Soulbound Token

The defining characteristic of an SBT is its non-transferable nature. Once issued to a 'Soul' (a blockchain account), it cannot be moved or sold to another entity. This prevents the financialization of reputation and ensures that credentials and affiliations are authentic representations of a specific entity's history, not tradable assets. This is enforced at the smart contract level, disabling standard transfer functions.

SBTs serve as a robust mechanism for verifiable credentials. An issuing authority (a university, DAO, or employer) can mint an SBT directly to a recipient's Soul. This token acts as a tamper-proof, cryptographically signed attestation of a fact, such as:

• A university degree
• A professional certification
• Membership in a decentralized organization
• Proof of attendance at an event

By aggregating a collection of non-transferable tokens, a Soul builds a provable, unique identity history. This creates a powerful Sybil resistance mechanism. It becomes computationally and socially expensive for a single entity to fake a comprehensive, long-lived reputation across multiple pseudonymous accounts, as they cannot simply buy or transfer the necessary credentials to a new identity.

SBTs enable the construction of a reputation graph that maps the relationships and trust between Souls and issuers. This graph is not a single score but a rich, decomposable network. A protocol can query this graph to assess a Soul's trustworthiness for a specific context, such as verifying a credit history without revealing the underlying transactions, or confirming DAO participation without exposing other affiliations.

While SBTs are public by default, advanced implementations integrate Zero-Knowledge Proofs (ZKPs). This allows a Soul to prove a claim about its SBTs without revealing the tokens themselves. For example, a Soul could prove 'I am a verified human with a credit score over 700' to a lending protocol without disclosing their exact score, wallet address, or the specific institutions that issued the underlying credentials.

The authority to issue and revoke SBTs is often governed by the community or a decentralized organization. Issuers can be other Souls or smart contracts. Crucially, revocation or a slashing condition can be implemented. If an entity acts maliciously, the issuing authority can burn the SBT representing their membership or certification, dynamically updating the reputation graph in response to real-world behavior.