Generally, CPFP isn't recommended for a few reasons.

Firstly, CPFP isn't a recognized standard that miners have to adopt. It is purely voluntary, unlike RBF where most of the nodes and miners will see the RBF flag and act accordingly. Thus, it is a method that is a hit or a miss, if a miner happens to adopt CPFP, then you'll get your transaction included and if they don't, then you have to wait a lot longer.

Secondly, the amount of fees that should be set is quite ambiguous, unlike RBF where you have the liberty of creating another transaction with a higher fee (and thereby superseding the first transaction), the miners can potentially require a higher fee for your CPFP transaction, after considering the total increase in the size.

Lastly, it is non-reversible as well. There is no way of removing your child transaction, even if the network fees were to dip and your first transaction happens to be confirmed without the need for CPFP. As such, I would consider CPFP as a last resort, if you don't have opt-in RBF for some reason or you cannot change your first transaction due to merchant limitations.

Steganography is not particularly new and the method of using it is quite well-known and have been utilized in quite a few instances. As mentioned, this is a form of security by obscurity where most people wouldn't know that a picture contains a wallet seed or a private key. Of course, it is not meant to be store unencrypted, if anyone catches wind of you doing so, then it wouldn't be too difficult to steal your keys.

Sure, it is safe if you know what you're doing. The only scenario where this is useful is if you require absolute plausible deniability where you are afraid of people trying to steal your Bitcoins. Though, in terms of resistance to the $5 wrench attack, not so much.

A lot of the Cloud GPU are machine learning workload optimized, think large and fast amount of RAM to store them in the memory for faster access. You would probably want to try Vast.AI, had some experience with it previously for an unrelated ML project and it worked like it should, though it is definitely a lot more expensive.

AWS EC2 would be a good idea as well though.

Both doesn't make sense. For the first point, an increased circulation results in the decrease in the value of each coin. There is no point in recovery that benefits all.

For the second, Bitcoin is actually designed to be deflationary in the long run. Economic concepts says that deflation is bad but that concerns more of the fiat and their function as financial stabilizers. Having a lower amount of Bitcoin doesn't actually affect Bitcoin. You can go beyond Satoshis as the lowest denomination.

Nope. If they have the access to grant you your own key, they essentially own your key.

The closest thing to trustless storage would be a client side encryption but that'll be complex to implement for it to be truly trustless. It is far, far easier for the user to just make their own backups of their key. Its that simple.

It certainly does. Store your seeds or your private key. Anything other than that requires a participation of a third party and is susceptible to identity theft.

Allowing any recovery process that requires any personal information of the user would result it being a custodial wallet. In that case, just use CoinBase.

The MultiSig created using Electrum doesn't allow P2PWKH wallet types and hence you can only use P2WSH Zpubs to generate the Multisig. The reason for this is to avoid ambiguity between the pubkey standards is that they want to avoid the scenario where the public keys for both P2PWKH and P2WSH are reused. To avoid this and further confusion about what type of keys to use, they just used a different version byte for the master key.

It has nothing to do with functionality or security but just to make it a more straightforward and less error prone process. You can also use tools to convert them, but going through Electrum is a bit longer but also much safer.

Bitcoin wallet activity are not logged, and there is no way of telling if a user has accessed his wallet because that is not how Bitcoin functions. Something like this would either require a central authority or for such activities to be included in the blockchain.

In addition, reclaiming or recovering lost Bitcoins presents an entire can of worms. There is no telling of the intentions of the owners, whether they would like to keep and preserve the Bitcoins or if they are truly lost. This process would just be outright stealing the Bitcoins from them, even if they were not moved for long periods of time. The network nor the algorithm shouldn't act as the government, to reclaim assets based on arbitrary criteria.

Redistribution of coins isn't necessary because there isn't any threat to Bitcoin's existence if we can just make the denominations a lot smaller. The scarcity of the network and the pre-determined supply of Bitcoins makes it valuable and predictable. Re-distribution of Bitcoin causes unnecessary stress to the economic system, rather than the fixed inflation rates, the market would experience inflation in certain years and deflation in certain years which makes it unstable. Scarcity is directly correlated to the value as well, if the miners were to expect rewards to rise in the future, they would intentionally manipulate the system such that they would instead mine in the more profitable years.

It won't. In fact, Bitcoin perpetuates inequality, same as any other currency. The whole premise of the blockchain gives the people with the most resources the ability to make more money and that by itself already makes Bitcoin a currency like any other. Those are societal problems and they cannot be solved using a new medium of exchange. Governments will never embrace Bitcoin as their sole currency, Bitcoin isn't backed by anything and is far too prone to market manipulation among other things.

