MultiBit

[jim618]

Thanks Kazimir - good that you are getting clean confirmations. Let me know if you see it again.

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[Kazimir]

Another question, regarding backups and creation of new keys/addresses.

As far as I understand, the default client (Bitcoin-Qt) precomputed 100 keys in advances. And whenever you make a payment (send some bitcoins to someone else), the change is not returned to the sending address, but to your next address in line. Reason: using a new address after every payment improves anonimity. And calculating 100 keys in advance is to make sure that a backup of your wallet does not become expired/incomplete as soon as you make a single payment (although it will if you'd make more than 100 payments since your last backup and your hdd crashes).

Does MultiBit also do something like this? When looking up my own payments on blockchain.info, I noticed the change is return to same address. So I guess not?

In that case, as long as I don't manually create any new addresses in a wallet myself, will a backup of my wallet remain valid? Even if I get or make new transactions (receive or send) afterwards? I understand I might lose notes, labels, comments, or other personal stuff that I filled in for those new transactions, but I mean 'remain valid' as in I won't lose any actual bitcoins.

Put differently: if I just export the private keys, would that be a sufficient backup (to not lose any bitcoins) as long as I don't add new keys/addresses myself?

(with 'backup' I mean copying up the wallet files or exporting the private keys, and storing them on a remote location (encrypted of course), to avoid losing bitcoins in case my harddisk crashes)

[jim618]

Hi Kazimir,

You are correct. The MultiBit change goes back to the first address used in the transaction inputs. There is not a pool of future addresses like in the Satoshi client.

You can backup the wallet with a private key export as you suggest.

There is a how-to in the MultiBit help (which is basically identical to what you have outlined) here:
http://multibit.org/help_backupWalletUsingPrivateKeys.html

If you have a non-trivial amount of money in any bitcoin wallet I would definitely recommend having an encrypted backup of your private keys somewhere safe.

You can also keep a backup of the actual wallet file with the keys in it too but the private keys are all you need.

The encrypted private key file is IMO superior as you can:
+ Decrypt it using openssl i.e. you do not need MultiBit to do the decrypt.
+ Import the keys into pretty much anything - they are standard Satoshi wallet import private key format.

[Kazimir]

Awesome. Thanks a lot Jim!

In fact I'll go ahead and create bunch of more new addresses in advance myself, for future usage. Then I'll export the private keys and back them up somewhere safe, and I should be good.
(Regardless, I will still making frequent backups of my regular wallet files as well, just to keep my personal labels and transaction notes and stuff)

One more thing, just wondering: what is in a wallet file, other than the keys + transaction data? For example I've got one wallet that is almost 6 MB now, and there aren't that many addresses or transactions from or to them so far (approx 15 addresses and 20 transactions in total). And a few labels, that's it. Does it contain tons of blockchain data or something?

[jim618]

Hi Kazimir,

Yes that should work.

The current wallet format is a bit 'bloat-ey' yes. It only contains keys and transactions but not in a very compact format.

The underlying library I use (bitcoinj) has a new wallet format that is a lot more compact (based on protobufs - what Google uses for its machine to machine chatter) and I will be moving to this format probably over the next month or so. That should trim the wallet sizes down quite a lot.

(The format change should be transparent to people).

To keep the label information backed up make sure you copy the <wallet name>.info files (stored in the same directory as the main wallet file) as the labels are in there at the moment.


Preserving anonymity
If you have an address that is publically linked to you (a donation address say) then you can improve your privacy by having two wallets:

+ A 'public' wallet with the donation address in
+ A separate more anonymous wallet with a completely distinct set of keys in.

If you make sure you fund the anonymous wallet "anonymously" then the two sets of transactions in the separate wallets will be completely unconnected.

You could then back them up with two separate private key exports.

[Kazimir]

Some feature requests / suggestions:

• 1. Ability to see how much bitcoins are on each individual address.
  Of course I can do so manually through http://blockchain.info/q/getreceivedbyaddress/MyAddressHere but it'd be nice to have an easy gui feature for this. An extra column or tab or something.
  You might wanna make this optional cause in a way it's 'extra clutter' that may confuse people.
  
  
• 2. Ability to move addresses to other wallets. E.g. select one or several addresses, then right click → move to wallet → New / Wallet 1 / Wallet 2 / etc.
  If you move all addresses out of a wallet, offer the option to delete that wallet, or to auto-generate a new address in it.
  (What would happen if you 'split' two addresses that have been in a single transaction together before: uhm, I guess the same as what happens when you export their private keys and import them to two separate wallets)
  
  
• 3. Encrypted wallets. I know this is already on your wish list, but two extra considerations:
  
  
  • 3a. Only requesting the password to send money (i.e. to sign a transaction), not just to open the wallet and see its contents.
    (Well in a way this is kinda obvious so maybe you were planning to do it like this already, just mentioning )
    
    
  • 3b. Different passwords per wallet. This allows for an "everyday wallet" with just some spare change, and a "savings wallet" with tons of bitcoins, for example.
    The idea here is to enhance security, by spreading the risk so to speak. Even if your system is compromised with a keylogger or whatever, as long as you are paying with your everyday wallet they still won't be able to access your savings account.
    
