initial commit

src/commonMain/kotlin/com/infendro/mac/HMAC.kt

@@ -0,0 +1,45 @@
+package com.infendro.mac
+
+import com.infendro.hash.*
+import kotlin.experimental.xor
+
+class HMAC(
+    val function: HashFunction,
+) {
+    val block: Int
+        get() = when (function) {
+            MD5, SHA1, SHA224, SHA256 -> 64
+            SHA384, SHA512 -> 128
+        }
+
+    fun hash(
+        key: ByteArray,
+        value: ByteArray,
+    ): ByteArray {
+        val paddedKey = pad(key)
+
+        val innerKey = paddedKey.map { it xor 0x36 }.toByteArray()
+        val outerKey = paddedKey.map { it xor 0x5C }.toByteArray()
+
+        return function.hash(outerKey + function.hash(innerKey + value))
+    }
+
+    private fun pad(
+        key: ByteArray,
+    ): ByteArray {
+        if (key.size > block) {
+            return function.hash(key)
+        }
+
+        if (key.size < block) {
+            return buildList {
+                addAll(key.toList())
+                repeat(block - size) {
+                    add(0x00)
+                }
+            }.toByteArray()
+        }
+
+        return key
+    }
+}