Cryptocurrency is a digital unit of value whose transfers are authorised cryptographically and validated under a distributed-ledger protocol. For a quant, identifying the unit is only the start: the position also needs a price, a trading venue and a custody arrangement. An unchanged coin balance can still suffer a large loss in its reporting currency.
The term describes a technological and economic category, not a single legal classification. It is also narrower than digital asset: a digital representation of a share, a collectible and a cryptocurrency need not give their holders the same rights.
What the network records
A blockchain records transactions or state changes according to its protocol's rules. Cryptographic signatures can establish that a transfer was authorised by the relevant key; network validation checks that the transfer obeys those rules. That does not establish a fair market price or promise repayment in ordinary currency.
Bitcoin is one example: wallets calculate spendable balances from the shared transaction ledger, and private keys sign spending transactions. Other networks have different rules and uses. Ether, the native cryptocurrency of Ethereum, pays for transaction execution and supports its proof-of-stake validation system. Ethereum is the network; ether is the unit. The official Bitcoin explanation and Ethereum introduction to ether describe these mechanisms.
A currency-like name does not by itself imply a deposit, an ownership stake in a business or a redemption promise. Any such claim must be established from the asset or product's actual terms.
A balance and a valuation are different records
Suppose a fictional cryptocurrency holding contains 2 units. At the first valuation, the stipulated price is USD 100 per unit. Later it is USD 90 per unit. There are no trades, transfers, rewards or costs during the interval.
Here is the number of units and is measured in USD per unit. The marked value falls from USD 200 to USD 180, producing USD 20 of marked loss, or 10% of the initial value. The holding still contains 2 units. Nothing in that ledger requires a sale to recognise the change in value.
Original fictional valuation ledger. Prices are USD per unit; marked values and P&L are USD. No transactions, rewards or costs occur.
This is market risk. An executable sale can also differ from the selected mark because of liquidity risk and transaction costs. A real valuation therefore specifies the price source, timestamp, quote currency and instrument identity; a ticker alone may not identify the network or token contract.
Who can authorise the transfer?
A wallet manages keys used to authorise transactions; it does not contain coins as physical objects. Self-custody puts key management with the holder. Third-party custody puts control of the keys with a provider, such as an exchange or custodian.
An exchange screen showing a cryptocurrency balance is the provider's account record. It does not, by itself, prove that the customer directly controls corresponding on-chain units. Withdrawal availability and the customer's rights depend on the custody arrangement, including segregation and any permitted lending of assets. Provider failure can interrupt access even while the underlying network continues operating. The SEC staff's custody bulletin explains these distinctions and the questions to ask a custodian.
Keep the protocol unit, the account claim and any issuer promise separate. Their risks can coexist, but they are not interchangeable exposures.
Legal treatment is likewise specific to the product, arrangement, jurisdiction and date. In Australia, ASIC's INFO 225 directs attention to the rights and benefits of the asset and connected arrangements when assessing financial-product status. The label “cryptocurrency” alone cannot settle that assessment.
Sources
- Bitcoin Project, “How does Bitcoin work?”, ledger, private-key signatures and network validation.
- Ethereum documentation, “Technical intro to ether”, native cryptocurrency, transaction fees and validation.
- SEC Office of Investor Education and Assistance, “Crypto Asset Custody Basics for Retail Investors”, 12 December 2025. Staff educational bulletin, not a Commission rule or legal classification.
- ASIC, “Digital assets: Financial products and services”, INFO 225, especially Part A on rights, benefits and connected arrangements. Official pages checked 27 October 2026.
- John C. Hull, Options, Futures, and Other Derivatives, ninth edition, Global Edition, Pearson, 2018, §1.8, pp. 36–37: cash-position gains and losses from changes in quoted prices. Used for valuation arithmetic, not cryptocurrency protocol or legal claims.