Added kdfForSizeInBytes method to KDF with tests and a new factory method to UniversalRing.

src/commonTest/kotlin/KDFTest.kt

@@ -9,6 +9,7 @@
  */
 
 import kotlinx.coroutines.test.runTest
+import net.sergeych.crypto2.Hash
 import net.sergeych.crypto2.KDF
 import net.sergeych.crypto2.initCrypto
 import kotlin.test.Test
@@ -16,6 +17,7 @@ import kotlin.test.assertContentEquals
 import kotlin.test.assertEquals
 import kotlin.test.assertFalse
 import kotlin.test.assertFailsWith
+import kotlin.test.assertIs
 
 class KDFTest {
     @Test
@@ -57,6 +59,24 @@ class KDFTest {
         assertEquals(3, kk.size)
     }
 
+    @Test
+    fun complexityKdfForSizeInBytesTest() = runTest {
+        initCrypto()
+        val size = KDF.Argon.minKeySize + 17
+        val domain = "kdf-size-in-bytes-test"
+        val expectedSalt = Hash.Blake2b.deriveSalt(domain, KDF.Argon.saltSize)
+
+        val kdf = KDF.Complexity.Sensitive.kdfForSizeInBytes(size, KDF.Complexity.FixedLow, domain)
+        assertIs<KDF.Argon>(kdf)
+
+        assertEquals(KDF.Argon.create(KDF.Complexity.FixedLow, expectedSalt, size), kdf)
+        assertEquals(size, kdf.keySize)
+        assertContentEquals(expectedSalt, kdf.salt)
+        assertFalse {
+            kdf.salt contentEquals Hash.Blake2b.deriveSalt("$domain-other", KDF.Argon.saltSize)
+        }
+    }
+
     @Test
     fun deriveFromBytesTest() = runTest {
         initCrypto()