Cryptocurrency can seem complicated until you understand what happens when a transaction is made. Discover how Bitcoin wallets, private keys, digital signature…
How Cryptocurrency Works: What Actually Happens When You Send Bitcoin
What Is Cryptocurrency?
Cryptocurrency is a type of digital asset that uses cryptographic techniques as part of its operation.
Unlike traditional money held in a bank account, a cryptocurrency network can be designed to operate without a central institution maintaining the master record of every transaction.
Bitcoin is the best-known example.
Bitcoin was introduced in 2008 through a paper published under the name Satoshi Nakamoto and launched as working software in 2009.
The original idea was to create a peer-to-peer electronic payment system that could operate without relying on a financial institution to process every payment.
What Makes Cryptocurrency Different?
When you send money through a conventional bank, there is normally a central organization maintaining records.
For example:
Your bank account
↓
Bank's database
↓
Recipient's bank account
The bank updates its records.
With a decentralized cryptocurrency such as Bitcoin, the system works differently.
Instead of one central database controlled by one organization, participating computers maintain and verify a shared record.
That shared record is the blockchain.
What Is a Blockchain?
A blockchain is a chronological record of transactions organized into blocks.
Each block is connected to the previous block using cryptographic information.
The result is a chain:
Block 1
↓
Block 2
↓
Block 3
↓
Block 4
↓
Block 5
Every participating node can independently verify whether blocks and transactions follow the rules of the network.
This is one of the fundamental ideas behind Bitcoin.
Why Is It Called a Blockchain?
Each block contains information about transactions.
It also contains information that links it cryptographically to the preceding block.
Changing an old block would therefore affect the cryptographic relationships connecting subsequent blocks.
The system is not literally an unchangeable database.
Rather, altering established history in a proof-of-work blockchain requires overcoming the computational work and network consensus protecting that history.
That distinction is important.
What Is a Bitcoin?
A Bitcoin is not a physical object.
There is no file called "one bitcoin" sitting inside your phone.
The Bitcoin network maintains a record of transactions and determines which transactions are valid according to the protocol rules.
Your wallet contains the cryptographic information necessary to authorize transactions involving funds associated with your keys.
This is why losing control of your private keys can mean losing control of your Bitcoin.
What Is a Bitcoin Wallet?
A cryptocurrency wallet is software or hardware that helps you manage your cryptographic keys and interact with the network.
A wallet can allow you to:
- Receive Bitcoin
- Create transactions
- Sign transactions
- Monitor balances
- Manage addresses
- Broadcast transactions
A wallet does not necessarily store coins in the same way a physical wallet stores banknotes.
The blockchain contains the relevant transaction history.
The wallet provides the keys used to control funds.
What Is a Private Key?
A private key is a secret piece of cryptographic information.
It can be used to create digital signatures authorizing transactions.
Think of it as an extremely important secret.
Anyone who obtains the necessary private-key information may be able to authorize transactions involving the associated funds.
That is why private keys, seed phrases, and recovery information must be protected.
What Is a Public Key?
Cryptographic systems can use a pair of related keys.
One is private.
The other is public.
The public key can be derived from the private key through cryptographic operations.
The private key is kept secret.
The public information can be used by others to verify signatures or derive addresses, depending on the Bitcoin address and script type involved.
What Is a Bitcoin Address?
A Bitcoin address is an identifier used when receiving Bitcoin.
It is not simply your public key written out directly.
Modern Bitcoin addresses can be generated from different types of scripts and public-key information.
You can give someone a Bitcoin address so they know where to send funds.
But knowing an address does not give someone the private key needed to authorize spending.
What Happens When You Receive Bitcoin?
Suppose someone sends you Bitcoin.
They create a transaction that assigns control of a specified amount of Bitcoin to conditions that your wallet can satisfy.
Your wallet provides an address to the sender.
The sender creates a transaction.
The transaction is digitally signed.
It is broadcast to the Bitcoin network.
Nodes verify it.
Eventually, it can be included in a block.
The network then records it as part of the blockchain.
Your wallet can now recognize that funds associated with your keys have become available for spending according to the network rules.
What Happens When You Send Bitcoin?
This is where things become interesting.
Suppose you want to send Bitcoin to another person.
The simplified process looks like this:
You enter the recipient's address.
↓
Your wallet constructs a transaction.
↓
Your wallet signs the transaction.
↓
The transaction is broadcast.
↓
Bitcoin nodes verify it.
