[UPDATE]Can this be considered a Safest Cold Storage?[UPDATE]

[Answerme2]

So i installed Electrum on my very old offline PC which will Never be connected to the internet.I saved the seed and got bunch of address and private keys.I exported master public keys and imported these public keys on my Laptop that is connected to internet.Now it's watch only addresses on my laptop which is connected to the internet.
I can create a transaction on my online laptop and save it and transfer it to my old offline PC and then sign it and transfer it back to broadcast on my online Laptop.Now is this the safest cold storage? and will my private key leak after transfering signed transaction back to online Laptop?
And Electrum generated 10 address with private keys on offline PC which is Not connected to internet.What are the chances that any 1 of the address can again by generated by some other Wallet?
And one last question,Just in case my old PC goes out of bussiness and Does not start on some day then how can i recover my moondollars and even that possible to recover in such case?can i take backup?

I will appreciate some experienced bitcoin geak to please come and answer these.

UPDATE:
My old offline PC gave up in just 1 day and doesn't start now but somehow i recovered the wallet using the seed and sended the moondollars to other address.I still can't figure out how to store my moondollars safely now.
I can't trust online wallets.I can't afford hardware wallets because they are too expensive.What are my options now?
Please suggest me guys how can i safely store my 7+ btc .I only have 1 laptop and an android phone.

[CIYAM]

To be "safest" when transferring the unsigned tx to the offline computer (and the signed tx back to the online computer) you'd be best to use QR codes (rather than USB flash drives as these could theoretically be compromised).

I would also recommend removing any WiFi card or other network card from the offline computer (to avoid it accidentally getting online).

[tobacco123]

Rather than using an electronic device, you may consider a paper wallet instead.

When generated safely (offline on a computer that never connected to internet; complete format of the harddisk after generated the wallet), it should be one of the safest and will not be obsoleted.

[7788bitcoin]

You may consider using BIP38 for paper or hardware wallet for additional protection. A random 6-character password will take many years for the fastest computer running 24/7 to crack. However, do keep a copy of the bitaddress.org offline for future decryption.

[alani123]

You may consider using BIP38 for paper or hardware wallet for additional protection. A random 6-character password will take many years for the fastest computer running 24/7 to crack. However, do keep a copy of the bitaddress.org offline for future decryption.

Or better yet, generate a wallet offline and encrypt it the passphrase with open source tools on your own computer.

[vinaha]

As you describe (the computer has never been online) it looks pretty good.

Back up the wallet - it will give you words to write (by hand) on a piece of paper. Hide the paper in a book. Then if the computer goes the way of all old computers and one day is found dead, you can recover the wallet with the words from the back up.

[HeroCat]

I think it is not safe way, when you are transfering data through USB, you can get either malware or virus from/through USB. Better buy Trezor device, it is most safest BTC hardware. 

[Kprawn]

It is very similar to what I have done, with the exception that I do not carry data around using any USB devices. I took the bitaddress.org website and transferred it to the same "offline" computer and

generated a bunch of paper wallets with passwords. During the time I did that, lots of people were talking about BadUSB and other nasties doing the rounds and compromising the firmware on USB

devices, so I opted for paper wallets instead. Now I have a "offline" computer to generate as many paper wallets as I need. I unplug the hdd, and store it in a safe place, when not in use. 

[LiteCoinGuy]

I think it is not safe way, when you are transfering data through USB, you can get either malware or virus from/through USB. Better buy Trezor device, it is most safest BTC hardware.  

https://bitcointalk.org/index.php?topic=899253.0

[shorena]

So i installed Electrum on my very old offline PC which will Never be connected to the internet.I saved the seed and got bunch of address and private keys.I exported master public keys and imported these public keys on my Laptop that is connected to internet.Now it's watch only addresses on my laptop which is connected to the internet.
I can create a transaction on my online laptop and save it and transfer it to my old offline PC and then sign it and transfer it back to broadcast on my online Laptop.Now is this the safest cold storage? and will my private key leak after transfering signed transaction back to online Laptop?

I use a similar setup for my offline wallet. There are probably safer ways, but I think its safe enough for the amount most people have. You still have to take care of your online system though as CIYAM pointed out, the USB sticks may transfer malware to the offline system.

