src/bloom.h

   1 // Copyright (c) 2012-2015 The Bitcoin Core developers
   2 // Distributed under the MIT software license, see the accompanying
   3 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
   4
   5 #ifndef BITCOIN_BLOOM_H
   6 #define BITCOIN_BLOOM_H
   7
   8 #include "serialize.h"
   9
  10 #include <vector>
  11
  12 class COutPoint;
  13 class CTransaction;
  14 class uint256;
  15
  16 //! 20,000 items with fp rate < 0.1% or 10,000 items and <0.0001%
  17 static const unsigned int MAX_BLOOM_FILTER_SIZE = 36000; // bytes
  18 static const unsigned int MAX_HASH_FUNCS = 50;
  19
  20 /**
  21  * First two bits of nFlags control how much IsRelevantAndUpdate actually updates
  22  * The remaining bits are reserved
  23  */
  24 enum bloomflags
  25 {
  26     BLOOM_UPDATE_NONE = 0,
  27     BLOOM_UPDATE_ALL = 1,
  28     // Only adds outpoints to the filter if the output is a pay-to-pubkey/pay-to-multisig script
  29     BLOOM_UPDATE_P2PUBKEY_ONLY = 2,
  30     BLOOM_UPDATE_MASK = 3,
  31 };
  32
  33 /**
  34  * BloomFilter is a probabilistic filter which SPV clients provide
  35  * so that we can filter the transactions we send them.
  36  *
  37  * This allows for significantly more efficient transaction and block downloads.
  38  *
  39  * Because bloom filters are probabilistic, a SPV node can increase the false-
  40  * positive rate, making us send it transactions which aren't actually its,
  41  * allowing clients to trade more bandwidth for more privacy by obfuscating which
  42  * keys are controlled by them.
  43  */
  44 class CBloomFilter
  45 {
  46 private:
  47     std::vector<unsigned char> vData;
  48     bool isFull;
  49     bool isEmpty;
  50     unsigned int nHashFuncs;
  51     unsigned int nTweak;
  52     unsigned char nFlags;
  53
  54     unsigned int Hash(unsigned int nHashNum, const std::vector<unsigned char>& vDataToHash) const;
  55
  56     // Private constructor for CRollingBloomFilter, no restrictions on size
  57     CBloomFilter(unsigned int nElements, double nFPRate, unsigned int nTweak);
  58     friend class CRollingBloomFilter;
  59
  60 public:
  61     /**
  62      * Creates a new bloom filter which will provide the given fp rate when filled with the given number of elements
  63      * Note that if the given parameters will result in a filter outside the bounds of the protocol limits,
  64      * the filter created will be as close to the given parameters as possible within the protocol limits.
  65      * This will apply if nFPRate is very low or nElements is unreasonably high.
  66      * nTweak is a constant which is added to the seed value passed to the hash function
  67      * It should generally always be a random value (and is largely only exposed for unit testing)
  68      * nFlags should be one of the BLOOM_UPDATE_* enums (not _MASK)
  69      */
  70     CBloomFilter(unsigned int nElements, double nFPRate, unsigned int nTweak, unsigned char nFlagsIn);
  71     CBloomFilter() : isFull(true), isEmpty(false), nHashFuncs(0), nTweak(0), nFlags(0) {}
  72
  73     ADD_SERIALIZE_METHODS;
  74
  75     template <typename Stream, typename Operation>
  76     inline void SerializationOp(Stream& s, Operation ser_action) {
  77         READWRITE(vData);
  78         READWRITE(nHashFuncs);
  79         READWRITE(nTweak);
  80         READWRITE(nFlags);
  81     }
  82
  83     void insert(const std::vector<unsigned char>& vKey);
  84     void insert(const COutPoint& outpoint);
  85     void insert(const uint256& hash);
  86
  87     bool contains(const std::vector<unsigned char>& vKey) const;
  88     bool contains(const COutPoint& outpoint) const;
  89     bool contains(const uint256& hash) const;
  90
  91     void clear();
  92     void reset(unsigned int nNewTweak);
  93
  94     //! True if the size is <= MAX_BLOOM_FILTER_SIZE and the number of hash functions is <= MAX_HASH_FUNCS
  95     //! (catch a filter which was just deserialized which was too big)
  96     bool IsWithinSizeConstraints() const;
  97
  98     //! Also adds any outputs which match the filter to the filter (to match their spending txes)
  99     bool IsRelevantAndUpdate(const CTransaction& tx);
 100
 101     //! Checks for empty and full filters to avoid wasting cpu
 102     void UpdateEmptyFull();
 103 };
 104
 105 /**
 106  * RollingBloomFilter is a probabilistic "keep track of most recently inserted" set.
 107  * Construct it with the number of items to keep track of, and a false-positive
 108  * rate. Unlike CBloomFilter, by default nTweak is set to a cryptographically
 109  * secure random value for you. Similarly rather than clear() the method
 110  * reset() is provided, which also changes nTweak to decrease the impact of
 111  * false-positives.
 112  *
 113  * contains(item) will always return true if item was one of the last N to 1.5*N
 114  * insert()'ed ... but may also return true for items that were not inserted.
 115  *
 116  * It needs around 1.8 bytes per element per factor 0.1 of false positive rate.
 117  * (More accurately: 3/(log(256)*log(2)) * log(1/fpRate) * nElements bytes)
 118  */
 119 class CRollingBloomFilter
 120 {
 121 public:
 122     // A random bloom filter calls GetRand() at creation time.
 123     // Don't create global CRollingBloomFilter objects, as they may be
 124     // constructed before the randomizer is properly initialized.
 125     CRollingBloomFilter(unsigned int nElements, double nFPRate);
 126
 127     void insert(const std::vector<unsigned char>& vKey);
 128     void insert(const uint256& hash);
 129     bool contains(const std::vector<unsigned char>& vKey) const;
 130     bool contains(const uint256& hash) const;
 131
 132     void reset();
 133
 134 private:
 135     int nEntriesPerGeneration;
 136     int nEntriesThisGeneration;
 137     int nGeneration;
 138     std::vector<uint64_t> data;
 139     unsigned int nTweak;
 140     int nHashFuncs;
 141 };
 142
 143 #endif // BITCOIN_BLOOM_H