What happens if a miner confirms their own double spend?


Thanks for clearing that up. I need to get my information from better sources..

Much of the confusion comes from the fact that it has become common to use the words "double spend" to mean something other than an actual double spend.

One of the truly innovative things that was accomplished with the creation of the bitcoin protocol was that it provided a decentralized way to make it impossible to double spend a digital asset. Prior to the creation of bitcoin, it was possible to use a digital signature system to provide a chain of custody proof that control of a digital asset was being transferred from one person to another. However, it required a centralized "clearing house" to make sure that the digital asset wasn't duplicated and control of multiple copies of it wasn't turned over to multiple recipients.

Without the centralized clearing house, a malevolent entity could make an exact duplicate of the digital asset and then "spend" both copies. There would...

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Unconfirmed transactions have always been a rather mysterious aspect of Bitcoin that doesn’t seem to get much attention. Although many Bitcoin users believe that they have received money as soon as it shows up in their Bitcoin wallet, that isn’t necessarily true. In reality, sending a message to the Bitcoin network about a transaction does not necessarily mean that the transaction will end up in a block.

There are now Bitcoin payment processors, such as Bitnet, who are willing to take responsibility for any losses caused by an unconfirmed transaction that never gets into the blockchain. These companies are willing go the extra mile in these situations because they have integrated advanced anti-double-spending mechanisms that they claim will allow them to limit their exposure to, what some would call, fraudulent Bitcoin transactions.

Peter Todd is a Bitcoin Core developer and blockchain researcher who has his hands in many different projects in the Bitcoin...

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One of the largest sources of confusion in the question of blockchain security is the precise effect of the block time. If one blockchain has a block time of 10 minutes, and the other has an estimated block time of 17 seconds, then what exactly does that mean? What is the equivalent of six confirmations on the 10-minute blockchain on the 17-second blockchain? Is blockchain security simply a matter of time, is it a matter of blocks, or a combination of both? What security properties do more complex schemes have?

Note: this article will not go into depth on the centralization risks associated with fast block times; centralization risks are a major concern, and are the primary reason not to push block times all the way down to 1 second despite the benefits, and are discussed at much more length in this previous article; the purpose of this article is to explain why fast block times are desirable at all.

The answer in fact depends crucially on the security model that we...

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If you are new to bitcoins and have no idea what double-spend is then you are not aware of one of the major flaws of cryptocurrency system. In this article I will explain in detail what double-spend is, different types of double-spend attack, and how to prevent double-spend attacks?

What is Double-Spend?

In simple words, double-spend means spending some money more than once. Since bitcoins are digital currency, the electronic files or digital token associated with a bitcoin transaction can be duplicated and used for spending the bitcoins twice. How? The digital data asscoiated with a bitcoin transaction is not deleted or removed even after the coins are spent and duplicating it will result in spending the same coins twice. Still did not get it? Look at these two examples:

1. Double spending means to create two transactions using the same digital token from a previous transaction, and presenting one of these transactions as a mode of payment (to scam...

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In the near future, Ethereum plans to switch from Proof-of-Work (PoW) based mining to Proof-of-Stake (PoS) mining. While both PoW and PoS are algorithms for reaching consensus on the blockchain, they go about it in different ways.

Since anyone can create a block, there needs to be a way that everyone on the blockchain can reach consensus, deciding together what block accurately represents recent transactions across the network. Without a central authority, trust comes from creating consensus algorithms that are very, very hard to cheat.

Proof-of-Work happens through miners trying to solve exceptionally difficult math problems. Finding a solution is basically a guessing game, but checking if a solution is correct is easy. Miners aren’t able to cheat the system because it takes real-world resources to work out these solutions.

That’s where a main issue with PoW stems from: these real-world resources are computers and electricity. It takes a lot of power to run...

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tnx i have a problem.

someone sent me $2679 and it did not confirm then i sent it out $2794 to my client lbc wallet. i had $110 sent to me which did not confirm. then later i sent out $135 to a bitpie wallet.

after some hrs someone sent me $6 it confirmed well. then also someone sent me $1000 which confirmed as well.

but the issue here is this, the $2679 after two days of no confirmation vanished from my wallet history, the $2794 i sent to my client lb wallet also vanished. then the $135 i sent to bitpie wallet reversed back to me together with another $105 i dont know where it came from which showed up in my wallet.

then the $110 a client sent to me confirmed.

This transaction of $2679 and the $2794 which i received and sent out is showing double spent. its since friday and 4 days now the harsh is still showing its heading to the destination wallet but when u login wallet it never there again.

now when i login to send out from...

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The blockchain is the new hot technology. If you haven’t heard about it, you probably know Bitcoin. Well, the blockchain is the underlying technology that powers Bitcoin. Experts say the blockchain will cause a revolution similar to what Internet provoked. But what is it really, and how can it be used to build apps today? This post is the first in a series of three, explaining the blockchain phenomenon to web developers. We’ll discuss the theory, show actual code, and share our learnings, based on a real world project.

To begin, let’s try to understand what blockchains really are.

What Is A Blockchain, Take One

Although the blockchain was created to support Bitcoin, the blockchain concept can be defined regardless of the Bitcoin ecosystem. The literature usually defines a blockchain as follows:

A blockchain is a ledger of facts, replicated across several computers assembled in a peer-to-peer network. Facts can be anything from monetary transactions to...

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Everyone already told you that you shouldn't do this and that it will cause undefined behavior. That is widely known, so let's elaborate on this on a lower level and let's see what actually happens.

Standard universal answer is that anything can happen, that's not entirely true. For example, the computer will not attempt to kill you for doing this (unless you are programming AI for a robot) :)

The reason why there can't be any universal answer is that as this is undefined, it may differ from compiler to compiler and even across different versions of same compiler.

