src/bloom.h

   1 // Copyright (c) 2012 The Bitcoin developers
   2 // Distributed under the MIT/X11 software license, see the accompanying
   3 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
   4 #ifndef BITCOIN_BLOOM_H
   5 #define BITCOIN_BLOOM_H
   6
   7 #include <vector>
   8
   9 #include "uint256.h"
  10 #include "serialize.h"
  11
  12 class COutPoint;
  13 class CTransaction;
  14
  15 // 20,000 items with fp rate < 0.1% or 10,000 items and <0.0001%
  16 static const unsigned int MAX_BLOOM_FILTER_SIZE = 36000; // bytes
  17 static const unsigned int MAX_HASH_FUNCS = 50;
  18
  19 // First two bits of nFlags control how much IsRelevantAndUpdate actually updates
  20 // The remaining bits are reserved
  21 enum bloomflags
  22 {
  23     BLOOM_UPDATE_NONE = 0,
  24     BLOOM_UPDATE_ALL = 1,
  25     // Only adds outpoints to the filter if the output is a pay-to-pubkey/pay-to-multisig script
  26     BLOOM_UPDATE_P2PUBKEY_ONLY = 2,
  27     BLOOM_UPDATE_MASK = 3,
  28 };
  29
  30 /**
  31  * BloomFilter is a probabilistic filter which SPV clients provide
  32  * so that we can filter the transactions we sends them.
  33  *
  34  * This allows for significantly more efficient transaction and block downloads.
  35  *
  36  * Because bloom filters are probabilistic, an SPV node can increase the false-
  37  * positive rate, making us send them transactions which aren't actually theirs,
  38  * allowing clients to trade more bandwidth for more privacy by obfuscating which
  39  * keys are owned by them.
  40  */
  41 class CBloomFilter
  42 {
  43 private:
  44     std::vector<unsigned char> vData;
  45     unsigned int nHashFuncs;
  46     unsigned int nTweak;
  47     unsigned char nFlags;
  48
  49     unsigned int Hash(unsigned int nHashNum, const std::vector<unsigned char>& vDataToHash) const;
  50
  51 public:
  52     // Creates a new bloom filter which will provide the given fp rate when filled with the given number of elements
  53     // Note that if the given parameters will result in a filter outside the bounds of the protocol limits,
  54     // the filter created will be as close to the given parameters as possible within the protocol limits.
  55     // This will apply if nFPRate is very low or nElements is unreasonably high.
  56     // nTweak is a constant which is added to the seed value passed to the hash function
  57     // It should generally always be a random value (and is largely only exposed for unit testing)
  58     // nFlags should be one of the BLOOM_UPDATE_* enums (not _MASK)
  59     CBloomFilter(unsigned int nElements, double nFPRate, unsigned int nTweak, unsigned char nFlagsIn);
  60     // Using a filter initialized with this results in undefined behavior
  61     // Should only be used for deserialization
  62     CBloomFilter() {}
  63
  64     IMPLEMENT_SERIALIZE
  65     (
  66         READWRITE(vData);
  67         READWRITE(nHashFuncs);
  68         READWRITE(nTweak);
  69         READWRITE(nFlags);
  70     )
  71
  72     void insert(const std::vector<unsigned char>& vKey);
  73     void insert(const COutPoint& outpoint);
  74     void insert(const uint256& hash);
  75
  76     bool contains(const std::vector<unsigned char>& vKey) const;
  77     bool contains(const COutPoint& outpoint) const;
  78     bool contains(const uint256& hash) const;
  79
  80     // True if the size is <= MAX_BLOOM_FILTER_SIZE and the number of hash functions is <= MAX_HASH_FUNCS
  81     // (catch a filter which was just deserialized which was too big)
  82     bool IsWithinSizeConstraints() const;
  83
  84     // Also adds any outputs which match the filter to the filter (to match their spending txes)
  85     bool IsRelevantAndUpdate(const CTransaction& tx, const uint256& hash);
  86 };
  87
  88 #endif /* BITCOIN_BLOOM_H */