zk-Call & Labs

"Zero-Knowledge" Proof Implementation with HMAC Communication in C++

_{Built by zk-Call :)}

Table of Contents

• Credits
• Purpose
• How it Works
• API
• Example Usage

Credits

This repository hosts a refined implementation of Schnorr's Protocol, innovatively incorporating a state seed for enhanced security measures. While the underlying proofs may appear intricate, I aim to elucidate their functionality to the best of my ability. However, for a deeper understanding, I encourage referencing the seminal research papers underpinning this implementation, as they offer comprehensive insights.

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For further exploration:

Elliptic Curve Based "Zero-Knowledge" Proofs and Their Applicability on Resource Constrained Devices by Ioannis Chatzigiannakis, Apostolos Pyrgelis, Paul G. Spirakis, and Yannis C. Stamatiou

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Additionally, this repository delves into the concepts of "Zero-Knowledge" Proofs (ZKPs) and Hash-based Message Authentication Codes (HMACs). ZKPs are cryptographic protocols that allow one party (the prover) to prove to another party (the verifier) that a given statement is true, without revealing any additional information beyond the validity of the statement itself. This property is particularly valuable for preserving privacy while establishing trust.

On the other hand, HMACs are a type of cryptographic hash function used for message authentication. They involve a cryptographic hash function (such as SHA-256) and a secret cryptographic key. HMACs provide a way to verify both the data integrity and the authenticity of a message, ensuring that it has not been altered or tampered with during transmission and that it indeed originates from the purported sender.

Purpose

In today's rapidly evolving IT and application development landscape, "Zero-Knowledge" Proofs (ZKPs) emerge as a pivotal paradigm for authentication security. Their capacity to affirm the validity of a claim, such as proving possession of a secret password — without revealing any sensitive information about the claim itself, such as passwords or hashes, revolutionizes the assurance of secure AAA operations (authentication, authorization, and accounting).

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zk-Call & Labs represents an implementation of a Non-Interactive "Zero-Knowledge" Proof (NIZKP) protocol tailored specifically for validating text-based secrets. This framework proves invaluable for safeguarding passwords and other authentication mechanisms, ensuring robust security measures without compromising privacy. Additionally, the integration of HMAC (Hash-Based Message Authentication Code) further fortifies the authentication process, enhancing data integrity and thwarting potential security breaches.

How It Works

The authentication protocol employed in this system operates based on two fundamental concepts: "Zero-Knowledge" Proofs (ZKPs) and Hash-Based Message Authentication Code (HMAC). Let's delve into each of these components and understand how they synergize to ensure secure authentication in messaging applications.

"Zero-Knowledge" Proofs (ZKPs)

"Zero-Knowledge" Proofs (ZKPs):

ZKPs form the bedrock of privacy-preserving authentication mechanisms. These proofs allow one party (the prover) to demonstrate the validity of a claim to another party (the verifier) without revealing any additional information beyond the claim's validity. In essence, ZKPs enable authentication without the need for the prover to disclose sensitive data, such as passwords or cryptographic keys.

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Application in Authentication:

In the context of messaging applications, ZKPs play a pivotal role in verifying a user's identity without the need to transmit explicit credentials over the network. Instead, users can generate cryptographic proofs attesting to their identity or possession of certain credentials without exposing those credentials themselves. This ensures that sensitive information remains confidential during the authentication process, bolstering security and privacy.

Hash-Based Message Authentication Code (HMAC)

Hash-Based Message Authentication Code (HMAC):

HMAC provides a robust mechanism for verifying the integrity and authenticity of messages exchanged between parties. It involves the use of a cryptographic hash function in conjunction with a secret key to generate a unique code (the HMAC) for each message. This code serves as a digital signature, allowing the recipient to verify that the message has not been tampered with or altered during transmission.

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Application in Authentication:

In messaging applications, HMAC can be employed to authenticate message senders and ensure the integrity of communication channels. By appending an HMAC to each message using a shared secret key, both the sender and recipient can validate the message's authenticity upon receipt. Any unauthorized modifications to the message would result in a mismatch between the computed HMAC and the received HMAC, thereby alerting the recipient to potential tampering.

Synergistic Operation

When combined, "Zero-Knowledge" Proofs and HMAC create a formidable framework for secure authentication in messaging applications. ZKPs facilitate identity verification without divulging sensitive information, while HMAC ensures the integrity and authenticity of messages exchanged between parties. Together, these mechanisms uphold the confidentiality, integrity, and authenticity of communication channels, safeguarding users' privacy and security in the digital realm.

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API

The "HMAC_Client" С++ API is meant to be simple and intuitive:

Core Components

The Core Components streamline secure Message Encryption and Decryption, supporting both Chunk and Character-Level processing for enhanced data protection.

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HMAC_Client.encrypt_message_by_chunks

Method to encrypt a message by processing it in chunks.

std::string encrypt_message_by_chunks(const std::string& message);

    message: string                    # The message to be encrypted, processed in chunks

HMAC_Client.encrypt_message

Method to encrypt a message by a chars.

std::string encrypt_message(const std::string& message);

    message: string                    # The message to be encrypted, processed in characters

HMAC_Client.decrypt_message_by_chunks

Method to decrypt a message by processing it in chunks.

 std::string decrypt_message_by_chunks(const std::string& message);

    message: string                    # The message to be decrypted, processed in chunks

HMAC_Client.decrypt_message

Method to decrypt a message by processing it in chars.

 std::string encrypt_message(const std::string& message);

    message: string                    # The message to be decrypted, processed in characters

