Cryptocurrency: Definition, Types, and How It Operates

Cryptocurrency is a class of digital asset secured by cryptographic protocols and recorded on distributed ledger infrastructure, most commonly a blockchain. This page covers the technical definition, the principal categories of cryptocurrency recognized by US regulatory bodies, the step-by-step mechanics of how transactions are processed, and the classification boundaries that determine how a given asset is treated under law. Understanding these distinctions matters because regulatory treatment, tax obligations, and consumer protections differ significantly depending on asset type and structure. For a broader orientation to the digital asset landscape, the Digital Currency Authority provides structured reference material across asset types and regulatory frameworks.

Definition and scope

Cryptocurrency occupies a contested definitional space across US federal agencies. The Financial Crimes Enforcement Network (FinCEN), in its 2013 guidance FIN-2013-G001, defined "virtual currency" as a medium of exchange that operates like currency in some environments but does not have legal tender status. The Commodity Futures Trading Commission (CFTC) has asserted that Bitcoin and Ether are commodities under the Commodity Exchange Act (7 U.S.C. § 1 et seq.), while the Securities and Exchange Commission (SEC) applies the Howey test — derived from SEC v. W.J. Howey Co., 328 U.S. 293 (1946) — to determine whether a digital token constitutes a security.

At the technical level, a cryptocurrency is defined by three structural properties:

Cryptographic ownership — Control is established through public-private key pairs; possession of a private key constitutes functional control of the associated assets.
Distributed consensus — Transaction validity is determined by a network of nodes running a consensus protocol rather than by a central authority.
Immutable ledger — Confirmed transactions are recorded in append-only data structures, making retroactive alteration computationally prohibitive at scale.

The Internal Revenue Service (IRS) classifies cryptocurrency as property for federal tax purposes under Notice 2014-21, meaning capital gains rules apply to disposals. This classification sits independently of the commodity or security designations applied by other agencies, creating a layered compliance environment. The full scope of that environment is detailed at Regulatory Context for Digital Currency.

How it works

A cryptocurrency transaction passes through a discrete sequence of stages from initiation to final settlement.

Transaction construction — The sender's wallet software assembles a transaction record specifying the recipient address, the transfer amount, and a transaction fee. This record is signed with the sender's private key using an algorithm such as ECDSA (Elliptic Curve Digital Signature Algorithm).
Broadcast to the network — The signed transaction is propagated across peer-to-peer nodes. Each node independently validates the signature and confirms the sender holds sufficient unspent balance.
Inclusion in a candidate block — Miners (in proof-of-work systems) or validators (in proof-of-stake systems) select pending transactions from the mempool and bundle them into a candidate block. Transaction fees create an economic incentive for inclusion.
Consensus and block finalization — The network reaches consensus on the next valid block. In Bitcoin's proof-of-work protocol, this requires finding a nonce that produces a hash below the current difficulty target — a process that Bitcoin's network adjusts every 2,016 blocks (Bitcoin Whitepaper, Satoshi Nakamoto, 2008). Ethereum shifted to proof-of-stake in September 2022, requiring validators to lock up 32 ETH as collateral.
Confirmation accumulation — Each subsequent block added after the transaction's block constitutes one confirmation. Bitcoin transactions are conventionally considered settled after 6 confirmations, which at an average 10-minute block time equals approximately 60 minutes.
Wallet balance update — The recipient's wallet reflects the new balance once the transaction achieves the threshold confirmation count recognized by the receiving party or platform.

Common scenarios

Peer-to-peer value transfer — The original Bitcoin use case involves direct transfer between two wallet addresses without an intermediary institution. Settlement occurs on-chain and is irreversible once confirmed.

Exchange-mediated trading — Most retail participants acquire cryptocurrency through registered exchanges such as those operating under FinCEN money services business (MSB) registration requirements. These platforms hold assets in custodial wallets, meaning the exchange controls the private keys rather than the user.

Stablecoin transactions — Stablecoins are tokens pegged to reference assets, most commonly the US dollar at a 1:1 ratio. Tether (USDT) and USD Coin (USDC) collectively represented over $130 billion in combined market capitalization as of data published by the President's Working Group on Financial Markets in its November 2021 Report on Stablecoins. Stablecoins are used extensively in decentralized finance protocols and cross-border remittance.

Tokenized asset representation — Smart contract platforms issue tokens that represent claims on external assets, including real estate, commodities, or equity instruments. Regulatory treatment of these instruments depends on whether they satisfy the Howey test.

Mining and staking income — The IRS treats mining and staking rewards as ordinary income at fair market value on the date of receipt, per Revenue Ruling 2023-14, which resolved a prior ambiguity regarding staking specifically.

Decision boundaries

Commodity vs. security — The primary classification question for any cryptocurrency is whether it is a commodity (subject to CFTC jurisdiction) or a security (subject to SEC jurisdiction). Proof-of-work coins with no issuing entity and no expectation of profit derived from a common enterprise tend toward commodity classification. Tokens issued through initial coin offerings (ICOs) with promised returns tied to a development team's efforts have repeatedly been found by the SEC to satisfy the Howey test.

Custodial vs. non-custodial — A custodial wallet arrangement (exchange holds keys) differs from a non-custodial arrangement (user holds keys) in both security profile and regulatory treatment. Custodial platforms are treated as money transmitters under FinCEN regulations at 31 C.F.R. § 1010.100(ff), while non-custodial wallet software is not.

Proof-of-work vs. proof-of-stake — These two consensus mechanisms differ in energy expenditure, validator set structure, and attack economics. Bitcoin's proof-of-work network consumed an estimated 127 terawatt-hours annually as of the Cambridge Centre for Alternative Finance's Bitcoin Electricity Consumption Index, comparable to the annual electricity consumption of Norway. Proof-of-stake systems require no competitive computation and derive security from economic collateral at risk of slashing.

Fungible vs. non-fungible — Standard cryptocurrencies (ERC-20 tokens, Bitcoin) are fungible: each unit is interchangeable with any other unit of equal denomination. Non-fungible tokens (NFTs) encode unique identifiers that make each token distinct, with different marketplace structures, valuation methods, and unresolved regulatory treatment.

References

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