2026/02/16 - AWS Key Management Service - 2 updated api methods
Changes Added support for Decrypt and ReEncrypt API's to use dry run feature without ciphertext for authorization validation
{'DryRunModifiers': ['IGNORE_CIPHERTEXT']}
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 and NitroTPM, which provide attested environments in Amazon EC2. To call Decrypt for a Nitro enclave or NitroTPM, 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 attested environment. 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 or Amazon Web Services NitroTPM, see Cryptographic attestation support in 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.
See also: AWS API Documentation
Request Syntax
client.decrypt(
CiphertextBlob=b'bytes',
EncryptionContext={
'string': 'string'
},
GrantTokens=[
'string',
],
KeyId='string',
EncryptionAlgorithm='SYMMETRIC_DEFAULT'|'RSAES_OAEP_SHA_1'|'RSAES_OAEP_SHA_256'|'SM2PKE',
Recipient={
'KeyEncryptionAlgorithm': 'RSAES_OAEP_SHA_256',
'AttestationDocument': b'bytes'
},
DryRun=True|False,
DryRunModifiers=[
'IGNORE_CIPHERTEXT',
]
)
bytes
Ciphertext to be decrypted. The blob includes metadata.
This parameter is required in all cases except when DryRun is true and DryRunModifiers is set to IGNORE_CIPHERTEXT.
dict
Specifies the encryption context to use when decrypting the data. An encryption context is valid only for cryptographic operations with a symmetric encryption KMS key. The standard asymmetric encryption algorithms and HMAC algorithms that KMS uses do not support an encryption context.
An encryption context is a collection of non-secret key-value pairs that represent 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 supported only on operations with symmetric encryption KMS keys. On operations with symmetric encryption KMS keys, an encryption context is optional, but it is strongly recommended.
For more information, see Encryption context in the Key Management Service Developer Guide.
(string) --
(string) --
list
A list of grant tokens.
Use a grant token when your permission to call this operation comes from a new grant that has not yet achieved eventual consistency. For more information, see Grant token and Using a grant token in the Key Management Service Developer Guide.
(string) --
string
Specifies the KMS key that KMS uses to decrypt the ciphertext.
Enter a key ID of the KMS key that was used to encrypt the ciphertext. If you identify a different KMS key, the Decrypt operation throws an IncorrectKeyException.
This parameter is required only when the ciphertext was encrypted under an asymmetric KMS key or when DryRun is true and DryRunModifiers is set to IGNORE_CIPHERTEXT. If you used a symmetric encryption KMS key, KMS can get the KMS key 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 KMS key that you intend.
To specify a KMS key, use its key ID, key ARN, alias name, or alias ARN. When using an alias name, prefix it with "alias/". To specify a KMS key in a different Amazon Web Services 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 KMS key, use ListKeys or DescribeKey. To get the alias name and alias ARN, use ListAliases.
string
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 KMS key. The default value, SYMMETRIC_DEFAULT, represents the only supported algorithm that is valid for symmetric encryption KMS keys.
dict
A signed attestation document from an Amazon Web Services Nitro enclave or NitroTPM, and the encryption algorithm to use with the public key in the attestation document. The only valid encryption algorithm is RSAES_OAEP_SHA_256.
This parameter supports the Amazon Web Services Nitro Enclaves SDK or any Amazon Web Services SDK for Amazon Web Services Nitro Enclaves. It supports any Amazon Web Services SDK for Amazon Web Services NitroTPM.
When you use this parameter, instead of returning the plaintext data, KMS encrypts the plaintext data with the public key in the attestation document, and returns the resulting ciphertext in the CiphertextForRecipient field in the response. This ciphertext can be decrypted only with the private key in the attested environment. The Plaintext field in the response is null or empty.
For information about the interaction between KMS and Amazon Web Services Nitro Enclaves or Amazon Web Services NitroTPM, see Cryptographic attestation support in KMS in the Key Management Service Developer Guide.
KeyEncryptionAlgorithm (string) --
The encryption algorithm that KMS should use with the public key for an Amazon Web Services Nitro Enclave or NitroTPM to encrypt plaintext values for the response. The only valid value is RSAES_OAEP_SHA_256.
AttestationDocument (bytes) --
The attestation document for an Amazon Web Services Nitro Enclave or a NitroTPM. This document includes the enclave's public key.
boolean
Checks if your request will succeed. DryRun is an optional parameter.
To learn more about how to use this parameter, see Testing your permissions in the Key Management Service Developer Guide.
list
Specifies the modifiers to apply to the dry run operation. DryRunModifiers is an optional parameter that only applies when DryRun is set to true.
When set to IGNORE_CIPHERTEXT, KMS performs only authorization validation without ciphertext validation. This allows you to test permissions without requiring a valid ciphertext blob.
To learn more about how to use this parameter, see Testing your permissions in the Key Management Service Developer Guide.
