IB-TOT: Identity-Based Traceable Oblivious Transfer and Its Applications

Oblivious Transfer (OT) is a fundamental cryptographic primitive for privacy-preserving data exchange. While traditional OT protocols guarantee unconditional receiver anonymity, they inherently lack the mechanisms to prevent abusive mass data harvesting. Traceable Oblivious Transfer (TOT) addresses this by introducing “conditional anonymity,” revoking the privacy of malicious users. However, existing TOT mechanisms either rely on computationally expensive dynamic assumptions or require continuous interaction with a Trusted Third Party (TTP) to manage credentials. To overcome these limitations, we present an Identity-Based Traceable Oblivious Transfer (IB-TOT) protocol. By synergizing polynomial-based secret sharing with Blind Identity-Based Encryption (Blind IBE), our scheme completely eliminates the TTP during the data transfer stage. The Blind IBE extraction algorithm serves as the primary oblivious channel, utilizing data indices as user identities. We strictly bound the receiver’s query quota by embedding a degree-k tracing polynomial directly into the key issuance phase. Honest clients enjoy fully protected retrieval of up to k items, whereas any attempt to exceed this quota deterministically exposes the violator’s identity. Comprehensive security proofs demonstrate that IB-TOT satisfies sender privacy, receiver privacy, and strict accountability under standard static assumptions (DBDH and DL).