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Hotp.scala
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Hotp.scala
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/*
* Copyright 2021 Typelevel
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package bobcats
import cats.Functor
import cats.syntax.functor._
import scodec.bits.ByteVector
object Hotp {
private val powersOfTen =
Array(1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000)
def generate[F[_]](
key: SecretKey[HmacAlgorithm.SHA1.type],
movingFactor: Long
)(implicit F: Functor[F], H: Hmac[F]): F[Int] =
generate(key, movingFactor, digits = 6)
def generate[F[_]](
key: SecretKey[HmacAlgorithm.SHA1.type],
movingFactor: Long,
digits: Int
)(implicit F: Functor[F], H: Hmac[F]): F[Int] = {
require(digits >= 6, s"digits must be at least 6, was $digits")
require(digits < 10, s"digits must be less than 10, was $digits")
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)
}
}
}