  
  
• 4. Advanced option when sending payments: ability to specify to what address the change is being returned.
  

Hope this helps! I ♥ MultiBit

[Kazimir]

Oh and while I'm at it:

• 5. Make MultiBit portable, i.e. having a data dir relative to the executable, rather than relying on %appdata%\MultiBit (or the Mac and Linux equivalents of that).
  And in the multibit.properties settings file, allow relative paths (relative to the properties file) for example ".\Wallets\mycoinz.wallet" would refer to a "Wallets" subdir inside the same dir where the .properties file is located.
  
  This will improve security: malware cannot simply scan %appdata%\MultiBit and find references to wallet files. There is no specific path or location where malware can start searching.
  And it also allows MultiBit to completely run on an encrypted location (e.g. truecrypt container). Or from a USB stick. Or both.
  
  Running from a USB stick is quite useful actually: I can choose to only mount it when I need to do some bitcoin business, and together with feature 3b above I could easily access my wallets and just send small transactions from my spare change wallet on my regular PC. And for rare transactions from my big fat savings wallet, I connect it to a separate ultra clean maximum security dedicated bitcoin laptop, and I will only ever enter the password for the savings wallet there.

Also this comes to mind: when MultiBit signs a transaction, does it need to send that transaction to the network immediately, and otherwise it fails? Or could it also sign the transaction (this is the only part that actually requires the private key, and its password it it's encrypted) and then store the signed transaction in some queue to be sent to the network. Normally this occurs instantly (it's being sent right after signing) but in the above scenario, I could also sign transactions on a dedicated ultra secure machine which is never connected to the internet and then later mount my MultiBit USB stick on a normal PC to actually send them to the network.

[jim618]

Hi Kazimir,

Thanks for your suggestions - if I go through them one by one:

1. Good idea. It could go as an extra column in the list of receiving addresses. You would want it optionally on though - it is quite easy to overwhelm new users with too much information.

2. This is actually a bit tricky to implement as a private key might be used for several of the transactions in a wallet - the receipts are ok but with the spends the transaction outputs for the the private key might be used in various transactions. Imagine trying to unpick a web to pull out a particular node.

There is potential to do things like merging wallets but to pick out a particular key from its 'brethren' when you have transaction connecting them all together would be confusing in practice I think.

The export/ reimport keys can also be confusing to people not familiar with the concept of private keys as you can easily get into the situation where the same key is in two wallets.  You have just doubled your bitcoin !   Well of course you have not but for the lay person it looks like you have.

It is a bit of a balancing act to make bitcoin 'look' like regular money and hide away the technicalities.


3a. This is what I am planning to do - encrypt just the private keys so that you can receive BTC and see all the transactions even when the wallet is password protected. There will probably be a password field in the 'Send Confirm' screen, maybe with a timeout so that you do not have to keep entering it everytime.
3b. Yes, this is the plan - one password per wallet.

4. There is definitely potential to improve the UI be able to specify the send and change addresses yes.

5. If you are willing to do a bit of file copying you can do this already: http://multibit.org/help_runFromUSBDrive.html
I would like actually to have a MultiBitPortable which adheres to the PortableApps.com specification so that it can be used in their app launcher. I have looked at the spec and it looks doable but of course it takes time to get it all working and get the build to produce the artifacts etc.   

Relative path support for wallets is a good idea yes. Will look into that.

RE: signing transactions. Bitcoinj (the library behind MultiBit) already has separated out the steps of signing and transmitting.
I am sure there was some discussion on the bitcoinj mailing list about enhancing the network layer to retransmit transactions if the network disappears but I am not sure what the status of it is.

To be honest Armory is doing such a good job of offline transaction support I am concentrating on other areas (there is only so much one person can do.   :-) ).   I am concentrating at the moment on backend improvements, the wallet encryption and a conversion of the wallet format so I expect it will be a while before I get back on pure UI improvements.

Thanks for the input - it gives me ideas for where improvements can be made in the future.

Cheers

 

[Mike Hearn]

Pending transactions are written to the wallet. When a new peer connects all pending transactions are announced to it (in the latest versions). So that "queue" already exists, it's in the wallet itself.

I think that code may have been in 0.5, don't recall. So it may require a multibit update.

[jim618]

Thanks for the clarification Mike.

[jim618]

Looking for guinea pigs (bleeding edge testers) !

Hi All,

I have just started upgrading MultiBit to use a new format for the wallet, called protobuf.
This format is a lot more compact than the previous one and is more extensible so will make it easier to add features in the future.

In a test I did today an old wallet of size 1.7MB is now only 12KB which is quite an improvement. It is actually the format Google uses for the majority of its machine-to-machine chatter. It can also be read easily by C++ and python code.

