Fiat Shamir Protocol Library

What's This ?

Fiat Shamir Protocol is one of Zero Knowledge Proof Protocol that doesn't require the sender to send his credentials . Instead One can prove his / her identity by using Digital Signatures (sort of)

Is this Secure ?

Well Kind of but can't be used in production yet... I mean the implementation is just a Proof Of Concept and Future scope of adding more to it exists

Implementation Details

Most of the Details are in the Code itself But I am including the same for Documentation Purposes here...

• This is intended to be on Authentication of Client -Server over TCP
• There is a Provision of 2 Structures one for the Verifier and other for the prover.

typedef struct FSP_snd{
	
	lli n,rand,x,y;
	lli secret;
	lli PUBLIC_KEY;
}fsp_snd;

typedef struct FSP_recv{
	lli prime2, prime1;
	lli n,challenge;
	lli PUBLIC_KEY;
}fsp_recv;

Verifier Native Functions :

• 1.Setup Reciever:

  Choose Arbitrary prime and send n to prover (Registration Phase )

lli Setup_reciever(fsp_recv*);

• 2.Challenge Prover:

  Challenge Can be any Rand Number

lli challenge_phase(fsp_recv*,lli);

• 3.Verify:

  Verify the same recieved from Response Phase(Prover) with y**2%n

bool verification_phase(fsp_recv*,lli,lli);

Prover Native Functions :

• 1.Setup Phase: Prover Has a secret Key : s And Sends Public Key to Reciever (Verifier)

    lli Setup_sender(fsp_snd*,lli,lli);

• 2.Commit Phase: Chooses a random value and bound it by common n and Send the same

lli  commit_phase(fsp_snd*);

• 3.Response Phase : Respond to the challenge

lli response_phase(fsp_snd*,lli);

Build Instructions

Clone this sub-repository and Maintain the Folder Structure as in this case .

Portablity : This library can be ported to Python and can be used as is in Vanilla C

For Testing Modify the test.c File and Run:

make  test

For Porting to python/JS : Run :

make Clean

make SharedLib

to create a shared object file and use the .so file as a starter.

Caveats

Do note that this was tested on a Linux System .. What may have compiled for me wouldn't for you if you would. So It is recommended to run the Make Clean && Make SharedLib commands above

This will not work on Windows . You need a MINGW / Equivalent compiler and compile the same to .dll file as opposed to .so file .

If you Have Troubles Working with generating shared library Run objdump -D lib.so

to identify if the Function Implementation is there and the namespace isn't mangled..

Future Scope

This current version is just a proof of concept version of ZKP . However there exist many complex algorithms in the wild out there The aim of the Entire Repository is to try and implement these algorithms with minimal dependencies. I mean from scratch ..

So What's Beyond this ?

If possible this shall be maintained regularly and I shall add a bit of complexity as such

Further improvements to use openssl for prime generation

Use longer datatypes rather than lli -> Port to gmp for arbitrary numerical precision

Need to add Public Key Infrastructure( PKI ) for Key Distribution Otherwise this is useless

Do Note that the sender public Key has to be registered.(Need to add Database Support YET!)

After this is done this should be a relatively well built Library which is cross-platform (partly)

Use Case

See Implementation for implementation in Python using this Library with the help of ctypes

Image Credits

Medium