Using AES256GCM to encrypt and decrypt a text

CryptoApp.scala

import cats.effect.{ ExitCode, IO, IOApp }
import tsec.cipher.symmetric.{ AAD, AADEncryptor, IvGen }
import tsec.cipher.symmetric.jca.{ AES256GCM, SecretKey }
import tsec.common._
import tsec.cipher.symmetric._

object CryptoApp extends IOApp {

  private val aad: AAD = AAD("KnQCxy4rW4KuxMRcvkVvAs9KufF7XR4b".utf8Bytes)

  private implicit val ctrStrategy: IvGen[IO, AES256GCM]                      = AES256GCM.defaultIvStrategy[IO]
  private implicit val cachedInstance: AADEncryptor[IO, AES256GCM, SecretKey] = AES256GCM.genEncryptor[IO]

  override def run(args: List[String]): IO[ExitCode] =
    for {
      secretKey <- AES256GCM.generateKey[IO]
      encrypted <- AES256GCM.encryptWithAAD[IO](PlainText("I'm a secret".utf8Bytes), secretKey, aad)
      base64 = encrypted.toConcatenated.toB64String
      _          <- IO.delay(println(base64))
      bytes      <- IO.fromOption(base64.b64Bytes)(new Exception("Could not decode base64"))
      cipherText <- IO.fromEither(AES256GCM.ciphertextFromConcat(bytes))
      decrypted  <- AES256GCM.decryptWithAAD(cipherText, secretKey, aad)
      _          <- IO.delay(println(decrypted.toUtf8String))
    } yield ExitCode.Success
}