Wladimir has actually had a version of this code on his github gists for several years now: https://gist.github.com/laanwj/0e689cfa37b52bcbbb44

Size of transaction = Number inputs * (Input Size) + Number of outputs * (Output Size) + 10 Bytes extra fixed fee required for the framework of the transaction

Thanks for explaining , Now everything  is clear , Alice is paying transaction fees for 1 input and 2 output (generating more bytes in transaction) that will be definitely more if Alice transactions contains only 1 input and 1 output.

Now it become tricky that how we pay the merchant , Alice can do 2 small transaction to make up the sum for the Merchant but Merchant might not be happy as Merchant will get 2 Input and merchant will incur double transactions fess while sending out (so profit decreased .)

Size of transaction = Number inputs * (Input Size) + Number of outputs * (Output Size) + 10 Bytes extra fixed fee required for the framework of the transaction

PREVOUT  + SCRIPTSIG + sequence = 32 + 4 + 1 + 1 + (71 or 72) + 1 + 33 (Compressed) + 4 = 147 or 148

PREVOUT: hash (32 bytes)
         index (4 bytes)
SCRIPTSIG: length (1 byte)
           CONTENTS: push opcode (1 byte)
                     signature (71 or 72 bytes)
                     push opcode (1 byte)
                     pubkey (33 bytes for compressed, 65 for uncompressed)
sequence (4 bytes)

    Legacy input size: 148 bytes (compressed)

    Legacy output size: 34 bytes (compressed)

    Segwit input size: 104 bytes
    Segwit output size: 32 bytes

So the transaction size ~= 13 * 148 + 2 * 34 + 10 ~= 226 Bytes

All in all, 51% attacks are of little threat to well-established cryptocurrencies and will likely continue to fade into obscurity as decentralization increases. However, these attacks still pose a significant threat to new coins, particularly if the attack is being maintained for a significant period of time, at which point the changes may become irreversible. Moving forwards, rig operators should refrain from joining the largest pools, despite the obvious benefits, whilst remaining vigilant.

And it is as useless and pointless as calculating 'how much I could earn if everyone who downloaded my homemade wideo on youtube would pay for watching it as if I were Dwayne Johnson and video were released by Universal'

We already know this ... i just wanted to make the calculation to exploit this side too.

6.2 billion. Meh. That means anyone in the Forbes Top 50 could take it down whenever they want?

As I already poited out in another similar puffy topic, there is no need to spend zillions of dollars for that (and then wait for delivery infinitly).

It's enough to pay much less to one or two biggest pool admin(s) for modifying their software (and you will get the entire hashpower immediately as a bonus).

Additional bonus for pool (i.e. miners) shall be a reward for all the 'overmined' (overriden) blocks.

Agree I just read some good news in my email regarding sec about bitcoin and its definitely a good news I dont know if it was just a rumor or real but I think some whales are preparing to go to the moon for another lambo lol.

I agree: Bitcoin is strong.

As others in the thread have noted, a group of miners that collectively control 51% or more of hashrate could decide this second to implement some change to Bitcoin's code, consensus rules, and/or presumably do all sorts of nefarious things to the blockchain.  If they started running new code, their blocks would be accepted, at least, by them (unless they don't know how to code and somehow break their fork, and I seem to recall a problem with exactly this in a certain fork that occured just under a year ago).

As of right now, there are currently 9938 nodes on the network, two of which are mine.  However, I do not mine (see what I did there?).  So, from one perspective, I have no say in what my nodes choose to accept into their local copies of the blockchain.  From another perspective, however, I also control those servers and can choose to stop running Bitcoin Core or upgrade the software as new releases are available.  So, in that way, the plurality of users do "have a say" in what happens to Bitcoin.

From this link, it looks like the three largest pools control 51% of hashrate.  So if they chose to collude, they could change the rules.  On the other hand, if at least one of those three did not participate in some fork, the rest of Bitcoin miners could not cause an "attack".

I trust Bitcoin Core.  Not just the software itself, I also trust the people that are involved with the project.  This could change, of course, but I don't expect that with the present contributors and the project as a whole.  If a nefarious attack threatened the viability of Bitcoin, I am virtually certain that they'd take countermeasures.  There exists at least one "emergency hardfork" repo to change the PoW algorithm if it's ever needed.  I'm confident they could ship such an update in hours if necessary.  I believe Core would treat certain circumstances with the same level of attention that they would treat security vulnerabilities, and implement, test, and ship mitigations as quickly as possible.

Other thoughts...

If I was a miner, I don't think it'd be in my best interest to mess up Bitcoin, so I doubt I'd go along with any concocted scheme to attack/fork/etc. the chain.  Confidence in a technology as well as in the integrity of the people behind it can be difficult to gain but very easy to lose.  Why risk it?

I strongly support measures to increase the resilience of Bitcoin.  My personal belief is that mining effort is too centralized and hope that problem is resolved in time.  I believe that multiple approaches to increasing resilience are merited for Bitcoin, given that it is the world's premier cryptocurrency.  I believe a sufficient number of nodes should be run in nuclear-hardened bunkers on multiple continents and that mining should be done in areas where it might just "break even" and that other, cheaper mining operations should work together as a collective (not any formal organization as that is more centralization) to share the costs and profits for these resilience pools, not to make a huge profit--but to ensure the continued resilience of Bitcoin (which also is part of profitability).  Measures of this type may sound elaborate or excessive, but I believe they are crucial to a technology that is digital money.  They are the type of things that instill the confidence that I previously mentioned.

In conclusion, even if you had the 6.2 billion dollars that you estimated it would cost to conduct a 51% attack, good luck getting the equipment necessary manufactured.  I believe you'd have to set up your own production facility to come up with enough ASIC's to get the job done.  And as LeGaulois said, good luck finding the necessary electricity.  I suppose with the money you saved from running your own ASIC shop, you could also build your own power plants.

There are far more profitable ways to invest 6.2 billion dollars and all of the work required to successfully 51% attack Bitcoin.  And in the end, for that reason, it is very unlikely to occur.

(Incidentally, I hope that last section stands the test of time and that I do not eat those words--that would be a shame.  Why would someone choose to focus on negatives, attacks, division?  There's so much good that can be accomplished through peer to peer, decentralized yet collaborative work towards greater goals.)

Best regards,
Ben

People loosing money not only because of hackers it is a down trend started several months ago and i am afraid BTC return back to 1 k again . imagine how many members at that time will left us here alone in darkness age.

in my opinion it does not make sense between bitcoin prices with hacking exchange because I do not think both of them have a hook, the ascending and declining bitcoins are not affected in the hacking crash.
bitcoin and other coin alt follow market development, if market is lonely i am sure price will go down and when market is crowded bitcoin and other coin will go up.
bitcoin falling below $ 7000 is common and there is nothing you need to worry about because it is a common thing that often happens and if compared with 2014 bitcoin fall so deep but you can see now and you can judge it yourself.

Yes and it was PundiX who was affected the most by this incident.
It was just a few months ago when they finished their ICO and they did bounty here.
Actually they have grew way much that many investors could have withdrawn too.
But back to the hacking, another glorious day for the hackers for millions of dollars are in there.
I guess exchanges should see this as a lesson for more protection.

Bitcoin affected heavily.

I think you should not trust information from the media! Perhaps this is specially created information in order to sow panic among the holders of crypto currency and make them sell what they have!

could it be that the stolen altcoin and btc are being sold off or people are just getting afraid and selling off to avoid stories?

wow, was wondering what happened. thanks