Simplified Payment Verification (SPV)

Understanding Simplified Payment Verification (SPV)

Simplified Payment Verification (SPV) is a lightweight client that is utilized for the verification of blockchain transactions. Unlike full nodes, SPVs solely download block headers and request proof of inclusion in the blockchain through the Merkle Tree.

The Merkle Tree is a cryptographic tree structure where each leaf node is tagged with the hash of a data block, and each non-leaf node is tagged with the cryptographic hash of its child nodes.

SPVs are particularly advantageous for light clients, such as wallets operating on low-end systems, as they enable them to determine whether a transaction has been included in the Bitcoin blockchain.

Running a full node with a Merkle Tree necessitates downloading the entire blockchain, which can be resource-intensive. However, SPVs simplify this process by only requiring the Merkle root of each block to verify the authenticity of transactions. This significantly reduces the storage requirement to just 80 bytes per block, compared to the larger size required by full nodes.

Despite their benefits, SPVs also have some drawbacks, particularly in terms of cybersecurity. In the event of a 51% attack on a cryptocurrency, hackers may manipulate SPV proofs to validate illegitimate transactions. However, ongoing research is focused on finding ways to mitigate this threat.

In his whitepaper, Nakamoto emphasized the importance and potential of Simplified Payment Verification (SPV) by highlighting that Bitcoin transactions can be verified without running a full node network.