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 user 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.
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. To perform this operation with a KMS key in a different Amazon Web Services account, specify
the key ARN or alias ARN in the value of the KeyId parameter.
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
Decryptoperation 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
KeyIdparameter 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 theKeyIdparameter to specify a KMS key, KMS only uses the KMS key you specify. If the ciphertext was encrypted under a different KMS key, theDecryptoperation 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
Decryptoperation on a particular KMS key, instead of using IAM policies. Otherwise, you might create an IAM user policy that gives the userDecryptpermission 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 forDecryptpermissions, 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.Applications in Amazon Web Services Nitro Enclaves can call this operation by using the Amazon Web Services Nitro Enclaves Development Kit. For information about the supporting parameters, see How Amazon Web Services Nitro Enclaves use 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. To perform this operation with a KMS key in a different Amazon Web Services account, specify the key ARN or alias ARN in the value of the
KeyIdparameter.Required permissions: kms:Decrypt (key policy)
Related operations:
Encrypt
GenerateDataKey
GenerateDataKeyPair
ReEncrypt
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 command = new DecryptCommand(input); const response = await client.send(command);DecryptCommandInput for command's
inputshape.DecryptCommandOutput for command's
responseshape.config for KMSClient's
configshape.