Request Syntax Request Parameters Response Syntax Response Elements Errors Examples See Also

DeriveSharedSecret

Derives a shared secret using a key agreement algorithm.

Note

You must use an asymmetric NIST-recommended elliptic curve (ECC) or SM2 (China Regions only) KMS key pair with a KeyUsage value of KEY_AGREEMENT to call DeriveSharedSecret.

DeriveSharedSecret uses the Elliptic Curve Cryptography Cofactor Diffie-Hellman Primitive (ECDH) to establish a key agreement between two peers by deriving a shared secret from their elliptic curve public-private key pairs. You can use the raw shared secret that DeriveSharedSecret returns to derive a symmetric key that can encrypt and decrypt data that is sent between the two peers, or that can generate and verify HMACs. AWS KMS recommends that you follow NIST recommendations for key derivation when using the raw shared secret to derive a symmetric key.

The following workflow demonstrates how to establish key agreement over an insecure communication channel using DeriveSharedSecret.

Alice calls CreateKey to create an asymmetric KMS key pair with a KeyUsage value of KEY_AGREEMENT.

The asymmetric KMS key must use a NIST-recommended elliptic curve (ECC) or SM2 (China Regions only) key spec.
Bob creates an elliptic curve key pair.

Bob can call CreateKey to create an asymmetric KMS key pair or generate a key pair outside of AWS KMS. Bob's key pair must use the same NIST-recommended elliptic curve (ECC) or SM2 (China Regions ony) curve as Alice.
Alice and Bob exchange their public keys through an insecure communication channel (like the internet).

Use GetPublicKey to download the public key of your asymmetric KMS key pair.

Note
AWS KMS strongly recommends verifying that the public key you receive came from the expected party before using it to derive a shared secret.
Alice calls DeriveSharedSecret.

AWS KMS uses the private key from the KMS key pair generated in Step 1, Bob's public key, and the Elliptic Curve Cryptography Cofactor Diffie-Hellman Primitive to derive the shared secret. The private key in your KMS key pair never leaves AWS KMS unencrypted. DeriveSharedSecret returns the raw shared secret.
Bob uses the Elliptic Curve Cryptography Cofactor Diffie-Hellman Primitive to calculate the same raw secret using his private key and Alice's public key.

To derive a shared secret you must provide a key agreement algorithm, the private key of the caller's asymmetric NIST-recommended elliptic curve or SM2 (China Regions only) KMS key pair, and the public key from your peer's NIST-recommended elliptic curve or SM2 (China Regions only) key pair. The public key can be from another asymmetric KMS key pair or from a key pair generated outside of AWS KMS, but both key pairs must be on the same elliptic curve.

The KMS key that you use for this operation must be in a compatible key state. For details, see Key states of AWS KMS keys in the AWS Key Management Service Developer Guide.

Cross-account use: Yes. To perform this operation with a KMS key in a different AWS account, specify the key ARN or alias ARN in the value of the KeyId parameter.

Required permissions: kms:DeriveSharedSecret (key policy)

Related operations:

Eventual consistency: The AWS KMS API follows an eventual consistency model. For more information, see AWS KMS eventual consistency.

Request Syntax


{
   "DryRun": boolean,
   "GrantTokens": [ "string" ],
   "KeyAgreementAlgorithm": "string",
   "KeyId": "string",
   "PublicKey": blob,
   "Recipient": { 
      "AttestationDocument": blob,
      "KeyEncryptionAlgorithm": "string"
   }
}

Request Parameters

For information about the parameters that are common to all actions, see Common Parameters.

The request accepts the following data in JSON format.

Note

In the following list, the required parameters are described first.

KeyAgreementAlgorithm

Specifies the key agreement algorithm used to derive the shared secret. The only valid value is ECDH.

Type: String

Valid Values: ECDH

Required: Yes

KeyId

Identifies an asymmetric NIST-recommended ECC or SM2 (China Regions only) KMS key. AWS KMS uses the private key in the specified key pair to derive the shared secret. The key usage of the KMS key must be KEY_AGREEMENT. To find the KeyUsage 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 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 KMS key, use ListKeys or DescribeKey. To get the alias name and alias ARN, use ListAliases.

Type: String

Length Constraints: Minimum length of 1. Maximum length of 2048.

Required: Yes

PublicKey

Specifies the public key in your peer's NIST-recommended elliptic curve (ECC) or SM2 (China Regions only) key pair.

