Must a Block contain a coinbase transaction?


Generating (coinbase) transaction is a special transaction which must be contained in each block. Usually this transaction is composed by a miner.

The following rules are to be kept:

There is only one generating transaction in a block. It has only one input of type "gen". No other inputs are allowed. This input contains only one field of type "height". It's value is equal to the actual height of it's block. No other fields are allowed. There is no restrictions about number of outputs, but the whole size of the transaction must not exceed XXXX KB. Every transaction's output must has syntactically correct target and amount. Sum of all transaction's output amounts must be equal to block reward + sum of transaction's fees Generating transaction may contain up to 255 arbitrary bytes in the field 'extra'. Unlock time should be equal or greater than current current...
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BIP: 22 Title: getblocktemplate - Fundamentals Author: Luke Dashjr Status: Accepted Type: Standards Track Created: 2012-02-28


This BIP describes a new JSON-RPC method for "smart" Bitcoin miners and proxies. Instead of sending a simple block header for hashing, the entire block structure is sent, and left to the miner to (optionally) customize and assemble.


Block Template Request

A JSON-RPC method is defined, called "getblocktemplate". It accepts exactly one argument, which MUST be an Object of request parameters. If the request parameters include a "mode" key, that is used to explicitly select between the default "template" request or a "proposal".

Block template creation can be influenced by various parameters:

getblocktemplate MUST return a JSON Object containing the following keys:

The Objects listed in the response's "transactions" key contains these keys:

Only the "data" key is...

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This week, we’ve invited Ofir Beigel to guest blog for us. We’ll let him take it from here.

Recently, scaling bitcoin has been a hot topic for the bitcoin community. Why is this? Well, as bitcoin grows and more users hop onboard, a big priority is to ensure the network can efficiently handle the increasing transaction volume. And lately, many users have been expressing their worries over transaction delays caused by network congestion. In this post I’m going to talk a bit about how transaction confirmations work, and the role that fees play in the process.

Miners, bounties, and newly-generated bitcoins

In order to understand transaction confirmations, we’ll need to cover some key concepts of bitcoin mining. I won’t attempt to explain the whole process of bitcoin mining in this post, but I’ll try to simplify the process with this short explanation. Every day hundreds of thousands of transactions are sent and received on the bitcoin network. These transactions...

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0-Confirmation (Zero-Confirmation)

See Unconfirmed Transaction and Confirmation Number.

51% Attack

Also known as >50% attack or a double spend attack. An attacker can make a payment, wait till the merchant accepts some number of confirmations and provides the service, then starts mining a parallel chain of blocks starting with a block before the transaction. This parallel blockchain then includes another transaction that spends the same outputs on some other address. When the parallel chain becomes more difficult, it is considered a main chain by all nodes and the original transaction becomes invalid. Having more than a half of total hashrate guarantees possibility to overtake chain of any length, hence the name of an attack (strictly speaking, it is "more than 50%", not 51%). Also, even 40% of hashrate allows making a double spend, but the chances are less than 100% and are diminishing exponentially with the number of confirmations that the merchant requires. This attack is...

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For a broader coverage related to this topic, see



A diagram of a bitcoin transfer

The bitcoin network is a peer-to-peer payment network that operates on a cryptographic protocol. Users send bitcoins, the units of currency, by broadcasting digitally signed messages to the network using bitcoin wallet software. Transactions are recorded into a distributed, replicated public database known as the blockchain, with consensus achieved by a proof-of-work system called "mining". The protocol was designed in 2008 and released in 2009 as open source software by "Satoshi Nakamoto", the name or pseudonym of the original developer/developer group.

The network requires minimal structure to share transactions. Messages are broadcast on a best effort basis, and nodes can leave and rejoin the network at will. Upon reconnection, a node downloads and verifies new blocks from other nodes to complete its local copy of the blockchain.[1][2]

The best chain...

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George Samman is a blockchain and cryptocurrency consultant and advisor who recently co-authored a seminal report on blockchain architecture with KPMG.

Here, Samman looks at how solutions like zero knowledge proofs can preserve privacy and confidentiality on blockchain platforms – if they can be made to achieve speed and scalability.

One of the bigger trends in the blockchain world, particularly when it comes to financial services and specifically capital markets operations, has been a need for privacy and confidentiality in the course of daily business. This has meant that blockchain solutions are being designed with this primary need in mind. This has led to all the private blockchain solutions being developed today.

When you build for privacy and confidentiality there are tradeoffs that come with that. Mainly you lose transparency, which was the major feature of the the first blockchain: bitcoin. As originally designed, a blockchain is a transparency...

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With websites operating under the constant threat of attacks, users have long been accustomed to looking for a little green lock in web browsers, signaling an SSL certificate, to ensure that the site is secure.

Today, SSL is used for transmitting sensitive information over the Internet, and it has long been a significant driver of e-commerce. Involved in this process are protocols including the Secure Sockets Layer (SSL) and Transport Layer Security (TLS), as well as certificate authorities (CAs), entities that issue digital certificates to organizations or individuals.

Now, digital identity startup Netki has announced that it is releasing what it considers to be the first digital identity certificate akin to the SSL for the blockchain in a bid to replicate both this technology and its top-lever services on the blockchain.

In interview, CEO and co-founder Justin Newton expanded on the vision for the product, which follows a wallet naming service it...

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All the recent media attention on Bitcoin inspired me to learn how Bitcoin really works, right down to the bytes flowing through the network. Normal people use software


that hides what is really going on, but I wanted to get a hands-on understanding of the Bitcoin protocol. My goal was to use the Bitcoin system directly: create a Bitcoin transaction manually, feed it into the system as hex data, and see how it gets processed. This turned out to be considerably harder than I expected, but I learned a lot in the process and hopefully you will find it interesting.

(Feb 23: I have a new article that covers the technical details of mining. If you like this article, check out my mining article too.)

This blog post starts with a quick overview of Bitcoin and then jumps into the low-level details: creating a Bitcoin address, making a transaction, signing the transaction, feeding the transaction into the peer-to-peer network, and observing the results.


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How does BitClub Mining Pool Work?

If you are not familiar with bitcoin mining here is a very basic overview… Every 10 minutes a new block of 25 Bitcoin is found by someone in the network who is hashing. In order to find a block you must attempt to solve a simple math problem using a cryptographic hashing function. To see an example of this go to our Pool Website and under Pool Stats you will see a column showing Total Shares in the Round. This is showing how many times we have attempted to solve the math problem since the last Block that we solved.

You will also see the column right above showing Current Block Difficulty. This difficulty is the entire network difficulty which is basically showing how many times on average it would take to guess the correct answer and be awarded the block of 25 Bitcoin. The more hashing power you have the higher the probability is to guess the correct answer and solve the problem. When the total shares in the round are equal to...

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