# signature(for:) Generates an Elliptic Curve Digital Signature Algorithm (ECDSA) signature of the data you provide over the P-521 elliptic curve, using SHA-512 as the hash function. ``` func signature(for data: D) throws -> P521.Signing.ECDSASignature where D : DataProtocol ``` ## Parameters `data` The data to sign. ## Return Value The signature corresponding to the data. The signing algorithm employs randomization to generate a different signature on every call, even for the same data and key. --- Copyright © 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)