What is User Activated SoftFork (UASF)


What is User Activated SoftFork (UASF)

UASF stands for User Activated Soft Fork – user-activated soft fork. UASF is a mechanism by which soft fork activation occurs on a specified date determined by full network nodes (nodes). This concept requires considerable support and coordination from the industry, and it is no coincidence that this model is also called the economic majority.

 What is soft fork

There are two main types of source code modification: soft forks and hard forks. The first can be called a “soft” modification, the second – “hard”. In the case of soft fork, changing the rules does not require updating the client (software) to execute the new rules. If the nodes on the network do not accept the new rules, they will still be able to interact with the nodes that use the new rules.

How is UASF different from other soft fork activation methods

The key difference between UASF is that usually all significant modifications in the source code are activated through MASF (Miner Activated Soft Fork) – a mechanism in which most miners signal readiness for updating.

How is the UASF related to the Segregated Witness decision

In March 2017, the concept of user-activated soft fork was combined with the activation of Segregated Witness (SegWit) – an update to the Bitcoin protocol, which aims to optimize the block size. It lays the foundation for future network scaling solutions. The offer is known as BIP 148.

Why was this union needed

Soft fork SegWit (BIP 9), included in the Bitcoin Core code base, faced the following problem: its fixing and subsequent activation are possible only with 95% support for the power of miners. However, as a result of the opposition of various approaches to the further development of bitcoin, some of the miners, having a fairly high hash power, successfully blocked activation. At the same time, a significant part of industry representatives, including processing services, wallet providers and miners, are convinced that the most correct way is to activate SegWit.

How does BIP 148 work

BIP 148 can be called non-standard UASF: it should trigger the activation of SegWit in existing software, however, in addition to the efforts of holders of nodes, it requires the participation of miners. The peculiarity of the situation is that usually the nodes begin to apply the forced mode on a predetermined day (flag day). However, more than 80% of the network has already updated the node software, signaling support for SegWit.

Miners will have to signal their readiness for SegWit from August 1, 2017, creating blocks with a bit of version 1. This will lead to the fact that all active SegWit nodes will begin to enforce the protocol.

What does the bitcoin network expect in case of rejection of BIP 148

As mentioned above, BIP 148 requires support from the economic majority, especially exchanges and wallets. Otherwise, the node software supporting BIP 148 should not be launched after August 1, as this will lead to a chain separation leading to the rejection of BIP 148. At the same time, there are strong economic incentives in the network for nodes to communicate and Remained in consensus to prevent the chain from breaking.

What does the bitcoin network expect when BIP 148 is activated

If the economic majority as of August 1 signals its support for BIP 148, miners will have quite a lot of incentives to also make this decision. Otherwise, the economic majority will not accept the blocks mined by them, and the miners themselves will actually produce altcoins that are not recognized by either users or exchanges.

What other scenarios are possible

• If miners activate SegWit before August 1, BIP 148 will not be applied. All users will remain on the same chain no matter which client they use.

• If miners do not activate SegWit, a chain split may occur in which different users will see different sets of transactions.

• If most miners accept BIP 148, the separation of the chain will be temporary, and ultimately all customers will see one chain, and SegWit will be activated for all SegWit-compatible clients (Bitcoin Core 0.13.1 and higher).

• If most miners do not accept BIP 148, the paths of users who accept BIP 148 and users who do not accept it will diverge.

• If most miners start supporting BIP 148 later than August 1, a chain that does not comply with BIP 148 rules can subsequently be reorganized, while a BIP 148 chain will have more support and become the main one. At the same time, users who work in the BIP 148 client can be calm, however, users using outdated clients may encounter a “history census” and, as a result, lose all means.


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