Add KeyManager interface

Sources/tbDEX/crypto/KeyManager.swift

@@ -0,0 +1,47 @@
+import Foundation
+
+/// Enum defining all supported cryptographic key types.
+public enum KeyType {
+    /// OctetKeyPair key along the ed25519 curve
+    case ed25519
+    /// Elliptic key along the secp256k1 curve
+    case secp256k1
+}
+
+/// A key management interface that provides functionality for generating, storing, and utilizing
+/// private keys and their associated public keys. Implementations of this interface should handle
+/// the secure generation and storage of keys, providing mechanisms for utilizing them in cryptographic
+/// operations like signing.
+///
+/// Example implementations might provide key management through various Key Management Systems (KMS),
+/// such as AWS KMS, Google Cloud KMS, Hardware Security Modules (HSM), or simple in-memory storage,
+/// each adhering to the same consistent API for usage within applications.
+public protocol KeyManager {
+
+    /// Generates and securely stores a private key based on the provided keyType,
+    /// returning a unique alias that can be utilized to reference the generated key for future operations.
+    ///  
+    /// - Parameter keyType: The `KeyType` to use for key generation
+    /// - Returns: A unique alias that can be used to reference the stored key.
+    func generatePrivateKey(keyType: KeyType) throws -> String
+
+    /// Retrieves the public key associated with a previously stored private key, identified by the provided alias.
+    ///
+    /// - Parameter keyAlias: The alias referencing the stored private key.
+    /// - Returns: The associated public key in JSON Web Key (JWK) format (if available).
+    func getPublicKey(keyAlias: String) -> Jwk?
+
+    /// Signs the provided payload using the private key identified by the provided alias.
+    ///
+    /// - Parameters:
+    ///   - keyAlias: The alias referencing the stored private key.
+    ///   - payload: The data to be signed
+    /// - Returns: The signature in JWS R+S format
+    func sign(keyAlias: String, payload: Data) throws -> Data
+
+    /// Return the alias of `publicKey`, as was originally returned by `generatePrivateKey`.
+    /// 
+    /// - Parameter publicKey: A public key in JSON Web Key (JWK) format
+    /// - Returns: The alias belonging to `publicKey`
+    func getDeterministicAlias(publicKey: Jwk) -> String
+}