Learn Bitcoin - COLDCARD

Bitcoin Basics

Foundational Bitcoin concepts for new self-custody users, from what Bitcoin is to why private keys matter.

What is Bitcoin?

Bitcoin is a peer-to-peer electronic cash system that operates without a central authority. Transactions are verified by a distributed network and recorded permanently on a public ledger. No institution can freeze accounts, reverse confirmed transactions, or issue coins beyond the fixed supply of 21 million.

How Does a Bitcoin Transaction Work?

Bitcoin transactions consume amounts you control and create new ones. Learn how inputs, outputs, fees, and confirmation work.

What are Private Keys and Public Keys?

Private keys prove ownership. Public keys enable verification. Learn how the Bitcoin key pair works and why the private key must stay secret.

What is a Bitcoin Wallet?

Bitcoin wallets store private keys, not bitcoin. Learn how they work and the difference between custodial and self-custodial arrangements.

What Gives Bitcoin Value?

Bitcoin derives value from its monetary properties: a fixed supply, no issuing authority, and verification that requires no trust.

Why Self Custody

Why holding your own keys matters, what custodians can and cannot do, and how to think about Bitcoin ownership.

What is Bitcoin Self-Custody?

Self-custody means controlling your Bitcoin private keys directly. Without it, you own a claim against someone else's balance, not bitcoin itself.

A History of Bitcoin Exchange Failures

Exchange failures have cost Bitcoin holders billions. This article documents the collapses that make the case for holding your own keys.

Bitcoin Security Threat Models

Learn to build a Bitcoin security threat model: what you are protecting, who might threaten it, and what measures are proportionate to the risk.

The Spectrum of Bitcoin Custody Options

Bitcoin custody exists on a spectrum from exchange accounts to air-gapped hardware. Learn what each arrangement means and who controls the keys.

The Risks of Holding Cash in a Bank

Bank deposits carry inflation, counterparty risk, and capital controls. Learn how these structural risks compare to Bitcoin self-custody.

Why Bitcoiners Choose Hardware Wallets

Hardware wallets keep private keys permanently offline. Learn why the distinction between online and offline key storage defines Bitcoin security.

How Bitcoin Works

Plain-English guides to transactions, UTXOs, fees, addresses, confirmations, and the mechanics behind Bitcoin payments.

How Bitcoin Wallets Work

A Bitcoin wallet generates and stores private keys, which authorize spending. Bitcoin itself exists as entries on the blockchain, not inside the wallet.

What is a Bitcoin Private Key?

A private key is a randomly generated 256-bit number from which every Bitcoin address it controls is mathematically derived.

What is Public Key Cryptography?

Public key cryptography lets Bitcoin prove ownership without revealing the private key. Learn how key pairs and digital signatures work.

What is a Bitcoin Address?

Bitcoin addresses are derived from public keys. Learn what address formats mean, how generation works, and why address reuse reduces privacy.

What Are Bitcoin Hash Functions?

Learn what hash functions are, why they are one-way, and how Bitcoin uses them across address generation, transaction IDs, and proof of work.

What is a Bitcoin Seed Phrase?

A seed phrase is 12 or 24 words that generates every key in a Bitcoin wallet. Learn how it works and why it is the only backup that matters.

HD Wallets and Bitcoin Derivation Paths

HD wallets derive every key from one seed. Learn how derivation paths work and why the path matters when restoring or recovering a wallet.

Hardware Wallets

How Bitcoin hardware wallets protect private keys, sign transactions, and reduce exposure to online attacks.

What is a Hardware Wallet?

A hardware wallet stores private keys in isolated hardware and signs transactions without exposing those keys to any connected computer.

Hot Wallet vs. Cold Wallet

A hot wallet keeps private keys on an internet-connected device. A cold wallet keeps them offline. Learn the difference, the risks of each, and when to use which.

What is Air-Gapped Signing?

Air-gapped signing means private keys never touch a networked device. The transaction moves via QR code or physical media, not a network connection.

What is a Bitcoin Software Wallet?

A Bitcoin software wallet stores your keys on a phone or computer. Learn the types, what threats they face, and when a software wallet is and is not the right tool.

What is Bitcoin Multisig?

Multisig requires signatures from more than one private key before a transaction can be authorized, eliminating any single point of failure.

2-of-3 Multisig Explained

A 2-of-3 multisig wallet requires any two of three keys to spend. Learn how to design a quorum, distribute keys, handle key loss, and why 2-of-3 is the most common multisig setup.

