Show HN: GoUmbral – ECC arithmetic layer, and soon-to-be proxy re-encryption lib | Hacker News Reader

Show HN: GoUmbral – ECC arithmetic layer, and soon-to-be proxy re-encryption lib

github.com

19 pointstuxxy7 comments

I don't understand why this is built on OpenSSL. I looked (not carefully! Very quickly!) and it looks like most of the cgo calls just hit OpenSSL's bignum interface. But Go already has a decent bignum interface, and for that matter curve implementations with rudiments sufficient to build additional curve support. A Go crypto library with an OpenSSL dependency is somewhat un-idiomatic.

What does OpenSSL provide that Go doesn't have? I'm asking because I'm sure there's something (or you wouldn't have done this), and I'm curious.

Go supports Bignums, this is true. I love Go's interfaces, but it doesn't support constant time arithmetic for all of the operations[0]. Go also doesn't support all the curves we need (mainly secp256k1).

We also have a `Point` struct that hits the OpenSSL EC_POINT API. Go only supports constant time arithmetic for a few specific curves (also not secp256k1).

0. https://github.com/golang/go/issues/20654

Hey, everyone! For some context, here's our blogpost about this pre-release. We're really excited to debut our cryptography arithmetic layer for Go. It's the first step to making our split-key threshold proxy re-encryption library available in Go.

https://blog.nucypher.com/introducing-goumbral-ce979e616359

What is “split-key threshold proxy re-encryption”? Can you give an example of the useful case here; what does this enable?

I read the README and the blog post, and found neither contains a “wat is this”. The repo links to an Umbral paper PDF that’s hard to read on mobile - requiring a separate PDF viewer app with tiny font - which also doesn’t contain a concrete example in the abstract.

¯\_(ツ)_/¯ Maybe I’m not the target audience.

Proxy re-encryption (PRE) is a form of public key encryption that allows a semi-trusted proxy to transform ciphertext from being encrypted under one key to another, without learning anything about the underlying plaintext. A "re-encryption key" is used by the proxy to do this transformation.

Umbral is a split-key version of PRE, which splits the re-encryption key into many shares. A threshold number of these shares are then required to re-encrypt the data (similar to Shamir’s Secret Sharing).

Here's a post describing split-key threshold proxy re-encryption in slightly more detail: https://blog.nucypher.com/unveiling-umbral-3d9d4423cd71

We have a more feature-complete reference implementation of Umbral called pyUmbral you may want to look into[0].

We (NuCypher) are using this to build a blockchain privacy layer in the form of a decentralized key management system similar to AWS KMS or Google Cloud KMS.

You can read our paper that describes our use-case here: https://www.nucypher.com/whitepapers/english.pdf

0. https://github.com/nucypher/pyUmbral

See also the python (and reference) implementation, which OP has also worked on (and, disclaimer, I have too :-) ): https://github.com/nucypher/pyUmbral

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