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Oblivious & Approximate Computing

A blog series exploring encrypted search, Bernoulli models, cipher types, and probabilistic data structures

25 parts

Oblivious & Approximate Computing

This series explores the mathematical foundations of computing on encrypted and approximate data—where we deliberately trade exactness for privacy, space efficiency, or computational tractability.

Core Themes

1. The Latent/Observed Duality

The fundamental insight: distinguish between latent (true) values and observed (approximate) values. This duality connects:

  • Probabilistic data structures (Bloom filters, sketches)
  • Privacy mechanisms (information-theoretic privacy)
  • Encrypted search systems (oblivious query processing)

2. Bernoulli Types

A type-theoretic framework for approximate computing:

  • Formal semantics for approximate operations
  • Composition rules with error propagation
  • Space-optimal constructions for any probability distribution

3. Cipher Maps & Algebraic Cipher Types

Category-theoretic foundations for encrypted computation:

  • Functorial lifting of algebraic structures
  • Homomorphic operations preserving structure
  • Privacy through rank-deficient observation functions

4. Information-Theoretic Privacy

Moving beyond computational hardness assumptions:

  • Privacy from controlled indistinguishability
  • Entropy-optimal index construction
  • Asymptotic privacy guarantees

Key Papers

  • Encrypted Search with Oblivious Bernoulli Types - Using approximate data structures for privacy
  • Maximizing Confidentiality Through Entropy - Optimal parameterization of secure indexes
  • Cipher Maps - Categorical foundations for encrypted computation
  • Perfect Hashing with Cryptographic Security - Space-optimal, maximum-entropy hash functions

Why This Matters

In an era where:

  • Privacy is non-negotiable, but exact computation leaks information
  • Scale demands approximation—you can’t store everything exactly
  • Streaming data requires constant-space algorithms
  • Encrypted search needs oblivious data structures

…these foundations provide principled ways to build systems that trade exactness for other desirable properties while maintaining formal guarantees.

About

This work builds on research spanning from my Master’s thesis (2015) on encrypted search through recent work on algebraic cipher types and entropy maps. The combination of Bernoulli types with categorical abstractions finally provides a unified mathematical foundation for practical privacy-preserving computation at scale.

Posts in this Series

Showing 25 of 25 posts
7 of 14

Entropy Maps

The PDF version of this post is available on GitHub.

The basic theory behind an entropy map is to map values in the domain to values in the codomain by hashing to a prefix-free code in the codomain. …