Secure enclave implementation

SecretKit/Common/OpenSSHKeyWriter.swift

@@ -0,0 +1,46 @@
+import Foundation
+import CryptoKit
+
+// For the moment, only supports ecdsa-sha2-nistp256 keys
+public struct OpenSSHKeyWriter {
+
+    public init() {
+    }
+
+    public func data<SecretType: Secret>(secret: SecretType) -> Data {
+        lengthAndData(of: Constants.curveType.data(using: .utf8)!) +
+            lengthAndData(of: Constants.curveIdentifier.data(using: .utf8)!) +
+            lengthAndData(of: secret.publicKey)
+    }
+
+    public func openSSHString<SecretType: Secret>(secret: SecretType) -> String {
+        "\(Constants.curveType) \(data(secret: secret).base64EncodedString())"
+    }
+
+    public func openSSHFingerprint<SecretType: Secret>(secret: SecretType) -> String {
+        Insecure.MD5.hash(data: data(secret: secret))
+            .compactMap { String($0, radix: 16, uppercase: false) }
+            .joined(separator: ":")
+    }
+
+}
+
+extension OpenSSHKeyWriter {
+
+    public func lengthAndData(of data: Data) -> Data {
+        let rawLength = UInt32(data.count)
+        var endian = rawLength.bigEndian
+        return Data(bytes: &endian, count: UInt32.bitWidth/8) + data
+    }
+
+    public func readData() {}
+}
+
+extension OpenSSHKeyWriter {
+
+    public enum Constants {
+        public static let curveIdentifier = "nistp256"
+        public static let curveType = "ecdsa-sha2-nistp256"
+    }
+
+}