The public key must be a DER-encoded X.509 public key, also known as SubjectPublicKeyInfo (SPKI), as defined in RFC 5280.

GetPublicKey returns the public key of an asymmetric KMS key pair in the required DER-encoded format.

Note

If you use AWS CLI version 1, you must provide the DER-encoded X.509 public key in a file. Otherwise, the AWS CLI Base64-encodes the public key a second time, resulting in a ValidationException.

You can specify the public key as binary data in a file using fileb (fileb://<path-to-file>) or in-line using a Base64 encoded string.

Type: Base64-encoded binary data object

Length Constraints: Minimum length of 1. Maximum length of 8192.

Required: Yes

DryRun

Checks if your request will succeed. DryRun is an optional parameter.

To learn more about how to use this parameter, see Testing your AWS KMS API calls in the AWS Key Management Service Developer Guide.

Type: Boolean

Required: No

GrantTokens

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 AWS Key Management Service Developer Guide.

Type: Array of strings

Array Members: Minimum number of 0 items. Maximum number of 10 items.

Length Constraints: Minimum length of 1. Maximum length of 8192.

Required: No

Recipient

A signed attestation document from an AWS Nitro enclave and the encryption algorithm to use with the enclave's public key. The only valid encryption algorithm is RSAES_OAEP_SHA_256.

This parameter only supports attestation documents for AWS Nitro Enclaves. To call DeriveSharedSecret for an AWS Nitro Enclaves, use the AWS Nitro Enclaves SDK to generate the attestation document and then use the Recipient parameter from any AWS SDK to provide the attestation document for the enclave.

When you use this parameter, instead of returning a plaintext copy of the shared secret, AWS KMS encrypts the plaintext shared secret under 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 enclave. The CiphertextBlob field in the response contains the encrypted shared secret derived from the KMS key specified by the KeyId parameter and public key specified by the PublicKey parameter. The SharedSecret field in the response is null or empty.

For information about the interaction between AWS KMS and AWS Nitro Enclaves, see How AWS Nitro Enclaves uses AWS KMS in the AWS Key Management Service Developer Guide.

Type: RecipientInfo object

Required: No

Response Syntax


{
   "CiphertextForRecipient": blob,
   "KeyAgreementAlgorithm": "string",
   "KeyId": "string",
   "KeyOrigin": "string",
   "SharedSecret": blob
}

Response Elements

If the action is successful, the service sends back an HTTP 200 response.

The following data is returned in JSON format by the service.

CiphertextForRecipient

The plaintext shared secret encrypted with the public key in the attestation document.

This field is included in the response only when the Recipient parameter in the request includes a valid attestation document from an AWS Nitro enclave. For information about the interaction between AWS KMS and AWS Nitro Enclaves, see How AWS Nitro Enclaves uses AWS KMS in the AWS Key Management Service Developer Guide.

Type: Base64-encoded binary data object

Length Constraints: Minimum length of 1. Maximum length of 6144.

KeyAgreementAlgorithm

Identifies the key agreement algorithm used to derive the shared secret.

Type: String

Valid Values: ECDH

KeyId

Identifies the KMS key used to derive the shared secret.

Type: String

Length Constraints: Minimum length of 1. Maximum length of 2048.

KeyOrigin

The source of the key material for the specified KMS key.

When this value is AWS_KMS, AWS KMS created the key material. When this value is EXTERNAL, the key material was imported or the KMS key doesn't have any key material.

The only valid values for DeriveSharedSecret are AWS_KMS and EXTERNAL. DeriveSharedSecret does not support KMS keys with a KeyOrigin value of AWS_CLOUDHSM or EXTERNAL_KEY_STORE.

Type: String

Valid Values: AWS_KMS | EXTERNAL | AWS_CLOUDHSM | EXTERNAL_KEY_STORE

SharedSecret

The raw secret derived from the specified key agreement algorithm, private key in the asymmetric KMS key, and your peer's public key.

If the response includes the CiphertextForRecipient field, the SharedSecret field is null or empty.

Type: Base64-encoded binary data object

Length Constraints: Minimum length of 1. Maximum length of 4096.

Errors

For information about the errors that are common to all actions, see Common Errors.

DependencyTimeoutException

The system timed out while trying to fulfill the request. You can retry the request.

HTTP Status Code: 500

DisabledException

The request was rejected because the specified KMS key is not enabled.

