Change goes to another existing address in your wallet. It does not create new addresses, it uses an existing address in the wallet but you can't easily control which of them this will be.

The key-import/export feature is not meant to import/export paper wallets. Mutibit is not designed to work with paper wallets.

If you want to spend from paper wallets then use a paper wallet spending software like for example Mycelium for Android which is specifically designed for this purpose.

There will be no confusion. MultiBit does not interfere with any other wallet software. Please also see the documentation of each wallet software in question to see where it stores its data files and its wallet files (its always a good idea to know where exactly each wallet stores its data (and know how to find that place in explorer), even if you don't normally need to manually poke around in these folders, you should still at least know where these folders are).

It will do the right thing automatically. Just spend the available balance and it will collect all outputs from all addresses. You just need to take care of the fee, it might want to add a fee that is larger than 0.0001 if your wallet contains many small outputs, if it says there is not enough balance then gradually reduce the send amount in increments of 0.0001 and try again until the amount to send plus the fees it deems necessary is exactly the total available balance.

And you should not delete your old wallet after you have emptied it, you might have given one of its addresses to somebody, maybe have it written in some old forum post and someone suddenly decides to tip you 2 years later [happened to me already], or maybe you didn't remember that you still have a bitbet.us bet running that resolves in 2018 and unexpectedly pays you 0.1237564 BTC which will be worth $543,564.42 in 2018 or things like that and then you don't want to have your old wallet file deleted. But on the other hand: If you delete it and forget about it you might never learn about that unexpected payment and so it also won't matter to you.

I did not say that Multibit is not functional. It does what it is supposed to do and it does things that other wallets can't do and it works very well. If you need a wallet for a certain type of usage then compare the feature list of all available wallets and choose the one that suits best. You can also use multiple wallets if none of the existing wallets provides all the needed features.

Multibit (classic) does not support cold storage (online watching / offline signing), you will need to wait for the new MultiuBit HD (I guess it will have this option (because there is no reason why it shouldn't, but I don't know it for sure)).

If you can't wait then I would recommend Electrum for easy to use cold storage (Armory is too heavy and overkill for casual users and its thousands of features are probably too overwhelming for non-experts).

I do not recommend paper wallets with single key+address anymore these days, this is antique 2009 stuff from the early days when people were brave enough to manually compose a transaction with copy and paste and a text editor (and sometimes messed up spectacularly), they have been superseded by much more user friendly and modern seed+mpk wallets for which proper software support exists (Electrum, Armory) that removes all the complications and pitfalls.

Use it only on a computer that is not likely to become infected with Malware, the usual recommendations for computer security apply.

I recommend redesignating an old Laptop for the sole purpose of Bitcoin (no other software installed or used on it), format the HDD and install Linux (you won't need any Windows software, so the usual excuses for not using Linux do not apply), I recommend Lubuntu for such old laptops because it runs on really old and otherwise already unusable hardware.

These recommendations apply to all wallets, not only Multibit.

Maybe install the old version, open the wallet and export the keys as .key file. Then uninstall and install the newest Version, create a new wallet and import the .key file again.

To get your old address labels back you can use the contents of the old .info file, maybe its even enough to replace the newly created .info with the old .info file.

Make backup copies of all files before you begin moving files around and opening them.

Unfortunately my Wallet-Key-Tool will probably not help here because its only using the original (and newest) Multibit code to read the .wallet files, so it will probably fail too.

No, its calculating the fee automatically based on the size (kilobytes) of the transaction and some other data (I believe its using the "officially" recommended algorithm to calculate it). I guess if it had the option to lower the fees then even more n00bs would post complaints about stuck or "lost" coins in MultiBit because they can't be bothered to read the user manual and deviate from the recommended defaults without knowing what they are doing and then blame it on the Software that only did what it was told to do.

They accumulate outputs (not inputs) of previously incoming transactions. They will be connected 1:1 to an equal amount of inputs of a new transaction once you send them.

It works like in the real world with small coins, if you only receive money in small amounts of cents then your wallet will become heavy and full of small pieces of copper. When you decide to spend it it must be counted and that costs fees.

Received bitcoin amounts (outputs of incoming transactions) are lying at the address that received them as individual pieces of data ("unspent outputs", "UTXO") and they don't move until they are spent again. They accumulate. Only when you spent a certain amount it will collect as many of these small outputs as needed and connect them to the inputs of a new transaction that "melts" them together to a larger amount. This transaction will have a lot of inputs and two outputs, one for the amount you want to pay (which is then again laying at the receiving address as long as it is not moved again by the receiver, but it will be all in one output) and another small output for your change (if the inputs didn't add up exactly there will be something over that must be directly sent back to you (again as a small output that will eventually spent by you later)).

This version will import compressed keys wrongly, the blockchain.info import function is broken!

