Confused?

[Sidney986]

What are the change addresses in Electrum for? 

I ask because my funds got moved from the address they were placed in to a (orange) change address after transfer small amounts to other (green) addresses?

I do hope electrum is not creating more addresses because I have only backed up the private keys on the air gapped computer which do not account for newly created addresses on the non air gapped computer.

Also how do I set the wallet the funds should be transferred from?  I only have the pay to address option. 

[jackg]

You can right click addresses and press "spend from" I also think there's a view>show coins at the top menu but I'm not sure.

Change addresses are used because they're enabled... If you don't want to use them, you'll have to import your addresses into the hot wallet if you insist on using that specific private keys.

Why aren't you using the mnemonic seed on both devices though? You just have to change the gap limit every so often on the airgapped wallet. Not doing so means you could lose coins if you make a mistake.

[DireWolfM14]

What are the change addresses in Electrum for?  

Privacy.  When you spend coins from on input the software sends your "change" to a change address, which can help obfuscate your spending habits.  

I ask because my funds got moved from the address they were placed in to a (orange) change address after transfer small amounts to other (green) addresses?

The software will continue to do so until you change the settings.  Go to Tools> Preferences> Transactions> and deselect the check box next "Use change addresses."

I do hope electrum is not creating more addresses because I have only backed up the private keys on the air gapped computer which do not account for newly created addresses on the non air gapped computer.

If you only backed up certain private keys you may have lost those funds.  I hope that's not what you did.  To back up a hierarchical deterministic wallet you should write down the 12-word seed phrase.  That will back up all the addresses that your wallet has already generated, and any that it will generate in the future, including change addresses.  

Also how do I set the wallet the funds should be transferred from?  I only have the pay to address option.  

Can you please rephrase your question?  I'm not sure what you mean by this last part.  If you mean you want to spend a specific input, then like jackg said, you can do so by enabling the "Coins" tab, then right click on the input, and select "Spend from."

[Sidney986]

Let me further explain.

I set Electrum up on Ubuntu with seed keys and transferred the public addresses via the master public key to the online computer.  I created all transaction with the online computer and sign them offline in Ubuntu.

On the air gapped computer I also backed up the private keys to txt document.  Now I don't want the online computer creating further addresses (if that's what it's doing) because I have no back up off private keys for those newly created addresses.

[Sidney986]

[/quote]

Can you please rephrase your question?  I'm not sure what you mean by this last part.  If you mean you want to spend a specific input, then like jackg said, you can do so by enabling the "Coins" tab, then right click on the input, and select "Spend from."
[/quote]

I have all the master public addresses in the online version and four of those addresses have funds available. 

When I click the "Send" tab there is a box "pay to" but no box to set which of those four address that hold fund will be used to make a payment.

[Abdussamad]

Let me further explain.

I set Electrum up on Ubuntu with seed keys and transferred the public addresses via the master public key to the online computer.  I created all transaction with the online computer and sign them offline in Ubuntu.

On the air gapped computer I also backed up the private keys to txt document.  Now I don't want the online computer creating further addresses (if that's what it's doing) because I have no back up off private keys for those newly created addresses.

don't rely on private key backups then. electrum wallets are deterministic wallets which means all private keys are derived from the seed. the seed is what you backup.

during normal operation it'll continue to create new addresses and each address will have a different key pair behind it. so any private key backup will soon become stale. backup the seed and/or the wallet files on the offline and online systems via file >save copy.

[nc50lc]

On the air gapped computer I also backed up the private keys to txt document.  Now I don't want the online computer creating further addresses (if that's what it's doing) because I have no back up off private keys for those newly created addresses.

Yes, Electrum will create more addresses once the current ones got used.
If you really don't want any more change addresses (orange), you can disable it in "Tools->Preferences->'Transactions' tab->Use change address".

I won't recommend it though, including the private keys backup, use the seed phrase instead.

[Sidney986]

Sorry not easy for me to explain.

