Adding common crypto_sign, called signature because object named Sign could be confusing

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

@@ -0,0 +1,73 @@
+package com.ionspin.kotlin.crypto.signature
+
+/**
+ * Created by Ugljesa Jovanovic (jovanovic.ugljesa@gmail.com) on 13/Sep/2020
+ */
+expect class SignatureState
+
+data class SignKeyPair(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
+
+class InvalidSignatureException() : RuntimeException("Signature validation failed")
+
+expect object Signature {
+    fun init(): SignatureState
+    fun update(state: SignatureState, data: UByteArray)
+    fun finalCreate(state: SignatureState, secretKey: UByteArray): UByteArray
+    fun finalVerify(state: SignatureState, signature: UByteArray, publicKey: UByteArray)
+
+    /**
+     * 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
+
+    /**
+     * 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
+
+    /**
+     * The crypto_sign() function prepends a signature to a message m whose length is mlen bytes, using the secret key sk.
+     * The signed message, which includes the signature + a plain copy of the message, is put into sm, and is crypto_sign_BYTES + mlen bytes long.
+     */
+    fun sign(message : UByteArray, secretKey : UByteArray) : UByteArray
+
+    /**
+     * The crypto_sign_open() function checks that the signed message sm whose length is smlen bytes has a valid signature for the public key pk.
+     * If the signature is doesn't appear to be valid, the function throws an exception
+     */
+    fun open(signedMessage: UByteArray, publicKey: UByteArray) : UByteArray
+
+    /**
+     * In detached mode, the signature is stored without attaching a copy of the original message to it.
+     * The crypto_sign_detached() function signs the message m whose length is mlen bytes, using the secret key sk,
+     * and puts the signature into sig, which can be up to crypto_sign_BYTES bytes long.
+     */
+    fun detached(message: UByteArray, secretKey: UByteArray): UByteArray
+
+    /**
+     * 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()
+
+    /**
+     * 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.
+     * While the public key can always be derived from the seed, the precomputation saves a significant amount of CPU cycles when signing.
+     */
+    fun ed25519SkToSeed(secretKey : 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.
+     * While the public key can always be derived from the seed, the precomputation saves a significant amount of CPU cycles when signing.
+     */
+    fun ed25519SkToPk(secretKey: UByteArray) : UByteArray
+}