写在前面最近有点懒散，竟然有一周没有读源码了。想来惭愧，今天重拾bitcoin源码，来看看比特币的共识机制。
我们都知道比特币采用的共识机制是工作量证明(POW),将区块链的记账的权利通过一个数学问题的解决来决定。前面，在用python搭建简单的区块链框架中，我们简单地通过一个简单的[url=https://www.jianshu.com/p/b39c361687c1][/url]模拟了POW机制的挖矿原理。
源码初窥[h2]Consensus[/h2]- 源码路径:.../src/consensus/params.h
- namespace Consensus {enum DeploymentPos{ DEPLOYMENT_TESTDUMMY, DEPLOYMENT_CSV, // Deployment of BIP68, BIP112, and BIP113. DEPLOYMENT_SEGWIT, // Deployment of BIP141, BIP143, and BIP147. // NOTE: Also add new deployments to VersionBitsDeploymentInfo in versionbits.cpp MAX_VERSION_BITS_DEPLOYMENTS};/** * Struct for each individual consensus rule change using BIP9. * **使用bip9改变共识规则的结构体 */struct BIP9Deployment { /** Bit position to select the particular bit in nVersion. */ /**用来标志nVersion中特定位的bit*/ int bit; /** Start MedianTime for version bits miner confirmation. Can be a date in the past */ /** 矿工确认版本位的平均开始时间。这个时间可以设置在过去*/ int64_t nStartTime; /** Timeout/expiry MedianTime for the deployment attempt. */ /** 尝试部署的平均超时时间*/ int64_t nTimeout; /** Constant for nTimeout very far in the future. */ static constexpr int64_t NO_TIMEOUT = std::numeric_limits::max(); /** Special value for nStartTime indicating that the deployment is always active. * This is useful for testing, as it means tests don't need to deal with the activation * process (which takes at least 3 BIP9 intervals). Only tests that specifically test the * behaviour during activation cannot use this. */ static constexpr int64_t ALWAYS_ACTIVE = -1;};/** * Parameters that influence chain consensus. * **影响链条共识的参数 */struct Params { uint256 hashGenesisBlock; //创世区块哈希 int nSubsidyHalvingInterval; //区块奖励减半的时间间隔 /** Block height at which BIP16 becomes active */ int BIP16Height; //区块高度 /** Block height and hash at which BIP34 becomes active */ int BIP34Height; uint256 BIP34Hash; //区块重量 /** Block height at which BIP65 becomes active */ int BIP65Height; /** Block height at which BIP66 becomes active */ int BIP66Height; /** * Minimum blocks including miner confirmation of the total of 2016 blocks in a retargeting period, * (nPowTargetTimespan / nPowTargetSpacing) which is also used for BIP9 deployments. * Examples: 1916 for 95%, 1512 for testchains. * **在2016个区块中至少要有多少个区块被矿工认可，规则改变才生效 * 在BIP9部署时还是使用(nPowTargetTimespan / nPowTargetSpacing) * eg:1916 for 95%, 1512 for 测试链 */ uint32_t nRuleChangeActivationThreshold; uint32_t nMinerConfirmationWindow; BIP9Deployment vDeployments[MAX_VERSION_BITS_DEPLOYMENTS]; /** Proof of work parameters */ /**POW参数*/ uint256 powLimit; //难度 bool fPowAllowMinDifficultyBlocks; //是否允许最低难度 bool fPowNoRetargeting; //不调整难度 int64_t nPowTargetSpacing; //区块产生平均时间 int64_t nPowTargetTimespan; //难度调整时间 10 //难度调整的比例 int64_t DifficultyAdjustmentInterval() const { return nPowTargetTimespan / nPowTargetSpacing; } uint256 nMinimumChainWork; //当前难度调整最小值 uint256 defaultAssumeValid; //再次区块之前的区块都认为是有效的};} // namespace Consensus
