json_schema: {
      "$schema": "http://json-schema.org/draft-06/schema#",
      "title": "Reward",
      "description": "a reward transaction",
      "type": "object",
      "properties": {
          "tx": {
              "type": "object",
              "properties": {
                  "id": {
                      "type": "string",
                      "pattern": "^[0-9a-f]{64}$"
                  },
                  "to": {
                      "type": "object",
                      "properties": {
                          "address": {
                              "type": "string"
                          },
                          "amount": {
                              "type": "integer",
                              "exclusiveMinimum": 0
                          }
                      },
                      "required": [
                          "address",
                          "amount"
                      ]
                  },
                  "msg": {
                      "type": "string",
                      "maxLength": 254
                  }
              },
              "required": [
                  "id",
                  "to",
                  "msg"
              ]
          },
          "sign": {
              "type": "string"
          }
      },
      "required": [
          "tx",
          "sign"
      ]
  }