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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.
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.
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.
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.
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.
Base exception class for all service exceptions from KMS service.
Example
To decrypt data with a symmetric encryption KMS key
// The following example decrypts data that was encrypted with a symmetric encryption KMS key. The KeyId is not required when decrypting with a symmetric encryption key, but it is a best practice. constinput = { "CiphertextBlob":"<binary data>", "KeyId":"arn:aws:kms:us-west-2:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab" }; constcommand = newDecryptCommand(input); constresponse = awaitclient.send(command); /* response == { "EncryptionAlgorithm": "SYMMETRIC_DEFAULT", "KeyId": "arn:aws:kms:us-west-2:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab", "Plaintext": "<binary data>" } */ // example id: to-decrypt-data-1
Example
To decrypt data with an asymmetric encryption KMS key
// The following example decrypts data that was encrypted with an asymmetric encryption KMS key. When the KMS encryption key is asymmetric, you must specify the KMS key ID and the encryption algorithm that was used to encrypt the data. constinput = { "CiphertextBlob":"<binary data>", "EncryptionAlgorithm":"RSAES_OAEP_SHA_256", "KeyId":"0987dcba-09fe-87dc-65ba-ab0987654321" }; constcommand = newDecryptCommand(input); constresponse = awaitclient.send(command); /* response == { "EncryptionAlgorithm": "RSAES_OAEP_SHA_256", "KeyId": "arn:aws:kms:us-west-2:111122223333:key/0987dcba-09fe-87dc-65ba-ab0987654321", "Plaintext": "<binary data>" } */ // example id: to-decrypt-data-2
Example
To decrypt data for a Nitro enclave
// The following Decrypt example includes the Recipient parameter with a signed attestation document from an AWS Nitro enclave. Instead of returning the decrypted data in plaintext (Plaintext), the operation returns the decrypted data encrypted by the public key from the attestation document (CiphertextForRecipient). constinput = { "CiphertextBlob":"<binary data>", "KeyId":"arn:aws:kms:us-west-2:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab", "Recipient": { "AttestationDocument":"<attestation document>", "KeyEncryptionAlgorithm":"RSAES_OAEP_SHA_256" } }; constcommand = newDecryptCommand(input); constresponse = awaitclient.send(command); /* response == { "CiphertextForRecipient": "<binary data>", "KeyId": "arn:aws:kms:us-west-2:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab", "Plaintext": "" } */ // example id: to-decrypt-data-for-a-nitro-enclave-2
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 theKeyId
parameter to specify a KMS key, KMS only uses the KMS key you specify. If the ciphertext was encrypted under a different KMS key, theDecrypt
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 userDecrypt
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 forDecrypt
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 callDecrypt
for a Nitro enclave, use the Amazon Web Services Nitro Enclaves SDK or any Amazon Web Services SDK. Use theRecipient
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
Example
Use a bare-bones client and the command you need to make an API call.
Param
DecryptCommandInput
Returns
DecryptCommandOutput
See
input
shape.response
shape.config
shape.Throws
DependencyTimeoutException (server fault)
The system timed out while trying to fulfill the request. You can retry the request.
Throws
DisabledException (client fault)
The request was rejected because the specified KMS key is not enabled.
Throws
IncorrectKeyException (client fault)
The request was rejected because the specified KMS key cannot decrypt the data. The
KeyId
in a Decrypt request and theSourceKeyId
in a ReEncrypt request must identify the same KMS key that was used to encrypt the ciphertext.Throws
InvalidCiphertextException (client fault)
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.
Throws
InvalidGrantTokenException (client fault)
The request was rejected because the specified grant token is not valid.
Throws
InvalidKeyUsageException (client fault)
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 beENCRYPT_DECRYPT
. For signing and verifying messages, theKeyUsage
must beSIGN_VERIFY
. For generating and verifying message authentication codes (MACs), theKeyUsage
must beGENERATE_VERIFY_MAC
. To find theKeyUsage
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.
Throws
KeyUnavailableException (server fault)
The request was rejected because the specified KMS key was not available. You can retry the request.
Throws
KMSInternalException (server fault)
The request was rejected because an internal exception occurred. The request can be retried.
Throws
KMSInvalidStateException (client fault)
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.
Throws
NotFoundException (client fault)
The request was rejected because the specified entity or resource could not be found.
Throws
KMSServiceException
Base exception class for all service exceptions from KMS service.
Example
To decrypt data with a symmetric encryption KMS key
Example
To decrypt data with an asymmetric encryption KMS key
Example
To decrypt data for a Nitro enclave