Principles of “SPV security” and does the average Bitcoin user need a full node?

You don't need to know how an engine works to drive a car. Likewise, you don’t need to understand how Bitcoin works “behind the scenes” in order to use it. However, if you want to participate in the discussion or form your own opinion about the future of Bitcoin, there are a few things you need to know.

The Great Scaling Debate

If you haven't heard yet, there's something of a civil war going on between Bitcoin developers, companies, miners, and investors. The issue is how to "scale" the network. And more broadly, who will control developments and financial flows in the network in the future.

The short version of the battle: one side wants to stick to the original idea of ​​P2P money and plans to increase the block size; the other side wants to maintain the current block size and transform the Bitcoin blockchain into a settlement network primarily for businesses—a next-generation SWIFT.

Your opinion matters more than you think

Bitcoin is a multi-billion dollar industry. It would be naive to think that powerful corporations won't try to manipulate it in some way. So, what is the role of the average Bitcoin user? A serious quote from comedian George Carlin would be quite appropriate. What do powerful corporations want?

"They want as much as possible for themselves and as little as possible for everyone else. But I'll tell you what they don't want. They don't want people who can think critically. They don't want well-informed, well-educated people… They're not interested in them. The existence of such people doesn't make their lives easier—it's contrary to their interests." —George Carlin

House of cards for small block size supporters

"House of cards" is an expression used to describe an idea or structure that is based on weak arguments, or a concept that can be easily destroyed if one of its main components is removed.

The " Bitcoin as a settlement network" argument defines the logic of the Bitcoin network, which looks something like this:

“The majority of network users must run a full node, hence running a full node must be available, hence the need to limit bandwidth and storage costs, hence we have no choice but to keep the block size small.”

Most users don't need to run a full node

If you debunk the main idea, the house of cards will collapse. Arguments for "most users need to run a full node" can generally be divided into two categories: 1) it is good for the network and 2) it is necessary for the security of the users themselves.

Each of the arguments deserves a separate article. For now, let's just look at the idea itself from the point of view of an ordinary user.

Simplified Payment Verification (SPV) has been around since the beginning

First of all, SPV is nothing new. It was described in Section 8 of Satoshi Nakamoto's original whitepaper ( Bitcoin: A Peer-to-Peer Electronic Cash System ). Bitcoin wallets like Electrum have been using SPV for years without any issues, eliminating the need for users to run a full network node.

How does SPV work?

In a nutshell, SPV allows you to verify your transactions without worrying about other users' transactions.

SPV is responsible for two main tasks: 1) it ensures that your transactions are in a block and 2) it provides proof of work that additional blocks have been added to the blockchain.

This is essentially all you need to know to understand whether your transaction is valid.

Security SPV Limitations and Full Node Benefits

Since the SPV wallet does not verify any other transactions in the block, the block could theoretically be invalid. In over 99.99% of cases this is not a problem since we can connect to many different nodes and ensure that everyone maintains the same blockchain.

Sometimes an unusual situation may arise. For example, the adoption of a new consensus rule and a relatively large group of nodes that does not accept the new rule because they forgot to update. Dissenting nodes will be quickly separated from the network, but until this happens, the SPV client may be temporarily misled into thinking that the non-updated nodes have the correct, longest chain (after a few more blocks, it will become obvious that another chain is correct ).

This is why running a full node is said to provide "faster" security - you can verify all transactions yourself, without having to wait for additional confirmations, which solve rare problems like this. In addition, running a full node theoretically provides greater privacy, since SPV clients must contact full nodes and request information about specific addresses and transactions.

Is it possible to attack SPV wallets?

This is practically impossible (no such case is known yet). In theory, an attacker would create a large number of fake nodes and prevent you from finding the real node on the real Bitcoin network. If your wallet can find at least one real node, the attack will be thwarted, since that node will be able to confirm that the real node contains the longest proof-of-work of the network.

Additionally, to sustain the attack, the attacker will need to continue mining blocks at the current difficulty level in order to continue expanding his chain. This would require huge hashing power, which is very expensive and economically impossible.

Some more good news

It is important to understand that an SPV wallet does not simply rely on other network nodes to determine the longest blockchain. It looks at the best header chain - the chain of valid block headers that has the greatest cumulative proof-of-work. A good SPV implementation will also ensure that this PoW has an appropriate level of hashing difficulty. Those interested in this topic can study the Electrum code to understand how it works.

The type of wallet you use does not affect the security of your private keys.

"Evidence of SPV Fraud"

Fraud proof proposals are an attempt to improve security in cases where a fraudulent chain contains more blocks than the real one. However, since such cases are extremely rare, the security improvements will be very minor.

Thomas van der Wansem, author of a recent proposal for a fraud proof using tracer trees , agrees:

"Contrary to popular belief, evidence of SPV fraud is exaggerated and full nodes are not significantly more secure than SPV nodes… I fear that the current stagnation and abandonment of Bitcoin's original scaling model is not due to a lack of evidence of fraud, but to a lack of understanding of Bitcoin's security and its scaling model."

Final World

SPV wallets provide a high level of security, and most users don't need to run full nodes if they plan to use Bitcoin only as a means of payment. Armed with this information, you can rest assured about your wallet and help counter some ridiculous arguments based on false assumptions.

Source: bits.media