I recently read about the Digitally project, an overlay payment scheme for use on mobile phones, whose goals are to extend mobile phone payments to areas with poor connectivity and reduce transaction fees.

In summary: DigiTally enables two people to do a payment transaction by simply copying short strings of numbers between their phones. This doesn't need either smartphones or a network connection. Either phone can upload the transaction later, once it gets a network connection.

I see the benefit of such a system working in underdeveloped economics, wherein branchless mobile banking is a way of life. Alice and Bob can engage in an offline transaction which is later verified and added to the blockchain once either of them get internet access.

Are there any technical implementations on Bitcoin or any other cryptocurrency which allow for asynchronous transactions such as the above? If not, then how can we imagine it would look like?

Is there a solution to the double spend problem that works on a delay tolerant network?

  • Effectively, you're asking if there's an offline asynchronous solution to the double-spend problem.
    – user58807
    Oct 9 '17 at 20:45
  • Yes - in a nutshell...
    – methuselah
    Oct 9 '17 at 20:45

As explained in the referenced paper [4] "SMAPs: Short Message Authentication Protocols", the security issue is the delay-tolerant networking. Bitcoin already requires a minimum of 6, or better 8, blocks before a transaction is sufficiently secured. The trade off is between delaying the settlement and lowering the risk.

  • I’m sorry but could you please clarify, and thanks for introducing a new dynamic to the discussion - how would bitcoin work on a delay tolerant network?
    – methuselah
    Oct 10 '17 at 6:35
  • Transaction is secured when is stored into the blockchain. If we are offline our transaction is not settled until one of us go online and notarize the transaction to a Bitcoin node. This aspect adds a delay to the usual time that we must wait for the settlement. More delay is equal to less security.
    – cisba
    Oct 10 '17 at 6:59
  • Is it possible to temporarily debit the senders account and credit the receivers account so that the funds are available for use immediately? If so, what are the risks that could arise?
    – methuselah
    Oct 10 '17 at 8:19
  • Funds are not available until settlement. Risk is the same of cheques. en.m.wikipedia.org/wiki/Cheque?wprov=sfla1
    – cisba
    Oct 10 '17 at 8:36

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