refactor, implement LCG

LCG ... Linear Congruential Generator

src/commonMain/kotlin/com/infendro/random/csprng/CSPRNG.kt

@@ -0,0 +1,16 @@
+package com.infendro.random.csprng
+
+import com.infendro.hash.HashFunction
+import com.infendro.random.prng.PRNG
+
+abstract class CSPRNG : PRNG() {
+    abstract fun reseed(
+        entropy: UByteArray,
+    )
+
+    companion object {
+        fun HMAC(
+            function: HashFunction,
+        ) = com.infendro.random.csprng.HMAC(function)
+    }
+}

src/commonMain/kotlin/com/infendro/random/csprng/HMAC.kt

@@ -0,0 +1,48 @@
+package com.infendro.random.csprng
+
+import com.infendro.hash.HashFunction
+import kotlin.math.min
+import kotlin.properties.Delegates.notNull
+
+class HMAC internal constructor(
+    private val function: HashFunction,
+) : CSPRNG() {
+    private val hmac = com.infendro.mac.HMAC(function)
+
+    private var k: UByteArray by notNull()
+    private var v: UByteArray by notNull()
+
+    override fun seed(
+        seed: UByteArray,
+    ) {
+        k = UByteArray(function.bytes) { 0x00U }
+        v = UByteArray(function.bytes) { 0x01U }
+        reseed(seed)
+    }
+
+    override fun reseed(
+        entropy: UByteArray,
+    ) {
+        k = hmac.hash(k, v + ubyteArrayOf(0x00U) + entropy)
+        v = hmac.hash(k, v)
+        k = hmac.hash(k, v + ubyteArrayOf(0x01U) + entropy)
+        v = hmac.hash(k, v)
+    }
+
+    override fun generate(
+        count: Int,
+    ): UByteArray {
+        val bytes = buildList {
+            while (size < count) {
+                v = hmac.hash(k, v)
+
+                addAll(v.take(min(count - size, function.bytes)))
+            }
+        }.toUByteArray()
+
+        k = hmac.hash(k, v + ubyteArrayOf(0x00U))
+        v = hmac.hash(k, v)
+
+        return bytes
+    }
+}