加密货币考试押题整理

散列hashing

• 定义： Converts a digital object of arbitrary length, like a document, an image into a single string of fixed length, called a hash.
• 性质：
  1. not continuous, two similar documents result in very different hashes;
  2. it is very hard to reverse engineer.
• 什么是SHA256和RIPEMD160
  1. SHA256 is a novel hash functions computed with 32-bit words;
  2. RIPEMD160 has a 160-bit hash value so it is used for shorted hash.

比特币地址Bitcoin address

• 定义：a bitcoin address is a string of 26-35 alphanumeric characters in Base58Check encoding, begining with the number 1 or 3.
• 如何获取：
  1. it is a hash of a public key------>P2PKH(Pay-to-Public-Key-Hash)。
  2. Public Key 经过 SHA256 + RIPEMD160 得到Public Key Hash, 再经过Base58Check Encode得到Bitcoin address。
  3. it is the hash of a script------>P2SH(Pay-to-Script=Hash)。

Merkle Tree

• 作用：To prove some transaction included in hash.
• 提供：交易的hash+交易的merkle path+Merkle root的hash，即可证明。

比特币基础知识

• 单位：1 satoshi = $10^{-8}$Bitcoin，satoshi is smallest possible unit;
  1 MilliBit = 0.001Bitcoin = 100,000 satoshis
• 比特币上限是固定的，有Almost 21 million BTC，2,099,999,997,690,000 satisgus
• 在2140年全部挖掘，共13.4million blocks
• 每十分钟出现一个新区快。每210,000个区块比特币的产出速率就会下降50%，目前是6.25bitcoin per block

比特币编程语言——script

• 介绍：reverse-Polish notation stack-based execution language
• 堆栈操作：
  1. Push:adds an item to the top of the stack;
  2. pop:removes the item at the top of the stack.
• 优点：
  1. Not hardware dependent
  2. enables execution on devices with limited memory, like embedded devices
  3. it is stateless. No state prior to execution and no state saved after execution.
• 不能循环的影响：Does not permit loops or complex program control features：
  1. This means predictable execution times
  2. precludes attacks
  3. no infinite loops
  4. not Turing-complete.

Wallets

• 什么是钱包？
  1. Wallets is the primary user interface. Controls access to a user’s bitcoin; Manages keys and address; Tracks current balance; Enables creation and signing or transactions.
• 钱包哪里？
  1. May be held on client machine or on an exchange.
• 钱包的功能？
  1. Wallets is the primary user interface. Controls access to a user’s bitcoin; Manages keys and address; Tracks current balance; Enables creation and signing or transactions.
  2. Wallets can keep a copy of the transaction; Can query the chain when needed.
  3. Wallet also refers to the data structure used to store and manage a user’s keys and address.
• 钱包在personal machine vs exchange
  Wallet on personal machine is a software program in which you store Bitcoin; Wallet on exchange let you convert ‘real money’ like US dollars to Bitcoin. You don’t have full control of this exchange wallet.

区块链的交易 transaction

• 交易过程
  
• 交易的组成部分：
  1. an amount of Bitcoin, denominated in satoshis;
  2. A locking script which needs intended recipient to provide something to redeem it.
• 如何赎回locking的script？
  1. They provide their signature and a hash of their public key or a hash of a script
• 根据赎回方式有五种交易标准：
  1. Pay-to-Public-Key-Hash(P2PKH):a hash of a specific public key is needed to redeem.
  2. Pay-to-Script-Hash(P2SH)
  3. Pay-to-Public-Key(P2PK):Mostly used in coinbase transactions
  4. Multiple-signature:limited to 15 keys
  5. Data Output: 40 bytes of non-payment data to a Transaction output.
• 区块的第一笔交易basecoin trsansaction：
  定义：the bitcoin earnt by mining are awarded via the first transaction of each new block.
  性质：There are no UTXO inpus for these transaction.

UTXO

• 什么是UTXO?
  Unspent Transaction Output (UTXO) is the output of a transaction which may be spent as an input in a subsequent transaction.
• UTXO与交易什么关系？
  ‘Sending’ a recipient some bitcoin is done by creating some UTXO registered to their address.
• UTXO的性质：
  1. All the UTXO of the system is known by every node, held in a database called UTXO set or UTXO pool.
  2. UTXO is locked to a specific address and may be scattered;
• UTXO与wallet的关系：
  1. a wallet will aggregate the UTXO belonging to a single address.

分散共识Decentralized consensus

• （节点如何验证一个交易）Independen verification of each trasaction, by every full node.
  
• Independent aggregation of those transactions into new blocks by mining nodes together with demonstrated computation through a Proof-of-Work algorithm
• （节点如何验证一个新块）Independent verification of the new blocks by every node and assembly into a chain
  
• independent selection, by every node, of the chain with the most cumulative computation demonstrated through Proof-of-Word.

PoW

• 目的：Proof-of-Work is designed to create a hurdle to mining
• 避免了什么问题：
  1. nodes might spin-up multiple sock-puppet nodes to win the reward
  2. a form of Sybil attack
• PoW的数学问题：Find the hash a specified object with a nonce parameter which is less than sum pre-specified total.
  对block header进行两次SHA256运算，得到的值小于目标值即可。
  block header：version+previous_block_hash+merkle_root+time+target_bits+nonce
• 这个数学问题的特点：
  1. Problem designed to be hard to do and easy to check
  2. Can only be solved by trial and error.
• 哪些未记录的transaction可以进入candidate block？
  1. Prioritized by age(how many blocks since the UTXO was recorded)
  2. Size of transaction(1 bitcoin, aged 1 day)