But this is what "roughly" happens in most cases:

delete consist of 2 primary operations:

it calls the destructor if it's defined it somehow frees the memory allocated to the object

So, if your destructor contains any code that access any data of class that already was deleted, it may segfault OR (most likely) you will read some nonsense data. If these deleted data are pointers then it...

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Radar has a backchannel, and sometimes we have interesting conversations on it. Mike Loukides and I recently had a long chat about bitcoin. Both of us were thinking out loud and learning as we went along, and on re-reading the thread I’m astonished by our advanced level of ignorance. I would like to publish it because it hints at just how hard it is to understand the bitcoin network. The founding papers that describe the system leave a lot of implementation to the imagination, and the level of mis(dis?)information around the web is staggering. It’s no small thing to get the basics right. But beyond the basics, the bitcoin network has that property of an inside-out onion, where the harder you look, the more (and bigger slices of) complexity you find.

Anyway, we’re not going to publish it. I don’t mind looking stupid, but I don’t want to look that stupid — also, the comments would be torture.

However, some of the things we were wondering about are worth wondering about...

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First of all: your wallet probably sucks, consider changing it.
Second: Don’t worry your coins are safe. Within three days your transaction either confirms or your coins “reappear” in your wallet. This is the short answer and it is probably correct about 99% of the times, but let’s dive deeper for in-depth understanding, then examine your options if you don’t want to just wait.
Update: As /u/ismith23 noted, from Bitcoin 0.14 “transaction reappearance” happens after 2 weeks.

A more correct answer might look like this: when you send a transaction with too low fees, it stays in the mempool of most full nodes (1) until it either expires, (2) until a miner picks it up and confirms in a block or (3) until some magic makes (1) or (2) happen.

Sweet, isn’t it? Let’s decompose this sentence in the rest of this article.

1. When you send a transactions with too low fees…
Ok, but how low?

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Find answers to recurring questions and myths about Bitcoin.

Table of contents


What is Bitcoin?

Bitcoin is a consensus network that enables a new payment system and a completely digital money. It is the first decentralized peer-to-peer payment network that is powered by its users with no central authority or middlemen. From a user perspective, Bitcoin is pretty much like cash for the Internet. Bitcoin can also be seen as the most prominent triple entry bookkeeping system in existence.

Bitcoin is the first implementation of a concept called "cryptocurrency", which was first described in 1998 by Wei Dai on the cypherpunks mailing list, suggesting the idea of a new form of money that uses cryptography to control its creation and transactions, rather than a central authority. The first Bitcoin specification and proof of concept was published in 2009 in a cryptography mailing list by Satoshi Nakamoto. Satoshi left the project in late 2010...

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Until Bitcoin becomes the dominant currency for payments around the world, it will be more popular among traders and price speculators. As a result, the price is subject to the market forces of supply and demand which, at this point in time, goes hand in hand with the trends and whims of speculators – as a result, the price can move suddenly and sharply up or down in response to news events.

As a rule of thumb: if a piece of news makes Bitcoin more likely to be widely adopted, the price rises. If it places extra hurdles towards mass adoption, the price will fall.

You can track all the latest Bitcoin price movements in real time with Bitcoin.com’s data charts, and convert the price to your local currency with our instant Price Converter.

These events may be based on issues affecting the Bitcoin world only – such as a large scale hack affecting a key Bitcoin exchange, wallet or essential software which causes the price to dip. This happened after the Mt. Gox...

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What is opt-in RBF?

Opt-in Replace-by-Fee (RBF) allows transactions to be flagged as replaceable until they are confirmed in a block.

Is it a new feature?

Transaction replacement was introduced by Satoshi in the first release of the Bitcoin software, but later removed due to denial-of-service problems. Opt-in RBF solves this issue by requiring transaction replacements to pay a higher fee.

What is it used for?

During the period when transactions are waiting to be confirmed, some wallets would like to be able to update those transactions in order to increase their fee (which may help them get confirmed faster), compress multiple transactions into one, create background coinjoins (to improve privacy), or to perform a number of other useful actions.

How does it work?

Opt-in RBF is a change to memory pool and network relay code that allows those wallets to optionally add a signal to their transactions which tells full nodes that those...

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Learn about the difference between full vs simplified modes, and how a bitcoinj app can be attacked.


bitcoinj supports two different modes for your application: full verification and simplified verification. The mode you choose controls the resource usage of your application and how much trust you need in other participants in the Bitcoin system. As a developer, it’s important you understand the differences and in which situations your app can or cannot be trusted.

Firstly, let’s recap how a regular full node works. The fundamental problem Bitcoin solves is achieving consensus on who owns what. Every node maintains a database of unspent outputs, and transactions that attempt to spend outputs that don’t exist or were already spent are ignored. Blocks are solved by miners and broadcast to ensure everyone agrees on the ordering of transactions, and so nodes that don’t see a broadcast transaction for some reason (eg, they were offline at the time) can...

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Double spending is the type of fraud prevented by a proof-of-work system. A double spend is defined by the same transaction inputs (bitcoin values) being used to create more than one transaction. Denial of confirmations is another problem caused by attackers, but this is less likely to lead to fraud (related:DDOS). The bitcoin network protocol and blockchain allow us to rule out several other types of fraud:

Full transaction denial (still propagates with 0 confirmations for the attack duration) Spending bitcoin the bad actor does not own (prevented by digital key signing) Creating bitcoin from nothing

If latter two were to occur, the resulting block would not produce a valid hash, and thus be rejected by the nodes comprising the bitcoin network.

Satoshi Nakamoto:

We need a way for the payee to know that the previous owners did not sign any earlier
transactions. For our purposes, the earliest transaction is the one that counts, so we don't care about later...

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