Quick and easy vigenere encoding

gistfile1.scala

val Alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

def vigenere(key:String, message:String) = { 
    val keyLength = key.length
    val builder = new StringBuilder(message.length)
    for((c, i) <- message.zipWithIndex) {
    	val index = (c + key(i % keyLength)) % 26
    	builder.append(Alphabet(index))
    }
    builder.toString()
}

vigenere("REDDIT", "TODAYISMYBIRTHDAY")