↓
The transaction waits to be included in a block.
↓
A miner includes it in a candidate block.
↓
The block is accepted by the network.
↓
The transaction becomes part of the blockchain.
That entire process can happen without a bank approving the payment.
What Is a Bitcoin Transaction?
A Bitcoin transaction is a structured piece of data describing how Bitcoin's spendable outputs are being consumed and how new outputs are being created.
Bitcoin uses the UTXO model.
UTXO stands for Unspent Transaction Output.
This is different from the conventional bank-account model most people are familiar with.
What Is a UTXO?
Imagine someone sends you 0.01 BTC.
That transaction can create an output worth 0.01 BTC that your wallet can later spend.
That output remains unspent until it is used as an input in another transaction.
It is therefore an unspent transaction output.
When you spend it, it becomes an input to a new transaction.
The new transaction creates new outputs.
This is roughly how Bitcoin tracks spendable value.
Bitcoin Does Not Really Have Account Balances
Your wallet application may show:
0.035 BTC
But the Bitcoin network does not necessarily store one simple number saying:
"Michael's balance = 0.035 BTC."
Instead, the wallet can calculate your available funds from the relevant unspent transaction outputs controlled by your keys.
This is one reason the underlying Bitcoin model differs significantly from an ordinary bank account.
What Is a Digital Signature?
A digital signature allows someone to demonstrate that they possess the private key associated with the transaction authorization.
The private key is used to create the signature.
Other participants can use the corresponding public information to verify it.
The private key itself does not need to be revealed.
Simplified:
Private key
↓
Digital signature
↓
Transaction
↓
Network verifies signature
This provides an important cryptographic mechanism for proving authorization.
Why Can't Someone Simply Change a Transaction?
Because transactions are protected by cryptographic signatures and network validation rules.
Suppose someone changes the recipient address after a transaction has been signed.
The signature would no longer correspond to the modified transaction.
Nodes would reject it.
Cryptography therefore provides a way to detect unauthorized modification.
What Is Double Spending?
Digital information can normally be copied.
If Bitcoin were simply a digital file, someone could theoretically make multiple copies of the same money.
This creates the double-spending problem.
Imagine:
Alice has 1 BTC.
Alice attempts to spend that same 1 BTC with Bob.
Then Alice attempts to spend the same 1 BTC with Charlie.
The network needs a way to determine which transaction is valid.
Bitcoin solves this using a combination of transaction validation, a distributed ledger, proof of work, and network consensus.
What Is a Bitcoin Node?
A Bitcoin node is a computer running software that participates in the Bitcoin network.
A full node maintains and verifies a copy of the blockchain according to the network's consensus rules.
Nodes can independently check whether transactions and blocks are valid.
This is important because the network does not depend on one central server.
Instead:
Node
↔ Node
↔ Node
↔ Node
↔ Node
The network is distributed.
What Does a Node Check?
A Bitcoin node can check many aspects of a transaction, including whether:
- The transaction follows the protocol rules
- The inputs exist
- The inputs have not already been spent
- The transaction is properly structured
- The required signatures are valid
- The transaction does not create unauthorized coins
If a transaction violates the rules, a node does not simply accept it because another computer sent it.
It rejects it.
What Is the Mempool?
When a valid transaction is broadcast but has not yet been included in a block, nodes can hold it in a memory pool, commonly called the mempool.
Think of the mempool as a waiting area.
Transactions:
Network
↓
Mempool
↓
Candidate block
↓
Blockchain
Different nodes can have somewhat different mempool contents because transactions propagate through the network at different speeds.
What Is Bitcoin Mining?
Bitcoin mining is the process used by the network's proof-of-work system to help establish the order of transactions and secure the blockchain.
Miners collect valid transactions and construct candidate blocks.
They then perform enormous numbers of cryptographic calculations in an attempt to produce a valid proof of work.
The first miner to find a valid result can broadcast the candidate block.
Other nodes verify it.
If it follows the consensus rules, it can become part of the blockchain.
What Is Proof of Work?
Proof of work requires miners to perform computational work.
The miner repeatedly changes information in a candidate block and calculates cryptographic hashes.
The goal is to find a hash satisfying the network's current difficulty requirement.
Because the result is unpredictable, miners have to perform enormous numbers of attempts.
Finding a valid result is difficult.
Checking the result is comparatively easy.
That asymmetry is fundamental to proof-of-work systems.
What Is a Hash?