(string) --
dict
Response Syntax
{
'KeyId': 'string',
'Plaintext': b'bytes',
'EncryptionAlgorithm': 'SYMMETRIC_DEFAULT'|'RSAES_OAEP_SHA_1'|'RSAES_OAEP_SHA_256'|'SM2PKE',
'CiphertextForRecipient': b'bytes',
'KeyMaterialId': 'string'
}
Response Structure
(dict) --
KeyId (string) --
The Amazon Resource Name ( key ARN) of the KMS key that was used to decrypt the ciphertext.
Plaintext (bytes) --
Decrypted plaintext data. When you use the HTTP API or the Amazon Web Services CLI, the value is Base64-encoded. Otherwise, it is not Base64-encoded.
If the response includes the CiphertextForRecipient field, the Plaintext field is null or empty.
EncryptionAlgorithm (string) --
The encryption algorithm that was used to decrypt the ciphertext.
CiphertextForRecipient (bytes) --
The plaintext data encrypted with the public key from the attestation document. This ciphertext can be decrypted only by using a private key from the attested environment.
This field is included in the response only when the Recipient parameter in the request includes a valid attestation document from an Amazon Web Services Nitro enclave or NitroTPM. For information about the interaction between KMS and Amazon Web Services Nitro Enclaves or Amazon Web Services NitroTPM, see Cryptographic attestation support in KMS in the Key Management Service Developer Guide.
KeyMaterialId (string) --
The identifier of the key material used to decrypt the ciphertext. This field is present only when the operation uses a symmetric encryption KMS key. This field is omitted if the request includes the Recipient parameter.
{'DryRunModifiers': ['IGNORE_CIPHERTEXT']}
Decrypts ciphertext and then reencrypts it entirely within KMS. You can use this operation to change the KMS key under which data is encrypted, such as when you manually rotate a KMS key or change the KMS key that protects a ciphertext. You can also use it to reencrypt ciphertext under the same KMS key, such as to change the encryption context of a ciphertext.
The ReEncrypt operation can decrypt ciphertext that was encrypted by using a KMS key in an KMS operation, such as Encrypt or GenerateDataKey. It can also decrypt ciphertext that was encrypted by using the public key of an asymmetric KMS key outside of KMS. However, it cannot decrypt 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.
When you use the ReEncrypt operation, you need to provide information for the decrypt operation and the subsequent encrypt operation.
If your ciphertext was encrypted under an asymmetric KMS key, you must use the SourceKeyId parameter to identify the KMS key that encrypted the ciphertext. You must also supply the encryption algorithm that was used. This information is required to decrypt the data.
If your ciphertext was encrypted under a symmetric encryption KMS key, the SourceKeyId 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 source KMS key is always recommended as a best practice. When you use the SourceKeyId parameter to specify a KMS key, KMS uses only the KMS key you specify. If the ciphertext was encrypted under a different KMS key, the ReEncrypt operation fails. This practice ensures that you use the KMS key that you intend.
To reencrypt the data, you must use the DestinationKeyId parameter to specify the KMS key that re-encrypts the data after it is decrypted. If the destination KMS key is an asymmetric KMS key, you must also provide the encryption algorithm. The algorithm that you choose must be compatible with the KMS key.
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. The source KMS key and destination KMS key can be in different Amazon Web Services accounts. Either or both KMS keys can be in a different account than the caller. To specify a KMS key in a different account, you must use its key ARN or alias ARN.
Required permissions:
kms:ReEncryptFrom permission on the source KMS key (key policy)
kms:ReEncryptTo permission on the destination KMS key (key policy)
To permit reencryption from or to a KMS key, include the "kms:ReEncrypt*" permission in your key policy. This permission is automatically included in the key policy when you use the console to create a KMS key. But you must include it manually when you create a KMS key programmatically or when you use the PutKeyPolicy operation to set a key policy.
Related operations:
Decrypt
Encrypt
GenerateDataKey
GenerateDataKeyPair
Eventual consistency: The KMS API follows an eventual consistency model. For more information, see KMS eventual consistency.
See also: AWS API Documentation
Request Syntax
client.re_encrypt(
CiphertextBlob=b'bytes',
SourceEncryptionContext={
'string': 'string'
},
SourceKeyId='string',
DestinationKeyId='string',
DestinationEncryptionContext={
'string': 'string'
},
SourceEncryptionAlgorithm='SYMMETRIC_DEFAULT'|'RSAES_OAEP_SHA_1'|'RSAES_OAEP_SHA_256'|'SM2PKE',
DestinationEncryptionAlgorithm='SYMMETRIC_DEFAULT'|'RSAES_OAEP_SHA_1'|'RSAES_OAEP_SHA_256'|'SM2PKE',
GrantTokens=[
'string',
],
DryRun=True|False,
DryRunModifiers=[
'IGNORE_CIPHERTEXT',
]
)
bytes
Ciphertext of the data to reencrypt.
This parameter is required in all cases except when DryRun is true and DryRunModifiers is set to IGNORE_CIPHERTEXT.
dict
Specifies the encryption context to use to decrypt the ciphertext. Enter the same encryption context that was used to encrypt the ciphertext.
An encryption context is a collection of non-secret key-value pairs that represent 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 supported only on operations with symmetric encryption KMS keys. On operations with symmetric encryption KMS keys, an encryption context is optional, but it is strongly recommended.
