{
  "slug": "deduplication-side-channel",
  "term": "Deduplication side channel",
  "aliases": [
    "duplicate-presence oracle"
  ],
  "definition": "A deduplication side channel leaks information about stored content through observable behavior caused by duplicate detection.",
  "note": "In the source-side, cross-user setting studied by Harnik and colleagues, upload suppression can reveal prior content presence without identifying its owner. Server-side matching after a complete upload removes that particular signal, not every possible side channel. Their observations concern historical service versions, not present-day provider behavior. [harnik2010]",
  "status": "research",
  "advantages": [],
  "limitations": [],
  "related": [
    "deduplication",
    "convergent-encryption",
    "content-defined-chunking",
    "proof-of-ownership"
  ],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "citations": [
    {
      "id": "harnik2010",
      "title": "Harnik, Pinkas and Shulman-Peleg. Side channels in cloud services, the case of deduplication in cloud storage (2010), sections 2-3.",
      "url": "https://www.pinkas.net/PAPERS/hps.pdf",
      "accessed": "2026-10-18"
    },
    {
      "id": "hesela-dedup-security",
      "title": "Hesela: Encrypted deduplication: who can test a file guess?",
      "url": "https://hesela.com/analyses/encrypted-deduplication-trust-boundaries/",
      "accessed": "2026-10-18"
    }
  ],
  "updated": "2026-10-18"
}