<!--
{
  "availability" : [
    "iOS: 12.2.0 - 18.0.0",
    "iPadOS: 12.2.0 - 18.0.0",
    "macCatalyst: 13.1.0 - 18.0.0",
    "macOS: 10.14.4 - 15.0.0",
    "tvOS: 12.2.0 - 18.0.0",
    "visionOS: 1.0.0 - 2.0.0",
    "watchOS: 6.2.0 - 11.0.0"
  ],
  "documentType" : "symbol",
  "framework" : "StoreKit",
  "identifier" : "/documentation/StoreKit/SKPaymentDiscount/signature",
  "metadataVersion" : "0.1.0",
  "role" : "Instance Property",
  "symbol" : {
    "kind" : "Instance Property",
    "modules" : [
      "StoreKit"
    ],
    "preciseIdentifier" : "c:objc(cs)SKPaymentDiscount(py)signature"
  },
  "title" : "signature"
}
-->

# signature

A string representing the properties of a specific promotional offer, cryptographically signed.

```
var signature: String { get }
```

## Discussion

The [`signature`](/documentation/StoreKit/SKPaymentDiscount/signature) is a string signed with your private key that represents the properties of a specific promotional offer. To keep your private key secure, generate the [`signature`](/documentation/StoreKit/SKPaymentDiscount/signature) on a server.

Generate the [`signature`](/documentation/StoreKit/SKPaymentDiscount/signature) using the Elliptic Curve Digital Signature Algorithm (ECDSA) with SHA 256. For more information, see [Generating a signature for promotional offers](/documentation/StoreKit/generating-a-signature-for-promotional-offers).

---

Copyright &copy; 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)