Section I: Bitcoin Core Concepts

Bitcoin emerged from the ashes of the 2008 global financial crisis. On January 3rd, 2009, its anonymous creator, Satoshi Nakamoto, inscribed a telling message into Bitcoin's genesis block, the first block in its blockchain. The headline from The Times read: "Chancellor on brink of second bailout for banks." It served as a permanent statement of purpose, a critique embedded in code against centralized financial systems that had failed the world.

Bitcoin's design draws from the cypherpunk movement, which championed using cryptography to protect individual freedom and financial sovereignty. Rather than relying on banks or governments, Bitcoin functions as a peer-to-peer electronic cash system with no trusted intermediaries.

Its monetary policy is transparent, predictable, and enforced by mathematics rather than central bankers. It's perhaps the only asset in the world with a limited supply that can be independently verified. This programmed scarcity stands in stark contrast to fiat currencies, which can be printed without limit, and to hard assets like gold, which has a theoretically finite supply but no one actually knows the total amount in existence.

But this vision raised a fundamental question: How could thousands of computers scattered across the globe reach consensus on who owns what, without any central authority to settle disputes?

Mining and Proof of Work

Bitcoin's Proof of Work system enables miners to prove they've expended enormous computational effort in a way that anyone can quickly verify. At the heart of this process is a hash function: a mathematical operation that takes any input data and transforms it into a fixed-length string of characters. What makes hash functions special is that they're one-way: you can't recover the input from the output, and even the tiniest change to the input produces a completely different, unpredictable result.

Miners bundle transactions into a block and then try to solve a computational puzzle. Think of it like rolling dice with astronomical odds, trying to get a number below a certain threshold. Except miners are "rolling" trillions of times per second. They do this by repeatedly running the block data through the SHA-256 hashing algorithm. SHA-256 is a cryptographic hash function standardized by the U.S. government, and Bitcoin applies it twice for additional security. Each run produces a random-looking output.

Each attempt uses a different number called a nonce, essentially just a counter that increments from zero to about 4 billion. Each nonce generates a different, unpredictable hash result. When a miner finally finds an output below the network's target threshold, they've solved the puzzle and can add their block to the blockchain.

But modern mining hardware is so fast it can exhaust all 4 billion nonce values in seconds. When that happens, miners need another way to vary their input. This is where the coinbase transaction comes in. Every block contains a special coinbase transaction that pays the miner their block reward plus any transaction fees, effectively "creating" new bitcoin. This transaction is unrelated to the exchange of the same name. Miners can modify a field within this coinbase transaction called the extra nonce, or they can increment the block's timestamp. Either change alters the block header hash and resets their search space.

The speed at which miners make these attempts is called hash rate, measured in terahashes or exahashes per second. It shows how many hashes a miner or the entire network can try each second. You might think a higher network hash rate would make blocks come faster, but the network automatically adjusts the difficulty to compensate. Every 2,016 blocks, roughly every two weeks, the network performs a difficulty retarget. It measures how long those blocks actually took and adjusts the target accordingly. To prevent wild swings, these adjustments are capped between one-quarter and four times the previous difficulty, keeping the average block time stable at 10 minutes.

Miners use specialized chips called ASICs, designed specifically for SHA-256 proof-of-work. These chips are thousands of times more efficient than regular computers for this task. Even with the best hardware, solo mining is like playing a massive lottery where you might wait years without finding a single block. To smooth out this variance, miners join mining pools. These pools use a communication standard called Stratum to coordinate work between miners. The pool combines everyone's computing power and shares rewards proportionally based on each miner's contribution. This provides steady, predictable payouts instead of long dry spells.

The newly created coins from a block's coinbase transaction can't be spent immediately. They must wait until 100 more blocks have been added on top, which takes about 16 to 17 hours. This delay makes it much harder for miners to profit from attempting to rewrite recent blockchain history.

Consensus and Chain Selection

Now that we understand how mining works, we can explore how the network reaches agreement on which chain is valid.

Bitcoin's network is composed of nodes, which are computers running Bitcoin software that independently verify every transaction and block to ensure they follow the rules. These nodes maintain a complete copy of the blockchain and relay valid information to other participants. Miners typically run nodes themselves to verify the blocks they build, but many participants run nodes without mining, simply to validate Bitcoin's state independently and contribute to the network's decentralization. When people refer to "nodes" in Bitcoin discussions, they usually mean these non-mining participants who verify but don't produce blocks.

Bitcoin solves consensus through a robust mechanism called Nakamoto Consensus, which is often simplified as the "longest chain rule" but is more accurately described as the chain with the most cumulative work. Think of two hikers taking different routes: one takes 1,000 easy steps, the other 600 hard steps. The system doesn't score by steps (block count) but by energy required (a stand in for work), so the steeper, harder route can "weigh" more even with fewer steps. Nodes follow the same principle, choosing whichever chain required the most cumulative computational work to produce. An attacker can't rewrite history by simply creating more blocks; they must produce at least as much total work as the honest chain, and then some.

Occasionally, two miners find valid blocks at nearly the same time, creating temporary forks in the blockchain. Different parts of the network will initially follow different blocks depending on which one they heard about first. The tie is broken when the next block is found. Whichever fork gets extended first becomes longer and automatically wins. At that point, all nodes on the network switch to follow the longer chain, abandoning the shorter one. The block on the losing fork becomes stale, meaning it's discarded and not included in the final blockchain, and its transactions go back to being unconfirmed. This whole process usually resolves within minutes.

These chain reorganizations (or "reorgs") are a normal and expected part of Bitcoin's operation. One-block reorgs occur occasionally, two-block reorgs are rare, three or more are extremely rare absent an attack or severe network partition. This probabilistic behavior is why confirmations matter: the probability that a transaction is affected by a reorg falls exponentially with each additional block. Merchants typically wait for multiple confirmations (often six) before considering large payments final.

Beyond natural forks, Bitcoin faces other potential attacks. Eclipse attacks involve isolating a node's network connections to feed it a distorted view of the blockchain. Selfish mining involves withholding found blocks to mine privately and publish strategically for a revenue advantage. Diversity of peers, network-level protections, and monitoring help mitigate these risks.

Monetary Policy

Bitcoin has a predictable, algorithmic monetary policy with a fixed issuance schedule. The block reward, or subsidy, is cut in half every 210,000 blocks, an event known as the "halving" that occurs roughly every four years. The subsidy began at 50 BTC and has since been reduced to 25, 12.5, 6.25, and most recently to 3.125 BTC after the 2024 halving.

This mechanism makes Bitcoin a disinflationary asset, as its inflation rate trends toward zero. Around the year 2140, the subsidy will cease, and miners will be compensated solely by transaction fees. Due to integer rounding in halvings, the terminal supply converges to ~20,999,999.9769 BTC. As of early 2026, roughly 95% of the eventual 21 million BTC has already been mined and is in circulation.

Miners earn revenue from two sources: the block subsidy (new issuance of BTC) and transaction fees paid by users. The vast majority of miner revenue comes from the block subsidy. In 2024, the block subsidy accounted for approximately 94% of total earnings. This combined revenue, known as the security budget, determines the cost of attacking the network, explored in detail in Section IV.

Bitcoin's predictable scarcity forms a cornerstone of its store of value proposition. However, scarcity alone doesn't guarantee price appreciation as price ultimately depends on sustained demand from buyers. Decreasing issuance creates favorable supply dynamics, but this only translates to price appreciation if accompanied by buying pressure that exceeds selling pressure in the market.