{
  "slug": "oblivious-ram",
  "term": "Oblivious RAM",
  "aliases": [
    "ORAM"
  ],
  "definition": "Oblivious RAM hides logical storage access patterns by making physical accesses for equal-length request sequences computationally indistinguishable.",
  "note": "Scope: The trusted client protects its state while the storage server observes physical accesses. The standard definition compares equal-length sequences; request timing and frequency are excluded from the Path ORAM model. Integrity and freshness require additional protection. [path2018]\n\nCost: Read/write traffic that waits for a requested block is online bandwidth. Overall bandwidth also includes maintenance such as eviction and reshuffling. Ring ORAM separates these costs; its constant online transfer variant requires server-side XOR computation, not just a passive store. [ring2015]",
  "status": "research",
  "advantages": [],
  "limitations": [],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-11-12",
  "related": [
    "path-oram",
    "authenticated-encryption",
    "deduplication-side-channel",
    "history-independence"
  ],
  "citations": [
    {
      "id": "path2018",
      "title": "Stefanov et al. Path ORAM: An Extremely Simple Oblivious RAM Protocol. JACM 65(4), 2018, sections 2-4 and 6.4. DOI 10.1145/3177872.",
      "url": "https://people.csail.mit.edu/devadas/pubs/PathORAMJACM.pdf",
      "accessed": "2026-11-12"
    },
    {
      "id": "ring2015",
      "title": "Ren et al. Constants Count: Practical Improvements to Oblivious RAM. USENIX Security 2015, sections 1.3, 3 and 5.",
      "url": "https://people.csail.mit.edu/devadas/pubs/ringoram.pdf",
      "accessed": "2026-11-12"
    },
    {
      "id": "hesela-oram",
      "title": "Hesela: What an encrypted access trace can reveal",
      "url": "https://hesela.com/analyses/encrypted-deduplication-trust-boundaries/#access-patterns",
      "accessed": "2026-11-12"
    }
  ],
  "provenance": [
    "Reviewed the author-hosted JACM 2018 and USENIX Security 2015 papers. This is a definition of their models, not a claim that a deployed service hides all metadata."
  ]
}