<p>Creates a <a href="https://en.wikipedia.org/wiki/Digital_signature">digital signature</a> for a message or message digest by using the private key in an asymmetric signing KMS key. To verify the signature, use the <a>Verify</a> operation, or use the public key in the same asymmetric KMS key outside of KMS. For information about asymmetric KMS keys, see <a href="https://docs.aws.amazon.com/kms/latest/developerguide/symmetric-asymmetric.html">Asymmetric KMS keys</a> in the <i>Key Management Service Developer Guide</i>.</p> <p>Digital signatures are generated and verified by using asymmetric key pair, such as an RSA or ECC pair that is represented by an asymmetric KMS key. The key owner (or an authorized user) uses their private key to sign a message. Anyone with the public key can verify that the message was signed with that particular private key and that the message hasn't changed since it was signed. </p> <p>To use the <code>Sign</code> operation, provide the following information:</p> <ul> <li> <p>Use the <code>KeyId</code> parameter to identify an asymmetric KMS key with a <code>KeyUsage</code> value of <code>SIGN_VERIFY</code>. To get the <code>KeyUsage</code> value of a KMS key, use the <a>DescribeKey</a> operation. The caller must have <code>kms:Sign</code> permission on the KMS key.</p> </li> <li> <p>Use the <code>Message</code> parameter to specify the message or message digest to sign. You can submit messages of up to 4096 bytes. To sign a larger message, generate a hash digest of the message, and then provide the hash digest in the <code>Message</code> parameter. To indicate whether the message is a full message or a digest, use the <code>MessageType</code> parameter.</p> </li> <li> <p>Choose a signing algorithm that is compatible with the KMS key. </p> </li> </ul> <important> <p>When signing a message, be sure to record the KMS key and the signing algorithm. This information is required to verify the signature.</p> </important> <note> <p>Best practices recommend that you limit the time during which any signature is effective. This deters an attack where the actor uses a signed message to establish validity repeatedly or long after the message is superseded. Signatures do not include a timestamp, but you can include a timestamp in the signed message to help you detect when its time to refresh the signature. </p> </note> <p>To verify the signature that this operation generates, use the <a>Verify</a> operation. Or use the <a>GetPublicKey</a> operation to download the public key and then use the public key to verify the signature outside of KMS. </p> <p>The KMS key that you use for this operation must be in a compatible key state. For details, see <a href="https://docs.aws.amazon.com/kms/latest/developerguide/key-state.html">Key states of KMS keys</a> in the <i>Key Management Service Developer Guide</i>.</p> <p> <b>Cross-account use</b>: Yes. To perform this operation with a KMS key in a different Amazon Web Services account, specify the key ARN or alias ARN in the value of the <code>KeyId</code> parameter.</p> <p> <b>Required permissions</b>: <a href="https://docs.aws.amazon.com/kms/latest/developerguide/kms-api-permissions-reference.html">kms:Sign</a> (key policy)</p> <p> <b>Related operations</b>: <a>Verify</a> </p>

{
  "success": true,
  "data": {
    "id": "abc123",
    "created_at": "2025-01-01T00:00:00Z"
  }
}

{
  "success": false,
  "error": {
    "code": "VALIDATION_ERROR",
    "message": "Invalid request parameters"
  }
}