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🗓️ Active from 2019-09-19 to 2019-10-12
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2023-06-07 18:20:40

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📅 Original date posted:2019-09-19
📝 Original message:Hello list,
Here is a link for a draft of a BIP for compact probabilistic block filters alternative of BIP 158
https://docs.google.com/document/d/1jH9tEUyb9w2OZd4-kxfGuyNIIZzmgkEb_z0qSxv80ik/edit?usp=sharing <https://docs.google.com/document/d/1jH9tEUyb9w2OZd4-kxfGuyNIIZzmgkEb_z0qSxv80ik/edit?usp=sharing>
Summary:
- BIP 158 false positive rate is low, we can achieve lower bandwidth with higher false positive rate filter while sync blockchain
- BIP 158 not do not support filter batching by design of used parameters for siphash and Golomb coding optimal parameters
- Alternative compression with delta coding and splitting data to 2 bit string sequences. First for data without prefixes, second one for information about bit length written to first sequence.
Second sequence have a lot of duplicates, compressed with 2 round of Huffman algorithm. (Effectivity about 98% vs Golomb with optimal parameters)
- Block filters batching reduce filter size significantly
- Separation of filters by address type allows lite client not to download redundant information without compromising privacy.
- Lite client filters download strategy: get biggest filter (smallest blocks/size rate) for blocks range, in case positive test -> get medium filters to reduce blocks range -> get block filters for affected range -> download affected blocks over TOR
Implementation (python): https://github.com/bitaps-com/pybtc/blob/bugfix/pybtc/functions/filters.py#L172 <https://github.com/bitaps-com/pybtc/blob/bugfix/pybtc/functions/filters.py#L172>
Exactly information from mainnet about size for separated filters by address types and batch size will be added within few days.
Thanks for any feedback.
Aleksey Karpov
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