FUNDAMENTALS OF CRYPTO
How Cryptocurrency Transactions Work
Every time you send cryptocurrency to another person, purchase something with crypto, or move assets between wallets, a transaction is occurring on a blockchain. Understanding what is actually happening beneath the surface of that transaction, how it is created, validated, recorded, and made permanent, is one of the most useful pieces of foundational knowledge a crypto investor can have.
It demystifies the process of sending and receiving crypto, explains why transactions sometimes take longer than expected, clarifies why gas fees exist and how they work, and provides the understanding needed to avoid the costly mistakes that come from sending crypto to the wrong address or on the wrong network.
The Anatomy of a Cryptocurrency Transaction
A cryptocurrency transaction is a digital instruction that says: move this amount of this asset from this address to that address. At its core, it contains three essential pieces of information.
The sender’s address. Every cryptocurrency wallet has a public address, a string of letters and numbers derived from the wallet’s private key. This address is what you share with others to receive funds. It is public information: anyone can see what assets are held at any address and the complete transaction history associated with it by searching the relevant blockchain explorer.
The recipient’s address. The destination address where the cryptocurrency is being sent. This must be a valid address on the same blockchain as the asset being sent. Sending an asset to an address on the wrong network is one of the most common and costly mistakes in crypto, and in most cases it results in permanent loss of funds.
The amount. The quantity of the cryptocurrency being transferred, specified precisely in the asset’s native denomination.
In addition to these three core elements, a transaction also includes a fee paid to the network for processing the transaction, a digital signature proving that the sender authorises the transfer, and various technical metadata depending on the specific blockchain.
How a Transaction Is Created and Signed
When you initiate a send from your wallet, whether through a hardware wallet, a software wallet, or an exchange interface, the wallet software constructs the transaction data and presents it to you for review before broadcasting.
The critical step before the transaction is sent is signing. Transaction signing uses your private key to generate a unique cryptographic signature that proves you are the authorised owner of the sending address without revealing the private key itself. This is the fundamental security mechanism of blockchain transactions: the mathematics of public key cryptography makes it computationally infeasible to forge a valid signature without possession of the private key, while simultaneously making it trivial for anyone to verify that a signature is valid using only the public address.
This is why private key security is so critical. Anyone with access to your private key can sign transactions from your address and move your funds. The seed phrase that backs up your wallet generates all of your private keys. Protecting it is protecting your funds. As covered in our private keys and seed phrase storage advanced techniques resources, this is the non-negotiable foundation of crypto security.
On a hardware wallet, the signing happens inside the device itself, which never exposes the private key to the connected computer. This is the primary security advantage of hardware wallets: even if your computer is compromised by malware, as covered in our advanced crypto security resource, the private key remains protected inside the hardware device.
Broadcasting the Transaction to the Network
Once signed, the transaction is broadcast to the blockchain network. Broadcasting means sending the signed transaction data to one or more nodes on the network, which then propagate it to other nodes across the globe through a peer-to-peer gossip protocol.
Within seconds of broadcasting, the transaction has typically reached thousands of nodes across the network and entered what is called the mempool: the memory pool of pending transactions waiting to be included in the next block. Every node maintains its own copy of the mempool, containing all valid transactions it has received that have not yet been confirmed in a block.
At this stage, the transaction is visible on blockchain explorers and can be tracked by anyone who knows the transaction ID. It is not yet confirmed, but it exists on the network and is effectively irreversible in most circumstances because it has propagated across thousands of nodes simultaneously.
Validation: How Nodes Check Transactions
Before a transaction enters the mempool of any node, that node performs a series of validation checks to ensure the transaction is legitimate.
The node verifies that the digital signature is valid and corresponds to the sending address. It verifies that the sending address actually has sufficient funds to cover the transaction amount plus the fee. It verifies that the transaction format is correct and conforms to the network’s rules. And it verifies that the same funds haven’t already been spent in another transaction, a protection against what is called a double-spend attack.
