aws kms decrypt

Decrypts ciphertext that was encrypted by a AWS KMS customer master key (CMK) 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 or asymmetric CMK. When the CMK is asymmetric, you must specify the CMK and the encryption algorithm that was used to encrypt the ciphertext. For information about symmetric and asymmetric CMKs, see Using Symmetric and Asymmetric CMKs in the AWS Key Management Service Developer Guide. The Decrypt operation also decrypts ciphertext that was encrypted outside of AWS KMS by the public key in an AWS KMS asymmetric CMK. However, it cannot decrypt ciphertext produced by other libraries, such as the AWS Encryption SDK or Amazon S3 client-side encryption. These libraries return a ciphertext format that is incompatible with AWS KMS. If the ciphertext was encrypted under a symmetric CMK, the KeyId parameter is optional. AWS 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 CMK ID. However, specifying the CMK is always recommended as a best practice. When you use the KeyId parameter to specify a CMK, AWS KMS only uses the CMK you specify. If the ciphertext was encrypted under a different CMK, the Decrypt operation fails. This practice ensures that you use the CMK that you intend. Whenever possible, use key policies to give users permission to call the Decrypt operation on a particular CMK, instead of using IAM policies. Otherwise, you might create an IAM user policy that gives the user Decrypt permission on all CMKs. This user could decrypt ciphertext that was encrypted by CMKs in other accounts if the key policy for the cross-account CMK permits it. If you must use an IAM policy for Decrypt permissions, limit the user to particular CMKs or particular trusted accounts. For details, see Best practices for IAM policies in the AWS Key Management Service Developer Guide. The CMK that you use for this operation must be in a compatible key state. For details, see How Key State Affects Use of a Customer Master Key in the AWS Key Management Service Developer Guide. Cross-account use: Yes. You can decrypt a ciphertext using a CMK in a different AWS account. Required permissions: kms:Decrypt (key policy) Related operations: Encrypt GenerateDataKey GenerateDataKeyPair ReEncrypt

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