Say Belly, Alice and Teddy are Bitcoin clients.

  1. Belly makes a transaction to send 1 btc to Alice.
  2. He broadcasts this transaction to the P2P network.
  3. Teddy calculates a valid hashcode and add Belly's transaction into his block chain.

Then here is the question. How does Belly know his transaction has been accepted? Even he knows Teddy has added it into his block chain, this block chain can be rejected later if there is a longer block chain on the network, right? And what if Teddy is malicious and lying?

I heard you need to wait until 6 clients accept your transaction. I'm not sure what this exactly means. And why 6, not 5 or 7?

  • @Jori you should make that an answer
    – Tim S.
    Commented May 18, 2014 at 12:23
  • 2
    This question seems to be based on misconceptions of how the blockchain works: The asker seems to think that transactions are validated by themselves and that everyone is running their own Blockchain. Perhaps reading these questions will help resolve the underlying question: What exactly is Mining?, Can someone explain how the Bitcoin Blockchain works?
    – Murch
    Commented May 19, 2014 at 12:45

1 Answer 1


6 blocks, not 6 clients. The chances of catching up to the block with the transactions that is buried 6 blocks deep is slim. Granted of course that the dishonest party has not a very significant part (say less than 15% or so) of the hashing power. These changes can be calculated using Poisson distribution, as done in Satoshi's original paper (last pages).

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