plus/minus epsilon

I used to work on the Crypto Team at my company, and while I was there I got introduced to a lot of different crypto projects and asked to evaluate if they were something it made sense for us to support. The answer was usually no.

For obvious reasons, I recently got interested in how to build websites that are widely accessible but also resistant to censorship. Naturally, my first instinct was to run off and come up with my own blue-sky designs of the most resilient, censorship-resistant website in the world. But censorship is not new and I realized it would be smart to learn from the past: in particular, The Pirate Bay and WikiLeaks, which both continue to operate even under immense pressure to shutdown.

Recently I was asked about the possibility of using MLS in groups with “hidden members”. That is, groups where the creator is known to all participants but the participants don’t know each other. This is the use-case of broadcast TV, private Twitter accounts, Instagram stories. The answer is no, MLS doesn’t work here.

The main issue is that MLS isn’t secure against malicious insiders, and therefore isn't suitable for most broadcast use-cases. A lesser issue is that MLS is designed for homogeneous groups, and would be wasteful to use in a scenario where one member has special authority.

E2E encryption possibly fits into the model for disruptive technology:

1. It’s disproportionately valued by a small set of people.
2. Established companies are unable to effectively deploy it because they either consider plaintext data valuable, or they’ve built a product which is technically unable to be offered in an end-to-end encrypted fashion.

However, it’s not clear that sufficiently developed E2E encryption is able to provide the same service better than an unencrypted alternative would be able to.

Certificate Transparency (CT) is a relatively new addition to the TLS ecosystem. Its fundamental goal is to provide the tools for website operators to detect the mis-issuance of certificates for their own websites. Historically, this is something that only large tech companies have been able to do successfully.

In Adi Shamir's paper titled How to Share a Secret, he quotes this problem from a combinatorics textbook:

Eleven scientists are working on a secret project. They wish to lock up the documents in a cabinet so that the cabinet can be opened if and only if six or more of the scientists are present. What is the smallest number of locks needed? What is the smallest number of keys to the locks each scientist must carry?

I've decided to start writing a regular series of short blog posts about crypto. The focus will be more on the social and problem-solving aspects of crypto rather than the math.

I've realized that some design choices in my bn256 implementation don't seem well-motivated to everybody... including myself. So I'd like to document here all of the tricks I find myself forgetting.

In short:

1. Because small functions have their runtime dominated by function-call overhead.
2. Because data is stored on the heap unnecessarily.
3. Because you can't take advantage of the featurefulness of assembly.

White-Box Cryptography is the study of securing symmetric encryption algorithms in the white-box attack context (WBAC), where an adversary obtains an implementation of the algorithm and is allowed to observe/alter every step of its execution (with instantiated cryptographic keys).

We know that a data structure is a particular way of organizing data so that we can efficiently solve a problem with it. Perhaps a cryptographic data structure would just be the same thing, but with a notion of security determined by an adversary's ability to win a certain game.

In a sense, they're minimal cryptosystems that can be glued together into more complex cryptosystems similar to the way that fundamental data structures can be glued together to give solutions to increasingly complicated problems.

To be pedantic, perhaps a better name for this post would be "A Criticism of In-Browser Cryptography," because it's really the "In-Browser" part that gets people--JavaScript is just another programming language.

A One-Time Attribute-Based Signature scheme allows a signer, who posses a set of attributes verified by an authority, to sign a message with a predicate that is satisfied by his attributes. The signature can reveal no more about the signer than the predicate requires, and it should be infeasible to link multiple signatures to the same signer (signatures should be anonymous). Multiple users, each with only a strict subset of the required attributes to satisfy a predicate, should not be able to collude and forge a signature that does satisfy the predicate (the scheme should be collusion-resistant).

SEAD, the Secure Efficient Ad hoc Distance vector routing protocol, is a recent secure ad-hoc routing protocol designed to use symmetric cryptographic primitives almost exclusively. Relying on symmetric cryptography, rather than asymmetric often requires 3 to 4 orders of magnitude less computation with a negligible increase in storage or network overhead.

Peer-to-peer distributed hash tables have been the subject of a large amount of research because they solve a significant problem in computer science: the secure and efficient distribution of large amounts of data amongst a loose collection of disparate nodes, lacking any centralized authorities or hierarchies.