The fact that it doesn't give the government the ability to enact economic policies nor impose capital control already makes it an inferior currency to them.

GetBlockTemplate is broken with the outdated miners and most of them are not well maintained, the last time I checked. Stratum is a low latency and bandwidth protocol that is used to connect your ASICs to a server which is why it gets recommended more than any other protocol. Antminer doesn't support GBT as well, only Stratum. Your best chance is to run a stratum proxy, which can be done with BFGMiner.

They aren't backdoor in the sense that they've always existed and the capabilities are always there. It's just a matter of if they want to, they can. The backdoor that we're referring to would be more of the covert ones that are inserted by the manufacturer to compromise the security/privacy which exists more on the hardware rather than the software level.

And yes, to answer your question, it isn't that difficult nor rare.

SD Card is just a way to transmit information, and technically anything that allows for a bidirectional transmission would suffice as a medium for transfer of signed and unsigned transactions. You can connect your computer directly to ColdCard through MicroUSB but SD card is just an alternative. IMO, it's just as about convenient as using a USB cable and the transfer is done in a jiffy.

Yes, you are right.

However, note that by definition, double spending is being able to spend your inputs more than once. Bitcoin uses blockchain which by design doesn't allow that because a single chain can't have the inputs being spent twice. If you were to go by that definition, double spending doesn't exist in Bitcoin. If you were to consider Bitcoin as something with multiple states (which rightfully it can be) and taking it as a system with multiple possible chains, then you can spend the coins multiple times, just not on the same chain.

Now, the definition has evolved into those that we have discussed which can involve multiple chains, but if you were to consider only a single chain and state, then it doesn't make sense. Only one transaction that spends a specific input can exist in that chain (and thus having a confirmation) , not two different transactions with confirmations.

Using BFG as a stratum proxy will work. You cannot use GBT with Bitcoin Core because most of the mining clients are affected by the change in the coinbase data in Bitcoin Core when using Bitcoin Core with GBT. Run BFGMiner with stratum port flag, and specify a port for your ASICs to connect to. If they're on the same network, then you should be able to connect the S9 to your BFGminer with a proxy. There's plenty of tutorials online for this.

Otherwise, running it on Testnet is a better idea.

Ah fair enough, I remember seeing this sometime ago.

I think the disparity is pretty big as compared to the other statistics that you find around and the accuracy can be quite skewed, even today (4k vs 6.4k). That is taking into account that you're only looking at the listening nodes. Anyhow, he has never shared the methodology and the last time I checked, he preferred to keep it a secret so I can't really vouch or check for the accuracy.

The caveat being that the amount that you're depositing has to be more than your block reward at least for the attack to the worthwhile. Given how well the mining pools are connected to each other, it's unlikely that your block would be able to propagate faster than them so the scenario whereby your block gets stale is much more likely. The minimum cost for this attack would likely be more than the block reward, if you were to factor everything in.

It would also fail if the person receiving the funds sees the other block first with how the topology of Bitcoin network is designed. A more worthwhile attack would be the selfish mining, where an attacker tries to withhold and generate blocks faster than the rest.

Insisting the use of QR codes to transfer information would just be unfounded paranoia. Any form of attack with that form of complexity would be quite expensive would require too much effort to execute. Besides, ColdCard doesn't execute any code within the PSBT, should be quite easy to verify that. ColdCard is a great wallet, nothing to worry about.

More than half of the nodes are onion nodes, so in terms of clearnet decentralization, not so much.

If you check the ASNs that the nodes are on, you will find that the overwhelming majority are datacenter related. There isn't a lot of people running it at home or on a different network which still introduces a centralized point of failure to some degree.

Yep, with relative ease but not directly of course. Though you could mistype one or two of the words and still be able to recover it since they are still using the same fixed wordlist. If you miss out a word or two, that's still fine. You can't get the correct versioning without a few specific phrases which would automatically eliminate most of the seeds without the need for further key derivation.

Jumbling them up sounds quite intentional, so that shouldn't be too much of an issue.

Yeah probably, and propagation time for blocks has gotten so much quicker in the recent years. There were accidents though, see the article I linked.
If you have a high amount of hashrate, it is totally possible. If not, trying to build on a potentially stale chain would be a giant waste of money. Without a significant amount of hashrate or the network being in your favour, your chances of mining consecutive blocks would be close to zero.