Collaborative Bitcoin Custody vs Solo Multisig

Collaborative custody gives a third party one key in your 2-of-3 wallet. Solo multisig means you hold all keys. Learn the tradeoffs: control, complexity, cost, and recovery.

What is a PSBT?

A PSBT is a standard format that separates transaction construction from signing. Learn how PSBTs work, why they matter for hardware wallets, and the difference between BIP174 and BIP370.

Seed Phrases

Backup and recovery guidance for seed phrases, passphrases, BIP-39, and long-term Bitcoin recovery planning.

How to Store Your Seed Phrase

Storing a seed phrase correctly means writing every word in order, choosing a durable medium, making two copies in separate locations, and testing recovery.

Paper vs Metal Seed Phrase Backups

Paper seed backups are free but burn and flood easily. Metal backups survive both. Learn why metal is better for savings wallets and what you need to know before choosing.

How to Choose a Metal Seed Backup

Metal seed backups record characters using three categories of approaches. Learn the criteria that matter and which method fits your setup.

Seed Phrase Storage and Physical Security

Where you store your seed phrase backup is as important as what you store it on. Learn the physical threats to protect against and how to choose the right storage locations.

Bitcoin Inheritance Planning

Bitcoin has no recovery path if keys are lost at death. Learn the four inheritance frameworks and how to choose the right one for your situation.

What is a Bitcoin Passphrase?

A Bitcoin passphrase is an optional word or phrase added to your seed phrase that creates an entirely separate wallet. Learn how it works, why it matters, and its risks.

Common Bitcoin Backup Mistakes

Photographing your seed phrase, storing a single copy, or pairing a passphrase with a seed backup are mistakes that cost Bitcoin holders their funds. Learn what to avoid and why.

Transaction Security

Practical security checks for sending, receiving, verifying addresses, and avoiding transaction mistakes.

Bitcoin Transaction Security

Most self-custody attention goes to seed phrase storage. But every send involves a separate set of security decisions, from address verification to fee selection to how the transaction reaches the signing device.

What is Bitcoin UTXO Management?

Bitcoin has no account balance, only UTXOs. Learn what UTXOs are, why managing them affects fees and privacy, and how to manage them well.

Bitcoin Address Reuse and Management

Reusing a Bitcoin address links all your transactions permanently on-chain. Learn why address reuse hurts privacy and how HD wallets and coin control prevent it.

What is the Bitcoin Mempool?

The Bitcoin mempool holds unconfirmed transactions waiting for miners. Learn how it works, how to read mempool.space, and what to do when a transaction gets stuck.

What are Bitcoin Transaction Fees?

Bitcoin fees are priced per virtual byte, not per transaction. Learn how sats/vbyte works, why SegWit addresses are cheaper, and how to set the right fee rate.

How to Verify Bitcoin Transactions

On-device verification is the last line of defense before a Bitcoin transaction is signed. Learn how to check addresses, amounts, and fees on your signing device before every send, and how to confirm your transaction after broadcast.

Bitcoin Privacy

Privacy concepts for Bitcoin users, including address reuse, transaction history, UTXOs, and metadata exposure.

What is Bitcoin Privacy?

Bitcoin transactions are permanently public. Addresses are pseudonymous by default, but chain analysis firms trace fund flows through transaction patterns and address reuse.

What is CoinJoin?

CoinJoin combines multiple Bitcoin inputs into a single transaction with equal-value outputs, breaking the deterministic link between input and output on-chain.

What is PayJoin?

PayJoin is a two-party Bitcoin transaction where both sender and receiver contribute inputs, defeating chain analysis change-detection heuristics without a coordinator.

Running a Bitcoin Node

Running a full Bitcoin node means verifying every transaction and block yourself, without relying on a third-party server that can observe your activity.

Using Tor with Bitcoin

Tor routes Bitcoin network traffic through relays to hide your IP address from peers, analytics firms, and network observers.

Advanced Concepts

Deeper self-custody topics such as multisig, PSBTs, Miniscript, BIP-85, and stronger operational security.

What are Bitcoin Improvement Proposals (BIPs)?

A Bitcoin Improvement Proposal is a formal document proposing a change or standardization to the Bitcoin protocol or related tooling.

The Most Important BIPs

BIP32, BIP39, BIP174, and BIP341 are the four proposals that define how modern Bitcoin wallets generate keys, sign transactions, and implement Taproot.

Bitcoin Air-Gap Signing Methods

BBQr, MicroSD, and NFC are the three methods used to carry PSBTs across the air gap between wallet software and a signing device.

What are Bitcoin Forks?

A fork is a change to Bitcoin's rules. Soft forks are backward-compatible upgrades. Hard forks split the network into two incompatible chains.

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