You need to create another transaction with a higher fee if you need the transaction to be confirmed now. That is impossible without the private key.

Since you've already destroyed the private key, you have to wait for the minimum mempool fees to be lower than the fees that you've paid for it to be in the mempool. Might be a good idea to have a backup of the raw transaction.

If you don't understand how it works, then Electrum would be the best for you as it simplifies the process by integrating it into the GUI.

Create an Electrum wallet on the offline computer, get the master public key and import it into the online computer. Create a transaction as usual, save the file as a PSBT or use QR code to transfer it to the offline computer, import it and sign it then transfer the signed transaction back into the online Electrum and broadcast it.

You'd be able to do the same thing with coinb.in as well, using the online instance to load the transactions and generate an unsigned transaction, transfer it to the offline computer to be signed with the private key on it.

Dumpwallet was introduced in 0.9.0. You'd have to update your client to do so. If your goal is to find the keys, then you can probably make a backup and upgrade your client.

It is a payment URI.

It contains the information for the payment and it will fill up the details automatically for the user; scanning the QR code with Electrum will result in the payment details being filled automatically, you can specify expiration as well as the amount. The time is in unix, and it is the time for which your payment request is created.

No. Chrome extensions are why people are getting hacked.

Please DO NOT key your private key into any website.

Storing your private keys offline doesn't make anything more secure. You'll probably be looking at making an air-gapped wallet in this case.

2FA is not perfectly bulletproof against malware attacks. There are many variants of malwares which seeks to exploit the user differently and the most common one is a clipboard malware which your 2FA won't protect unless you double check your transactions.

Are you using TrustedCoin's 2FA wallet in Electrum?

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I believe that decoding your redeem script would help you to see the public keys required for a valid signature and possibly aid you in finding the correct keys to use. Let me know if you don't understand anything about this.

If done correctly, this should be shown on your verify tab:

1000 satoshis/vKB is far from the standard, in fact it is lower than the minimum fees to enter the mempool.

As mentioned, miners have to prioritize the fee rates over the total fees in order to maximize the profit from their very limited block size. It doesn't make sense for them to prioritize total fees, just won't be a good way to maximize the amount of fees collected.

Different wallets/exchange has different fees estimation. Certain exchange tends to overestimate the fees to err on the side of caution as there would be a huge influx of complains if the transaction doesn't confirm within a reasonable period of time due to various external factors. If you're using Coinbase as an exchange (there is a wallet which is non-custodial), it would make sense for them to take a portion of the transaction fees as well; depositing into any exchange/services will require them to move the funds from your deposit address and that could incur a fee as well. Doubt that this is actually the case though.

Fees are not dependent on the value of the transaction. It is dependent on the amount of data within that transaction, you're essentially paying for the data that you're storing on the blockchain. Hence, more inputs/outputs = higher total fees and vice versa.

The fee rate is what you should be looking at. Certain services can provide various subsidies for the user's transaction fees to incentivise them to keep their funds with them or they can afford to do so as they're sending to multiple recipients in the same transaction; (ie. Transaction batching) total transaction size is effectively smaller. Spending 1 inputs to 10 addresses would be far more efficient than 10 different transactions each.

With non-custodial wallet, the fees are defined by the user and with respect to the fees of the transaction in the mempool (paying more in terms of fee rates would likely net you a faster confirmation). I'd probably be looking to do regular consolidation transactions if I were you, by sending the funds back to yourself periodically during period of low fees. This effectively consolidates your multiple inputs into one and if you were to spend it the next time the fees are high, the transaction size would be far smaller as you'll only include one input.

If you've received a 12 word seed phrase during creation, Electrum only generates addresses that would be recoverable from that specific seed phrase so your funds will never be lost either ways.

I'll recommend you to generate an address using the receive tab instead of manually selecting an address. When using the receive tab, Electrum can organize your payments and associate them with the description selected. In addition, addresses are also not reused.

The remainder of the Bitcoins that are not spent in the transaction are sent to the change address. It has a different derivation path but it is also still recoverable using the seed phrase.

