# P521.KeyAgreement.PrivateKey A P-521 private key used for key agreement. ``` struct PrivateKey ``` ## Topics ### Creating a private key [`init(compactRepresentable: Bool)`](/documentation/CryptoKit/P521/KeyAgreement/PrivateKey/init(compactRepresentable:)) Creates a random P-521 private key for key agreement. [`init(rawRepresentation: Bytes) throws`](/documentation/CryptoKit/P521/KeyAgreement/PrivateKey/init(rawRepresentation:)) Creates a P-521 private key for key agreement from a collection of bytes. [`init(derRepresentation: Bytes) throws`](/documentation/CryptoKit/P521/KeyAgreement/PrivateKey/init(derRepresentation:)) Creates a P-521 private key for key agreement from a Distinguished Encoding Rules (DER) encoded representation. [`init(pemRepresentation: String) throws`](/documentation/CryptoKit/P521/KeyAgreement/PrivateKey/init(pemRepresentation:)) Creates a P-521 private key for key agreement from a Privacy-Enhanced Mail PEM) representation. [`init(x963Representation: Bytes) throws`](/documentation/CryptoKit/P521/KeyAgreement/PrivateKey/init(x963Representation:)) Creates a P-521 private key for key agreement from an ANSI x9.63 representation. ### Representing the key [`var rawRepresentation: Data`](/documentation/CryptoKit/P521/KeyAgreement/PrivateKey/rawRepresentation) A data representation of the private key. [`var derRepresentation: Data`](/documentation/CryptoKit/P521/KeyAgreement/PrivateKey/derRepresentation) A Distinguished Encoding Rules (DER) encoded representation of the private key. [`var pemRepresentation: String`](/documentation/CryptoKit/P521/KeyAgreement/PrivateKey/pemRepresentation) A Privacy-Enhanced Mail (PEM) representation of the private key. [`var x963Representation: Data`](/documentation/CryptoKit/P521/KeyAgreement/PrivateKey/x963Representation) An ANSI x9.63 representation of the private key. ### Finding the public key [`var publicKey: P521.KeyAgreement.PublicKey`](/documentation/CryptoKit/P521/KeyAgreement/PrivateKey/publicKey) The corresponding public key. ### Creating a shared secret [`func sharedSecretFromKeyAgreement(with: P521.KeyAgreement.PublicKey) throws -> SharedSecret`](/documentation/CryptoKit/P521/KeyAgreement/PrivateKey/sharedSecretFromKeyAgreement(with:)) Computes a shared secret with the provided public key from another party. [`struct SharedSecret`](/documentation/CryptoKit/SharedSecret) A key agreement result from which you can derive a symmetric cryptographic key. ### Default Implementations [DiffieHellmanKeyAgreement Implementations](/documentation/CryptoKit/P521/KeyAgreement/PrivateKey/DiffieHellmanKeyAgreement-Implementations) [HPKEDiffieHellmanPrivateKeyGeneration Implementations](/documentation/CryptoKit/P521/KeyAgreement/PrivateKey/HPKEDiffieHellmanPrivateKeyGeneration-Implementations) ## Relationships ### Conforms To [`Escapable`](/documentation/Swift/Escapable) [`DiffieHellmanKeyAgreement`](/documentation/CryptoKit/DiffieHellmanKeyAgreement) [`Sendable`](/documentation/Swift/Sendable) [`HPKEDiffieHellmanPrivateKey`](/documentation/CryptoKit/HPKEDiffieHellmanPrivateKey) [`SendableMetatype`](/documentation/Swift/SendableMetatype) [`Copyable`](/documentation/Swift/Copyable) [`HPKEDiffieHellmanPrivateKeyGeneration`](/documentation/CryptoKit/HPKEDiffieHellmanPrivateKeyGeneration) --- 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)