The safest method at the moment is to use "wallet key tool" (github/prof7bit). It can also repair previously wrongly imported compressed keys by allowing the user to generate the compressed counterparts of uncompressed keys with a simple click of the mouse.

Steps to reproduce:

* switch to the send tab, the previously sent amount is in the amount field (in the above example 5 BTC)
* click new, enter a new bitcoin address to send to, optionally a new label
* click into the amount field, clear it entirely using delete or backspace
* middle-click to paste the contents of PRIMARY into the amount (in the above example 0.0038625 BTC)
* the fiat currency text field is not updated (stays empty)
* click send
* see screenshot

________
PS:

please PLEASE while you are at it before you close your IDE again after fixing this bug: after sending please, please, please clear the amount, the address, the label immediately automatically, so when I switch from the transactions to the send tab I find it completely *empty* and can immediately begin entering address and amount. I cannot count the numbers of times anymore where I messed up my labels because quickly pasting an address into the send tab for quickly sending some coins. This is the single one most annoying user interface glitch of all, noobs will regularly fail to use it properly.

Alternatively you can also implement it so that if I replace the address in the send tab then it will also clear the label and the amount and have the same effect as pressing "new", maybe this ls less invasive but serves the same problem.

The easiest and least dangerous / most foolproof way would be to not allow thousands-separators at all and parse "," or "." always as decimal separator and flag it as an error if more than one is detected.

Also it should accept number literals like

123m

123u

because other software that accepts large ranges of numbers does that too and it has been proven to be very convenient.

This is not related to MultiBit.

Multibit also has a file->open menu where you can just open any wallet file directly, no matter where it is located without having to rename or move it around.

Fortunately this is pretty simple with standard tools like openssl, it can be done on the command prompt of any bootable linux live-cd without needing any additional software, the one relatively short command that needs to be executed is mentioned here: https://github.com/jim618/multibit/wiki/Export%20and%20limited%20import%20of%20private%20keys near the bottom of the page where you just replace <ciphertext file> with the file name of your .key file and <plaintext file> with the file name you want to have the decrypted output written to.

There are also 3rd party tools to convert between multiple different wallet and backup file formats for people who don't want to use the command line.

For every address there will be a private key (safely stored inside the wallet file, you usually don't need to see the keys, you just need to know that they are there and that you should have backups to avoid losing them). Every Bitcoin address is derived from its own private key, if you have the key you can calculate the address from it (thats the reason why the .key file only contains keys and does not also the corresponding addresses, the addresses can be easily generated from the keys when you import it again).

You cannot generate a key from the address, if you lose a key then you lose access to the bitcoins that are lying at that particular address. If you make backups of the .wallet (or of the .key files) you can't lose your keys. Please always password protect your wallet and the key export files.

You can safely replace every occurrence of "generate a new address" with "generate a new key" and vice versa, it means the same thing. Under the hood a new key is generated (and stored in the wallet file) and from this its corresponding address is calculated and shown to you so you can use it to receive coins. You never see the key itself displayed in the user interface because you don't actually have any use from looking at it, only the wallet app needs it under the hood for its calculations when signing a bitcoin transaction.

You need to make a new backup when you created new addresses.

The way I did it myself is I created a few dozen addresses in advance and labeled them all "reserve", then made my backups. Now if I quickly need a new receiving address I just pick one of my reserve addresses and rename it and use it. When I'm running low on reserve addresses I create another bunch of them and make new backups. This way I am not forced to do it too often, I don't need to do it when I'm in a hurry (and then forget to do it), I can make new backups at the times when it is most convenient for me.

Bitcoin-core maintains a pool of 100 reserve addresses hidden from the user and creates new ones all the time, this has the disadvantage that you can never be quite sure when its time to make a new backup unless you painstakingly count all events that took addresses from the pool since you made the last backup. In Multibit on the other hand with the above technique you know **exactly** when to backup because it will never generate new addresses on its own automatically, it only happens when you explicitly request new addresses and you have 100% control over it.

You could port the UI to something like libgdx. The Java bytecode of the entire app can then be compiled to native code with robovm and the libgdx GUI framework is cross platform. You would even get a standalone desktop app for free and even a compiled javascript version to run it in the browser.

Because they might have old keys that are still in use (for example bunch of open bitbet bets that are not yet closed or some old tip addresses in old forum posts or in old software). Or they might want to import/sweep a wallet from a broken/lost/stolen phone. Its very important to know how to import the keys from a stolen mobile wallet and have practiced the procedure a few times so you can act quickly should it ever be needed.

Wait... you copied the wallet file itself (obtained from a rooted phone)? You should use the key export file it generates with its backup function. Last time I tried this with my own wallet it worked just fine (half a year ago).

You could also try loading it with wallet-key-tool and then saving as wallet, maybe that works.