https://coinsutra.com/bitcoin-double-spending/

Bitcoin is gaining rapid popularity and adoption across the globe. It is re-defining the way we use money by being the world’s first fully functional digital currency.

You might be surprised to know that even before Bitcoin, there were attempts to create a sustainable digital monetary system. But all those attempts failed because an obvious problem with digital money is that transactions can be copied and spent twice.

Let me simply the concept…

Bitcoin has been able to survive and thrive because it solves the “double spending”problem.

What Does Double Spending Mean?

Double spending means spending the same money twice.

Let’s consider this example:

You go to Starbucks and order a cappuccino worth $10. You pay in cash. Now that $10 in cash is in the cash vault of Starbucks. By all means, you simply cannot spend the same $10 somewhere else to make another purchase.

Unless you steal it…!!!

As you paid with your $10 bill, the service provider at Starbucks instantly confirmed that you have paid, and you received your coffee in exchange for the money.

But Bitcoin is digital money, not physical cash. Hence, Bitcoin transactions have a possibility of being copied and rebroadcasted. This opens up the possibility that the same BTC could be spent twice by its owner.

How?

In our Starbucks example, you paid cash, so the payment was confirmed and verified instantly by another human. But with digital currency like BTC, if this verification mechanism is missing, it can lead to double spending.

Anyone can just copy that digital money and pay somewhere else.

And here is where the unique invention lies…

Bitcoin, although being digital currency, solves the problem of being copied and getting spent twice.

How Bitcoin Handles The Double Spending Problem

Bitcoin manages the double spending problem by implementing a confirmation mechanism and maintaining a universal ledger (called “blockchain”), similar to the traditional cash monetary system.

Bitcoin’s blockchain maintains a chronologically-ordered, time-stamped transaction ledger from the very start of its operation in 2009.

Every 10 mins, a block (i.e. a group of transactions) is added to the ledger. And all the nodes on the Bitcoin network keep a copy of this global ledger (the blockchain).

Let’s see how the Bitcoin network prevents double spending:

Let’s suppose you have 1 BTC which you try to spend twice.

You made the 1 BTC transaction to a merchant. Now, you again sign and send the same 1 BTC on another Bitcoin address to try and trick the merchant.

Both transactions go into the unconfirmed pool of transactions. But only your first transaction got confirmations and was verified by miners in the next block. Your second transaction could not get enough confirmations because the miners judged it as invalid, so it was pulled from the network.

But wait… what if both the transactions are taken simultaneously by the miners?

When miners pull the transactions simultaneously from the pool, then whichever transaction gets the maximum number of confirmations from the network will be included in the blockchain, and the other one will be discarded.

You might say that this is unfair for the merchant, as the transaction might fail in getting confirmations. Yeah, this can happen!!!

That’s why it is recommended for merchants to wait for a minimum of 6 confirmations.

Here, “6 confirmations” simply means that after a transaction was added to the blockchain, 6 more blocks containing several other transactions were added after it.

“Confirmations” are nothing but more blocks containing more transactions being added to the blockchain. Each transaction and blocks are mathematically related to the previous one.

All these confirmations and transactions are time-stamped on the blockchain, making them irreversible and impossible to tamper with.

So if a merchant receives his/her minimum number of confirmations, he/she can be positive it was not a double spend by the sender.

Why can the merchant be assured?

Because to be able to double spend that coin, the sender has to go back and reverse all transactions in the 6 blocks that have been added after their transaction, which is computationally impossible.

How Double-Spend Attacks Can Happen

  • Attack 51%

If somehow an attacker captures 51% of the hash power of the network, double spending can happen.

“Hash power” means the computational power which verifies transactions and blocks. If an attacker has this control, he/she can reverse any transaction and make a private blockchain which everyone will consider as real.

But so far, no such attack has happened because controlling 51% of the network is highly cost intensive. It depends on the present difficulty of mining, the hardware price, and the electricity cost, all of which is infeasible to acquire.

  • Race Attack

When an attacker sends the same coin in rapid succession to two different addresses, the obvious outcome is that only one of them will get included.

Now, if you as a merchant don’t wait for confirmations of payment, then in a case like this, there’s a 50% chance you got the double spent coin (and you won’t receive that money).

Let’s see how…

Your customer can trick you if he/she sends the same coins again to his/her address.

Once the customer does both transactions, both transactions go to an unconfirmed pool of transactions. Whichever transaction gets verified first and gets 6 confirmations will be accepted, and the other will be discarded.

As a merchant, you might get the 6 confirmations first, but if the attacker gets the confirmations first, then you won’t receive your funds. That’s why it is said to wait for a minimum of 6 confirmations.

So far, in the 8-year history of Bitcoin, no such attack has been successful. The Bitcoin mechanism of maintaining a universal transaction ledger based on confirmations has yet to be tricked.

