Centralized and Decentralized Crypto Exchanges: How It Works

Centralized and decentralized crypto exchanges can both facilitate trades, but they place execution, custody, and operational responsibilities in different parts of the system. A centralized exchange (CEX) can match trades within its own service after users deposit assets. In the public permissionless decentralized exchange (DEX) model discussed by the Bank for International Settlements (BIS), users can retain control of assets while trades execute or settle through blockchain smart contracts. The distinction is useful, but it is not absolute: DEX designs vary, and some depend on interfaces, relayers, administrators, or off-chain order components.

The practical question is therefore not simply whether an exchange is “centralized” or “decentralized.” It is where assets are held, where orders or trade instructions are processed, what state is recorded on-chain, and which people and systems a transaction depends on.

What Centralized and Decentralized Crypto Exchanges means

A CEX is an exchange operating model in which users deposit assets with a service, and the service can provide near-real-time trading, liquid order books, and advanced order functionality after those deposits. This describes a general operating model, not a performance guarantee. Trading speed and liquidity vary by venue, asset pair, and market conditions. The service and its internal systems handle important parts of the trading process; the user’s exchange balance should not be assumed to be the same as direct control of assets in a personal wallet.

A DEX, in the public permissionless model used in the BIS comparison, allows users to retain control of assets while trades execute or settle through smart contracts on a blockchain. That does not mean every DEX uses the same architecture, or that every part of the user experience is decentralized. Interfaces, relayers, administrators, or off-chain order components may remain dependencies.

An important DEX design is the automated market maker (AMM). In the AMM model discussed by BIS, trading is implemented through smart contracts and liquidity pools, with transactions settled when included in a blockchain block. Other designs—including order-book, auction, intent-based, cross-chain, and hybrid DEXs—can use different execution paths. It is inaccurate to treat the AMM flow as a universal description of every DEX.

These categories describe operating models, not a complete assessment of safety, service quality, or suitability. The useful comparison is a component-level one: custody, execution, settlement, interfaces, and dependencies.

Core components of Centralized and Decentralized Crypto Exchanges

A typical CEX operating model includes a user interface, an account or deposit process, exchange-operated trading systems, and a way to record or reflect a user’s position. The accepted source claim establishes that a CEX can provide trading after assets are deposited; it does not specify a particular venue’s account architecture, custody controls, withdrawal process, order-matching implementation, or safeguards. Those details must be checked against the specific service’s documentation.

A DEX may involve several distinct components:

  • Wallet and signing: A user interacts through a wallet or other signing mechanism. Which steps require signatures depends on the design and transaction.
  • Interface: A website or application can present token identity, allowances, quoted outputs, slippage, price impact, network fees, and transaction state. Ethereum’s DEX design guidance says these should be communicated clearly. Interface clarity, however, does not prove that the underlying contracts or assets are safe.
  • Smart contracts: For an AMM, contracts implement trading through liquidity pools. Other DEX designs may use different contract and execution arrangements.
  • Blockchain: In the cited AMM model, a transaction settles when included in a blockchain block. The chain is therefore part of the settlement path.
  • Other dependencies: A DEX may rely on relayers, administrators, or off-chain order components. Whether these exist, and what control they have, is design-specific.

Token interfaces are another component, but they should not be mistaken for a guarantee about the token itself. For example, ERC-20 defines a common fungible-token interface that includes total supply, balances, transfers, allowances, approvals, and Transfer and Approval events. ERC-20 does not establish a token’s backing, issuance policy, market value, compliance, or implementation safety.

How Centralized and Decentralized Crypto Exchanges works

The following workflows show the broad distinction. They are operating-model illustrations, not instructions for using a particular product.

CEX workflow:

  1. A user deposits assets with the exchange. The accepted comparison describes the CEX’s trading capability as occurring after assets are deposited.
  2. The user submits a trade through the service. The CEX can provide near-real-time trading, liquid order books, and advanced order functionality, subject to variation by venue, asset pair, and market conditions.
  3. The exchange’s service processes the trade and reflects the resulting position through its operating systems. The source pack does not establish how any specific service implements matching, accounting, custody, or withdrawals.

This model places the deposit and exchange-operated service within the trade’s operational path. A user evaluating a particular CEX must verify how that service describes custody, trading, settlement, and access to deposited assets rather than infer those details from the category label.

AMM DEX workflow:

  1. The user identifies the token and trade through an interface. Ethereum’s DEX guidance calls for clear communication of token identity, allowances, quoted outputs, slippage, price impact, network fees, and transaction state.
  2. The user reviews the transaction and any requested allowance. If the token uses ERC-20, the standard defines interfaces for balances, transfers, allowances, and approvals, among other functions. The standard alone does not establish what a particular token or application does beyond the relevant implementation.
  3. The transaction is directed to the relevant smart-contract system. In the AMM model discussed by BIS, trading uses smart contracts and liquidity pools.
  4. The transaction settles when included in a blockchain block. The user retains control of assets in the public permissionless DEX model described by BIS, while the trade execution or settlement involves smart contracts.
  5. The interface reports transaction state. The interface’s presentation is useful for informed interaction, but it does not by itself verify contract safety or asset properties.