A cryptographic hash function takes data as input and produces a fixed-length output.
For example:
Data
↓
Hash function
↓
Hash
A small change in the input produces a dramatically different hash.
This makes hashes useful for detecting changes in data.
Bitcoin uses cryptographic hashing throughout its architecture.
Why Do Miners Need So Much Computing Power?
Finding a proof-of-work solution is essentially a probability game involving enormous numbers of hash calculations.
A miner can try:
Hash attempt 1
Hash attempt 2
Hash attempt 3
Hash attempt 4
...
Millions
...
Billions
...
More attempts
The more computational work a miner can perform, the more attempts it can make.
Bitcoin's difficulty mechanism adjusts the mining target over time so that blocks continue to be produced at approximately the intended rate.
What Is a Block?
A Bitcoin block contains a collection of transactions and other information needed by the protocol.
Among other things, it references the previous block and contains proof-of-work information.
Simplified:
Previous block
↓
New block
↓
Next block
↓
Next block
This creates the blockchain.
Why Does Each Block Reference the Previous Block?
This creates a cryptographic connection between blocks.
Suppose someone tries to modify an old block.
The block's contents change.
Its hash changes.
That affects the information referenced by the following block.
The alteration therefore creates a chain of inconsistencies.
An attacker would have to redo the proof of work and catch up with the honest chain while also competing with the network's ongoing work.
This is a major part of Bitcoin's security model.
What Happens After a Transaction Enters a Block?
A transaction included in a valid block becomes part of the blockchain history accepted by the network.
But users often wait for additional blocks before considering a transaction highly settled.
Why?
Because a later chain with more accumulated proof of work can potentially replace a shorter competing chain under Bitcoin's consensus rules.
As more blocks are built on top of a transaction, reversing it becomes increasingly difficult.
These are commonly called confirmations.
What Is a Confirmation?
If your transaction is included in the newest accepted block, it has one confirmation.
If another block is added after that:
Two confirmations.
Another:
Three confirmations.
And so on.
The more confirmations a transaction has, the more computational work stands between it and a potential chain reorganization.
The appropriate number of confirmations depends on the transaction and risk involved.
Why Doesn't One Miner Control Bitcoin?
Bitcoin mining is competitive.
Many independent miners attempt to produce valid blocks.
If one miner finds a block, other nodes verify it.
A miner cannot simply invent arbitrary transactions and expect the network to accept them.
The block must satisfy the protocol's rules.
This distinction is important:
Mining creates candidate blocks.
Nodes enforce consensus rules.
Who Controls Bitcoin?
There is no single central organization that can simply rewrite Bitcoin's rules for everyone.
Bitcoin software follows a set of consensus rules.
Users operating nodes independently verify transactions and blocks against those rules.
Developers can propose software changes, but a change does not automatically become part of the network simply because developers publish code.
Participants have to adopt compatible software for the change to become effective across the network.
Is Bitcoin Anonymous?
Bitcoin is often described as anonymous.
That is misleading.
Bitcoin transactions are generally pseudonymous rather than inherently anonymous.
The blockchain is public.
Transactions and addresses can be examined.
If an address can be linked to a real-world identity through other information, activity associated with that address may become identifiable.
Blockchain analysis can therefore reveal relationships between addresses and transactions.
What Is a Blockchain Explorer?
A blockchain explorer is a website or application that allows people to inspect publicly available blockchain information.
Depending on the explorer, you may be able to search for:
- Transactions
- Addresses
- Blocks
- Fees
- Confirmations
- Transaction amounts
- Block times
This illustrates one of Bitcoin's unusual characteristics:
The ledger is publicly inspectable.
What Are Transaction Fees?
Bitcoin transactions can include fees paid to miners.
Fees help allocate limited block space.
When demand for block space is high, users may compete by offering higher fees to have transactions included sooner.
The fee is therefore related to the transaction's use of network resources and the market for block space.
It is not simply a fixed percentage of the amount being sent.
Sending 1 BTC does not inherently require a fee equal to a particular percentage of that 1 BTC.
What Is the Bitcoin Supply?
Bitcoin's protocol specifies rules governing the creation of new bitcoins.
The total eventual supply is designed to approach 21 million bitcoins.
New bitcoin is introduced through the mining process according to the protocol's issuance schedule.
The amount of new bitcoin awarded to miners has periodically decreased through events commonly called halvings.
What Is a Bitcoin Halving?
A halving reduces the block subsidy paid to miners by half.
