src/script/sigcache.cpp

   1 // Copyright (c) 2009-2010 Satoshi Nakamoto
   2 // Copyright (c) 2009-2016 The Bitcoin Core developers
   3 // Distributed under the MIT software license, see the accompanying
   4 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
   5
   6 #include "sigcache.h"
   7
   8 #include "memusage.h"
   9 #include "pubkey.h"
  10 #include "random.h"
  11 #include "uint256.h"
  12 #include "util.h"
  13
  14 #include "cuckoocache.h"
  15 #include <boost/thread.hpp>
  16
  17 namespace {
  18
  19 /**
  20  * We're hashing a nonce into the entries themselves, so we don't need extra
  21  * blinding in the set hash computation.
  22  *
  23  * This may exhibit platform endian dependent behavior but because these are
  24  * nonced hashes (random) and this state is only ever used locally it is safe.
  25  * All that matters is local consistency.
  26  */
  27 class SignatureCacheHasher
  28 {
  29 public:
  30     template <uint8_t hash_select>
  31     uint32_t operator()(const uint256& key) const
  32     {
  33         static_assert(hash_select <8, "SignatureCacheHasher only has 8 hashes available.");
  34         uint32_t u;
  35         std::memcpy(&u, key.begin()+4*hash_select, 4);
  36         return u;
  37     }
  38 };
  39
  40 /**
  41  * Valid signature cache, to avoid doing expensive ECDSA signature checking
  42  * twice for every transaction (once when accepted into memory pool, and
  43  * again when accepted into the block chain)
  44  */
  45 class CSignatureCache
  46 {
  47 private:
  48      //! Entries are SHA256(nonce || signature hash || public key || signature):
  49     uint256 nonce;
  50     typedef CuckooCache::cache<uint256, SignatureCacheHasher> map_type;
  51     map_type setValid;
  52     boost::shared_mutex cs_sigcache;
  53
  54 public:
  55     CSignatureCache()
  56     {
  57         GetRandBytes(nonce.begin(), 32);
  58     }
  59
  60     void
  61     ComputeEntry(uint256& entry, const uint256 &hash, const std::vector<unsigned char>& vchSig, const CPubKey& pubkey)
  62     {
  63         CSHA256().Write(nonce.begin(), 32).Write(hash.begin(), 32).Write(&pubkey[0], pubkey.size()).Write(&vchSig[0], vchSig.size()).Finalize(entry.begin());
  64     }
  65
  66     bool
  67     Get(const uint256& entry, const bool erase)
  68     {
  69         boost::shared_lock<boost::shared_mutex> lock(cs_sigcache);
  70         return setValid.contains(entry, erase);
  71     }
  72
  73     void Set(uint256& entry)
  74     {
  75         boost::unique_lock<boost::shared_mutex> lock(cs_sigcache);
  76         setValid.insert(entry);
  77     }
  78     uint32_t setup_bytes(size_t n)
  79     {
  80         return setValid.setup_bytes(n);
  81     }
  82 };
  83
  84 /* In previous versions of this code, signatureCache was a local static variable
  85  * in CachingTransactionSignatureChecker::VerifySignature.  We initialize
  86  * signatureCache outside of VerifySignature to avoid the atomic operation per
  87  * call overhead associated with local static variables even though
  88  * signatureCache could be made local to VerifySignature.
  89 */
  90 static CSignatureCache signatureCache;
  91 }
  92
  93 // To be called once in AppInitMain/BasicTestingSetup to initialize the
  94 // signatureCache.
  95 void InitSignatureCache()
  96 {
  97     // nMaxCacheSize is unsigned. If -maxsigcachesize is set to zero,
  98     // setup_bytes creates the minimum possible cache (2 elements).
  99     size_t nMaxCacheSize = std::min(std::max((int64_t)0, GetArg("-maxsigcachesize", DEFAULT_MAX_SIG_CACHE_SIZE)), MAX_MAX_SIG_CACHE_SIZE) * ((size_t) 1 << 20);
 100     size_t nElems = signatureCache.setup_bytes(nMaxCacheSize);
 101     LogPrintf("Using %zu MiB out of %zu requested for signature cache, able to store %zu elements\n",
 102             (nElems*sizeof(uint256)) >>20, nMaxCacheSize>>20, nElems);
 103 }
 104
 105 bool CachingTransactionSignatureChecker::VerifySignature(const std::vector<unsigned char>& vchSig, const CPubKey& pubkey, const uint256& sighash) const
 106 {
 107     uint256 entry;
 108     signatureCache.ComputeEntry(entry, sighash, vchSig, pubkey);
 109     if (signatureCache.Get(entry, !store))
 110         return true;
 111     if (!TransactionSignatureChecker::VerifySignature(vchSig, pubkey, sighash))
 112         return false;
 113     if (store)
 114         signatureCache.Set(entry);
 115     return true;
 116 }