# Simplified Payment Verification (SPV)

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**Simplified Payment Verification (SPV)** is a method that allows users to verify transactions without the need to run a full network node. This approach is particularly beneficial for those who wish to engage with the Bitcoin network without the overhead of maintaining a complete copy of the blockchain. Instead, users only need to keep **a copy of the block headers from the longest proof-of-work chain**. This can be achieved by querying various network nodes until the user is confident they possess the longest chain.

To verify a transaction, the user must **obtain the Merkle branch** that links the transaction to the block in which it is timestamped. Although the **user cannot independently check the transaction**, they can ascertain that **a network node has accepted it** by linking it to a specific point in the chain. Furthermore, subsequent blocks added to the chain serve to further confirm the network's acceptance of the transaction.

This verification method is **reliable as long as the network is controlled by honest nodes**. However, it becomes more susceptible to manipulation if an attacker gains control over a significant portion of the network. In such scenarios, the attacker could potentially fabricate transactions that appear valid. To mitigate this risk, users can implement strategies such as **accepting alerts from network nodes that detect invalid blocks**, **prompting their software to download the full block** and any alerted transactions to confirm inconsistencies.


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