Add HOTP algorithm

core/js/src/main/scala/bobcats/HotpPlatform.scala

@@ -0,0 +1,5 @@
+package bobcats
+
+private[bobcats] trait HotpPlatform[F[_]] {}
+
+private[bobcats] trait HotpCompanionPlatform {}

core/jvm/src/main/scala/bobcats/HotpPlatform.scala

@@ -0,0 +1,5 @@
+package bobcats
+
+private[bobcats] trait HotpPlatform[F[_]] {}
+
+private[bobcats] trait HotpCompanionPlatform {}

core/shared/src/main/scala/bobcats/Hotp.scala

@@ -0,0 +1,42 @@
+package bobcats
+
+import cats.effect.kernel.Sync
+import cats.syntax.functor._
+import scodec.bits.ByteVector
+
+sealed trait Hotp[F[_]] extends HotpPlatform[F] {
+  def generate(
+      key: SecretKey[HmacAlgorithm.SHA1.type],
+      movingFactor: Long,
+      digits: Int = 6
+  ): F[Int]
+}
+
+private[bobcats] trait UnsealedHotp[F[_]] extends Hotp[F]
+
+object Hotp extends HotpCompanionPlatform {
+  private val powersOfTen =
+    Array(1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000)
+
+  def apply[F[_]](implicit hotp: Hotp[F]): hotp.type = hotp
+
+  implicit def forSync[F[_]](implicit F: Sync[F], H: Hmac[F]): Hotp[F] =
+    new UnsealedHotp[F] {
+      override def generate(
+          key: SecretKey[HmacAlgorithm.SHA1.type],
+          movingFactor: Long,
+          digits: Int
+      ): F[Int] = {
+        H.digest(key, ByteVector.fromLong(movingFactor)).map { hmac =>
+          val offset = hmac.last & 0xf
+
+          val binaryCode = ((hmac.get(offset.longValue) & 0x7f) << 24) |
+            ((hmac.get((offset + 1).longValue) & 0xff) << 16) |
+            ((hmac.get((offset + 2).longValue) & 0xff) << 8) |
+            (hmac.get((offset + 3).longValue) & 0xff)
+
+          binaryCode % powersOfTen(digits)
+        }
+      }
+    }
+}

core/shared/src/test/scala/bobcats/HotpSuite.scala

@@ -0,0 +1,38 @@
+package bobcats
+
+package bobcats
+
+import cats.Functor
+import cats.effect.IO
+import cats.effect.SyncIO
+import munit.CatsEffectSuite
+import cats.syntax.functor._
+
+import scala.reflect.ClassTag
+import scodec.bits.ByteVector
+
+class HotpSuite extends CatsEffectSuite {
+
+  val key = ByteVector.fromHex("3132333435363738393031323334353637383930").get
+
+  val expectedValues = List(
+    755224, 287082, 359152, 969429, 338314, 254676, 287922, 162583, 399871, 520489
+  )
+
+  def tests[F[_]: Hotp: Functor](implicit ct: ClassTag[F[Nothing]]) = {
+    expectedValues.zipWithIndex.foreach {
+      case (expected, counter) =>
+        test(s"RFC4226 test case ${counter} for ${ct.runtimeClass.getSimpleName()}") {
+          Hotp[F]
+            .generate(SecretKeySpec(key, HmacAlgorithm.SHA1), counter.toLong, digits = 6)
+            .map { obtained => assertEquals(obtained, expected) }
+        }
+    }
+  }
+
+  if (Set("JVM", "NodeJS").contains(BuildInfo.runtime))
+    tests[SyncIO]
+
+  if (BuildInfo.runtime != "JVM")
+    tests[IO]
+}