Thanks for the advice.

I'll upgrade. I just don't like touching the cold storage machine, just in case...

But, with the seed phrase, I can always recreate things at any time in the future - or can I?

I understand that "if it works don't touch it", and I would prefer not to change the cold storage laptop, which is running Electrum 3.3.8

Assume that I keep the watching version up to date.

Then, how likely is it that the format of transactions, generated by the watching version to be signed, will change? Or, is it 'set in stone' and fixed by the Bitcoin protocols?

Some time ago I bought some satoshis and installed Electrum v3.x on a fresh install of Windows 10 on a spare laptop, to use as a cold storage setup. This is always off line and only ever used to sign transactions.

I upgraded to a watching version of Electrum to 4.x on an online pc.

The question is, do I ever need to upgrade Electrum on the cold storage laptop, assuming the laptop continues to work?

Not a major problem, either way.

My seed phrase is there if needed, and I can stay on 4.2.

I just thought it useful to raise the question, as I had not come across the issue/feature before.

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I saw another thread explaining how to export and import labels.

A wallet backup running on the older version 4.1.5, let me export the labels (menu option). I then imported these labels into the wallet running on the new version 4.2

I now have what I want - wallet on newest version, and labels too.

[moderator's note: consecutive posts merged]

I have a wallet which was created with v3.8 and in use with v4.1.5.

I installed v4.2 and opened the wallet, and it looked OK. But when I try to open it with v4.1.5 it fails with error message:

This version of Electrum is too old to open this wallet.
(highest supported storage version: 18, version of this file: 44)

Is this an expected behaviour? Am I now forced to use 4.2 forever? I didn't see any warnings about this.

I could recreate the wallet for 4.1.5 using the seed phrase, but that loses the transaction descriptions.

Thanks.

The verification was successful. I can now trust the validity of the download.

On Windows 7 I downloaded GPG4WIN to verify the latest Electrum 4.2 download.

I followed the procedure given on the Electrum Download page => https://bitzuma.com/posts/how-to-verify-an-electrum-download-on-windows/

Having got GPG4WIN verified, I run Kleopatra and do a Lookup on Server for the key for ThamasV = 0x2bd5824b7f9470e6

It does find an entry for ThomasV, which I import. However, the result of the import is
Certificates
Total number processed: 0
Imported: 0

When I decrypt/verify using electrum-4.2.0.exe.asc the result is:

Verified ‘electrum-4.2.0.exe’ with ‘electrum-4.2.0.exe.asc’: 3 signatures could not be verified.

It then gives options for 3 signatures to search for or import the 3 signatures.. Search gives no results and I don't have files to import from.

What am I doing wrong?

Will the seed phrase (12 words) from a version 3.x wallet successfully create the private keys with Electrum V4.x ?

SCADA stands for Supervisory Control and Data Acquisition.

In most manufacturing processes, you have devices, usually called PLC or Programable Logic Controllers. These will be simple controllers to measure values, or turn relays on or off, start or stop motors etc.

SCADA gives the human operator a GUI across one or more PLCs. It's just computer software, often written in C or similar languages, that sits above and controls the PLCs.

Iranian centrifuges were damaged when hacked SCADA was showing operators one thing, eg safe rotational speed, while doing something else entirely, eg winding them up to damaging speeds.

Thanks to all for the illuminating comments.

I'll shut up and stop worrying about theoretical issues and I'll follow o_e_l_e_o's advice:
The weakest part of bitcoin is almost always the user. Rather than worrying about the impossible (someone breaking 128 bits of security), worry about all the other ways you are risking your coins instead.

My paranoid thought experiment relies on the fact that the words for the Electrum passphrase are fixed and known.

By default, the 12 words from 2048 do offer a huge combination. As has been pointed out, the risk of accidental duplication is small.

However, if my understanding is correct, in my thought experiment it is easily possible to generate the private keys and addresses that would be created by a real Electrum wallet using the 12 words. A large number of addresses that would result from these keys could be generated relatively easily.

In the attack, the blockchain could be scanned for one of these addresses, and finding any one would confirm that there exists (or existed) a valid wallet with potentially unspent coins. The wallet funds could then be stolen by generating new spends and sent to addresses owned by the attacker.

While large amounts of computing power might be needed, this attack would work against airgapped wallets as well as those on-line.

Is this a feasible (if computationally expensive) attack, or have I misunderstood?

Adding more words would make the computation exponentially more expensive.

I know it's very unlikely, but there is nothing to stop a hacker from generating wallets using the 12 word Electrum seeds, to steal bitcoins.

With luck, they might generate a valid wallet, which had been previously created, and which contains bitcoins

Similarly, a non malicious user might accidentally generate a duplicate wallet.

Should users be encouraged to add some random words to reduce these (admittedly minuscule) risk?

How could they spy on you if it's air gapped? You're supposed to never connect the internet.

I did read  that some researchers demonstrated that they were able to pick up the sounds from a hard disk seeking, and thus reconstruct data from the disk, even if the computer was not connected to the internet. However, that does seem a bit impractical, even for the most dedicated hacker..

Having read the replies, my thinking is that it might be good to use tails for any significant transactions.

As these would be infrequent, one could recreate the wallet each time from the memorised seed phrase, and an online watching wallet.

Which is a more secure Electrum setup?

Airgapped on Windows or Tails?

Thanks to all for the clear explanations.

So, does that mean that if Electrum disappeared from the face of the earth, that a tool, such as Ian Coleman's BIP39 tool https://forkdrop.io/using-ian-colemans-bip-39-tool would permit recovery of the private keys?

Is the order of the 12 words in the seed phrase important?

Coinfloor clients are all now transferred to CoinCorner.

To me, this seems a retrograde step as CoinCorner's website does not have any of the market tools of CoinFloor. CoinCorner seems like an expensive MickeyMouse option.

Does anyone have an opinion?

Can anyone offer any recommendations for a good UK based exchange offering competitive rates, and with decent market tools?

Is it possible to convert a 'normal' electrum wallet to multi-sig?

Also, is multi-sig more secure?

Electrum Personal Server is fairly easy to set up.

I'm no techie, but the guide for EPS is comprehensive and accurate; I had no problems getting it to work.

I had a look at HodlHodl and bisq. While they're great in theory, in practice the costs of BTC on offer are around 4% more than centralized exchange prices. Quantities on offer are low, 0.1 BTC or less.

What about using Electrum Personal Server?

If you buy BTC from an exchange, not only do they know the address to which the bitcoin have been sent, but they also know where you live or work. You will have supplied this as part of the KYC information that exchanges require when you sign up.

That, to me, is a very worrying weak point which could be exploited by criminals; eg they could coerce an exchange employee to reveal the data, or, indeed, an exchange employee could be part of a criminal organisation.

I'm not sure how one can protect oneself here. But as the value of BTC continues to increase, targeting and threatening or kidnapping owners becomes more lucrative.