Bitcoin Forum

Hi there,

Sorry for the beginner-level question here! I'm using Bitcoin Core as my wallet software. I have already read the Bitcoin Wiki about backing up my wallet.dat file, but I'm still confused about how often I need to be backing up my wallet.dat file. I ask because I'm getting close to having 100 "receiving addresses", and I'm trying to figure out if I need to start making a backup of my wallet.dat file after every single transaction.

From what I understand, my wallet.dat file started off by creating 100 addresses for me (even though I can't see all 100 private addresses from within Bitcoin Core's GUI). Also, it is my understanding that every time I send Bitcoins, another one of my 100 addresses is (potentially) used up as the "change address" for that transaction.

So my concern is that I'm getting very close to using up all of my 100 original addresses, and that I may have even gone over the original 100 addresses if you count the "change addresses". What happens if I go over the 100 addresses? Does Bitcoin Core create 1 new address whenever a new address is needed? Or does Bitcoin Core create a set of 100 new addresses in the background for me at some point? Or, even better, does Bitcoin Core ALWAYS keep a pool of 100 unused addresses in the background, so that when I make a backup of my wallet.dat file, it is always backing up the next 100 addresses?

Am I even understanding this at all?? I suppose my question is: how often should I be backing up my wallet.dat file, and should I be backing it up after every single transaction?

Thanks so much!!

It's the later: There is a pool of 100 keys in your wallet. See https://en.bitcoin.it/wiki/Key_pool (https://en.bitcoin.it/wiki/Key_pool)

Ah, excellent. Thanks so much! So, there is always a queue of 100 new keys waiting in the background… so if I only make a backup after every 2 or 3 transactions, I should be fine… because each backup will also contain the current pool of 100 keys.

Thanks! :)

Interesting.. I was under the impression if I backed up my wallet.dat file I could come back 50 years form now and there would be no issue(say for hackers).

It seems like that would only be the case with a "deterministic wallet", which determines all of your addresses FOREVER at the time of wallet creation. I believe that Armory is a deterministic wallet.

Meanwhile, with Bitcoin Core, it appears like each backup is only valid for the next 100 addresses.

You are correct. That is simply because all the addresses are created from a single seed and so when the process is repeated it creates replicable results.  Currently, both Electrum and Armory offer the option of deterministic wallets.

If you want to ensure you don't lose any coins, backing up every 100 transactions is perfectly fine. Personally, I'm not inclined to download the whole blockchain (anymore) and have to consistently back up my wallet, so I'd really just advise Electrum. One solid wallet backup is all you need to do (have multiple copies spread over of course) and you don't need to waste time updating your blockchain data.

Hum.... so as long as my offline QT wallet doesn't send/receive to many trasnactions I'm okay..?