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 Key Management Service Developer Guide.
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,
Decrypt operation fails. This practice ensures that you use the KMS key that
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
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.
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
Required permissions: kms:Decrypt (key policy)