• Technological for online identity

    • Weak proxies: on-demand accounts (e.g., E-mail, phone)

      • Artificial barriers or entry costs: CAPTCHAs, PoW, PoS, …

    • Biometric authentication and/or identity

      • Many varieties with different properties (fingers, eyes, palm, genome, …)

        • Reliability: false-positives and false negatives, configuration

      • Uses: authentication (1-to-1 comparison) versus identity (1-to-many)

        • 1-to-many comparison requires a queryable database

        • Deduplication, false positive amplification, multi-factor necessary

    • Transferring government/paper identities online: e.g., KYC processes for AML

      • Certificate authorities; in-person, mail-in, or online verification processes

      • AI-based video-chat identity verification

    • Self-sovereign identity

      • Prove attributes in “zero knowledge” (name, address, age, degrees…)

      • Risk: most relying parties will just demand enough to de-anonymize

      • Risk: identity theft, loss; reliance on central trusted parties to mitigate

    • Social/trust networks

      • PGP key signing parties, transitive path-finding and trust calculations

      • Sybil-resistance: naive or based on graph bottleneck assumptions

  • Technologies for online anonymity

    • Anonymous communication tools

      • Naive: anonymity through obscurity, “IP addresses look anonymous”

      • Trusted third party: anonymous remailers, VPN services

      • Decentralized systems: MIX nets, onion routing (Tor), DC-nets, research

    • Cryptographic tools for anonymity and pseudonymity

      • Weak pseudonymity: e.g., 4chan tags, public keys, Bitcoin wallets

        • Numerous traceability, deanonymization risks/weaknesses

      • Single-use pseudonyms: e.g., per-transaction keypairs, wallets

        • Stronger but less useful: no way to associate reputation, … 

      • Anonymous credentials, group or ring signatures

        • Prove membership in a group without revealing which member

        • Don’t necessarily protect against Sybil attacks or sock puppetry

      • 1-to-1 mappings of anonymous to real identities

        • Verifiable shuffles used in E-voting, accountable anonymity

          • Used in AnonRep, coin mixing currencies like Monero

        • Single-use or linkable group/ring signatures

      • Blacklistable anonymous credentials

        • Unlinkable unless user “misbehaves” according to some authority


Post-lecture blackboard snapshot 2019:



Last modified: Thursday, 19 November 2020, 13:59