BloomFilter is a probabilistic filter which SPV clients provide so that we can filter the transactions we send them.
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BloomFilter is a probabilistic filter which SPV clients provide so that we can filter the transactions we send them.
This allows for significantly more efficient transaction and block downloads.
Because bloom filters are probabilistic, a SPV node can increase the false positive rate, making us send it transactions which aren't actually its, allowing clients to trade more bandwidth for more privacy by obfuscating which keys are controlled by them.
Definition at line 44 of file bloom.h.
CBloomFilter::CBloomFilter 
( 
const unsigned int 
nElements, 


const double 
nFPRate, 


const unsigned int 
nTweakIn, 


unsigned char 
nFlagsIn 

) 
 
Creates a new bloom filter which will provide the given fp rate when filled with the given number of elements Note that if the given parameters will result in a filter outside the bounds of the protocol limits, the filter created will be as close to the given parameters as possible within the protocol limits.
The ideal size for a bloom filter with a given number of elements and false positive rate is:
This will apply if nFPRate is very low or nElements is unreasonably high. nTweak is a constant which is added to the seed value passed to the hash function It should generally always be a random value (and is largely only exposed for unit testing) nFlags should be one of the BLOOM_UPDATE_* enums (not _MASK)
 nElements * log(fp rate) / ln(2)^2 We ignore filter parameters which will create a bloom filter larger than the protocol limits The ideal number of hash functions is filter size * ln(2) / number of elements Again, we ignore filter parameters which will create a bloom filter with more hash functions than the protocol limits See https://en.wikipedia.org/wiki/Bloom_filter for an explanation of these formulas
Definition at line 22 of file bloom.cpp.