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DecryptCommand

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

Encrypt
GenerateDataKey
GenerateDataKeyPair
GenerateDataKeyWithoutPlaintext
GenerateDataKeyPairWithoutPlaintext

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 Key Management Service Developer Guide.

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

If the ciphertext was encrypted under a symmetric encryption KMS key, the KeyId 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 KMS key is always recommended as a best practice. When you use the KeyId parameter to specify a KMS key, 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 Key Management Service Developer Guide.

Decrypt also supports Amazon Web Services Nitro Enclaves , which provide an isolated compute environment in Amazon EC2. To call Decrypt for a Nitro enclave, use the Amazon Web Services Nitro Enclaves SDK or any Amazon Web Services 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 KMS and Amazon Web Services Nitro Enclaves, see How Amazon Web Services Nitro Enclaves uses KMS in the 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 KMS keys in the Key Management Service Developer Guide.

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

Required permissions: kms:Decrypt (key policy)

Related operations:

Encrypt
GenerateDataKey
GenerateDataKeyPair
ReEncrypt

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

Example Syntax

Use a bare-bones client and the command you need to make an API call.

import { KMSClient, DecryptCommand } from "@aws-sdk/client-kms"; // ES Modules import
// const { KMSClient, DecryptCommand } = require("@aws-sdk/client-kms"); // CommonJS import
const client = new KMSClient(config);
const input = { // DecryptRequest
  CiphertextBlob: new Uint8Array(), // e.g. Buffer.from("") or new TextEncoder().encode("")   // required
  EncryptionContext: { // EncryptionContextType
    "<keys>": "STRING_VALUE",
  },
  GrantTokens: [ // GrantTokenList
    "STRING_VALUE",
  ],
  KeyId: "STRING_VALUE",
  EncryptionAlgorithm: "SYMMETRIC_DEFAULT" || "RSAES_OAEP_SHA_1" || "RSAES_OAEP_SHA_256" || "SM2PKE",
  Recipient: { // RecipientInfo
    KeyEncryptionAlgorithm: "RSAES_OAEP_SHA_256",
    AttestationDocument: new Uint8Array(), // e.g. Buffer.from("") or new TextEncoder().encode("")
  },
  DryRun: true || false,
};
const command = new DecryptCommand(input);
const response = await client.send(command);
// { // DecryptResponse
//   KeyId: "STRING_VALUE",
//   Plaintext: new Uint8Array(),
//   EncryptionAlgorithm: "SYMMETRIC_DEFAULT" || "RSAES_OAEP_SHA_1" || "RSAES_OAEP_SHA_256" || "SM2PKE",
//   CiphertextForRecipient: new Uint8Array(),
// };

Example Usage

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DecryptCommand Input

See DecryptCommandInput for more details

Parameter	Type	Description
`CiphertextBlob` Required	`Uint8Array \| undefined`	Ciphertext to be decrypted. The blob includes metadata.
`DryRun`	`boolean \| undefined`	Checks if your request will succeed. `DryRun` is an optional parameter. To learn more about how to use this parameter, see Testing your KMS API calls in the Key Management Service Developer Guide.
`EncryptionAlgorithm`	`EncryptionAlgorithmSpec \| undefined`	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.
`EncryptionContext`	`Record<string, string> \| undefined`	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 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 Key Management Service Developer Guide.
`GrantTokens`	`string[] \| undefined`	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 Key Management Service Developer Guide.
`KeyId`	`string \| undefined`	Specifies the KMS key that 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, 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 Amazon Web Services 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.
`Recipient`	`RecipientInfo \| undefined`	A signed attestation document from an Amazon Web Services 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 Amazon Web Services Nitro Enclaves. To include this parameter, use the Amazon Web Services Nitro Enclaves SDK or any Amazon Web Services SDK. When you use this parameter, instead of returning the plaintext data, 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 KMS and Amazon Web Services Nitro Enclaves, see How Amazon Web Services Nitro Enclaves uses KMS in the Key Management Service Developer Guide.

DecryptCommand Output

See DecryptCommandOutput for details

Parameter	Type	Description
`$metadata` Required	`ResponseMetadata`	Metadata pertaining to this request.
`CiphertextForRecipient`	`Uint8Array \| undefined`	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 Amazon Web Services Nitro enclave. For information about the interaction between KMS and Amazon Web Services Nitro Enclaves, see How Amazon Web Services Nitro Enclaves uses KMS in the Key Management Service Developer Guide.
`EncryptionAlgorithm`	`EncryptionAlgorithmSpec \| undefined`	The encryption algorithm that was used to decrypt the ciphertext.
`KeyId`	`string \| undefined`	The Amazon Resource Name (key ARN ) of the KMS key that was used to decrypt the ciphertext.
`Plaintext`	`Uint8Array \| undefined`	Decrypted plaintext data. When you use the HTTP API or the Amazon Web Services 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.

Throws

Name	Fault	Details
DependencyTimeoutException	server	The system timed out while trying to fulfill the request. You can retry the request.
DisabledException	client	The request was rejected because the specified KMS key is not enabled.
DryRunOperationException	client	The request was rejected because the DryRun parameter was specified.
IncorrectKeyException	client	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	client	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	client	The request was rejected because the specified grant token is not valid.
InvalidKeyUsageException	client	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.
KeyUnavailableException	server	The request was rejected because the specified KMS key was not available. You can retry the request.
KMSInternalException	server	The request was rejected because an internal exception occurred. The request can be retried.
KMSInvalidStateException	client	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	client	The request was rejected because the specified entity or resource could not be found.
KMSServiceException		Base exception class for all service exceptions from KMS service.

Getting Started

References