I have read that Electrum never is given your private keys (which makes sense), but I'm still unsure what sacrifices it makes in order to not require you to not store the entire ~14GB blockchain.

So is the gist of it "you make transactions on your own using your information, but we watch the blockchain and tell you anything relevant that happens"? Am I understanding this at all correctly?

If so, who is "we" in that? And can't whoever I am trusting lie to me about how many bitcoins I have?


"We" are volunteers running Electrum servers. There's almost no trust in them, the absolute worst they can do is feed you false negatives about the balance of your wallet, or they can also choose not to broadcast your transactions and pretend that they have. You trade some privacy in that they can see the contents of your entire wallet and associate it with your IP address. The client supports Tor connections if this is an issue for you.

The blockchain is 22Gb now, actually.

  • 1
    According to Blockchain Size, the raw size is just about 14 GB today. The extra size on your client may be due to additional indexes or other tracking data. Feb 15 '14 at 19:41
  • Yeah, the size of my Bitcoin-Qt (OS X) data directory is 17 GB. It varies by client. Feb 15 '14 at 20:46
  • "the absolute worst they can do is feed you false negatives about the balance of your wallet" According to the new version this not possible anymore. >>1. A Patricia tree data structure, also called "Ultimate Blockchain Compression", will be implemented in Electrum servers. This data structure allows a client to get the balance of any address instantly, and it will also generate a "proof of completeness" (the root hash of the patricia tree), that can be used to check that the server sent all UTXOs related to a given address to the client.<< bitcointalk.org/index.php?topic=427617.0
    – rdymac
    Feb 15 '14 at 23:06
  • @GregHewgill With indexes it's a bit larger, and it depends quite a bit on your node. Some are smaller than others.
    – user13413
    Feb 16 '14 at 3:22
  • @rdymac Yep, I wasn't sure if that was applicable or not yet though.
    – user13413
    Feb 16 '14 at 3:23

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