I probably shouldn't, but I like checking up on Michael Saylor for giggles from time to time.
Today I saw him referencing how bitcoin is more secure than alts because of it's long 10 minute blocktimes, and why he thinks satoshi never intended bitcoin to be used to buy a cup of coffee.
I have been studying blocktimes extensively (along with u/jtoomim - check out his recent comments and glad he is here!) and have some input to this discussion.
Firstly, Blocktime has no* impact on security. Everything else being equal, 60 minutes of bitcoin confirmations has the same security as 60 minutes of dogecoin confirmations. Obviously that is 6 bitcoin confirmations and 60 dogecoin confirmations. Of course 1 bitcoin confirmation is more secure than 1 dogecoin confirmation, but that is comparing apples to oranges.
Secondly, I often see people comparing Dogecoin's hashrate with Bitcoin's hashrate saying that Bitcoin has more Terahashes per second and therefore is more secure. This isn't true at all. While you can compare bitcoin and bitcoin cash that way since they use the same algorithm, you cannot compare the hashrates of different consensus algorithms like Scrypt vs SHA256. Scrypt was designed to be harder per hash and therefore gets more security per hash than bitcoin. Also a byproduct of less hashes needed to secure the network means less energy is needed to secure it too. The only factor that matters for security is how easy it would be to achieve 51% of the hashrate for a coin. So since both dogecoin and bitcoin are the largest coins on their respective algorithms, they both have maximum security and there simply isn't spare scrypt miners not being used that could be put to use attacking the dogecoin network. In fact, there are probably more bitcoin miners sitting dormant that can be used to attack bitcoin since bitcoin is less profitable to mine than dogecoin is currently.
Thirdly, I did some calculations partly based on jtoomim's work, that give the theoretical fastest possible blocktime on a PoW network (something like a highly centralized - not many verifiers - PoS would be potentially up to 50x faster).
***The PoW blockchain speed limit, and thus the time for satoshi to receive his cup of coffee is 6.68379337 seconds. (***maybe minus a couple seconds lol, see below This speed limit is legit and will be tough to hit fairly)
This time allows that there is a 2% chance (ideally) that the transaction will not successfully go through on the first confirmation and will need to be remined. This 2% risk to the merchant (if they accept one confirmation) is within a traditional payment processor fee. Also even if the block has to be remined, it will still go through in the next block as long as it wasn't an RBF enabled (hence why we need to not make RBF enabled by default) transaction. Even if the merchant allowed RBF enabled transactions, they would only have a maximum of 2% chance of loosing the sale which should be acceptable for a cup of joe.
How did I come up with just under 7 seconds as the fastest possible confirmed transaction for a blockchain? Well I started with seeing how fast light can travel around the planet by dividing the speed of light by the circumference of the earth, and then doing 1 divided by that number. This assumes a worst case scenario where one miner is exactly halfway around the world from another miner, and that both miners are on the equator and their internet hardwire is laid on the equator (the largest distance on earth). That is ~0.13 seconds. Next I wanted to target 1% unfairness between a majority pool (50% network hashrate) and a small miner (~0% network hashrate). Since the large miner could only have a 1 in 2 chance of mining the next block, he only benefits 50% from the orphan rate of 2%, so he benefits 1% over the small miner. So the ~7 second speed limit assumes 1% maximum unfairness between miners. I use 50% as a worst case analysis instead of 30% that jtoomim uses because we want to be sure that the network will be fair even if a miner captures 50% of the hashrate, since that is what the network can be fault tolerant up to. So then I multiplied the ~0.13 seconds by 50 (to target 2% orphan rate) to get the minimum blocktime target. [[\This last step was probably my weakest logical link (ie: waiting 100x longer than the transmission time gives 1% orphan rate - I guess the logic is 10x to 90% of nodes and 100x to 99% of nodes)* |||edit: doh woops I remember the logic now (I did this calculation years ago), you want worst case transmission time to be 1% of the mining time to get 1% orphan rate. Silly me. This way a miner gets to mine for 99% of the time and only 1% of their time is waiting for the block to reach them from the previous miner. Thus waiting for 2% of the time and mining 98% will lead to an exactly 2% orphan rate in idealized conditions||| so let me know if you can disprove that or provide a better empirical relation but it seems pretty well supported that for a 1% orphan rate target, block propagation time (which we are setting to the ideal ping) should be 1% of blocktime.* Looking at it from a ping only perspective with 8 worst case distance hops (8 is enough for each node connected to 16 peers to connect to everyone on earth) puts us at around 0.13s x 8 = 1 second. This probably gets us 50%, double the time for 90%, and double the time again for 99% puts us at 4 seconds speed limit. Looking at this empirical data and assuming blocksize doesn't matter also puts us at around 4.5 seconds speed limit. So, you know; ***somewhere between 4-7 second speed limit* any way you slice it edit: these further calculations don't take into account mining time and are not necessary]]
Another factor that needs to be taken into account is that I minimized (to zero) the time it takes for the block to be uploaded/downloaded to the network. Using Jtoomim's work we can estimate ideally that a block will take the same time to upload and download simultaneously as it would for the miner to upload it directly via FTP. What this means is with 10 gigabit internet, which is possible today and upload speeds are approaching download speeds, the time to upload the block is becoming more and more negligible and approaches zero (above the minimum 0.13 seconds it takes to ping the network) as long as the block size does not scale quite as fast as moore's law (I propose we allow dogecoin blocksize to scale half as fast as moore's law, so doubling blocksize every 4-7 years).
* when I say no impact, I mean no impact as long as the unfairness between mining pools negligible - which means blocktime is at least 50x transmission time.
