, Hi, here is my .NET code:

    public static string ExportPublicKeyFile(this RSA rsa)
    {
        var privateKeyBytes = rsa.ExportRSAPublicKey();
        var builder = new StringBuilder("-----BEGIN PUBLIC KEY-----");

        var base64PrivateKeyString = Convert.ToBase64String(privateKeyBytes);
        var offset = 0;
        const int LINE_LENGTH = 64;

        for (var i = 0; i < base64PrivateKeyString.Length; ++i)
        {
            if (i % (LINE_LENGTH - 1) == 0)
                builder.Append("\n");
            builder.Append(base64PrivateKeyString[i]);
        }
        if (builder[builder.Length-1] != '\n')
            builder.Append("\n");

        builder.AppendLine("-----END PUBLIC KEY-----");
        return builder.ToString();
    }

(There's some extra fluff around the outside to save to a file)

Here's my Kotlin:

class App {
    companion object {
        @JvmStatic
        fun main(args: Array<String>) {
            //App().run()
            //val parts = "/ss/dsa".split('/')
            //println(parts)

            val key = PublicKeyReader.get("C:\\Path\\To\\public.key")

        }

        object PublicKeyReader {
            @kotlin.Throws(Exception::class)
            operator fun get(filename: String): PublicKey {
                val keyBytes: ByteArray = Files.readAllBytes(Paths.get(filename))
                val spec = X509EncodedKeySpec(keyBytes)
                val kf: java.security.KeyFactory = java.security.KeyFactory.getInstance("RSA")
                return kf.generatePublic(spec)
            }
        }

    }
}

The Kotlin isn't running an Android, it's an IntelliJ application currently.

I get the following exception when running:

Caused by: java.security.InvalidKeyException: invalid key format

I have tried removing the BEGIN\END lines manually, and it didn't help.