So the offline version was created with a seed.

I transferred the master public key from offline version to online version.

The online version did not have a seed created, just the imported master public key.

The online version is creating more addresses that were not shown in the offline version and does not seem to be creating private keys for them.

So Is the offline version able to display those newly created addresses that the online version created?, if not then Electrum is putting my funds at risk by creating new addresses that I cannot recreate with the offline seed version.  Also the online version is not showing any private keys for those newly created addresses.

[Sidney986]

On the air gapped computer I also backed up the private keys to txt document.  Now I don't want the online computer creating further addresses (if that's what it's doing) because I have no back up off private keys for those newly created addresses.

Yes, Electrum will create more addresses once the current ones got used.
If you really don't want any more change addresses (orange), you can disable it in "Tools->Preferences->'Transactions' tab->Use change address".

I won't recommend it though, including the private keys backup, use the seed phrase instead.

I did not create a seed with the online version as that's a watch only wallet using the "master public key" that was imported.  I only have the seed version offline for signing transactions, but the online wallet is creating new addresses and putting my funds in them, so i'm guessing my offline seed version cannot sign transactions for those newly created addresses which means my funds are at risk.  So why would Electrum create those new addresses and putting my funds into them when my offline version cannot sign them?

[joniboini]

So you have 2 electrum wallets, one is always online and the other is offline. Basically the online is a watch-only wallet that monitors all addresses related to the offline wallet?

As long as it comes from the same seed then you should be fine. Your offline version should be able to sign it still as the watch-only wallet is related to it. Maybe this could help you: https://en.bitcoin.it/wiki/Deterministic_wallet#Master_public_key.

[pooya87]

So Is the offline version able to display those newly created addresses that the online version created?, if not then Electrum is putting my funds at risk by creating new addresses that I cannot recreate with the offline seed version.  Also the online version is not showing any private keys for those newly created addresses.

no. this is how HD wallets work.
you have a "master-key-pair" and similar to "key-pairs" you have one public and one private. with certain settings (using non-hardened paths which Electrum uses) each master key is capable of creating the same exact set of addresses:
- the master private key creates child private keys > computes each public key > creates their corresponding address
- the master public key (cannot create private key) > creates child public key > creates their corresponding address

when you use an address, your Electrum automatically generates a new one which is the next key index (eg. if you have 10 already created it creates number 11).
- when you are online with your master public key it creates the public key and the address of it.
- when you are offline it won't know how many addresses are used (since it has no access to the internet and blockchain) so it won't create any new one BUT it can do it if it is asked to. and it is asked to create the new one as soon as you try signing a new transaction that is spending funds from those addresses.

[nc50lc]

-snip-
I won't recommend it though, including the private keys backup, use the seed phrase instead.

I did not create a seed with the online version as that's a watch only wallet using the "master public key" that was imported.  I only have the seed version offline for signing transactions, but the online wallet is creating new addresses and putting my funds in them, so i'm guessing my offline seed version cannot sign transactions for those newly created addresses which means my funds are at risk.  So why would Electrum create those new addresses and putting my funds into them when my offline version cannot sign them?

Your offline Electrum will be able to sign those transactions even though the addresses aren't yet generated as long it has the seed.
Your online wallet's master public key is paired with your offline wallet's master private key, there shouldn't be any issue with signing transactions.

The additional warning is for keeping private keys backup instead of the seed.

Note: I have successfully signed a transaction that spent an input beyond the offline wallet's gap limit using the development version 4.0.0a0.

[HCP]

On the air gapped computer I also backed up the private keys to txt document.  Now I don't want the online computer creating further addresses (if that's what it's doing) because I have no back up off private keys for those newly created addresses.

If the online watching-only wallet was created using the master public key from your offline wallet that has the seed... then the seed mnemonic is all the backup that you need. It will enable to you restore everything.

That's the whole point of deterministic wallets. They are able to be reliably recreated from a given starting point... in this case, the 12 word seed mnemonic.