Complicated conditions like these are which depends on certain unpredictable conditions cannot be expressed in a script for P2SH addresses.

You need a mediator with a Multisig transaction which can decide whether or not to release the coins in the event of a dispute.

This assumes that the attacker won't also replace the PGP public key for ThomasV as well. PGP is best used in conjunction with an established web of trust which can be hard to get for some users and I would probably recommend users to at least get another source of information to validate if the imported public key is also correct.

I agree with the above sentiments as well. Using solely the hash of the files as a validation is insecure. There is a reason why Bitcoin Core hash sums are included within a PGP signed message and users are encouraged to verify them first before trusting it. Using the hashes as it is would merely serve as a way to verify data integrity but not guarantee its security.

Nope it isn't. The open source nature of Bitcoin gives everyone the ability to review the code (provided that they have the technical competency to do so). It has little to no effect to any backdoors and conversely, any possible backdoors would be evident as you can see what the code does.

The generation transaction would only be included in the blockchain (or the current longest chain difficulty wise), if they're able to mine a valid block that further extends that chain. The consensus is reached by selecting the longest chain difficulty-wise. Given that the nodes which forms the network enforces protocol rules, there is no way for miners to be able to include more than the current block subsidy and the transaction fees in that coinbase transaction. Doing so would result in the entire block being invalid and gets rejected by the network.

Bitcoin has a specific block subsidy as defined in the code as well as a halving every pre-defined amount of blocks. As a result, the supply of Bitcoin follows a geometrical progression; halving is per 210,000 blocks, total amount of Bitcoin in the first period is 210,000 * 50 = 10,500,000. Sum to infinity: 10,500,000/0.5. While this result of 21,000,000 only holds true if there is no limit to the decimal place, since the smallest denomination is a satoshi, the total possible supply is actually slightly less than 21 million.

The block subsidy is defined in the protocol and enforced by the node. Miners can include no more than the current enforced limit of the coins being generated which is 6.25BTC. The coins are included into the circulation by the use of the coinbase transaction in the block mined by the miner. The coinbase transaction (or generation transaction)[1] contains the block rewards but doesn't need any references to any TXID within the transaction or scriptsig. During the creation of the block, the miner will create a coinbase transaction that sends both the transaction fees within the block as well as the block rewards to their address as well as other relevant data (witness commitment, etc).

[1] https://blockchair.com/bitcoin/transaction/94218fd3c820f4b75c93af58ef560ac2839097eb767005d172f4515362a7684c

Electrum removed the fees selection from the settings and displays it when the user initiates a transaction. You should be prompted for the fees with the selection methodology (mempool, ETA or static) during the creation of the transaction. Does that not appear for you?

You can open a wallet or install/update your Electrum offline. The only operation that requires internet are those that updates your wallet with the transactions, etc.

Using it offline after having connected to the internet won't be very beneficial, security-wise. Using it offline requires an air-gap setup which keeps your wallet offline which minimizes any attack vector that uses the internet to transfer information. Keeping your computer free from malware should be something that is done all the time, not only when you're updating your client. As long as you can validate the files, you're probably fine.

I think the best way to identify whichever key you're looking for is to find the redeem script.

Copy the string from the script column in your inputs and it should be a format like 0047....ae. Remove the zeros and check the number after that, if it is 47, remove 142 characters, 48, remove 144 characters or if it is 49, remove 146 characters. So, you'll be removing ... 0047(142/144/146 characters) and the remainder should be 52....53ae, if not then try again. Paste the rest of the string back into coinb.in/#Verify and it should display the redeem script and the addresses associated with that multisig.
 
Unfortunately, I can't recall any site that displays the redeemscript from a raw transaction so this is actually quite an inelegant solution.

Pressing the message should show you a link to Electrum.org. While it doesn't present any security risk, I would still advice you to check the link if it is correct again and also validate your download with ThomasV's PGP.

If the order is canceled and the transaction is confirmed, you need to contact the merchant to refund you. Coinb.in can't help because you won't have access to the private key that belongs to the recipient.