{
  "nftables": [
    {
      "metainfo": {
        "version": "VERSION",
        "release_name": "RELEASE_NAME",
        "json_schema_version": 1
      }
    },
    {
      "table": {
        "family": "inet",
        "name": "portknock",
        "handle": 0
      }
    },
    {
      "chain": {
        "family": "inet",
        "table": "portknock",
        "name": "input",
        "handle": 0,
        "type": "filter",
        "hook": "input",
        "prio": -10,
        "policy": "accept"
      }
    },
    {
      "set": {
        "family": "inet",
        "name": "clients_ipv4",
        "table": "portknock",
        "type": "ipv4_addr",
        "handle": 0,
        "size": 65535,
        "flags": [
          "timeout",
          "dynamic"
        ]
      }
    },
    {
      "set": {
        "family": "inet",
        "name": "candidates_ipv4",
        "table": "portknock",
        "type": [
          "ipv4_addr",
          "inet_service"
        ],
        "handle": 0,
        "size": 65535,
        "flags": [
          "timeout",
          "dynamic"
        ]
      }
    },
    {
      "rule": {
        "family": "inet",
        "table": "portknock",
        "chain": "input",
        "handle": 0,
        "expr": [
          {
            "match": {
              "op": "==",
              "left": {
                "payload": {
                  "protocol": "tcp",
                  "field": "dport"
                }
              },
              "right": 10001
            }
          },
          {
            "set": {
              "op": "add",
              "elem": {
                "elem": {
                  "val": {
                    "concat": [
                      {
                        "payload": {
                          "protocol": "ip",
                          "field": "saddr"
                        }
                      },
                      10002
                    ]
                  },
                  "timeout": 1
                }
              },
              "set": "@candidates_ipv4"
            }
          }
        ]
      }
    },
    {
      "rule": {
        "family": "inet",
        "table": "portknock",
        "chain": "input",
        "handle": 0,
        "expr": [
          {
            "match": {
              "op": "==",
              "left": {
                "payload": {
                  "protocol": "tcp",
                  "field": "dport"
                }
              },
              "right": 10002
            }
          },
          {
            "match": {
              "op": "==",
              "left": {
                "concat": [
                  {
                    "payload": {
                      "protocol": "ip",
                      "field": "saddr"
                    }
                  },
                  {
                    "payload": {
                      "protocol": "tcp",
                      "field": "dport"
                    }
                  }
                ]
              },
              "right": "@candidates_ipv4"
            }
          },
          {
            "set": {
              "op": "add",
              "elem": {
                "elem": {
                  "val": {
                    "concat": [
                      {
                        "payload": {
                          "protocol": "ip",
                          "field": "saddr"
                        }
                      },
                      10003
                    ]
                  },
                  "timeout": 1
                }
              },
              "set": "@candidates_ipv4"
            }
          }
        ]
      }
    },
    {
      "rule": {
        "family": "inet",
        "table": "portknock",
        "chain": "input",
        "handle": 0,
        "expr": [
          {
            "match": {
              "op": "==",
              "left": {
                "payload": {
                  "protocol": "tcp",
                  "field": "dport"
                }
              },
              "right": 10003
            }
          },
          {
            "match": {
              "op": "==",
              "left": {
                "concat": [
                  {
                    "payload": {
                      "protocol": "ip",
                      "field": "saddr"
                    }
                  },
                  {
                    "payload": {
                      "protocol": "tcp",
                      "field": "dport"
                    }
                  }
                ]
              },
              "right": "@candidates_ipv4"
            }
          },
          {
            "set": {
              "op": "add",
              "elem": {
                "elem": {
                  "val": {
                    "concat": [
                      {
                        "payload": {
                          "protocol": "ip",
                          "field": "saddr"
                        }
                      },
                      10004
                    ]
                  },
                  "timeout": 1
                }
              },
              "set": "@candidates_ipv4"
            }
          }
        ]
      }
    },
    {
      "rule": {
        "family": "inet",
        "table": "portknock",
        "chain": "input",
