Could it theoretically be possible to perform a network attack on nodes to influence the difficulty adjustment algorithm of Bitcoin mining, by providing inaccurate timestamps?
As this is the technical section of the forum, I will assume that readers of this thread have an existing intermediate level of knowledge on Bitcoin mining, and so I won't define all concepts here. However, given the decentralised nature of the Bitcoin blockchain there is a reliance on the use of time, and timestamps, to create the chain of mined blocks, and determine the difficulty adjustment algorithm.
In the early days it was very easy to mine Bitcoin rapidly on a CPU on a single personal computer, as the set difficulty was much lower. What if it would be possible to influence a Bitcoin node into believing the current time, is a date far in the past where the difficulty was lower, and therefore it might be easier to mine a block and get newly generated Bitcoins as a reward?
To start building a possible attack chain to alter the timestamp of a Bitcoin node, we must first understand how Bitcoin nodes and blocks define their time. To quote some reading from here:
https://en.bitcoin.it/wiki/Block_timestampEach block contains a Unix time timestamp. In addition to serving as a source of variation for the block hash, they also make it more difficult for an adversary to manipulate the block chain.
A timestamp is accepted as valid if it is greater than the median timestamp of previous 11 blocks, and less than the network-adjusted time + 2 hours. "Network-adjusted time" is the median of the timestamps returned by all nodes connected to you. As a result block timestamps are not exactly accurate, and they do not need to be. Block times are accurate only to within an hour or two.
Whenever a node connects to another node, it gets a UTC timestamp from it, and stores its offset from node-local UTC. The network-adjusted time is then the node-local UTC plus the median offset from all connected nodes. Network time is never adjusted more than 70 minutes from local system time, however.
If you generated and run sufficient Bitcoin nodes with an altered internal clock, then other nodes could connected to it, then the "Network-adjusted time" which is the median of timestamps returned by all nodes connected to you, could be adjusted to an arbitrary time where the difficulty algorithm is weaker.
Therefore, would it be possible to manipulate a victim Bitcoin nodes' view of the current time, and make it believe the date is 2009 or 2010 as example to mine blocks faster and easier?
Note: At present I believe this is a theoretical attack and not practical as you would need significant resources and compute to influence Bitcoin nodes median network clock time.