And Electrum generated 10 address with private keys on offline PC which is Not connected to internet.What are the chances that any 1 of the address can again by generated by some other Wallet?

The chance that someone else has the same address is you is 1 in 2¹⁶⁰ or 1 in 1461501637330902918203684832716283019655932542976.

And one last question,Just in case my old PC goes out of bussiness and Does not start on some day then how can i recover my bitcoins and even that possible to recover in such case?can i take backup?

Yes, but you dont have to as long as you have the seed.

I will appreciate some experienced bitcoin geak to please come and answer these.

This setup is very secure in terms of viruses or online attacks, but less secure in terms of physical attacks. The laptop can be stolen, so I suggest you encrypt the disk and/or set a password for the offline wallet. Its also not very convenient for regular payments, thus its probably best if you keep one or more hot wallets for smaller amounts and refill from the cold wallet as needed.

[Answerme2]

So i installed Electrum on my very old offline PC which will Never be connected to the internet.I saved the seed and got bunch of address and private keys.I exported master public keys and imported these public keys on my Laptop that is connected to internet.Now it's watch only addresses on my laptop which is connected to the internet.
I can create a transaction on my online laptop and save it and transfer it to my old offline PC and then sign it and transfer it back to broadcast on my online Laptop.Now is this the safest cold storage? and will my private key leak after transfering signed transaction back to online Laptop?

I use a similar setup for my offline wallet. There are probably safer ways, but I think its safe enough for the amount most people have. You still have to take care of your online system though as CIYAM pointed out, the USB sticks may transfer malware to the offline system.

And Electrum generated 10 address with private keys on offline PC which is Not connected to internet.What are the chances that any 1 of the address can again by generated by some other Wallet?

The chance that someone else has the same address is you is 1 in 2¹⁶⁰ or 1 in 1461501637330902918203684832716283019655932542976.

And one last question,Just in case my old PC goes out of bussiness and Does not start on some day then how can i recover my bitcoins and even that possible to recover in such case?can i take backup?

Yes, but you dont have to as long as you have the seed.

I will appreciate some experienced bitcoin geak to please come and answer these.

This setup is very secure in terms of viruses or online attacks, but less secure in terms of physical attacks. The laptop can be stolen, so I suggest you encrypt the disk and/or set a password for the offline wallet. Its also not very convenient for regular payments, thus its probably best if you keep one or more hot wallets for smaller amounts and refill from the cold wallet as needed.

Thank You
Can you please tell me or suggest me how to set a recommended fees in electrum when sending bitcoins?
Is there any way electrum can suggest me the recommended fees? How to calculate the size of the actual transaction before sending?

[Wendigo]

OP your setup seems pretty safe but you should do a back up of your private keys to a safe location in the event that your old PC breaks down irreparably. By the way if you have an Android phone you could try out the Mycelium wallet. It has a feature to spend funds from a cold wallet and after that it deletes every trace of your activity like the private keys used etc. so the chance of your coins in the cold storage getting compromised is null. 

[shorena]

So i installed Electrum on my very old offline PC which will Never be connected to the internet.I saved the seed and got bunch of address and private keys.I exported master public keys and imported these public keys on my Laptop that is connected to internet.Now it's watch only addresses on my laptop which is connected to the internet.
I can create a transaction on my online laptop and save it and transfer it to my old offline PC and then sign it and transfer it back to broadcast on my online Laptop.Now is this the safest cold storage? and will my private key leak after transfering signed transaction back to online Laptop?

I use a similar setup for my offline wallet. There are probably safer ways, but I think its safe enough for the amount most people have. You still have to take care of your online system though as CIYAM pointed out, the USB sticks may transfer malware to the offline system.

And Electrum generated 10 address with private keys on offline PC which is Not connected to internet.What are the chances that any 1 of the address can again by generated by some other Wallet?

The chance that someone else has the same address is you is 1 in 2¹⁶⁰ or 1 in 1461501637330902918203684832716283019655932542976.

And one last question,Just in case my old PC goes out of bussiness and Does not start on some day then how can i recover my bitcoins and even that possible to recover in such case?can i take backup?

Yes, but you dont have to as long as you have the seed.

I will appreciate some experienced bitcoin geak to please come and answer these.