What is Double Spending & How Does Bitcoin Handle It?的更多相关文章

  1. Bitcoin: A Peer-to-Peer Electronic Cash System

    Bitcoin: A Peer-to-Peer Electronic Cash System Satoshi Nakamoto October 31, 2008 Abstract A purely p ...

  2. How the Bitcoin protocol actually works

    sklearn实战-乳腺癌细胞数据挖掘(博客主亲自录制视频教程) https://study.163.com/course/introduction.htm?courseId=1005269003&a ...

  3. 比特币_Bitcoin 简介

    2008-11   Satoshi Nakamoto  Bitcoin: A Peer-to-Peer Electronic Cash System http://p2pbucks.com/?p=99 ...

  4. p3.BTC-协议

    数字货币是文件,难伪造,但是容易复制,不像实体货币,花出去就没了,数字货币存在double spending attack,双花攻击. 去中心化的货币,需要解决两个问题: 1.货币的发行 挖矿 2.交 ...

  5. Blockchain technology and Application

    BTC-密码学原理 比特币本质:crypto currency[加密货币] 比特币用到的两个功能: 1.哈希 crypto graphic hash function 2.签名(非对称加密) 哈希cr ...

  6. Block Chain Learning Notes

    区块链是什么 区块链技术是由比特币创造的,本文也将从比特币开始进行引导,一步一步告诉大家什么是区块链.如果你想立马知道区块链是什么,也可以直接转到文章末尾的区块链定义. 区块链,可能是当下最有前景又充 ...

  7. [No00009E]几种常见的命名规则

    变量命名规则 必须遵循的命名规则 1.    变量名首字母必须为字母(a-z A-Z),下划线(_),或者美元符号($)开始php编程中所有变量必须以$开始. 2.    变量名只能是字母(a-z A ...

  8. effectiveC++ 内存管理 学习笔记

    1.尽量使用初始化列表而不要再构造函数里赋值,初始化顺序和声明的顺序一致,一些类型如const,引用等,必须使用初始化.对于非内部数据类型成员对象应当采用初始化表,以获取更高的效率.example:B ...

  9. Delphi编程建议遵守的规范2---命名规范

    1.1.形参命名建议 所有形参的名称都应当表达出它的用途.如果合适的话,形参的名称最好以字母a 为前缀,例如: procedure SomeProc(aUserName:string; aUserAg ...

随机推荐

  1. 图论:Floyd-多源最短路、无向图最小环

    在最短路问题中,如果我们面对的是稠密图(十分稠密的那种,比如说全连接图),计算多源最短路的时候,Floyd算法才能充分发挥它的优势,彻彻底底打败SPFA和Dijkstra 在别的最短路问题中都不推荐使 ...

  2. Angular2.0 基础: User Input

    1.Angular 2.0 中的变量 对输入值的获取,我们可以通过$event 来获取,也可以通过变量来获取. template: ` <input (keyup)="onKey($e ...

  3. JVM在遇到OOM(OutOfMemoryError)时生成Dump文件

    方法一: 命令:jmap -dump:format=b,file=heap.bin file:保存路径及文件名pid:进程编号(windows通过任务管理器查看,linux通过ps aux查看) du ...

  4. Android控件——ImageView

     android:orientation="vertical"  修改布局文件垂直排列 放置图片: 1.通过src引入图片: 2.通过background引入背景图片 3.baco ...

  5. LCD实验学习笔记(八):中断

    s3c2440有60个中断源(其中15个为子中断源). 31个32位的通用寄存器,6个程序状态寄存器.有6种工作模式(系统/用户模式,快中断模式,管理模式,数据访问中止模式,中断模式,未定指令中止模式 ...

  6. centos 搭建 ss

    download:https://files.cnblogs.com/files/xishaonian/ShadowsocksR-4.7.0-win.7z 使用方法:使用root用户登录,运行以下命令 ...

  7. Memcached内存缓存技术

    Memcached是什么,有什么作用? Memcached是一个开源的.高性能的内存缓存软件,从名称上看Mem就是内存的意思,而Cache就是缓存的意思. Memcached通过在事先规划好的内存空间 ...

  8. 查看linux 下进程运行时间(转)

    原文地址:http://blog.csdn.net/tspangle/article/details/11731317 可通过ps 来查看,通过参数 -o 来查看 如: ps -eo pid,tty, ...

  9. Ta-Lib用法介绍 !

    一.函数索引 重叠研究 BBANDS Bollinger Bands DEMA Double Exponential Moving Average EMA Exponential Moving Ave ...

  10. LeetCode解题报告—— Combination Sum & Combination Sum II & Multiply Strings

    1. Combination Sum Given a set of candidate numbers (C) (without duplicates) and a target number (T) ...