ERC-3643 (permissioned tokens)

ERC-3643, originally developed as the T-REX protocol, keeps the familiar ERC-20 interface but adds a permission layer. Every holder must be linked to an on-chain identity carrying verified claims, such as having passed KYC or being an accredited investor. Before a transfer executes, the token asks a compliance module whether both parties are eligible and whether rules like country limits or maximum holder counts are respected.

That design makes it a common choice for tokenised securities, funds, bonds and other real-world assets, where issuers are legally required to know who owns their instruments. Issuers and their agents can also freeze balances, pause the token or force a transfer to recover assets after a lost key or a court order, functions regulators expect but standard ERC-20 tokens lack.

Those same powers are the trade-off: ERC-3643 tokens are deliberately not permissionless. They cannot circulate freely in DeFi pools unless the protocol is whitelisted, and holders rely on the issuer's honesty and operational security. It is one of several approaches to compliant tokens rather than the only one.