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A transfers ETH to B: who needs to be in sync with the blockchain? My comprehension is that A only needs to be sync, is that correct ?

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    I'm tempted to say it's possible to sign transactions without any synced client on both sides cause the network decides whether the transaction is valid. But I leave the answer to the experts. – Afr Mar 23 '16 at 9:47
  • I think you may be correct. You can sign transactions offline. Whether they are accepted is up to the network – dbryson Mar 23 '16 at 9:58
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Neither of the clients need to be in sync to get the transaction through.

For a transaction to be valid you only need to have enough funds on the sender balance, use the correct nonce for the sender account (that you could retrieve from a block explorer for example) and sign the entire thing with the sender's private key. If you inject just a transaction into the network, it will happily accept and process it.

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  • ok that's the nonce part I was missing...thanks it's very clear – euri10 Mar 23 '16 at 15:56
  • is there anyway to know if the current geth instance is in sync with the network so that it will use a correct nonce? – knocte May 24 '16 at 7:15
  • (and I meant, programmatically, via API) – knocte May 24 '16 at 7:15
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Péter provides the answer to the general question about transactions.

In practical terms, when using a wallet, a sender of Ether needs to be in sync, otherwise the wallet may generate an invalid transaction that will never be processed.

For example, a wallet that's not synced (and unaware of Ether the sender may have already spent) might use a wrong nonce or try to send more Ether than what the sender actually has.

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  • that's effectively an important point, there is theory and there is practice. – euri10 Apr 11 '16 at 6:58
  • But it's not dangerous, right? It just won't work occasionally, possibly, if the wallet is not in sync. So we can try and the sky won't fall down on us. – Vesa May 23 '16 at 5:25
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    @Vesa not dangerous because you can't overdraw and get charged fees like a bank would do; but it could be inconvenient if you make many payments and find out that 90% of them didn't work because you didn't have the actual funds: you'd probably have to redo those failed payments again. – eth♦ May 23 '16 at 7:24
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    Right, yeah. Inconvenient but not unsafe, then. – Vesa May 28 '16 at 11:36

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