The event occurs after a specified number of blocks rather than on a fixed calendar date.
The first subsidy was 50 BTC per block.
It was later reduced to:
25 BTC
↓
12.5 BTC
↓
6.25 BTC
↓
3.125 BTC
The next reductions continue according to the protocol's rules.
The transaction-fee component of miner revenue is separate from the block subsidy.
Where Does Bitcoin's Value Come From?
Bitcoin does not have value simply because cryptography exists.
Its market value is determined by what participants are willing to pay for it.
Different people may value Bitcoin for different reasons.
Some view it as a digital monetary asset.
Others use it for payments or transfers.
Others treat it as a speculative asset.
The market price can change substantially.
Understanding how Bitcoin works does not imply anything about whether its market price will rise or fall.
Cryptocurrency Is Bigger Than Bitcoin
Bitcoin was the first widely successful implementation of its particular cryptocurrency architecture, but thousands of other crypto projects have been created.
They can differ dramatically.
Some use proof of stake rather than proof of work.
Some support programmable smart contracts.
Some focus on payments.
Others focus on decentralized applications, tokens, stablecoins, privacy, gaming, or other uses.
The word "cryptocurrency" therefore describes a broad category rather than one single technology.
What Is a Smart Contract?
A smart contract is software deployed on a blockchain platform that can execute according to programmed rules.
For example:
User submits transaction
↓
Smart contract executes
↓
Conditions checked
↓
State updated
A smart contract is not necessarily a legal contract.
It is software running within a blockchain environment.
Ethereum helped popularize general-purpose smart-contract platforms.
What Is a Stablecoin?
A stablecoin is a cryptocurrency token designed to maintain a relatively stable value relative to another asset or reference currency.
Some stablecoins attempt to maintain a relationship with the U.S. dollar.
Their mechanisms differ considerably.
Some use reserves.
Others use cryptocurrency collateral.
Others use algorithmic mechanisms.
The term therefore describes a design goal rather than one specific technical architecture.
What Is a Cryptocurrency Exchange?
An exchange is a service where users can trade digital assets.
Many exchanges operate more like conventional financial platforms than like decentralized blockchain networks.
When you leave cryptocurrency on an exchange, you may not personally control the private keys associated with the underlying assets.
This is where the phrase:
"Not your keys, not your coins"
comes from.
The phrase is a warning about custodial risk, not a technical rule of Bitcoin.
What Happens When You Send Bitcoin?
Let's put everything together.
You enter the recipient's address.
↓
Your wallet constructs a transaction.
↓
Your wallet signs it with your private key.
↓
The transaction is broadcast to Bitcoin nodes.
↓
Nodes validate it.
↓
Valid nodes relay it.
↓
The transaction enters miners' candidate transaction pools.
↓
A miner includes it in a candidate block.
↓
The miner performs proof of work.
↓
A valid block is broadcast.
↓
Nodes verify the block.
↓
The block becomes part of the accepted chain.
↓
Additional blocks may be added later.
The recipient's wallet can then recognize the transaction and its confirmation status.
No bank database has to approve the transaction.
The network itself performs the verification.
A Simplified Bitcoin Diagram
The entire system can be reduced to this:
Wallet
↓
Digital signature
↓
Transaction
↓
Peer-to-peer network
↓
Nodes verify
↓
Mempool
↓
Miner
↓
Proof of work
↓
Block
↓
Blockchain
↓
More blocks
↓
Network consensus
That is the basic architecture behind Bitcoin.
The Bigger Picture
Cryptocurrency is sometimes presented as mysterious technology that exists somewhere between finance and computer science.
The underlying ideas are actually easier to understand when separated into their components.
Cryptography provides digital signatures and hashes.
Networking allows computers to communicate directly.
Nodes independently verify transactions.
The blockchain provides a shared history.
Proof of work provides a mechanism for ordering blocks and making historical revision computationally expensive.
Consensus rules determine which transactions and blocks the network accepts.
Wallets give users the cryptographic tools needed to control funds.
Put all of these pieces together and you get a digital payment system that can operate without a conventional central clearing institution.
That does not make cryptocurrency risk-free or guarantee any particular economic outcome.
It simply explains the technology.
Cryptocurrency in One Sentence
A cryptocurrency such as Bitcoin is a decentralized digital system in which cryptography, peer-to-peer networking, consensus rules, and a distributed blockchain work together to record and authorize transfers of digital value.
Further Reading