# init(_:kem:) Creates a NIST P-521 elliptic curve public key for use with Diffie-Hellman key exchange. ``` init(_ serialization: D, kem: HPKE.KEM) throws where D : ContiguousBytes ``` ## Discussion - serialization: The serialized bytes of the public key. - kem: The Key Encapsulation Mechanism to use with the public key. > Throws: ``doc://com.apple.CryptoKit/documentation/CryptoKit/HPKE/Errors/inconsistentCiphersuiteAndKey`` if the key encapsulation mechanism requested is incompatible with this public 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)