# PoS Is Trusted

### The Fundamental Problem with Proof of Stake

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In 2014, Vitalik Buterin published a blog post titled: “[Proof of Stake: How I Learned to Love Weak Subjectivity](https://blog.ethereum.org/2014/11/25/proof-stake-learned-love-weak-subjectivity)”. 
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In a Proof-Of-Stake system, a node syncing is unable to be 'subjective' about which fork to choose, without a centralized (weak) intervention. This is because the mechanism that allows a chain to determine the 'correct fork' is defined by the chain itself and not an external subjective measure like 'work'. <mark style="color:red;">**This means Proof-of-Stake chains can't trustlessly sync their own blockchain.**</mark>

This is a matters because:

* ❌ It threatens the finality of transactions, breaking the crypto economy&#x20;
* ❌ It can cause a [Chain Halt](/docs/canopy-network/core-features/chain-halt-rescue.md#whats-a-chain-halt) — preventing forward progress
* ❌ It can partition the network, isolating nodes and dividing the community
* ❌ It can be leveraged to pull off major attacks, like a **Long-Range Attack**

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*Did you know*? Proof-of-Stake chains can't be synced by participants without trust
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### What's a Long-Range Attack?

A long-range attack is where an adversary uses old validator keys that once controlled a super-majority of the validator set to rewrite the chain’s history from a point far in the past. This is possible because the economic value that the keys once held has diminished, and the attacker is presumably able to acquire them cheaply. Using these keys, an attacker is able to quickly rewrite the forward history of the blockchain to become the ‘longest chain’ and potentially convince peers to join the fork, enabling economic attacks.&#x20;

### How does Ethereum solve this?

In his post, Vitalik proposed the use of “weak subjectivity”, having syncing nodes rely on **social consensus** by publishing finalized block hashes to **centralized sources**.&#x20;

He suggested checkpointing every **12.8 minutes** for Ethereum, aligning with the network's epoch system. <mark style="color:red;">This approach is widely regarded as one of the only effective mechanisms to prevent Long-Range Attacks.</mark>

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While more energy efficient than PoW, basically all PoS chains rely on some form of centralized checkpointing.
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