TownCrier Contract

• mainnet: 0x89c1b3807d4c67df034fffb62f3509561218d30b
• Rinkeby0x9ec1874ff1def6e178126f7069487c2e9e93d0f9

Thanks to Microsoft for hosting the TC Server.

Get the attestation for Town Crier enclave

$ curl -d '{"id": 123, "jsonrpc": "2.0", "method": "attest"}' status.town-crier.org:8123
{"id":123,"jsonrpc":"2.0","result":"AgABAG4NAAAEAAQAAAAAAIiIiIiIiIiIiIiIiIiIiIgAAAAAAAAAAAAAAAAAAAAABAT//wEBAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABwAAAAAAAAAHAAAAAAAAABzbbPKy++5Ts5JzgiKEEwAgTpRQfqkNCQ1uN4xSNZI0AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAACD1xnnferKFHD2uvYqTXdDA8iZ22kCD5xw7h38CMfOngAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAACQkJCQkJCQkJCQkJCQkJCQkJCQkJCQkJCQkJCQkJCQkJCQkJCQkJCQkJCQkJCQkJCQkJCQkJCQkJCQkJCQkJCQqAIAAILdpDlCK4jEqK+V7CFVXAlqCoM5H8Srrkb4I4zs7zAWxWfeJMZodhRq5UDxEUwYCIFu6VxuSO9KeeWZbBKIser3usUDlxsBlAWiVlMjLkKoGJ5rMT4W8FashifSDoR/qySmAUJWxejSrj7EqqKufLvCzZoRZ4V3KrqkRKitRvAh2jbDswf9uEmYaK68fjDh2sTQIijz43jgFockshF7Uay8VeA5EJc9H2FnTGEPWXctuilaWGMl48iP1RDgzz3WO/Ptd1brJZ1zOhGmbMXqeFqgnJmT9+KuxOSTn1LC3t88UPpItx1v+Tq0EkJT1Y+WI83SqEgor9nUxyVJUEX39N0LIzMYD3OKfghhqmt0lh+F5oWGDNbhTHAZLYqi+Q3sfJKV4gD+P3pmCvVce2gBAADXxVsQnIOefnYNAdFg4N/BC/NEcU3aRQfEemP+a6BlAe9+xZKH6hTY4hF5+aVRl8tJ8XJaOMB8T3FPYzvFZGXkrej11fFf4P7tK7pKTStpnTVKeeCRj+91lAZcD0cNUBh9CuOW0s3SvgoKabKEoPR9lCMdogIoLHUrXn6IN+1BKKnV75wednX34it82U1O4wm4qBcL3ty7zXA7RpfeyVaXMRcDb4bACQhed75ddOhDXcklKeeowAtHL3vbsIKLZSedSp6jud3oavSbmjWzhX71xqVO25+mRxXrO9vn6YDR/s7iSU6OEc/5i+Jz8gt5KSSnuSqJcF8IiJzswAK/IQ+vwQoDPX8Rx8xwMZ4uat2exjY5vXrEz5FroedC7Yt69Z8L9iBUK+3IZ+LpUgrzftuctxCJXYzVaIpheuIi5Lbs/2GhpjninGijI1SCe1G5xJZZMja1hthuHBd9jkCGxDotNjKFOHmU0g5erOy8cEgo8j5a5C1lye2x"}

Town Crier Scrapers

Open API

Confidential API

Query interfaces

Flight Departure Delay

This scraper returns the departure delay of a given flight.

• Data source: http://flightaware.com/
• Input to TC (64 bytes):
  1. flight number
     • size: 32 bytes
     • type: string converted to bytes32, right padded with 0s
     • example: FJM273 should be 0x464a4d3237330000000000000000000000000000000000000000000000000000
  2. scheduled departure time in UNIX epoch time:
     • size: 32 bytes
     • type: uint256, big-endian encoded integer with leading zeros
     • example: 1492100100 should be 0x0000000000000000000000000000000000000000000000000000000058efa404
• Return value : delay = uint256(respData)
  • delay = 0: flight not departed yet or not delayed
  • delay > 0 && delay < 2147483643: flight delay in seconds
  • delay = 2147483643: flight cancelled
• Geth script snippet:

  TownCrier.request.sendTransaction(
      1, TC_CALLBACK_ADD, TC_CALLBACK_FID, 0,
      [0x464a4d3237330000000000000000000000000000000000000000000000000000,
      0x0000000000000000000000000000000000000000000000000000000058efa404],
      {value: fee})
  

Stock ticker

This scraper returns the closing price of a given stock symbol on a specified date in USD.