Not every DEX follows these steps in the same way. An order-book or intent-based design, for example, may use a different execution path; a hybrid design may combine on-chain and off-chain components. The design must be examined directly before assigning responsibilities to a particular component.

Trust and control boundaries

The central trust distinction concerns where control sits during the trade. In the general CEX model, assets are deposited with the exchange before the service provides its trading functions. The user consequently depends on the exchange’s operations for that model of trading. The accepted claims do not establish the custody terms or controls of any individual venue.

In the public permissionless DEX model compared by BIS, users can retain control of assets while trades execute or settle through smart contracts. This shifts some dependencies to contracts and blockchain execution, but it does not remove every intermediary or operational dependency. Interfaces, relayers, administrators, and off-chain order components can still matter, depending on the design.

It is helpful to separate four questions:

  1. Who controls the assets before a trade? A CEX model involves a deposit; the cited DEX model allows the user to retain control during execution or settlement.
  2. Where is the trade processed? A CEX can provide exchange-operated trading functionality. An AMM DEX uses smart contracts and liquidity pools; other DEX architectures may differ.
  3. What does the settlement description cover? For the cited AMM model, settlement occurs when the transaction is included in a blockchain block. That statement should not be generalized to every exchange design.
  4. What does an interface or token standard prove? A clear interface can communicate important transaction information, and ERC-20 specifies a common token interface. Neither establishes the safety of contracts or assets, or a token’s backing, issuance policy, market value, or compliance.

These boundaries help prevent a common category error: treating “decentralized” as proof that a system has no operational dependencies, or treating a standard interface as proof of an asset’s properties.

Limitations and failure modes

The source claims support several important limits, but not a universal incident taxonomy or comparative security ranking. For CEXs, the documented trading benefits are conditional: performance and liquidity vary by venue, asset pair, and market conditions. The general operating model also involves depositing assets, but the source pack does not establish the controls or recovery options of a particular service.

For DEXs, the architecture varies. A claim about an AMM cannot be transferred automatically to an order-book, auction, intent-based, cross-chain, or hybrid design. A DEX may also depend on interfaces, relayers, administrators, or off-chain order components. Smart-contract execution and blockchain settlement describe parts of the system; they do not establish the safety of a contract, interface, token, or broader application.

Transaction information can also be difficult to assess if an interface does not communicate it clearly. Ethereum’s guidance identifies token identity, allowances, quoted outputs, slippage, price impact, network fees, and transaction state as information an interface should communicate. That guidance is about interface design and user safety; it does not prove that the underlying implementation is safe.

Likewise, ERC-20 is an interface standard, not an assurance about token economics or quality. A token can implement the standard’s functions without the standard establishing its backing, issuance policy, market value, compliance, or implementation safety. These are separate verification questions.

What teams should verify

Builders, operators, institutions, and technical decision-makers can use the following evidence-led checklist when assessing an exchange design or service:

  • Map custody: Identify whether assets must be deposited with a service or whether users retain control during the relevant trade flow. Record which documentation supports that conclusion.
  • Trace execution: Locate the component that processes trade instructions. For a claimed AMM, verify whether smart contracts and liquidity pools implement trading; do not assume another DEX design uses the same path.
  • Trace settlement: Establish what event marks settlement in the documented design. The BIS claim for the AMM model is settlement when a transaction is included in a blockchain block; confirm whether that scope matches the system being assessed.
  • List dependencies: Check for interfaces, relayers, administrators, and off-chain order components. Determine which are present and what role the documentation assigns them.
  • Review interface disclosures: Confirm whether the interface communicates token identity, allowances, quoted outputs, slippage, price impact, network fees, and transaction state. Treat this as an interface review, not proof of contract or asset safety.
  • Check token-standard scope: If a token claims ERC-20 compatibility, verify the relevant interface behavior and distinguish it from questions about backing, issuance policy, market value, compliance, or implementation safety.
  • Keep service claims conditional: For a CEX, verify the specific venue’s descriptions of deposits and trading operations. Do not treat general claims about near-real-time trading, liquid order books, or advanced order functionality as guarantees; performance and liquidity vary by venue, pair, and market conditions.
  • Separate documented facts from assumptions: Record the design, version, and documentation examined, and mark unverified implementation details as unknown rather than inferring them from the words “centralized,” “decentralized,” or “ERC-20.”

The result is a more precise comparison than a simple label. CEX and DEX models differ chiefly in asset control and the location of trade execution, while the actual operational design depends on the components and dependencies documented for each system.

Sources and references