decrypt

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.

Samples

import aws.sdk.kotlin.services.kms.model.EncryptionAlgorithmSpec

fun main() { 
   //sampleStart 
   // 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.
val resp = kmsClient.decrypt {
    ciphertextBlob = "<binary data>".encodeAsByteArray()
    keyId = "0987dcba-09fe-87dc-65ba-ab0987654321"
    encryptionAlgorithm = EncryptionAlgorithmSpec.fromValue("RSAES_OAEP_SHA_256")
} 
   //sampleEnd
}

import aws.sdk.kotlin.services.kms.model.EncryptionAlgorithmSpec

fun main() { 
   //sampleStart 
   // 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.
val resp = kmsClient.decrypt {
    ciphertextBlob = "<binary data>".encodeAsByteArray()
    keyId = "arn:aws:kms:us-west-2:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab"
} 
   //sampleEnd
}