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diff --git a/content/development/golang_spake2_crypto.rst b/content/development/golang_spake2_crypto.rst new file mode 100644 index 0000000..6f3b0a0 --- /dev/null +++ b/content/development/golang_spake2_crypto.rst @@ -0,0 +1,117 @@ +SPAKE2 In Golang: Journey to Cryptoland begins +############################################## + +:date: 2018-07-22 13:43 +0530 +:slug: golang_spake2_1 +:tags: go, golang, spake2, cryptograph, ecc, magic-wormhole +:author: copyninja +:summary: My notes on SPAKE2 implementation in Golang, my first Golang and + cryptographic library + + +.. + + Disclaimer: This or the series of SPAKE2 related posts are inspired from + `Jonathan Lange's <https://jml.io>`_ `series on SPAKE2 + <https://jml.io/tag/spake2.html>`_ when he ported it to Haskell, which is + also the reference I used for my implementation in Golang. + + +Brief Background +================ + +Before I can go to detail I should tell why/how I came to implementing SPAKE2 in +Golang. Story starts a couple of month back when I started contributing to +`*magic-wormhole.rs* <https://github.com/warner/magic-wormhole.rs>`_, a Rust port +of original Python project of magic-wormhole. You can read `this LWN article +<https://lwn.net/Articles/692061/>`_ to understand more about what +magic-wormhole is. + +During contribution my friend `Ramakrishnan Muthukrishnan +<https://rkrishnan.org/>`_ said to me that I should try to port the +magic-wormhole to Golang. I was not a expert Go programmer but had understanding +of language basics and thought why not use it to improve my language +understanding. And this is where it all started. + +What is SPAKE2 why is it used? +============================== + +At this point we need to know why SPAKE2 is needed and how magic-wormhole uses +it. `SPAKE2 <http://www.di.ens.fr/~mabdalla/papers/AbPo05a-letter.pdf>`_ is +*Simple Password Authenticated Key Exchange* protocol. It allows 2 parties +having a shared weak password to derive a strong shared key which can then be +used by the parties to setup a encrypted+authenticated channel between them. + +*magic-wormhole* uses SPAKE2 to negotiate a shared session key between +communicating parties which is then used by magic-wormhole to derive different +keys needed for different *purpose*. + +So I hit my first road block after agreeing to implement the *magic-wormhole* in +Golang, there is no SPAKE2 implementation readily available in Go!. + +Enter Cryptography and My knowledge about it +============================================ + +Ram convinced me that its easy to implement SPAKE2 in Go and I agreed. But my +knowledge on cryptography was limited. I knew Cryptography is + +* basically math with big numbers and relies on fact that factoring big prime + number is hard for computers. +* These big numbers are derived from *Abelian Group* and related concepts from + number theory, which I have studied in academics but since I've never learnt a + practical use case for them, its eating dust some where inside my memory. + +I've taken some theoretical course on Cryptography but never thought of +implementing one myself. With these weak foundation I set out for a new +adventure. + +Python SPAKE2 Implementation +---------------------------- + +Since magic-wormhole is implemented in python, SPAKE2 implementation in Python +is considered as reference for other language implementation. SPAKE2 paper does +not specify much about where or how the requirement public constants are +defined, so implementer can take liberty at defining those. Python code uses 2 +groups one is *Twisted Edwards Curve* group *Ed25519* and others are +multiplicative group over Integer of 1024, 2048 and 3072 bits. + +In Python code Warner himself has defined Ed25519 and other Integer group and +related operations. In Rust code though there is only Ed25519 group but its +created using *curve25519-dalek* library. Haskell code also defines the group +operations by itself instead of depending on any other libraries (possibly +Cryptonite). So as a first step I started for searching any library equivalent +to *curve25519-dalek* as I've no clue what is an Elliptic curve.(forget groups +I don't know basic itself). + +First Try, Bruteforce +--------------------- + +I've this bad habit of tackling problem with brute force some times it works but +most time it just exhausts me taking me nowhere. So with my normal habit I +started looking for Ed25519 curve operations library. (Without actually knowing +what operations are and how it works). I tried to read through +*curve25519-dalek* but invain, nothing entered into my head. I found *ed25519* +package for Go written by *Adam Langley* but eventually it turned out to be +actually a signature package. I found an internal package defined in *ed25519* +package called *edwards25519*, which seem to have some operations defined but I +was unable to understand it nor figure out why its made internal. I later even +took a dig at embedding *edwards25519* as part of my implementation of ed25519 +group but finally had to drop it for my own version that story will be part of +another post in this series. + +Conclusion +========== + +During all these I was constantly in talk with Ram and first thing he told me +was to slow down a bit and go from scratch. And that's what was the learning +point for me. In short I can say the following. + +.. + + Nothing can be done in single day, before you code understand the basic + concepts and then build it from there. As they say you can't build house on + weak foundation. + +In the next post in this series I will write about my learning on Elliptic +Curves and Elliptic curve groups, followed by experiment with number groups and +finally learning and decision I had to make in writing *gospake2*. |