HTTP Status Code: 400

DryRunOperationException

The request was rejected because the DryRun parameter was specified.

HTTP Status Code: 400

InvalidGrantTokenException

The request was rejected because the specified grant token is not valid.

HTTP Status Code: 400

InvalidKeyUsageException

The request was rejected for one of the following reasons:

The KeyUsage value of the KMS key is incompatible with the API operation.
The encryption algorithm or signing algorithm specified for the operation is incompatible with the type of key material in the KMS key (KeySpec).

For encrypting, decrypting, re-encrypting, and generating data keys, the KeyUsage must be ENCRYPT_DECRYPT. For signing and verifying messages, the KeyUsage must be SIGN_VERIFY. For generating and verifying message authentication codes (MACs), the KeyUsage must be GENERATE_VERIFY_MAC. For deriving key agreement secrets, the KeyUsage must be KEY_AGREEMENT. To find the KeyUsage of a KMS key, use the DescribeKey operation.

To find the encryption or signing algorithms supported for a particular KMS key, use the DescribeKey operation.

HTTP Status Code: 400

KeyUnavailableException

The request was rejected because the specified KMS key was not available. You can retry the request.

HTTP Status Code: 500

KMSInternalException

The request was rejected because an internal exception occurred. The request can be retried.

HTTP Status Code: 500

KMSInvalidStateException

The request was rejected because the state of the specified resource is not valid for this request.

This exceptions means one of the following:

The key state of the KMS key is not compatible with the operation.

To find the key state, use the DescribeKey operation. For more information about which key states are compatible with each AWS KMS operation, see Key states of AWS KMS keys in the AWS Key Management Service Developer Guide .
For cryptographic operations on KMS keys in custom key stores, this exception represents a general failure with many possible causes. To identify the cause, see the error message that accompanies the exception.

HTTP Status Code: 400

NotFoundException

The request was rejected because the specified entity or resource could not be found.

HTTP Status Code: 400

Examples

Example Request

The following example is formatted for legibility.


POST / HTTP/1.1
Host: kms.us-east-2.amazonaws.com
Content-Length: 48
X-Amz-Target: TrentService.DeriveSharedSecret
X-Amz-Date: 20161107T213532Z
Content-Type: application/x-amz-json-1.1
Authorization: AWS4-HMAC-SHA256\
 Credential=AKIAI44QH8DHBEXAMPLE/20161107/us-east-2/kms/aws4_request,\
 SignedHeaders=content-type;host;x-amz-date;x-amz-target,\
 Signature=2cea34fe55d5858295a377448a1e053d0edd45ce571da7cf69b202905759f272

{    
    "KeyId": "1234abcd-12ab-34cd-56ef-1234567890ab",
    "PublicKey": "MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAvH3Yj0wbkLEpUl95Cv1cJVjsVNSjwGq3tCLnzXfhVwVvmzGN8pYj3U8nKwgouaHbBWNJYjP5VutbbkKS4Kv4GojwZBJyHN17kmxo8yTjRmjR15SKIQ8cqRA2uaERMLnpztIXdZp232PQPbWGxDyXYJ0aJ5EFSag+iSK341kr2kFTpINN7T1ZaX9vfXBdGR+VtkRKMWoHQeWzHrPZ+3irvpXNCKxGUxmPNsJSjPUhuSXT5+0VrY/LEYLQ5lUTrhU6z5/OK0kzaCc66DXc5ipSloS4Xyg+QcYSMxe9xuqO5HtzFImUSKBm1W6eDT6lHnSbpi7vXzNbIX7pWxKw9nmQvQIDAQAB",
    "KeyAgreementAlgorithm": "ECDH"  
}

Example Response

This example illustrates one usage of DeriveSharedSecret.


HTTP/1.1 200 OK
Server: Server
Date: Mon, 07 Nov 2016 21:35:35 GMT
Content-Type: application/x-amz-json-1.1
Content-Length: 0
Connection: keep-alive
x-amzn-RequestId: 1e76aa81-a532-11e6-a265-d3aef78e1a90

{   
   "KeyId": "1234abcd-12ab-34cd-56ef-1234567890ab",
   "KeyAgreementAlgorithm": "ECDH",
   "SharedSecret": "MEYCIQCKZLWyTk5runarx6XiAkU9gv3lbwPO/pHa+DXFehzdDwIhANwpsIV2g/9SPWLLsF6p/hiSskuIXMTRwqrMdVKWTMHG"
}