Bitcoin Forum

I believe the difficulty re-targeting algorithm is by far bitcoins biggest weakness and ill explain.

Imagine that another alt coin very similar to bitcoin comes onto the scene and gains prominence. Lets say its similar to bitcoin in that it uses sha256 proof of work and re-targets in the same manner as bitcoin. So what happens is miners first mine bitcoin and the difficulty re-targets up, when this happens miners begin to jump ship and instead mine altcoin. After the next re-target bit coin re-targets down and altcoin re-targets up, with each new re-target more miners switch back and forth between bitcoin and altcoin attempting to capitalize on the chain that has a lower difficulty.

This COULD create oscillations that resonate and exacerbate with time. Untill eventually it gets so bad that no miners bother to mine the coin whos blocks are coming in once per hour or once per day. One of the two coins dies entirely or is forced to fork and adopt a more adaptive re-targeting algo.

the good news is it should be relatively simple to get consensus on this fork since the chain would be totally unusable until after the fork.

ok tell me what you guys think about this observation. Im pretty sure im right about this but open to the possibility that im not. If i am correct, is gaven aware of this?

I think this is already happening to altchains like TRC recently and maybe PPC to a lesser extent. The former recently had to change the retargeting algo (following a takeover attempt that was explained here on bitcointalk), the latter already had, AFAIK.

I believe Bitcoin can learn from these real-life experiences should any SHA256 chain become too attractive and most miners switch to it (still unlikely at this stage IMHO). Both of them have survived until now, though TRC's future looked uncertain for a couple of days.

Any SHA256 alt-coin which doesn't use merged mining runs the risk of being 51% attacked in the cradle.  Any SHA256 based alt-coin which does use merged mining means the hashrate for both chains (btc & alt) will remain stable regardless of the shifting demand between the two coins.

yea thats the thing about this vulnerability, it would almost certainly kill the alt coin and not the bitcoin though not necessarily if the altcoin is atleast close to the popularity of bitcoin.

A solution to this is to apply control theory to the adjustment.

idk much about control theory but i can think of a crude solution pretty easily. Retarget every block and compare the last 10 blocks to the 10 blocks before that. If the average hashing power for the last 10 blocks was lower than the average hashing power for the 10 blocks before that adjust down, if the average hashing power for the last 10 blocks was higher than the average hashing power for the 10 blocks before that adjust up.

but yea im sure thats a pathetic attempt compared to what a "control theorist" could devise