Bitcoin based close currency for mobile payment system

[ayoubmtd]

A customer of mine want to launch a payment system in 3rd world country based on crypto-currencies and the block-chain (for transaction) with no public mining and no public trading of the currency.

    - people can register online and get a wallet
    - install the app on the phone.
    - people would buy the currency using scratch cards
    - the seller would tablet / phone
    - the transaction will be done using qrCodes

I would like to have some feedback about this project especially the security aspect of the currency.

[domob]

If there's no public mining and everything is controlled by your customer, you do not need a blockchain (unless you want it purely for marketing purposes).  Just use a database, which is much more efficient.

[ayoubmtd]

The currency will be mined internally. The blockchain would help with the offline transactions. 

[domob]

The currency will be mined internally. The blockchain would help with the offline transactions. 

I still don't get why you need a blockchain.  The purpose of the blockchain in Bitcoin is precisely to be a decentralised timestamping mechanism, so that double spends can be prevented.  If you control everything and only mine internally, you don't have to mine at all.

As far as I can think of, blockchain and offline transactions are totally orthogonal.  Can you give more details how a blockchain helps with the latter?

[ayoubmtd]

how can we impliment offline payment without the blockchain, at least we can check if the coin is valid if the blockchain on the sellers computer is recent we can ensure no double spending until the last time the blockchain was Synced.

[domob]

how can we impliment offline payment without the blockchain, at least we can check if the coin is valid if the blockchain on the sellers computer is recent we can ensure no double spending until the last time the blockchain was Synced.

I think, when you talk about "blockchain", you actually mean the "UTXO set" or even "account balances".  When you trust the central server, you can simply keep a list of balances at each address (or the UTXO set) to validate coins.  Still no need to do a blockchain with mining and all that.

BTW, you could look into Chaumian cash.

[cr1776]

how can we impliment offline payment without the blockchain, at least we can check if the coin is valid if the blockchain on the sellers computer is recent we can ensure no double spending until the last time the blockchain was Synced.

You can just have a database that you sync with when you would be syncing with the block chain.  If you are worried that someone could corrupt the database on the computer, they could do the same thing with the block chain stored on their computer.  Your "check to see if the coin is valid" would not be foolproof.

It sounds like the customer just wants to be able to use a buzzword of "block chain" without understanding the benefits and drawbacks.

And this is pretty off-topic for here, it should be in the alt-coin section.

[fbueller]

Just because you don't expect someone else to mine your coin (or see any reason why they might do this), it doesn't mean they can't, without possibly disasterous consequences for your coin.

Internal mining means you will have a modest, but still low hashrate to secure your chain. If someone decides to mine it, they could forbid any transactions from confirming, effectively being able to disrupt your currency until you buy more gear.

Also - I suspect you're trying to bundle in AML and KYC, or at least identify all users in your closed system through your website. If you use a straight bitcoin clone, you won't be able to prevent users from creating their own wallet, regardless of whether they've registered on your website or not.

In fact, using a blockchain would enable virtually anyone to write a wallet undermining your AML/KYC, and opening a can of worms that leads you back to the question I've avoided asking til now, which is why do you want a decentralized currency when a centralized one sounds more like what you need?

You don't need a blockchain in order to have a mobile payment system powered by QR codes.

[TrackCoin]

In the Digital world electronic technology is much highly improved. 3rd, 4th and 5th generation technology already came in the market. So day by day invention doing every moments somewhere. I think by mobile many companies management systems controlling many places for that Bitcoin mobile payment systems also much possible and well decision can be...