{"schema_version":"0.1","map_id":"paper-56-map","publication_id":56,"publication_anchor":"paper-56","slug":"paper-56","canonical_path":"/knowledge/papers/paper-56/","machine_path":"/knowledge/papers/paper-56.json","root_node_id":"paper-56","stage":"mapped_draft","contribution_type_vocabulary_version":"0.1","contribution_types":["scheme"],"title":"Optimizing Registration Based Encryption","year":2021,"status":"Published","venue":"18th IMA International Conference on Cryptography and Coding (IMACC)","topic":"algorithms-foundations","labels":["Theory","Applied"],"authors":["Kelong Cong","Karim Eldefrawy","Nigel P. Smart"],"keywords":["registration-based encryption","key escrow","crit-bit trees","hash garbling"],"research_question":"Can registration-based encryption preserve its no-key-escrow and asymptotic efficiency goals while reducing the enormous concrete ciphertext and decryption costs of existing constructions?","central_answer":"Replacing Merkle trees with authenticated crit-bit trees shortens garbled inputs, and publishing a small square-root-sized identity filter lets encryptors skip roughly half the tree snapshots. The paper analytically estimates a 57.5 percent combined ciphertext reduction, proves standard RBE security for the crit-bit construction, and states important remaining security and practicality gaps.","curation":{"drafted_at":"2026-07-11","drafted_by":[{"actor_type":"ai","name":"OpenAI Codex","role":"full-text extraction, theorem-and-cost mapping, and initial assessment"}],"method":"Complete review of the 28-page IACR ePrint PDF through the public archive and the author-uploaded ResearchGate full text. Direct local download attempts were blocked by anti-bot responses, so no local hash is claimed. Cost reductions are recorded as analytical estimates, not benchmark measurements.","source_scope":"full_source_audit","approval":{"status":"pending","note":"AI-authored source map awaiting full author verification. Security scope, performance arithmetic, and tradeoff interpretations should be checked before approval."}},"sources":[{"id":"source-paper-56-archive-pdf","type":"public_archive_copy","title":"Optimizing Registration Based Encryption","url":"https://eprint.iacr.org/2021/499.pdf","provenance_category":"archive","media_type":"application/pdf","page_count":28},{"id":"source-paper-56-author-copy","type":"author_hosted_copy","title":"ResearchGate author-uploaded full text","url":"https://www.researchgate.net/publication/354783718_Optimizing_Registration_Based_Encryption","provenance_category":"author"},{"id":"source-paper-56-official","type":"official_publication_record","title":"IMACC 2021 publisher record","url":"https://doi.org/10.1007/978-3-030-92641-0_7","provenance_category":"official"},{"id":"source-paper-56-citations","type":"citation_index_snapshot","title":"OpenAlex work 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information.","source_anchor_ids":["anchor-paper-56-model"]},{"id":"paper-56-scope-security","kind":"threat_model","parent_id":"paper-56-scope","order":1,"epistemic_status":"explicitly_scoped","title":"Message-hiding, not chosen-ciphertext security","summary":"The proof targets the standard RBE message-hiding definition used by prior work and does not provide a decryption oracle; active chosen-ciphertext security remains open.","source_anchor_ids":["anchor-paper-56-model","anchor-paper-56-boundaries"]},{"id":"paper-56-scheme","kind":"scheme","parent_id":"paper-56","order":4,"epistemic_status":"specified","title":"Crit-bit-tree RBE","summary":"Authenticated crit-bit trees replace balanced Merkle trees in snapshot-based registration. Each internal node stores a critical bit and two hash pointers, shortening the garbled input while preserving searchable authenticated paths.","source_anchor_ids":["anchor-paper-56-critbit","anchor-paper-56-construction"]},{"id":"paper-56-scheme-security","kind":"claim","parent_id":"paper-56-scheme","order":1,"epistemic_status":"proved_under_assumptions","title":"Standard RBE security","summary":"A single-user argument combines hash-garbling simulation with semantic PKE security; the general theorem replaces path programs through hybrids and concludes message-hiding for the crit-bit construction.","source_anchor_ids":["anchor-paper-56-assumptions","anchor-paper-56-security"]},{"id":"paper-56-scheme-compact","kind":"claim","parent_id":"paper-56-scheme","order":2,"epistemic_status":"analytical_estimate","title":"Compact-parameter reduction","summary":"For the paper's two-billion-user, 256-bit example, shorter tree nodes are estimated to reduce encryptor public-key operations and ciphertext size by about 15 percent and decryptor work by about 30 percent on average.","source_anchor_ids":["anchor-paper-56-cost"]},{"id":"paper-56-scheme-largepp","kind":"method","parent_id":"paper-56","order":5,"epistemic_status":"specified_tradeoff","title":"Larger public parameter","summary":"Publishing membership information for a square-root-sized minority of snapshot users lets encryption ignore roughly half the trees. A cuckoo filter is proposed to represent that set compactly.","source_anchor_ids":["anchor-paper-56-larger-pp"]},{"id":"paper-56-claim-combined","kind":"claim","parent_id":"paper-56-scheme-largepp","order":1,"epistemic_status":"analytical_estimate","title":"57.5 percent combined ciphertext reduction","summary":"Combining the 15 percent crit-bit reduction with a further one-half encryptor reduction yields the stated 57.5 percent decrease; the larger-parameter example adds about 187 KB for two billion users.","source_anchor_ids":["anchor-paper-56-problem","anchor-paper-56-larger-pp"]},{"id":"paper-56-evidence","kind":"evidence_group","parent_id":"paper-56","order":6,"epistemic_status":"formal_and_analytical","title":"Evidence boundary","summary":"Security is supported by definitions and hybrid proofs, while performance is supported by operation counts and asymptotic tree-depth facts. The paper does not implement or benchmark an RBE system.","source_anchor_ids":["anchor-paper-56-security","anchor-paper-56-cost"]},{"id":"paper-56-verifiability","kind":"claim","parent_id":"paper-56","order":7,"epistemic_status":"argued_not_fully_proved","title":"Verifiable registration compatibility","summary":"Adjacent authenticated paths support non-membership and unique-membership proof sketches, but the paper explicitly does not provide the full verification algorithm or prove its soundness and completeness.","source_anchor_ids":["anchor-paper-56-verifiability"]},{"id":"paper-56-boundaries","kind":"limitation_group","parent_id":"paper-56","order":8,"epistemic_status":"material","title":"Limitations","summary":"The optimized ciphertext remains extremely large in the motivating regime, performance is estimated rather than measured, chosen-ciphertext security is absent, the verifiability extension is incomplete, and the second optimization weakens public-parameter compactness from polylogarithmic in users to square-root dependence.","source_anchor_ids":["anchor-paper-56-problem","anchor-paper-56-boundaries"]},{"id":"paper-56-resources","kind":"artifact_group","parent_id":"paper-56","order":9,"epistemic_status":"full_text_available","title":"Publication resources","summary":"The IACR archive, author-uploaded full text, and official DOI make the construction and proofs inspectable. No implementation or benchmark artifact is represented.","source_anchor_ids":["anchor-paper-56-problem","anchor-paper-56-publication"]},{"id":"paper-56-scrutiny","kind":"scrutiny","parent_id":"paper-56","order":10,"epistemic_status":"venue_reviewed","title":"External scrutiny","summary":"The paper appeared at IMACC 2021. 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