What is a MASF?

A MASF is a mechanism by which blockchain miners can introduce new updates without affecting its operation. 

Un Miner Active Soft Fork (MASF) o miner-activated soft fork It is a mechanism, which like a UASF, generates a change or transition from the network to a new set of consensus rules. The difference between MASF and UASF is that MASF is activated by miners using their hashing power instead of being activated by nodes. complete. 

To activate this mechanism, miners are required to state or reveal their willingness to accept changes or modifications to the protocol. And to accomplish this, miners use their hashing power. This is because miners make a change to the version bit numbers of the blocks they mine. So by the time a certain amount of mined blocks is reached with the change in version bit numbers, full nodes can enforce the new consensus rules.

Un MASF is a smooth fork that relies on miners signaling through the hash power to activate it.

Implementation of a MASF in Bitcoin

La Bitcoin Improvement Proposal (BIP) 34 BIP, for updating and improving the transactions and versioned blocks of the network, provided a MASF in the protocol. Where the miners had to indicate their position to accept or not the proposed changes in the consensus. For this, the change that the miners had to make was to put a number greater than 1 in the version number of the block; in addition to requesting that the number of the block height be reflected in the entrance of the coinbase transaction of each of the mined blocks.  

So, to activate this mechanism, the miners had to indicate the block version number. Being "1" for the old rules, and changing from "1" to "2" to signal acceptance and transition to the new rules. 

Therefore, by implementing this mechanism, miners could choose to accept the changes or not; that is, choose to perform the fork or reject it. So, in the last 1000 blocks generated by the miners in the network, 75% (representing a total of 750 blocks) must contain the signage from version “1” to “2” to indicate that the changes would be applied. In addition, that those same 750 blocks must contain the block height indicated in the entry of the coinbase transaction of each block. 

At this point, the miners that generate blocks with version “1” emit blocks that are accepted by the network. This was because all the parameters of BIP 34 were not fulfilled, so the version 1 blocks were still valid. However, as of 95% (representing a total of 950 blocks) of the last 1000 blocks generated, new blocks produced by miners marked with version “1” are considered invalid and are rejected. Since from here, the only valid blocks were those that were marked with version “2” and that had the block height at the entry of the coinbase transaction.

This two-part transition allowed miners to have time to update their systems to accept the proposed changes, on a continuous and systematic basis. Without requiring all miners to implement the change instantly and at the same time. 

Other MASF implementations

After the successful implementation of BIP 34, this mechanism was used in the same way for the activation of the 66 BIP (restriction of strict DER signatures) and 65 BIP (OP_CHECHECKLOCKTIMEVERIFY). Where the same signaling structure was implemented, only for 66 BIP, the miners had to signal their acceptance of the fork by changing version "2" to version "3" in the last 1000 blocks generated. All blocks of version "2" are invalid when 95% of the mined blocks will accept version "3". 

Likewise, for the activation of 65 BIP, the miners had to make a transition from version "3" to version "4", in the same way, in the last 1000 blocks generated in the network. Invalidating the blocks of version "3" when 95% of those 1000 mined blocks had made the change to version "4". 

But this mechanism to increase the versions from 1 to 1 with each activation became clearly limited. Mainly because it was only possible to increment versions 1 at a time, and because it was also limited to having to activate the previous soft fork in order to activate the next one. 

Therefore, new proposed changes were subsequently implemented in the 9 BIP, where the signaling mechanism by the miners changed. At this point the version number of the block did not mark the signage. Instead, it would be based on interpreting the version field as a bit vector. In other words, the activation of the soft fork would be carried out by means of different bits in the version field. In this way, the procedure of increasing the version number was left behind. 

This allowed a great advantage over the previous version, since it allowed adding and activating a greater number of soft fork simultaneously, instead of one at a time. 

Implications of MASF implementation

All the soft miner-activated forks (MASF) they allow new consensus rules to be activated in the protocol once most nodes are updated and accepted. 

However, since miners use only their hash power to carry out this process, this can be inconvenient. This because it implies that the computational power or hash rate indicates that the fork is executing. However, they are actually operating on the older versions without the soft fork. Something like this happened with BIP 66. At that time, many miners indicated the rules but did not apply them. This led the miners to create a new chain (hard fork). Although this is rejected by the miners who did apply the BIP 66. Which meant that those miners lost all the rewards and the computational power invested.