Added js and jvm implementations of _kx_

multiplatform-crypto-libsodium-bindings/src/jvmMain/kotlin/com/ionspin/kotlin/crypto/keyexchange/KeyExchange.kt

@@ -0,0 +1,57 @@
+package com.ionspin.kotlin.crypto.keyexchange
+
+import com.ionspin.kotlin.crypto.LibsodiumInitializer.sodium
+
+actual object KeyExchange {
+    actual fun clientSessionKeys(clientPublicKey: UByteArray, clientSecretKey: UByteArray, serverPublicKey: UByteArray) : KeyExchangeSessionKeyPair {
+        val receiveKey = UByteArray(crypto_kx_SESSIONKEYBYTES)
+        val sendKey = UByteArray(crypto_kx_SESSIONKEYBYTES)
+
+        sodium.crypto_kx_client_session_keys(
+            receiveKey.asByteArray(),
+            sendKey.asByteArray(),
+            clientPublicKey.asByteArray(),
+            clientSecretKey.asByteArray(),
+            serverPublicKey.asByteArray()
+        )
+
+
+
+        return KeyExchangeSessionKeyPair(receiveKey, sendKey)
+    }
+
+    actual fun keypair() : KeyExchangeKeyPair {
+        val publicKey = UByteArray(crypto_kx_PUBLICKEYBYTES)
+        val secretKey = UByteArray(crypto_kx_SECRETKEYBYTES)
+
+
+        sodium.crypto_kx_keypair(publicKey.asByteArray(), secretKey.asByteArray())
+
+
+        return KeyExchangeKeyPair(publicKey, secretKey)
+    }
+
+    actual fun seedKeypair(seed: UByteArray) : KeyExchangeKeyPair {
+        val publicKey = UByteArray(crypto_kx_PUBLICKEYBYTES)
+        val secretKey = UByteArray(crypto_kx_SECRETKEYBYTES)
+
+        sodium.crypto_kx_seed_keypair(publicKey.asByteArray(), secretKey.asByteArray(), seed.asByteArray())
+
+        return KeyExchangeKeyPair(publicKey, secretKey)
+    }
+
+    actual fun serverSessionKeys(serverPublicKey: UByteArray, serverSecretKey: UByteArray, clientPublicKey: UByteArray) : KeyExchangeSessionKeyPair {
+        val receiveKey = UByteArray(crypto_kx_SESSIONKEYBYTES)
+        val sendKey = UByteArray(crypto_kx_SESSIONKEYBYTES)
+
+        sodium.crypto_kx_server_session_keys(
+            receiveKey.asByteArray(),
+            sendKey.asByteArray(),
+            serverPublicKey.asByteArray(),
+            serverSecretKey.asByteArray(),
+            clientPublicKey.asByteArray()
+        )
+
+        return KeyExchangeSessionKeyPair(receiveKey, sendKey)
+    }
+}