Adding _sign_ native implementation and started writing tests

multiplatform-crypto-libsodium-bindings/src/commonMain/kotlin/com.ionspin.kotlin.crypto/signature/Signature.kt

@@ -5,12 +5,13 @@ package com.ionspin.kotlin.crypto.signature
  */
 expect class SignatureState
 
-data class SignKeyPair(val publicKey: UByteArray, val secretKey: UByteArray)
+data class SignatureKeyPair(val publicKey: UByteArray, val secretKey: UByteArray)
 
 const val crypto_sign_BYTES = 64
 const val crypto_sign_SEEDBYTES = 32
 const val crypto_sign_PUBLICKEYBYTES = 32
-const val crypto_sign_SECRETKEY2BYTES = 64
+const val crypto_sign_SECRETKEYBYTES = 64
+const val crypto_scalarmult_curve25519_BYTES = 32
 
 class InvalidSignatureException() : RuntimeException("Signature validation failed")
 
@@ -24,14 +25,14 @@ expect object Signature {
      * The crypto_sign_keypair() function randomly generates a secret key and a corresponding public key.
      * The public key is put into pk (crypto_sign_PUBLICKEYBYTES bytes) and the secret key into sk (crypto_sign_SECRETKEYBYTES bytes).
      */
-    fun keypair(): SignKeyPair
+    fun keypair(): SignatureKeyPair
 
     /**
      * The crypto_sign_keypair() function randomly generates a secret key and a corresponding public key.
      * The public key is put into pk (crypto_sign_PUBLICKEYBYTES bytes) and the secret key into sk (crypto_sign_SECRETKEYBYTES bytes).
      * Using crypto_sign_seed_keypair(), the key pair can also be deterministically derived from a single key seed (crypto_sign_SEEDBYTES bytes).
      */
-    fun seedKeypair(seed: UByteArray): SignKeyPair
+    fun seedKeypair(seed: UByteArray): SignatureKeyPair
 
     /**
      * The crypto_sign() function prepends a signature to a message m whose length is mlen bytes, using the secret key sk.
@@ -56,9 +57,16 @@ expect object Signature {
      * The crypto_sign_verify_detached() function verifies that sig is a valid signature for the message m whose length
      * is mlen bytes, using the signer's public key pk.
      */
-    fun verifyDetached(signature: UByteArray, message: UByteArray, publicKey: UByteArray): Boolean
-    fun ed25519PkToCurve25519()
-    fun ed25519SkToCurve25519()
+    fun verifyDetached(signature: UByteArray, message: UByteArray, publicKey: UByteArray)
+    /**
+     * The crypto_sign_ed25519_pk_to_curve25519() function converts an Ed25519 public key ed25519_pk to an X25519 public key and stores it into x25519_pk.
+     */
+    fun ed25519PkToCurve25519(ed25519PublicKey: UByteArray) : UByteArray
+
+    /**
+     * The crypto_sign_ed25519_sk_to_curve25519() function converts an Ed25519 secret key ed25519_sk to an X25519 secret key and stores it into x25519_sk.
+     */
+    fun ed25519SkToCurve25519(ed25519SecretKey: UByteArray) : UByteArray
 
     /**
      * The secret key actually includes the seed (either a random seed or the one given to crypto_sign_seed_keypair()) as well as the public key.