Added _kdf_ all implementations and a simple and probably pointless test, also noted which functions are not available as they are not part of LazySodium

multiplatform-crypto-libsodium-bindings/src/jsMain/kotlin/com/ionspin/kotlin/crypto/JsSodiumInterface.kt

@@ -174,7 +174,15 @@ interface JsSodiumInterface {
     fun crypto_sign_verify_detached(signature: Uint8Array, message: Uint8Array, publicKey: Uint8Array) : Boolean
 
 
-    // ---- Sign end
+    // ---- Sign end ----
+
+
+    // ---- KDF ----
+
+    fun crypto_kdf_derive_from_key(subkey_len: UInt, subkeyId : UInt, ctx: String, key: Uint8Array) : Uint8Array
+    fun crypto_kdf_keygen() : Uint8Array
+
+    // ---- KDF end -----
 
     //util
     fun memzero(array: Uint8Array)

multiplatform-crypto-libsodium-bindings/src/jsMain/kotlin/com/ionspin/kotlin/crypto/kdf/Kdf.kt

@@ -0,0 +1,43 @@
+package com.ionspin.kotlin.crypto.kdf
+
+import com.ionspin.kotlin.crypto.getSodium
+import ext.libsodium.com.ionspin.kotlin.crypto.toUByteArray
+import ext.libsodium.com.ionspin.kotlin.crypto.toUInt8Array
+
+actual object Kdf {
+    /**
+     * The crypto_kdf_derive_from_key() function derives a subkey_id-th subkey subkey of length subkey_len bytes using
+     * the master key key and the context ctx.
+     * subkey_id can be any value up to (2^64)-1.
+     * subkey_len has to be between crypto_kdf_BYTES_MIN (inclusive) and crypto_kdf_BYTES_MAX (inclusive).
+     * Similar to a type, the context ctx is a 8 characters string describing what the key is going to be used for.
+     * Its purpose is to mitigate accidental bugs by separating domains. The same function used with the same key but
+     * in two distinct contexts is likely to generate two different outputs.
+     * Contexts don't have to be secret and can have a low entropy.
+     * Examples of contexts include UserName, __auth__, pictures and userdata.
+     * They must be crypto_kdf_CONTEXTBYTES bytes long.
+     * If more convenient, it is also fine to use a single global context for a whole application. This will still
+     * prevent the same keys from being mistakenly used by another application.
+     */
+    actual fun deriveFromKey(
+        subkeyId: Int,
+        subkeyLength: Int,
+        context: String,
+        masterKey: UByteArray
+    ): UByteArray {
+        return getSodium().crypto_kdf_derive_from_key(
+            subkeyLength.toUInt(),
+            subkeyId.toUInt(),
+            context,
+            masterKey.toUInt8Array()
+        ).toUByteArray()
+    }
+
+    /**
+     * The crypto_kdf_keygen() function creates a master key.
+     */
+    actual fun keygen(): UByteArray {
+        return getSodium().crypto_kdf_keygen().toUByteArray()
+    }
+
+}