for cryptographic operations with a symmetric encryption KMS key. The standard asymmetric encryption algorithms and HMAC algorithms that AWS KMS uses do not support an encryption context.

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

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 and Using a 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

KeyId

Specifies the KMS key that AWS KMS uses to decrypt the ciphertext.

Enter a key ID of the KMS key that was used to encrypt the ciphertext. If you identify a different KMS key, the Decrypt operation throws an IncorrectKeyException.

This parameter is required only when the ciphertext was encrypted under an asymmetric KMS key. If you used a symmetric encryption KMS key, AWS KMS can get the KMS key 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 KMS key that you intend.

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: No

Recipient

A signed attestation document from an AWS Nitro enclave and the encryption algorithm to use with the enclave's public key. The only valid encryption algorithm is RSAES_OAEP_SHA_256.

This parameter only supports attestation documents for AWS Nitro Enclaves. To include this parameter, use the AWS Nitro Enclaves SDK or any AWS SDK.

When you use this parameter, instead of returning the plaintext data, AWS KMS encrypts the plaintext data with the public key in the attestation document, and returns the resulting ciphertext in the CiphertextForRecipient field in the response. This ciphertext can be decrypted only with the private key in the enclave. The Plaintext field in the response is null or empty.

For information about the interaction between AWS KMS and AWS Nitro Enclaves, see How AWS Nitro Enclaves uses AWS KMS in the AWS Key Management Service Developer Guide.

Type: RecipientInfo object

Required: No

Response Syntax


{
   "CiphertextForRecipient": blob,
   "EncryptionAlgorithm": "string",
   "KeyId": "string",
   "Plaintext": blob
}

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.

CiphertextForRecipient

The plaintext data encrypted with the public key in the attestation document.

This field is included in the response only when the Recipient parameter in the request includes a valid attestation document from an AWS Nitro enclave. For information about the interaction between AWS KMS and AWS Nitro Enclaves, see How AWS Nitro Enclaves uses AWS KMS in the AWS Key Management Service Developer Guide.

Type: Base64-encoded binary data object

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

EncryptionAlgorithm

The encryption algorithm that was used to decrypt the ciphertext.

Type: String

Valid Values: SYMMETRIC_DEFAULT | RSAES_OAEP_SHA_1 | RSAES_OAEP_SHA_256 | SM2PKE

KeyId

The Amazon Resource Name (key ARN) of the KMS key that was used to decrypt the ciphertext.

Type: String

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

Plaintext

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

If the response includes the CiphertextForRecipient field, the Plaintext field is null or empty.

Type: Base64-encoded binary data object

Length Constraints: Minimum length of 1. Maximum length of 4096.

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. You can retry the request.

HTTP Status Code: 500

DisabledException

The request was rejected because the specified KMS key is not enabled.

HTTP Status Code: 400

DryRunOperationException

The request was rejected because the DryRun parameter was specified.

HTTP Status Code: 400

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.

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 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. For deriving key agreement secrets, the KeyUsage must be KEY_AGREEMENT. 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.

HTTP Status Code: 400

KeyUnavailableException

The request was rejected because the specified KMS key 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.

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 AWS KMS operation, see Key states of AWS KMS keys in the AWS 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.

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 Decrypt.


POST / HTTP/1.1
Host: kms.us-west-2.amazonaws.com
Content-Length: 293
X-Amz-Target: TrentService.Decrypt
X-Amz-Date: 20160517T204035Z
Content-Type: application/x-amz-json-1.1
Authorization: AWS4-HMAC-SHA256\
 Credential=AKIAI44QH8DHBEXAMPLE/20160517/us-west-2/kms/aws4_request,\
 SignedHeaders=content-type;host;x-amz-date;x-amz-target,\
 Signature=545b0c3bfd9223b8ef7e6293ef3ccac37a83d415ee3112d2e5c70727d2a49c46

{
  "KeyId": "arn:aws:kms:us-west-2:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab",  
  "CiphertextBlob": "CiDPoCH188S65r5Cy7pAhIFJMXDlU7mewhSlYUpuQIVBrhKmAQEBAgB4z6Ah9fPEuua+Qsu6QISBSTFw5VO5nsIUpWFKbkCFQa4AAAB9MHsGCSqGSIb3DQEHBqBuMGwCAQAwZwYJKoZIhvcNAQcBMB4GCWCGSAFlAwQBLjARBAxLc9b6QThC9jB/ZjYCARCAOt8la8qXLO5wB3JH2NlwWWzWRU2RKqpO9A/0psE5UWwkK6CnwoeC3Zj9Q0A66apZkbRglFfY1lTY+Tc="
}

Example Response

This example illustrates one usage of Decrypt.


HTTP/1.1 200 OK
Server: Server
Date: Tue, 17 May 2016 20:40:40 GMT
Content-Type: application/x-amz-json-1.1
Content-Length: 146
Connection: keep-alive
x-amzn-RequestId: 9e02f41f-1c6f-11e6-af63-ab8791945da7

{
  "KeyId": "arn:aws:kms:us-west-2:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab",
  "Plaintext": "VGhpcyBpcyBEYXkgMSBmb3IgdGhlIEludGVybmV0Cg==",
  "EncryptionAlgorithm": "SYMMETRIC_DEFAULT" 
}