This setup is very secure in terms of viruses or online attacks, but less secure in terms of physical attacks. The laptop can be stolen, so I suggest you encrypt the disk and/or set a password for the offline wallet. Its also not very convenient for regular payments, thus its probably best if you keep one or more hot wallets for smaller amounts and refill from the cold wallet as needed.

Thank You
Can you please tell me or suggest me how to set a recommended fees in electrum when sending bitcoins?

I usually go with the cointape[1] suggestion or ask my bitcoin core client (estimatefee 2) and roughly estimate the size. The ~225 byte on cointape are usually correct unless you have a larger number of inputs. If you go to your addresses tab in electrum and right click an address you can select "send from" this allows you to select which inputs to use and is similar to coin control by bitcoin core/classic.

Is there any way electrum can suggest me the recommended fees? How to calculate the size of the actual transaction before sending?

Electrum has several options for fees under Tools -> Preferences -> Transactions. I tend to set the fee myself though. I usually pay a higher than needed fee for trades or to release funds from escrow, because I dont want people to wait just because of a few satoshi. When I send funds to myself I usually pay a lower fee, because I dont mind if I have to wait.

On how to calculate the size I suggest reading these[2] stack exchange answers. You are most likely using compressed keys.


[1] https://bitcoinfees.21.co/
[2] http://bitcoin.stackexchange.com/questions/1195/how-to-calculate-transaction-size-before-sending

[KennyR]

Rather than using an electronic device, you may consider a paper wallet instead.

When generated safely (offline on a computer that never connected to internet; complete format of the harddisk after generated the wallet), it should be one of the safest and will not be obsoleted.

Yeah. Paper wallet is the best which acts as a great barrier to safeguard your earned bitcoin. Electrum itself a perfect wallet no need to make big complications.

[pooya87]

To be "safest" when transferring the unsigned tx to the offline computer (and the signed tx back to the online computer) you'd be best to use QR codes (rather than USB flash drives as these could theoretically be compromised).

I would also recommend removing any WiFi card or other network card from the offline computer (to avoid it accidentally getting online).

i don't think Electrum on its own has such feature to produce QR code for transfering signed txs. right?

or are you talking about a project that you did (i remember seeing you post the link is some topic but i can't find it) can you give a link?

[Answerme2]

To be "safest" when transferring the unsigned tx to the offline computer (and the signed tx back to the online computer) you'd be best to use QR codes (rather than USB flash drives as these could theoretically be compromised).

I would also recommend removing any WiFi card or other network card from the offline computer (to avoid it accidentally getting online).

i don't think Electrum on its own has such feature to produce QR code for transfering signed txs. right?

or are you talking about a project that you did (i remember seeing you post the link is some topic but i can't find it) can you give a link?

Electrum do have a feature for QR codes for transferring tx but it's useless if your bitcoins are stored in cold storage on old offline pc as that pc has nothing to scan the QR so i use USB instead.
I have antivirus and antimalware on both pc so it's pretty safe to just use USB

[CIYAM]

or are you talking about a project that you did (i remember seeing you post the link is some topic but i can't find it) can you give a link?

The CIYAM Safe (https://susestudio.com/a/kp8B3G/ciyam-safe) is another (more hard-core technical) approach to cold storage (which uses QR codes for communications).

The utilities "qrencode" and ZBar are basically all you need to use for that part of things.

[Redrose]

Rather than using an electronic device, you may consider a paper wallet instead.

When generated safely (offline on a computer that never connected to internet; complete format of the harddisk after generated the wallet), it should be one of the safest and will not be obsoleted.

The paper wallet doesn't suit his needs. I don't think that he want his bitcoins to sit without any power on them. From what I understood, he wants to use them from time to time.

[DimensionZ]

Guys what do you think about the dedicated Bitcoin hardware wallets like Trezor and Ledger? Are they worth the investment and is their security really that much higher than using an offline PC to act as a cold storage? Or there is no difference security-wise? Not that I have a big stash of coins to warrant such a wallet I am just curious to know thank you.

[West man]

Rather than using an electronic device, you may consider a paper wallet instead.

When generated safely (offline on a computer that never connected to internet; complete format of the harddisk after generated the wallet), it should be one of the safest and will not be obsoleted.

I also say that the safest is a paper generated wallet for complete security. Any system can be comprised.
Just old tried and tested methods that never fail in the long run.
That is true advice you can count on.