Decrypts ciphertext that was encrypted by a AWS KMS customer master key (CMK) using any of the following operations:
encrypt
generate_data_key
generate_data_key_pair
generate_data_key_without_plaintext
generate_data_key_pair_without_plaintext
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
generate_data_key
generate_data_key_pair
re_encrypt
kms_decrypt(CiphertextBlob, EncryptionContext, GrantTokens, KeyId,
EncryptionAlgorithm)A list with the following syntax:
list(
KeyId = "string",
Plaintext = raw,
EncryptionAlgorithm = "SYMMETRIC_DEFAULT"|"RSAES_OAEP_SHA_1"|"RSAES_OAEP_SHA_256"
)
[required] Ciphertext to be decrypted. The blob includes metadata.
Specifies the encryption context to use when decrypting the data. An encryption context is valid only for cryptographic operations with a symmetric CMK. The standard asymmetric encryption algorithms that AWS KMS uses do not support an encryption context.
An encryption context is a collection of non-secret key-value pairs that represents additional authenticated data. When you use an encryption context to encrypt data, you must specify the same (an exact case-sensitive match) encryption context to decrypt the data. An encryption context is optional when encrypting with a symmetric CMK, but it is highly recommended.
For more information, see Encryption Context in the AWS Key Management Service Developer Guide.
A list of grant tokens.
For more information, see Grant Tokens in the AWS Key Management Service Developer Guide.
Specifies the customer master key (CMK) that AWS KMS uses to decrypt the ciphertext. Enter a key ID of the CMK that was used to encrypt the ciphertext.
This parameter is required only when the ciphertext was encrypted under an asymmetric CMK. If you used a symmetric CMK, AWS KMS can get the CMK from metadata that it adds to the symmetric ciphertext blob. However, it is always recommended as a best practice. This practice ensures that you use the CMK that you intend.
To specify a CMK, use its key ID, Amazon Resource Name (ARN), alias
name, or alias ARN. When using an alias name, prefix it with "alias/".
To specify a CMK in a different AWS account, you must use the key ARN or
alias ARN.
For example:
Key ID: 1234abcd-12ab-34cd-56ef-1234567890ab
Key ARN:
arn:aws:kms:us-east-2:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab
Alias name: alias/ExampleAlias
Alias ARN: arn:aws:kms:us-east-2:111122223333:alias/ExampleAlias
To get the key ID and key ARN for a CMK, use
list_keys or describe_key. To
get the alias name and alias ARN, use
list_aliases.
Specifies the encryption algorithm that will be used to decrypt the
ciphertext. Specify the same algorithm that was used to encrypt the
data. If you specify a different algorithm, the decrypt
operation fails.
This parameter is required only when the ciphertext was encrypted under
an asymmetric CMK. The default value, SYMMETRIC_DEFAULT, represents
the only supported algorithm that is valid for symmetric CMKs.
svc$decrypt(
CiphertextBlob = raw,
EncryptionContext = list(
"string"
),
GrantTokens = list(
"string"
),
KeyId = "string",
EncryptionAlgorithm = "SYMMETRIC_DEFAULT"|"RSAES_OAEP_SHA_1"|"RSAES_OAEP_SHA_256"
)
if (FALSE) {
# The following example decrypts data that was encrypted with a customer
# master key (CMK) in AWS KMS.
svc$decrypt(
CiphertextBlob = "",
KeyId = "arn:aws:kms:us-west-2:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab"
)
}
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