Privacy Management for J. Alex Halderman Brent Waters Edward W. Felten Princeton University Department of Computer Science Portable Recording Devices J. A. Halderman1 of 10

Camera Phones 170 million in 2004 =+ × 170 million= New Privacy Threats Ubiquitous Recording J. A. Halderman1 of 10

New Privacy Threats J. A. Halderman2 of 10 A Breakdown of Social Norms

Augment them, don’t replace them Previous Approaches Law/Policy Usage Restrictions Local Bans Technology Signal from beacon disables recording features J. A. Halderman3 of 10  Based on location, not full context  Decide before recording, not playback Coarse-Grained Restrictions

Our Approach J. A. Halderman4 of 10 Privacy protection built into trusted recording devices

Our Approach J. A. Halderman4 of 10 Recording subjects control use Negotiate using their devices (assume discovery method)

Defers privacy decision to last possible moment Our Approach J. A. Halderman4 of 10 Encrypt recording before storing Key share retained by privacy stakeholders Must ask permission to decrypt

Our Privacy Requirements J. A. Halderman5 of Unanimous Consent 2. Confidentiality of Vetoes Colluder

Our Applications J. A. Halderman6 of 10 Laptops/WiFiAOL Instant Messenger Protects audio recordings Manual discovery Protects chat logs Discovery handled by AIM

Alice and Bob tell Carol k Alice  k Bob without revealing other information about k Alice or k Bob to anyone Variation on Chaum’s “Dining Cryptographers” Secure XOR J. A. Halderman7 of 10 Bob Alice k Bob Secret Secret k Alice Carol

A & B choose and exchange random blinding factors A & B each XOR both blinding factors with their secret input and send the result to Carol Carol XORs these messages to learn k Alice  k Bob Bob Alice k Bob Secret Secret k Alice Secure XOR J. A. Halderman7 of 10 B Bob Blinding factor Blinding factor B Alice B Bob B Alice k Alice  B Bob  B Alice B Bob  B Alice  k Bob Carol k Alice  B Bob  B Alice  B Bob  B Alice  k Bob = k Alice  k Bob Carol does not learn k Alice or k Bob

Private Storage Protocol 8 of 10 “Create” Operation J. A. Halderman Identify stakeholders Need a trusted recording device for now

Private Storage Protocol 8 of 10 “Create” Operation J. A. Halderman Choose random keyshares k 1 = k 2 = Securely tell recorder k1  k2 Secure XOR k 1  k 2 = Encrypt using k1  k2 as key key= Recorder discards plaintext, key Stakeholders hold on to shares

id= owners=Alice,Bob k Alice = Secure XOR Private Storage Protocol 8 of 10 “Decrypt” Operation J. A. Halderman id= owners=Bob,Alice k Bob = id= owners=Alice,Bob Requestor sends request May we decrypt ? Cryptography provides strong protection Stakeholders apply policies Secure XOR To grant, input keyshare into XOR key= ? To deny, give random input to XOR key= ? Vetoes remain confidential

Private Storage Protocol J. A. Halderman8 of 10 “Create” Location Service Storage Recorder BRecorder A Data In Persistent Agent A Persistent Agent B Player Agent AAgent B Keyshare Encrypted Recording “Decrypt” Policy Data Out

Privacy in Practice J. A. Halderman9 of 10 A Problem of Compliance Community of like-minded people: Social pressures, local policies, etc. Privacy law can provide further incentives Convince manufacturers to build it in: Regulatory pressure, customer demand

Conclusions J. A. Halderman10 of 10 Ubiquitous recording brings privacy threats Technology can give control back to recording subjects Widespread compliance among like-minded groups

Privacy Management for J. Alex Halderman Brent Waters Edward W. Felten Princeton University Department of Computer Science Portable Recording Devices