[cryptography] Introducing SC4 -- feedback appreciated

zaki at manian.org zaki at manian.org
Fri Apr 17 14:26:55 EDT 2015

At some level, this is in the same conceptual space as Peerio / Minilock.

The primary notable difference I see is you have used a binary format for
keys and messages.

Minilock uses a compressed curve25519 point without any metadata as public
key. This is more compact than your format. It'sBase58 encoded it is
tweetable which is very nice.

Minilock uses JSON for the message format rather than a binary format. I
also really like using a protocol buffers for message formats which is what
TextSecure does.

It looks like your key portability strategy is for users to manage their
keys directly as file they provide to instances. Peerio has switched to
providing users with a wordlist from which the private key can be derived
through a KDF for portability.

Text Secure
Public Key

On Fri, Apr 17, 2015 at 10:56 AM, Ron Garret <ron at flownet.com> wrote:

> TL;DR: I took tweet-NaCl-JS and wrapped a little PGP-like webapp around
> it.  I would like to solicit feedback and code review from this community
> before I submit it for a formal audit and release it to the general public.
> Links:
> Source code: https://github.com/Spark-Innovations/SC4
> Live demo: https://sc4.us/sc4.html
> FAQ for experts: http://sc4.us/expert_faq.html
> FAQ for non-experts: http://sc4.us/regular_faq.html
> Note that the FAQ links are not secure.  This will be fixed eventually.
> The production push process is a work-in-progress.
> Unique features of SC4:
> 1.  It is a standalone web application.  The server only serves static
> files.  You can even run SC4 from a FILE: URL, though this requires the
> keys to be embedded in the code.  SC4 includes code to automatically
> generate a standalone version.  This is mainly intended to be a
> proof-of-concept, but it does work.
> 2.  It’s tiny, and therefore easy to audit.  It consists of three standard
> libraries (tweet-NaCl, jQuery, and purify) plus <1000 lines of additional
> code, and that includes the HTML and CSS.
> 3.  It runs in FF, Chrome and Safari.  It might even run in IE but I
> haven’t tried it.
> SC4 aims for a point in the design space that balances security against
> ease of use.  PGP is bullet-proof, but not widely deployed because there is
> a lot of friction in getting it up and running.  SC4 aims to eliminate this
> friction while remaining reasonably secure.  It is also based on open
> standards so that more secure implementations can be easily produced in the
> future.  (Part of my long-term plan is to build an HSM dongle using a
> Teensy 3 board.)
> Feedback and constructive criticism much appreciated.  Also, I’m seeking
> someone to serve as a paid consultant on this project.  If you’re
> interested please contact me off-line.  My SC4 key is:
> ---START KEY---
> X-sc4-content-type: public-key
> From: ron at spark-innovations.com
> Timestamp: Fri, 17 Apr 2015 17:40:56 GMT
> RBDrBehSHbm1x/o+yPFrpdD6kWwSV3QQI8S/y8MdeEg=
> JaP8eUTkBh2OKRPJYSti9uTuB/vd8a+HV9rCCknw7l95
> a9C8lRa1PfP7/rcR8qwUM3BvXkBvT8kaZMJhcCoPCw==
> ---END KEY---
> Thanks,
> Ron Garret
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