Random string password generator in Scala

Managing our research cluster, I frequently need to generate some string for new users’ password. How to generate them automatically and randomly in Scala? The passwords need characters ‘a’ – ‘z’, ‘A’ – ‘Z’ and ‘0’ – ‘9’ only.

This piece of code works very well for me:

  def randomString(len: Int): String = {
    val rand = new scala.util.Random(System.nanoTime)
    val sb = new StringBuilder(len)
    val ab = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
    for (i <- 0 until len) {
      sb.append(ab(rand.nextInt(ab.length)))
    }
    sb.toString
  }

The characters are selected pseudo randomly selected from the alphabet (ab). You can add/delete characters to include/exclude them in the passwords.

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Since you’re dealing with passwords, you probably want to have a safer generation method. Here’s an example with SecureRandom taken from here:

object RandomUtil {
  private val random = SecureRandom.getInstanceStrong

  def alphanumeric(nrChars: Int = 24): String = {
    new BigInteger(nrChars * 5, random).toString(32)
  }
}