So what exactly does/can the standard backup .dat file do?

[Neverest]

I am reading about securing the wallet, about people losing access, keyloggers, Trust No One, Backups and more.
I am running the basic Bitcoin client and it offers the option to back up the wallet, which creates a .dat file.

1) What does this dat file do, what is possible with it?
2) Does it contain access to your current wallet or just to your wallet (and BTC) at the time of the backup? I.e. if somebody gets a copy of my first .dat back up, can they use it to hack/empty my wallet?
3) I am still confused about the easiest way to secure/encrypt the wallet, any tips welcome.
4) Can an encrypted wallet be backed up in the same way? Or do I encrypt the back up file?

I have constant back ups of my desktop PC, to a HDD and online. But is it safe to have .dat files online (whether it is on Crashplan, sending it to your own Gmail etc)?

Thanks!

[BitSlut69]

This is unfortunately fairly complicated when you consider every detail of how a wallet works. I'll try to answer your questions accurately without getting into a bunch of details.

1) The .dat file stores all of your "keys" for your bitcoin addresses, both public and private keys. Private keys are what are used to prove ownership of the public address and should be protected and/or secured.

2)

Does it contain access to your current wallet or just to your wallet (and BTC) at the time of the backup?

Well, that gets tricky because there are "invisible" addresses/keys stored in your wallet too (I believe the number is of these phantom addresses/keys is 100). These become visible when you click to create a new address and are also used to send "change" back into your wallet when you send coins to an address that is of an amount less than a single input to one of your addresses. Some invisible/future addresses are stored in the .dat file, but if the .dat file is too old it won't contain all of the addresses/keys that have been used.

So if a .dat backup is too old (IE, if the sum of the number of sends you made plus the number of new addresses you created is more than 100) it will not have access to all your coins. This scenario is bad, you want your backup to have access to all your keys/addresses/coins because that is the purpose of the backup. Make frequent backups and you'll be all set.

The simplified answer is yes your backup wallet will have access to all your bitcoins, even if the transaction occurred after you made the backup, and yes if someone gets an old .dat file they have access to empty you wallet!

3) Use the "encrypt wallet" feature in the Bitcoin-QT client and/or store your .dat file(s) on an encrypted TrueCrypt volume. Do that for the live/running wallet file that the client is currently using in addition to all backup wallet files.

4) I believe an encrypted wallet can be backed up the same way as an un-encrypted wallet and will create a file with a .dat extension. A password will be necessary to import that encrypted wallet though.

Well, I guess I got into some of the details. Someone let me know if I missed any other details or gave any inaccurate information.

[Neverest]

Thanks very much, that is already very helpful!

[factual22]

This is unfortunately fairly complicated when you consider every detail of how a wallet works. I'll try to answer your questions accurately without getting into a bunch of details.

1) The .dat file stores all of your "keys" for your bitcoin addresses, both public and private keys. Private keys are what are used to prove ownership of the public address and should be protected and/or secured.

2)

Does it contain access to your current wallet or just to your wallet (and BTC) at the time of the backup?

Well, that gets tricky because there are "invisible" addresses/keys stored in your wallet too (I believe the number is of these phantom addresses/keys is 100). These become visible when you click to create a new address and are also used to send "change" back into your wallet when you send coins to an address that is of an amount less than a single input to one of your addresses. Some invisible/future addresses are stored in the .dat file, but if the .dat file is too old it won't contain all of the addresses/keys that have been used.

So if a .dat backup is too old (IE, if the sum of the number of sends you made plus the number of new addresses you created is more than 100) it will not have access to all your coins. This scenario is bad, you want your backup to have access to all your keys/addresses/coins because that is the purpose of the backup. Make frequent backups and you'll be all set.

The simplified answer is yes your backup wallet will have access to all your bitcoins, even if the transaction occurred after you made the backup, and yes if someone gets an old .dat file they have access to empty you wallet!

3) Use the "encrypt wallet" feature in the Bitcoin-QT client and/or store your .dat file(s) on an encrypted TrueCrypt volume. Do that for the live/running wallet file that the client is currently using in addition to all backup wallet files.

4) I believe an encrypted wallet can be backed up the same way as an un-encrypted wallet and will create a file with a .dat extension. A password will be necessary to import that encrypted wallet though.

Well, I guess I got into some of the details. Someone let me know if I missed any other details or gave any inaccurate information.

How do you store your actual wallet.dat (not your backup) in a TrueCrypt volume?  I have my backups in a TrueCrypt volume, however how can you do that with an active wallet.dat file that Bitcoin-QT "boots" from?  I guess what I am asking is how to "import" that wallet.dat file into Bitcoin-QT so if I change the location of it (i.e. in a volume) Bitcoin-QT will by default load the .dat file from that location.

[Haole]

How do you store your actual wallet.dat (not your backup) in a TrueCrypt volume?  I have my backups in a TrueCrypt volume, however how can you do that with an active wallet.dat file that Bitcoin-QT "boots" from?  I guess what I am asking is how to "import" that wallet.dat file into Bitcoin-QT so if I change the location of it (i.e. in a volume) Bitcoin-QT will by default load the .dat file from that location.

You just keep your wallet.dat file inside your TrueCrypt volume until needed.  When you want to use your Bitcoins in that wallet, just copy the file inside the TrueCrypt volume back into your Bitcoin Folder (all the while offline) and then run the client as usual.  I don't think there is any way to load your wallet.dat while it is contained within an encrypted volume but I'm as far from a geek as it gets.  Perhaps someone with much more knowledge and savvy can offer better suggestions.

[nebulus]

The only time I used this feature was to set up an online wallet. You don't really need it to back up your private keys like that. Just move the wallet.dat file to an offline and delete the file.