The double-spend problem is one of the fundamental challenges that blockchain technology solves. In digital systems, copying data is trivial. Before blockchain, it was not possible to create a digital asset that could only be spent once without a central authority tracking ownership. Bitcoin’s blockchain consensus mechanism was the first successful solution to this problem in a decentralised system, which is why it represented such a significant technological breakthrough.
Mining and Block Confirmation
Validated transactions in the mempool are waiting to be selected and included in the next block. On Bitcoin’s proof-of-work network, miners compete to solve a computationally intensive mathematical puzzle. The first miner to find a valid solution earns the right to propose the next block and collects the block reward of newly minted Bitcoin plus the fees from all transactions included in the block.
When selecting transactions for inclusion in their proposed block, miners prioritise transactions that offer higher fees relative to their size. This is why gas fees exist and why they rise during periods of network congestion: when the mempool is full of pending transactions, miners select the highest-fee transactions first, and users who want their transactions confirmed quickly must offer higher fees to compete. Users willing to wait can offer lower fees and accept slower confirmation times.
On proof-of-stake networks like Ethereum, the selection mechanism is different. Validators are chosen to propose new blocks based on their staked Ethereum rather than through competitive mining, as covered in our blockchain consensus explained resource. The fee dynamics are similar: priority fees tip validators to include transactions promptly, and base fees are burned by the protocol rather than going to validators.
A Bitcoin block is produced approximately every 10 minutes. An Ethereum block is produced approximately every 12 seconds. A transaction included in a block receives its first confirmation at that point.
Confirmations: Why They Matter
A single confirmation means the transaction has been included in one block. But a single confirmation is not considered final for most purposes, particularly for larger transactions, because of the theoretical possibility that the block containing the transaction could be reorganised out of the chain.
A chain reorganisation, or reorg, occurs when a competing version of the blockchain with more cumulative proof-of-work or stake than the current chain is discovered. The network switches to the longer chain, and any transactions in blocks that were on the old chain but not the new one return to the mempool as unconfirmed. This is a theoretical attack vector as well as an occasional occurrence from natural network latency.
Each additional confirmation makes a reorganisation that would reverse the transaction progressively more difficult and expensive because it would require overriding not just the block containing the transaction but all subsequent blocks as well. This is the blockchain’s immutability property: the deeper a transaction is buried under subsequent blocks, the more computationally infeasible it becomes to alter.
For Bitcoin, six confirmations, approximately one hour, is the conventional standard for considering a transaction final for most purposes. For smaller amounts, one to three confirmations is typically sufficient. For very large transactions, some recipients wait for more.
Ethereum introduced the concept of “finality” through its proof-of-stake consensus, where transactions can be considered cryptographically finalised after approximately 15 minutes rather than relying on the probabilistic finality of confirmation accumulation.
Gas Fees: The Cost of Blockchain Computation
Gas fees are the fees paid to validators or miners for processing transactions on a blockchain network. The term “gas” originated on Ethereum where it specifically refers to the unit of computational effort required to execute an operation.
Every operation on the Ethereum network consumes a defined amount of gas: a simple ETH transfer consumes 21,000 gas units, while a complex smart contract interaction consuming more computation might use hundreds of thousands of gas units. The total fee is the gas used multiplied by the gas price, denominated in gwei (a small fraction of ETH).
Ethereum’s EIP-1559 upgrade introduced a base fee that is algorithmically determined by network demand and burned (destroyed) by the protocol, plus a priority fee (tip) that goes directly to validators for expediting inclusion. When the network is congested, the base fee rises automatically, making transactions more expensive and reducing demand to match the network’s capacity.
On Bitcoin, fees are calculated based on the transaction’s size in bytes (the data weight of the transaction) multiplied by the fee rate the sender chooses in satoshis per byte. Larger transactions, those with more inputs, consume more block space and therefore cost more.
Layer 2 networks like Arbitrum and Optimism dramatically reduce fees by batching many transactions into a single Ethereum Layer 1 transaction, spreading the Layer 1 cost across many users.
UTXO vs Account Model: Two Transaction Architectures
Bitcoin and Ethereum use fundamentally different transaction architectures that are worth understanding at a basic level.
