Hello list,
Here is a link for a draft of a BIP for compact probabilistic block filters alternative of BIP 158
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
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