        "handle": 0,
        "expr": [
          {
            "match": {
              "op": "==",
              "left": {
                "payload": {
                  "protocol": "tcp",
                  "field": "dport"
                }
              },
              "right": 10004
            }
          },
          {
            "match": {
              "op": "==",
              "left": {
                "concat": [
                  {
                    "payload": {
                      "protocol": "ip",
                      "field": "saddr"
                    }
                  },
                  {
                    "payload": {
                      "protocol": "tcp",
                      "field": "dport"
                    }
                  }
                ]
              },
              "right": "@candidates_ipv4"
            }
          },
          {
            "set": {
              "op": "add",
              "elem": {
                "elem": {
                  "val": {
                    "concat": [
                      {
                        "payload": {
                          "protocol": "ip",
                          "field": "saddr"
                        }
                      },
                      10005
                    ]
                  },
                  "timeout": 1
                }
              },
              "set": "@candidates_ipv4"
            }
          }
        ]
      }
    },
    {
      "rule": {
        "family": "inet",
        "table": "portknock",
        "chain": "input",
        "handle": 0,
        "expr": [
          {
            "match": {
              "op": "==",
              "left": {
                "payload": {
                  "protocol": "tcp",
                  "field": "dport"
                }
              },
              "right": 10005
            }
          },
          {
            "match": {
              "op": "==",
              "left": {
                "concat": [
                  {
                    "payload": {
                      "protocol": "ip",
                      "field": "saddr"
                    }
                  },
                  {
                    "payload": {
                      "protocol": "tcp",
                      "field": "dport"
                    }
                  }
                ]
              },
              "right": "@candidates_ipv4"
            }
          },
          {
            "set": {
              "op": "add",
              "elem": {
                "elem": {
                  "val": {
                    "payload": {
                      "protocol": "ip",
                      "field": "saddr"
                    }
                  },
                  "timeout": 600
                }
              },
              "set": "@clients_ipv4"
            }
          },
          {
            "log": {
              "prefix": "Successful portknock: "
            }
          }
        ]
      }
    },
    {
      "rule": {
        "family": "inet",
        "table": "portknock",
        "chain": "input",
        "handle": 0,
        "expr": [
          {
            "match": {
              "op": "==",
              "left": {
                "payload": {
                  "protocol": "tcp",
                  "field": "dport"
                }
              },
              "right": 22
            }
          },
          {
            "match": {
              "op": "==",
              "left": {
                "payload": {
                  "protocol": "ip",
                  "field": "saddr"
                }
              },
              "right": "@clients_ipv4"
            }
          },
          {
            "counter": {
              "packets": 0,
              "bytes": 0
            }
          },
          {
            "accept": null
          }
        ]
      }
    },
    {
      "rule": {
        "family": "inet",
        "table": "portknock",
        "chain": "input",
        "handle": 0,
        "expr": [
          {
            "match": {
              "op": "==",
              "left": {
                "payload": {
                  "protocol": "tcp",
                  "field": "dport"
                }
              },
              "right": 22
            }
          },
          {
            "match": {
              "op": "in",
              "left": {
                "ct": {
                  "key": "state"
                }
              },
              "right": [
                "established",
                "related"
              ]
            }
          },
          {
            "counter": {
              "packets": 0,
              "bytes": 0
            }
          },
          {
            "accept": null
          }
        ]
      }
    },
    {
      "rule": {
        "family": "inet",
        "table": "portknock",
        "chain": "input",
        "handle": 0,
        "expr": [
          {
            "match": {
              "op": "==",
              "left": {
                "payload": {
                  "protocol": "tcp",
                  "field": "dport"
                }
              },
              "right": 22
            }
          },
          {
            "reject": {
              "type": "tcp reset"
            }
          }
        ]
      }
    }
  ]
}