implement PBKDF2

src/commonMain/kotlin/com/infendro/kdf/PBKDF2.kt

@@ -0,0 +1,45 @@
+package com.infendro.kdf
+
+import com.infendro.hash.HashFunction
+import com.infendro.kdf.util.addAll
+import com.infendro.kdf.util.toByteArray
+import com.infendro.kdf.util.xor
+import com.infendro.mac.HMAC
+
+class PBKDF2(
+    function: HashFunction,
+) {
+    private val size = function.bytes
+    private val hmac = HMAC(function)
+
+    fun hash(
+        value: ByteArray,
+        salt: ByteArray,
+        iterations: Int,
+        length: Int,
+    ): ByteArray {
+        val key = mutableListOf<Byte>()
+
+        for (i in 1..(length + size - 1) / size) {
+            val input = salt + i.toUInt().toByteArray()
+
+            var u = hmac.hash(value, input)
+            var result = u
+            repeat(iterations - 1) {
+                u = hmac.hash(value, u)
+                result = result xor u
+            }
+
+            key.addAll(result)
+
+            if (key.size >= length) {
+                println(key.size)
+                break
+            }
+        }
+
+        return key
+            .take(length)
+            .toByteArray()
+    }
+}

src/commonMain/kotlin/com/infendro/kdf/util/ByteArray.kt

@@ -0,0 +1,26 @@
+package com.infendro.kdf.util
+
+import kotlin.experimental.xor
+
+internal infix fun ByteArray.xor(
+    that: ByteArray,
+): ByteArray {
+    if (this.size != that.size) throw Exception()
+
+    return ByteArray(size) { i ->
+        this[i] xor that[i]
+    }
+}
+
+internal fun MutableCollection<Byte>.addAll(
+    bytes: ByteArray,
+): Boolean {
+    return addAll(bytes.toList())
+}
+
+internal fun UInt.toByteArray(): ByteArray {
+    return ByteArray(4) { i ->
+        val offset = (3 - i) * 8
+        (this shr offset).toByte()
+    }
+}