rules.txt

{
  "rules": {
    ".read": "auth != null",
    ".write": "auth != null",
    "game": {
      ".read": "auth != null",
      ".write": "auth.uid != null
      && data.child('board').val().length == 16
      &&  data.child('correct').val().length == 16",
      
      "correct": { ".validate": "newData.isString()"},
      "board": { ".validate": "newData.isString()" },
      "turnId": { ".validate": "newData.isString()" },
      "counter": { ".validate": "newData.isNumber()" },
      "card1": { ".validate": "newData.isNumber()" },
    	"card2": { ".validate": "newData.isNumber()" },
      "$other" :{".validate": false}
    },
    "players": {
      "$uid": {
        ".write": "auth != null && auth.uid == $uid",
        "id": {".validate": "newData.isString()" },
        "name": {".validate": "newData.isString()" },
        "points": { ".validate": "newData.isNumber()" },
        "$other": { ".validate": false }
      }
    },
    "$others": {".validate": false}
  }
}