Bitcoin uses a blockchain record of transactions among the participating nodes. Since the size of the record is huge, there is a thin participating node that is interested in a subset of the records.

But how to find the subset in the complete list of records. Bloom Filters help here. BF answers “does exist” query on a set.

Does A exist in a set S?
Yes (may not be true, so double-check with the DB or another mechanism)
No (definitely true)

Remember, Bloom Filter never returns the wrong and negative (False Positive) answer.

How it Works?

So the thin nodes in a Blockchain share a BloomFilter of transactions with Full Nodes (ones that have a full copy of blockchain records). Full Node lookup its blockchain transaction records with the passed BloomFilter.

Each transaction is checked in the Bloom Filter. All positives are sent to the thin node. The thin node eliminates false positives.

Reference

• https://medium.com/@tara.annison/bloom-filters-and-spv-nodes-within-the-bitcoin-blockchain-66c36ea673f2
• https://bitcoin.stackexchange.com/questions/57328/the-use-of-bloom-filter-in-spv-nodes

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