Oblivious Digital Tokens

TL;DR

This work introduces Oblivious Digital Tokens (ODTs) to realize digital emblems in cyber-conflicts without revealing verification activity. The scheme combines a Trusted Execution Environment–based Witness Generation system with a Privacy-Preserving Equality Test (PPET) that is tightly integrated into TLS handshakes, enabling verifiers to confirm device protection while remaining oblivious to observers. The authors provide concrete SGX- and TrustZone-based instantiations, a TLS-compatible PPET protocol, and a full TLS-integrated ODT workflow, along with a formal security analysis via the Tamarin prover and a practical prototype with measured overheads (e.g., roughly $144\,\mathrm{ms}$ extra per handshake). Their results demonstrate binding integrity, verification obliviousness, and security preservation under a compromise-then-verify model, offering a practical path toward ethically responsible digital emblems in cyberspace. The work also discusses TLS compatibility, side-channel considerations, and limitations, pointing to future research on absence proofs and broader deployment scenarios.

Abstract

A computing device typically identifies itself by exhibiting unique measurable behavior or by proving its knowledge of a secret. In both cases, the identifying device must reveal information to a verifier. Considerable research has focused on protecting identifying entities (provers) and reducing the amount of leaked data. However, little has been done to conceal the fact that the verification occurred. We show how this problem naturally arises in the context of digital emblems, which were recently proposed by the International Committee of the Red Cross to protect digital resources during cyber-conflicts. To address this new and important open problem, we define a new primitive, called an Oblivious Digital Token (ODT) that can be verified obliviously. Verifiers can use this procedure to check whether a device has an ODT without revealing to any other parties (including the device itself) that this check occurred. We demonstrate the feasibility of ODTs and present a concrete construction that provably meets the ODT security requirements, even if the prover device's software is fully compromised. We also implement a prototype of the proposed construction and evaluate its performance, thereby confirming its practicality.

Figures (6)

• Figure 1: Overview of ICRC digital emblem use-case. $D$ is $\mathcal{N\!T}\mathcal{\!P}$-protected while $D'$ is not.
• Figure 2: A system view of the ODT scheme. O-TEE mediates four TLS handshake sessions and produces distinct ODTs. Red lines indicate $\mathcal{A}dm$'s attack on binding integrity.
• Figure 3: PPET Protocol $\mathit{PPET}$.
• Figure 4: Message flows in the TLS v1.3 handshake.
• Figure 5: Process $P$'s TLS handshake through O-TEE.

Theorems & Definitions (12)

• Definition 1
• Definition 2: Privacy Preservation
• Theorem 1
• Definition 3: Verification Obliviousness
• Definition 4: Verifier Message Uniformity
• Lemma 1
• proof
• Theorem 2
• proof
• Definition 5: Security preservation