For more information, see Encryption context in the Key Management Service Developer Guide.
(string) --
(string) --
string
Specifies the KMS key that KMS will use to decrypt the ciphertext before it is re-encrypted.
Enter a key ID of the KMS key that was used to encrypt the ciphertext. If you identify a different KMS key, the ReEncrypt operation throws an IncorrectKeyException.
This parameter is required only when the ciphertext was encrypted under an asymmetric KMS key or when DryRun is true and DryRunModifiers is set to IGNORE_CIPHERTEXT. If you used a symmetric encryption KMS key, KMS can get the KMS key 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 KMS key that you intend.
To specify a KMS key, use its key ID, key ARN, alias name, or alias ARN. When using an alias name, prefix it with "alias/". To specify a KMS key in a different Amazon Web Services 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 KMS key, use ListKeys or DescribeKey. To get the alias name and alias ARN, use ListAliases.
string
[REQUIRED]
A unique identifier for the KMS key that is used to reencrypt the data. Specify a symmetric encryption KMS key or an asymmetric KMS key with a KeyUsage value of ENCRYPT_DECRYPT. To find the KeyUsage value of a KMS key, use the DescribeKey operation.
To specify a KMS key, use its key ID, key ARN, alias name, or alias ARN. When using an alias name, prefix it with "alias/". To specify a KMS key in a different Amazon Web Services 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 KMS key, use ListKeys or DescribeKey. To get the alias name and alias ARN, use ListAliases.
dict
Specifies that encryption context to use when the reencrypting the data.
A destination encryption context is valid only when the destination KMS key is a symmetric encryption KMS key. The standard ciphertext format for asymmetric KMS keys does not include fields for metadata.
An encryption context is a collection of non-secret key-value pairs that represent 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 supported only on operations with symmetric encryption KMS keys. On operations with symmetric encryption KMS keys, an encryption context is optional, but it is strongly recommended.
For more information, see Encryption context in the Key Management Service Developer Guide.
(string) --
(string) --
string
Specifies the encryption algorithm that KMS will use to decrypt the ciphertext before it is reencrypted. The default value, SYMMETRIC_DEFAULT, represents the algorithm used for symmetric encryption KMS keys.
Specify the same algorithm that was used to encrypt the ciphertext. If you specify a different algorithm, the decrypt attempt fails.
This parameter is required only when the ciphertext was encrypted under an asymmetric KMS key.
string
Specifies the encryption algorithm that KMS will use to reecrypt the data after it has decrypted it. The default value, SYMMETRIC_DEFAULT, represents the encryption algorithm used for symmetric encryption KMS keys.
This parameter is required only when the destination KMS key is an asymmetric KMS key.
list
A list of grant tokens.
Use a grant token when your permission to call this operation comes from a new grant that has not yet achieved eventual consistency. For more information, see Grant token and Using a grant token in the Key Management Service Developer Guide.
(string) --
boolean
Checks if your request will succeed. DryRun is an optional parameter.
To learn more about how to use this parameter, see Testing your permissions in the Key Management Service Developer Guide.
list
Specifies the modifiers to apply to the dry run operation. DryRunModifiers is an optional parameter that only applies when DryRun is set to true.
When set to IGNORE_CIPHERTEXT, KMS performs only authorization validation without ciphertext validation. This allows you to test permissions without requiring a valid ciphertext blob.
To learn more about how to use this parameter, see Testing your permissions in the Key Management Service Developer Guide.
(string) --
dict
Response Syntax
{
'CiphertextBlob': b'bytes',
'SourceKeyId': 'string',
'KeyId': 'string',
'SourceEncryptionAlgorithm': 'SYMMETRIC_DEFAULT'|'RSAES_OAEP_SHA_1'|'RSAES_OAEP_SHA_256'|'SM2PKE',
'DestinationEncryptionAlgorithm': 'SYMMETRIC_DEFAULT'|'RSAES_OAEP_SHA_1'|'RSAES_OAEP_SHA_256'|'SM2PKE',
'SourceKeyMaterialId': 'string',
'DestinationKeyMaterialId': 'string'
}
Response Structure
(dict) --
CiphertextBlob (bytes) --
The reencrypted data. When you use the HTTP API or the Amazon Web Services CLI, the value is Base64-encoded. Otherwise, it is not Base64-encoded.
SourceKeyId (string) --
Unique identifier of the KMS key used to originally encrypt the data.
KeyId (string) --
The Amazon Resource Name ( key ARN) of the KMS key that was used to reencrypt the data.
SourceEncryptionAlgorithm (string) --
The encryption algorithm that was used to decrypt the ciphertext before it was reencrypted.
DestinationEncryptionAlgorithm (string) --
The encryption algorithm that was used to reencrypt the data.
SourceKeyMaterialId (string) --
The identifier of the key material used to originally encrypt the data. This field is present only when the original encryption used a symmetric encryption KMS key.
DestinationKeyMaterialId (string) --
The identifier of the key material used to reencrypt the data. This field is present only when data is reencrypted using a symmetric encryption KMS key.