• Data source: https://finance.yahoo.com/
• Input to TC (32 bytes):
  1. stock symbol
     • size: 32 bytes
     • type: string converted to bytes32, right padded with 0s
     • example: GOOG should be 0x474f4f4700000000000000000000000000000000000000000000000000000000
  2. UNIX epoch time for the date at 00:00 GMT:
     • size: 32 bytes
     • type: uint256, big-endian encoded integer with leading zeros
     • example: 1262390400, standing for Jan 2nd, 2010, should be 0x000000000000000000000000000000000000000000000000000000004b3e8c80
• Return value : price = uint256(respData), the closing price in USD.
• Geth script snippet:

  TownCrier.request.sendTransaction(
      3, TC_CALLBACK_ADD, TC_CALLBACK_FID, 0,
      [0x474f4f4700000000000000000000000000000000000000000000000000000000,
      0x000000000000000000000000000000000000000000000000000000004b3e8c80],
      {value: fee})
  

UPS tracking

This scraper returns the status of a UPS package.

• Data source: https://www.ups.com/
• Input to TC (64 bytes):
  1. UPS tracking number
     • size: 32 bytes
     • type: string converted to bytes32, right padded with 0s
     • example: 1ZE331480394808282 should be 0x315a453333313438303339343830383238320000000000000000000000000000
• Return value : status = uint256(respData)
  • status = 0: package not found,
  • status = 1: order processed
  • status = 2: shipped
  • status = 3: in transit
  • status = 4: out for delivery
  • status = 5: delivered
• Geth script snippet:

  TownCrier.request.sendTransaction(
      4, TC_CALLBACK_ADD, TC_CALLBACK_FID, 0,
      [0x315a453333313438303339343830383238320000000000000000000000000000],
      {value: fee})
  

Coin market price

This scraper returns the current exchange rate of the queried cryptocurrency in USD.

• Data source: https://coinmarketcap.com/
• Input to TC (64 bytes):
  1. Cryptocurrency name
     • size: 32 bytes
     • type: string converted to bytes32, right padded with 0s
     • example: bitcoin should be 0x626974636f696e00000000000000000000000000000000000000000000000000
• Return value : rate = uint256(respData), current exchange rate in USD.
• Geth script snippet:

  TownCrier.request.sendTransaction(
      4, TC_CALLBACK_ADD, TC_CALLBACK_FID, 0,
      [0x626974636f696e00000000000000000000000000000000000000000000000000],
      {value: fee})
  

Weather

• To be filled

Future Town Crier features

• Preprogrammed response delays

  Currently TC can only respond to a query immediately. This limitation meants that the FlightInsurance Contract, for example, requires two separate transactions---calls to its Insure() and Request() functions respectively---for a single user and policy. Once TC supports the feature of responding with a preprogrammed delay, the FlightInsurance Contract will be able to specify a future query time for a given flight by using the parameter timestamp in the request() interface for TC. With this usage, TC will fetch data from the target flight-information website only at the scheduled departure time, eliminating the need for a user to call Request() in the FlightInsurance Contract.

• Sensitive-data management

  In some applications, TC must manage sensitive data beyond query parameters, such as user credentials. An example is the SteamTrade Contract described in the Town Crier paper. This contract allows users to buy and sell games from one another. It requires that TC have access to a user's account credentials in order to verify that ownership of a game has been transfered in the course of a trade. In the near future, TC will be instrumented to perform secure management of credentials and other sensitive data.

• More websites

  In the current alpha version of TC, only a few scrapers are supported. We look forward to your ideas about what new scrapers and applications TC should support!