This Bitcoin Core update will protect full node operators from hacks

Core developers have released an update to the world’s most popular Bitcoin software that will protect node operators from malicious actors introducing a fake version of Bitcoin’s blockchain. The revision, which developers have designated Bitcoin Core 25717, also adds defenses against various Denial-of-Service (DoS) attacks.

When a node operator downloads Bitcoin Core software for the first time, they must also download the current Bitcoin blockchain (a large 426GB file). During this initial block download, the old software would only perform relatively rudimentary checks of block headers to look for a canonical version of the blockchain.

However, Bitcoin Core 25717 adds a long-awaited “Headers Presync” phase to the software’s presync protocol. The upgrade replaces easy-to-hack, hard-coded values ​​in Headers Presync with far more secure Proof of Work assignments. This protects node operators from a malicious actor introducing a fake version of Bitcoin’s blockchain into their node.

A full node operator in Bitcoin stores the entire blockchain since its inceptionincluding every transaction that has occurred since 2009. This way, operators can validate all proposed transactions – on their own hard drive, without trusting anyone – to guarantee that no one is double-using coins.

Other improvements in Bitcoin Core 25717

In addition to addressing vulnerabilities in the initial block download, Bitcoin Core 25717’s new Headers Presync adds security during synchronization. Because a new block of data is added to Bitcoin every 10 minutes, nodes must re-sync after downloading the 426 GB file. As time passes, nodes also need to be synchronized periodically, especially after power or internet outages. Bitcoin Core 25717 improves the security of these syncs.

The software update also addresses DoS attack vectors, which can prevent nodes from downloading the canonical blockchain. In addition, the update reduces memory “overhead” by downloading pre-sync data before downloading the entire blockchain.

Finally, the update also adds support for transient, disposable addresses for the Invisible Internet Project (I2P). I2P is a network layer for censorship-resistant, anonymous, peer-to-peer communication.

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Is Bitcoin still vulnerable to other hacks?

With over a decade of operation and a bounty of several hundred billion dollars that no hacker has yet managed to steal, experts generally agree that hacking Bitcoin is becoming increasingly unlikely. Considering the large amount of mining machines securing Bitcoin, a 51% attack has become prohibitively expensive.

Any other attack, such as hacking the GitHub repository or compromising a Bitcoin Core lead maintainer, would have to introduce a change and bypass other lead maintainers, node operators, and miners. A compromised full node that accidentally downloaded a fake blockchain would be incompatible with the Bitcoin network because the data on the blockchain would not “unify” with the data on other nodes.

At least one attempt to circumvent user consensus — a Bitcoin fork called Bitcoin XT — failed because it failed to get enough supporters on board.

Bitcoin Core 25717 provides an additional layer of security by making it more difficult to introduce a malicious blockchain into new full nodes or perform DoS attacks. Bitcoin Core’s update makes nodes less likely to accept malicious data or suffer from silent attacks that prevent them from downloading the valid, canonical Bitcoin chain.

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