Because it is people's BTC we are talking about, I would like to have a few guinea pigs to try it out beforehand to make sure the migration process for the wallets works with zero problems. Obviously this is in addition to the testing I am doing as I work on it.

The testing should be a matter of:
1) backing up your wallets
2) installing a new version of MultiBit (from github, not off the multibit.org website)
3) starting up MultiBit and checking that everything works (send, receive a few transactions etc).
4) stopping MultiBit.
5) restarting it to check all the wallets load ok.

That is pretty much it.

Older versions of MultiBit will not be able to read the new format so it is important it works properly. (I will be putting in an automatic wallet backup in the old format just to be safe).

If you would like to try out the new beta version (which will probably appear later on this week) please post here.  Please also post if you are Win/ Linux/ Mac so that we get good coverage of operating systems. I program on a Mac but it would be good to have independant testers for all three.

Thanks in advance.

[Kazimir]

I trust the risk of accidentally sending transaction to wrong destination addresses is non-existent?

Cause for insurance reasons I'll just export my private keys and keep them safe, separated from my MultiBit wallet dir. So even if it totally corrupts my wallet or whatever, I could still switch back to the previous version and reimport the keys.

(P.S. sounds like a great improvement!)

[jim618]

Hi Kazimir,

The wallet storing and loading is isolated in the code so it is very unlikely that an address would be displayed as one thing but actually be another as a result of this change.

Exporting the private keys and putting all of the export file, the wallet file (yourName.wallet) and extra information file (yourName.info) somewhere elsewhere would be a good safety measure before upgrading yes.

[jim618]

Mainly in preparation of the wallet upgrade utility I will be writing, I have added a 'Messages' screen to MultiBit.
All the messages that were being put on the statusbar now also go to a store and appear on a screen thus:



It gives a bit more visibility to what is going on.

At the moment it just does 'local' messages but in the future I would like to add the Satoshi network message notifications and also MultiBit specific broadcasts (new versions, emergency announcements etc).

[Tittiez]

Feature Request:

Dynamic Fee's based on the transaction size.

Reason being, smaller transactions get quickly confirmed even having a 0 fee, while others, like the one I'm waiting for

http://blockchain.info/tx-index/aa4ddd098dd12d58b26ab8e9f452e4be1937f32106e72944b0b489bbe5aa6935

don't get confirmed quickly, even with a 0.0005 fee.

[PTseller]

i have 11.6995 BTC in my wallet but when i click on send it asked me for 0.0005 fee so i reduce amount to 11.6990 or 11.6980 but i can't send Sad multibit allow me to send only 7.3 BTC right now donno why ?? i got BTC few days back please help me out how can i make this transaction happen

Thank you !!

[Kazimir]

Feature Request:

Dynamic Fee's based on the transaction size.

+1
Or better yet: allow to edit the fee per transaction, i.e. in the Send dialog (with the default fee, or a dynamic value depending on the transaction size, pre-filled in).

By the way, you can already change the fee manually. Closing MultiBit, edit the file "%appdata%\multibit\multibit.properties" (or the equivalent on Mac or Linux) and look for sendFee=xxxx.

i have 11.6995 BTC in my wallet but when i click on send it asked me for 0.0005 fee so i reduce amount to 11.6990 or 11.6980 but i can't send Sad multibit allow me to send only 7.3 BTC right now donno why ?? i got BTC few days back please help me out how can i make this transaction happen

Hmm strange, I personally even tried a fee of 0.0001 for much larger transactions and didn't experience any problems.
Is it possible you still got some of your coins pending? (does it say "available to spend: 7.3" or something?)

[Tittiez]

By the way, you can already change the fee manually. Closing MultiBit, edit the file "%appdata%\multibit\multibit.properties" (or the equivalent on Mac or Linux) and look for sendFee=xxxx.

Or you can just go to preferences and change it inside the actual program.

[jim618]

Mike Hearn mentioned that fees were pretty much at the top of his list of TODOs for bitcoinj so I will track that development. That should enable me to work out the minimum fee for any given transaction and both simplify things and make confirmation by the miners more certain.

It is a bit complicated working out the fees, not least because to pay a fee you might have to add another transaction output to pay for it : but that changes the transaction and hence can change the fee !

[PTseller]

author=PTseller link=topic=43616.msg959092#msg959092 date=1339559428]
i have 11.6995 BTC in my wallet but when i click on send it asked me for 0.0005 fee so i reduce amount to 11.6990 or 11.6980 but i can't send Sad multibit allow me to send only 7.3 BTC right now donno why ?? i got BTC few days back please help me out how can i make this transaction happen

Hmm strange, I personally even tried a fee of 0.0001 for much larger transactions and didn't experience any problems.
Is it possible you still got some of your coins pending? (does it say "available to spend: 7.3" or something?)

yeah it showing me available to spend: 7.3 what the hell is that i got BTC 3 days back and it is much time to get confirmation ! how can i solve this ? any idea mate ?