Bitcoin uses the UTXO (Unspent Transaction Output) model. Rather than maintaining a running balance for each address, Bitcoin’s blockchain tracks individual coins: specific outputs from previous transactions that haven’t yet been spent. When you send Bitcoin, your wallet selects from your available UTXOs, combines them as needed to cover the transaction amount, sends the intended amount to the recipient, and returns the change to your own wallet as a new UTXO. This is why Bitcoin transactions sometimes look like they contain two outputs: one to the recipient and one back to the sender as change.
Ethereum uses the account model, which is more similar to a traditional bank account. Each address maintains a balance that is directly debited and credited by transactions. When you send ETH, your account balance decreases and the recipient’s increases. This model is simpler to reason about and is more naturally suited to the complex smart contract interactions that Ethereum enables.
Common Transaction Mistakes and How to Avoid Them
Understanding how transactions work provides the foundation for avoiding the mistakes that cost crypto users significant sums every year.
Sending to the wrong address. Blockchain transactions are irreversible. Once confirmed, a transaction to the wrong address cannot be recalled. Always double-check the recipient address, particularly the first and last four characters, before confirming. Copy and paste addresses rather than typing them manually to eliminate transcription errors. Be aware of clipboard hijacking malware that replaces copied addresses with an attacker’s address, as covered in our advanced crypto security resource.
Sending on the wrong network. Sending Ethereum-based assets to a Bitcoin address, or sending assets on Ethereum mainnet to an address expecting assets on a Layer 2 network, can result in permanent loss. Always confirm that both the sending and receiving wallet are configured for the same network before sending. Our how to transfer cryptocurrency from one wallet to another and how to safely withdraw crypto from an exchange resources cover this in detail.
Setting fees too low. Transactions with fees below the current minimum relay threshold may not be accepted by nodes and will remain stuck in the mempool, or in some implementations be dropped entirely after a defined period. Using your wallet’s recommended fee setting rather than setting fees manually below the suggested minimum avoids this problem.
Sending a test transaction first. For large transfers, particularly to new addresses you haven’t transacted with before, sending a small test amount first and verifying it arrives correctly before sending the full amount is a sound practice that has saved many investors from costly mistakes.
As covered in our how to send and receive cryptocurrency safely resource, these practices form the baseline standard for safe transaction management.
Transaction Privacy: What Is and Isn't Visible
A common misconception about blockchain transactions is that they are anonymous. They are not. They are pseudonymous.
Every transaction on the Bitcoin and Ethereum blockchains is publicly visible to anyone with access to a blockchain explorer. The sending address, the receiving address, the amount, the fee, and the timestamp are all public. What isn’t immediately visible is the real-world identity behind each address.
However, the moment an address is linked to a real identity, through an exchange KYC process, a public disclosure, or blockchain analytics, the entire transaction history of that address becomes associated with that identity. As covered in our how the ATO tracks your crypto transactions and can you buy crypto anonymously resources, the ATO and other regulatory bodies have access to sophisticated blockchain analytics tools that can trace transaction flows across addresses.
Key Takeaways
A cryptocurrency transaction is a digitally signed instruction to transfer an asset from one address to another, broadcast to a peer-to-peer network, validated by nodes, included in a block by miners or validators, and made permanent through the accumulation of subsequent blocks. The digital signature using your private key is the security mechanism that proves authorisation without revealing the key itself. Gas fees compensate the network for the computational work of processing and validating transactions, rising during periods of high demand. Transactions are irreversible once confirmed and are publicly visible on the blockchain, making address management and network selection critical before every send. Bitcoin uses the UTXO model and Ethereum uses the account model, two different architectures for tracking ownership and processing transfers.
Understanding these mechanics is the foundation for sending and receiving cryptocurrency safely, managing fees effectively, and appreciating why the security of your private keys is the most important aspect of crypto ownership.
For everyday investors who want to deepen their understanding of how blockchain technology works and build the practical knowledge to manage their crypto safely and confidently, our Runite Tier Membership provides the education and community to do exactly that.
Find out more at shepleycapital.com/membership.
WRITTEN & REVIEWED BY Chris Shepley
UPDATED: MARCH 2026
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