Data Security

• Access controls
  • Regulate the reading, changing, and deletion of data and programs. Three assumptions:
    1. Proper user identification
    2. Unanticipated observers do not gain access
    3. Privilege-information is heavily protected
  • Controls for transaction-processing systems: data-dependent restrictions, history-dependent restrictions.
  • Controls for general purpose systems: object-dependent controls regulate access to an object irrespective of the values stored in that object. Capability addressing: capability, capability list. Revocation of privileges is hard if capabilities are scattered throughout lists.
  • Some limitations:
    • High overhead in managing small memory segments.
    • Excessive privilege vested in the operating system.
• Flow controls
  • Flow policy specifies the channels along which information is allowed to move.
  • Some limitations:
    • Flow controls based on security classes tend to overclassify information.
    • Covert channels.
• Inference controls
  • Deduction of confidential information by inference.
  • Defenses include
    • Controls that withhold response for improper query set sizes and overlaps.
    • Controls that distort the responses by rounding or falsifying data.
    • Controls that apply queries to random samples of the database.
• Cryptographic controls
  • Symmetric encryption
    • One-time pad, DES (Data Encryption Standard).
    • Key management is important.
  • Asymmetric encryption
    • Public-key encryption.