So why would Electrum create those new addresses and putting my funds into them when my offline version cannot sign them?

Your offline version will in fact be able to sign them...

[Sidney986]

Thanks to all of you, much appreciated that you helped me out with these issues. 

So after reading all your replies this is my understanding;

The "master public key" is linked to my air gapped seed version.  Any addresses added to the "master public key" addresses whilst running Electrum online (watch only wallet) can still be signed by the air gapped version even though the online version was not created with the seed.  But I may have to increase the gap limit in the offline version to sign transactions for those added addresses.

By the way.  I could have made life simple and used the seed on the online version of Electrum as suggested, but I thought the whole point of a air gapped system was to make my funds much safer.

[DireWolfM14]

I thought the whole point of a air gapped system was to make my funds much safer.

That is still true.  You can leave your seed on the air-gapped PC and still use the master public key on your watch only wallet.  Any addresses created by the watch only wallet are automatically backed up by your seed phrase.

[o_e_l_e_o]

Any addresses added to the "master public key" addresses whilst running Electrum online (watch only wallet) can still be signed by the air gapped version even though the online version was not created with the seed.

This is correct.

Your seed phrase is used to create a master private key and a master public key. The both are then needed to create all your individual private keys, but the master public key on its own is enough to create all your individual public keys and addresses. Using the master public key on your watch only wallet allows it to generate all the same addresses as your airgapped wallet, but none of the private keys required for signing.

I could have made life simple and used the seed on the online version of Electrum as suggested, but I thought the whole point of a air gapped system was to make my funds much safer.

You are absolutely right. Using your seed phrase, and therefore your private keys, with your online copy of Electrum, although quicker to set up and use is significantly less secure.

[nc50lc]

By the way.  I could have made life simple and used the seed on the online version of Electrum as suggested, but I thought the whole point of a air gapped system was to make my funds much safer.

I don't know where you get that "suggestion" because no one recommended using the seed in the online machine...
You must be talking about this post:

Yes, Electrum will create more addresses once the current ones got used.
If you really don't want any more change addresses (orange), you can disable it in "Tools->Preferences->'Transactions' tab->Use change address".

I won't recommend it though, including the private keys backup, use the seed phrase instead.

What I mean by "use your seed instead" is for not using "private keys backup".
What I'm not recommending is disabling change addresses.

Do not just backup the private keys, it's not a reliable backup as pointed out by others.

[bob123]

So after reading all your replies this is my understanding;

The "master public key" is linked to my air gapped seed version.  Any addresses added to the "master public key" addresses whilst running Electrum online (watch only wallet) can still be signed by the air gapped version even though the online version was not created with the seed. 

Yes.
The master public key has been generated from the master private key, which has been generated from the 12 word mnemonic code (you did back it up, right?).

All you need to generate the private keys from the address your watch-only (online) wallet is creating, is this 12 word mnemonic.
You don't need to back up individual private keys.

[Sidney986]

Again, thanks for the replies.

Yes, the first thing I did when creating the wallet air gapped was to write down the seed keys and the extended keys.

However I still think it's important to back up my private keys in case of potential future issues with Electrum.  Those private keys will allow the recovery of my fund on other wallets, they will also allow me to create QR codes on paper wallets using software such as walletgenerator.

I understand that the private keys are not generated for the change addresses (or are they) and that it's important to make sure I keep the seed keys to protect my funds regardless. 

[khaled0111]

However I still think it's important to back up my private keys in case of potential future issues with Electrum. 

as long as you have the seed you will be able to retrieve all your wallet's private keys whenever you want regardless of what could happen to Electrum (it's an open source after all).

I understand that the private keys are not generated for the change addresses (or are they)

that's not correct. Electrum generates private keys for all its addresses and change addresses are not an exempt otherwise how would you spend coins that were sent back to your change addresses from previous transactions!
In fact, each address is derived from a public key which is derived from a private key. So there should be a private key in first place.