- //获取下一次需要的工作量量unsigned int GetNextWorkRequired(const CBlockIndex* pindexLast, const CBlockHeader *pblock, const Consensus::Params& params){ assert(pindexLast != nullptr); //工作量证明的限制值 unsigned int nProofOfWorkLimit = UintToArith256(params.powLimit).GetCompact(); // Only change once per difficulty adjustment interval // 难度发生调整时才有所改变 if ((pindexLast->nHeight+1) % params.DifficultyAdjustmentInterval() != 0) { // 判断是否允许最小难度值 if (params.fPowAllowMinDifficultyBlocks) { // Special difficulty rule for testnet: // If the new block's timestamp is more than 2* 10 minutes // then allow mining of a min-difficulty block. /**测试网络的特殊难度规则： * 如果新区块的时间戳超过两个区块的产生时间20min,那么返回限制挖矿难度 */ if (pblock->GetBlockTime() > pindexLast->GetBlockTime() + params.nPowTargetSpacing*2) return nProofOfWorkLimit; else { // Return the last non-special-min-difficulty-rules-block const CBlockIndex* pindex = pindexLast; while (pindex->pprev && pindex->nHeight % params.DifficultyAdjustmentInterval() != 0 && pindex->nBits == nProofOfWorkLimit) pindex = pindex->pprev; return pindex->nBits; } } //返回新区快的nBits值 return pindexLast->nBits; } // Go back by what we want to be 14 days worth of blocks int nHeightFirst = pindexLast->nHeight - (params.DifficultyAdjustmentInterval()-1); assert(nHeightFirst >= 0); const CBlockIndex* pindexFirst = pindexLast->GetAncestor(nHeightFirst); assert(pindexFirst); //计算工作量证明 return CalculateNextWorkRequired(pindexLast, pindexFirst->GetBlockTime(), params);}//计算工作量证明unsigned int CalculateNextWorkRequired(const CBlockIndex* pindexLast, int64_t nFirstBlockTime, const Consensus::Params& params){ //如果不调整难度值 if (params.fPowNoRetargeting) return pindexLast->nBits; // Limit adjustment step // 难度调整的限制 int64_t nActualTimespan = pindexLast->GetBlockTime() - nFirstBlockTime; if (nActualTimespan < params.nPowTargetTimespan/4) nActualTimespan = params.nPowTargetTimespan/4; if (nActualTimespan > params.nPowTargetTimespan*4) nActualTimespan = params.nPowTargetTimespan*4; // Retarget //计算调整后的难度值 const arith_uint256 bnPowLimit = UintToArith256(params.powLimit); arith_uint256 bnNew; bnNew.SetCompact(pindexLast->nBits); bnNew *= nActualTimespan; bnNew /= params.nPowTargetTimespan; if (bnNew > bnPowLimit) bnNew = bnPowLimit; return bnNew.GetCompact();}//检验工作量证明bool CheckProofOfWork(uint256 hash, unsigned int nBits, const Consensus::Params& params){ bool fNegative; bool fOverflow; arith_uint256 bnTarget; bnTarget.SetCompact(nBits, &fNegative, &fOverflow); // Check range if (fNegative || bnTarget == 0 || fOverflow || bnTarget > UintToArith256(params.powLimit)) return false; // Check proof of work matches claimed amount if (UintToArith256(hash) > bnTarget) return false; return true;}
工作量证明本质是在计算一个符合系统设定条件的哈希值，这个哈希值是通过对区块头信息进行哈希得到的。为了得到这个符合条件的哈希值，必须创建一个不超过特定值的区块块头的哈希。例如，如果最大可能的散列值是2 256 - 1，则可以通过产生小于2 255的散列值来证明您尝试了两种组合。
如果新的区块的哈希值符合共识协议期望的目标难度值条件，那么只会将新区块添加到区块链中。每2016 个块网络使用存储在每个区块头中的时间戳 来计算在生成最后2016 个区块的第一个和最后一个之间所经过的秒数。理想值是1209600秒（两周）。
- 如果生成2016 个区块的时间少于两个星期，则预期难度值会按比例增加（最多达300％），以便下一个2016 [个块]应该花费两周时间，以便以相同速率检查哈希值。
- 如果花费两个多星期来生成这些区块，出于同样的原因，预期的 难度值会成比例地下降（最高达75％）。
.
.
.
.[h2]互联网颠覆世界，区块链颠覆互联网![/h2] --------------------------------------------------20180502 23:03 |
|
转播
