Risk with old wallet transactions?

[MarkusM22]

Hello Everyone
I have the private key of an old wallet with a bit of bitcoins (dating back before segwit ~ 2013). The key is completely offline.

What I've done is the following:
- Created an Electrum wallet with the key (old type single key, no seed)
- The public key showing for the wallet matches and I see the transactions for the old key (so far so good).

What I would like to do is:
- Install Electrum on another internet enabled computer, downloading the blockchain and creating a wallet (like above) using the. public key.
- This should allow me to create unsigned transactions (?) which I would then transfer over to the offline computer to be signed, transfer the signed transaction back and publish it.

My question is:
- Are there any issue using the "old style wallet"?
- If I only use parts of the funds, is there any issue with the the rest "remaining" on the old key (can the "return" amount be sent to the old key)?
- Are there any other risks with this legacy approach? (excluding either computer being compromised)

My concerns are (generic concerns without any data to back them up):
- That for whatever reason the transaction would not be accepted
- If a "chunk" is sent exceeding the amount of the transaction, the return amount wouldn't be correctly returned
- I couldn't use the same key pair again

I highly appreciate you feedback

Best regards
Richard

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[ranochigo]

Electrum doesn't require the entire blockchain to be downloaded to function. You aren't talking about old wallets and private keys has largely remained unchanged throughout.

You can indeed send the funds back to the origin address. If I were you, I would probably just transfer it by creating another wallet with a 12 word seed and send the remainder to one of the addresses within it. It'll help with your privacy immensely and also gives you the benefits of using a HD wallet. As long as both of your Electrum clients are recent (preferably 4.0.9), then it's perfectly fine.

[BlackHatCoiner]

What I would like to do is:
- Install Electrum on another internet enabled computer, downloading the blockchain and creating a wallet (like above) using the. public key.

Let me clarify you something. Electrum is an SPV client (Simple Payment Verification). You don't download blockchain, you're receiving information from electrum nodes and thus, you don't need to store any block. Bitcoin Core on the other hand is a full node which means that with it, you verify every incoming information.

My question is:
- Are there any issue using the "old style wallet"?
- If I only use parts of the funds, is there any issue with the the rest "remaining" on the old key (can the "return" amount be sent to the old key)?

There is no issues using the "old style wallet". You can normally sign your transaction from the offline machine and broadcast it through blockchair or by using SharpPusher.

My concerns are (generic concerns without any data to back them up):
- That for whatever reason the transaction would not be accepted
- If a "chunk" is sent exceeding the amount of the transaction, the return amount wouldn't be correctly returned
- I couldn't use the same key pair again

If you are sure that the address has unspent bitcoins and you set an allowed fee then it should be accepted. You can use the same key pair again, but I'd recommend you do what ranochigo says. Download the latest version of electrum and generate a seed. It's better than keeping a private key since you can derive nearly unlimited addresses this way.

[MarkusM22]

Dear All
Based on the replies, I read:

- Using a single key pair (old) even for multiple transactions isn't an issue, with the exception of privacy concerns.
- Ensure that the Electrum clients are up to date
- Ensure that the fee is "appropriate"
- I mixed up some concepts: No need to download the whole chain (just recalled that the client shows the current fund level on the key which is from where I got this)

I would say this clarifies my concerns.

My primary concern was that there is no way I can "lose the coins" this way (naturally excluding compromised machines and incorrect target addresses).
Like e.g. it not being able to return the remaining funds (these concerns were answered or something similar.

I'm a bit paranoid because back in the days I was unaware that there could be multiple key pairs in a wallet, had a backup of only one of the keys in the wallet and was wondering why the balance was off when I imported it to another instance... Fortunately I did learn the reason and found the other key, but this kinda left me scarred in regards to making mistakes in the future.

Regarding privacy, "this isn't an issue" as the current and all future transactions will go to a single trusted destination.  I know it's bad practice, but as long as it doesn't result in missing coins, it's acceptable.

I would like to express a very big  *THANK YOU* for the helpful replies I've gotten!! This was highly appreciated! In case there are any points I've missed, I'm still more than grateful for having these pointed out!

Best regards
Richard

[o_e_l_e_o]

My primary concern was that there is no way I can "lose the coins" this way (naturally excluding compromised machines and incorrect target addresses).
Like e.g. it not being able to return the remaining funds (these concerns were answered or something similar.

I'm a bit paranoid because back in the days I was unaware that there could be multiple key pairs in a wallet, had a backup of only one of the keys in the wallet and was wondering why the balance was off when I imported it to another instance... Fortunately I did learn the reason and found the other key, but this kinda left me scarred in regards to making mistakes in the future.

Electrum's default behavior when using a wallet with a single imported private key is to automatically send any change back to the address it came from. So any funds you do not spend should still be on the same address with the same private key after you have made your transaction.

When you create the transaction on your watch only wallet on your internet enabled computer, you will get a pop up window with the transaction details in it for your to finalize before exporting the transaction to transfer it to your airgapped wallet. In that window, there is a box at the the bottom entitled "Outputs". Simply double check that any change from your transaction is being sent back to the same address. If all looks correct, then you are good to go.