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Example Usage

TODO: Include Example Usage

Example 1

#include <iostream> // Include the input/output stream standard header
#include <thread> // Include the thread standard header
#include <queue> // Include the queue standard header
#include <string> // Include the string standard header
#include "src/HMAC/core/base.h" // Include the header file for HMAC_Client functionality
#include "src/SeedGeneration/core/base.h" // Include the header file for SeedGenerator functionality

constexpr bool DEBUG = true; // Define a constexpr boolean variable DEBUG with value true

void print_msg(const std::string &who, const std::string &message) { // Define a function to print messages
    if (DEBUG) { // Check if debugging is enabled
        std::cout << "[" << who << "] " << message << std::endl; // Print the message with source identifier
    }
}

bool check_if_queue_empty(std::queue<std::string> &socket) { // Define a function to check if a queue is empty
    while (true) { // Infinite loop
        if (!socket.empty()) { // Check if the queue is not empty
            return true; // Return true if the queue is not empty
        }
    }
}

std::string get_content_from_socket(std::queue<std::string> &socket) { // Define a function to get content from a socket (queue)
    if (check_if_queue_empty(socket)) { // Check if the queue is not empty
        std::string val = socket.front(); // Get the front element of the queue
        socket.pop(); // Remove the front element from the queue
        return val; // Return the retrieved value
    }
}

void client(std::queue<std::string> &client_socket, std::queue<std::string> &server_socket) { // Define the client function
    // Generating the main seed
    SeedGenerator seed_generator("job"); // Create an instance of SeedGenerator
    std::vector<unsigned char> main_seed = seed_generator.generate(); // Generate the main seed

    // Creating an instance of HMAC_Client for encrypting messages
    print_msg("client", "first");
    HMAC_Client obj("sha256", main_seed, 1); // Create an instance of HMAC_Client

    // Sending the main seed to the server
    server_socket.emplace(main_seed.begin(), main_seed.end()); // Convert the main seed vector to a string and send it to the server
    print_msg("client", "after obj");

    // Checking if the server has successfully received the seed
    if (get_content_from_socket(client_socket) == obj.encrypt_message("")) { // Check if the server received the seed
        print_msg("client", "after if");

        // If successful, send a message to the server
        std::string message = "hello"; // Define the message to be sent
        server_socket.push(obj.encrypt_message_by_chunks(message)); // Encrypt and send the message to the server
        print_msg("client", "client sent message " + message);

        // Checking if the server has successfully decrypted the message
        if (get_content_from_socket(client_socket) == obj.encrypt_message(message)) { // Check if the server decrypted the message
            print_msg("client", "server has decrypted message");
        }
    }
}

void server(std::queue<std::string> &server_socket, std::queue<std::string> &client_socket) { // Define the server function
    // Receiving the main seed from the client
    std::string main_seed = get_content_from_socket(server_socket); // Receive the main seed from the client

    // Creating an instance of HMAC_Client for encrypting messages
    HMAC_Client obj("sha256", std::vector<unsigned char>(main_seed.begin(), main_seed.end()), 1); // Create an instance of HMAC_Client

    // Sending an empty message to the client as acknowledgment
    client_socket.push(obj.encrypt_message("")); // Encrypt and send an empty message to the client as acknowledgment

    // Receiving the encrypted message from the client
    std::string msg = get_content_from_socket(server_socket); // Receive the encrypted message from the client
    print_msg("server", "message encrypted: " + msg);

    // Decrypting the message
    print_msg("server", "before decrypt ");
    std::string msg_raw = obj.decrypt_message_by_chunks(msg); // Decrypt the received message
    print_msg("server", "message raw: " + msg_raw);

    // Sending the encrypted message back to the client
    client_socket.push(obj.encrypt_message(msg_raw)); // Encrypt and send the decrypted message back to the client
}

int main() { // Main function
    std::queue<std::string> client_socket, server_socket; // Create queues for client and server sockets
    std::thread client_thread(client, std::ref(client_socket), std::ref(server_socket)); // Create a thread for the client function
    std::thread server_thread(server, std::ref(server_socket), std::ref(client_socket)); // Create a thread for the server function

    // Joining the threads to wait for their completion
    client_thread.join(); // Wait for the client thread to finish
    server_thread.join(); // Wait for the server thread to finish

    return 0; // Return 0 to indicate successful execution
}

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Example 2

#include "src/ZeroKnowledge/core/base.h" // Include the header file for ZeroKnowledge class

int main() { // Main function
    // Creating a ZeroKnowledge object for the client with specified curve and hash algorithm
    ZeroKnowledge clientObject = ZeroKnowledge::createNew("secp256k1", "sha3_256");

    // Creating a ZeroKnowledge object for the server with specified curve and hash algorithm
    ZeroKnowledge serverObject = ZeroKnowledge::createNew("secp384r1", "sha3_512");

    // Setting the server password
    std::string serverPassword = "SecretServerPassword";

    // Creating a signature for the server password
    ZeroKnowledgeSignature serverSignature = serverObject.createSignature(serverPassword);

    // Creating a signature for the client identity
    std::string identity = "John";
    ZeroKnowledgeSignature clientSignature = clientObject.createSignature(identity);
    std::cout<<"before\n";

    // Generating a token signed by the server for the client
    std::cout<<clientObject.token()<<"\n";

    ZeroKnowledgeData token = serverObject.sign(serverPassword, clientObject.token());
    std::cout<<"after\n";

    // Generating proof using client identity and token
    ZeroKnowledgeData proof = clientObject.sign(identity, token.data);

    // Verifying the received proof
    bool serverVerification = serverObject.verify(token, serverSignature);
    if (!serverVerification) { // Check if server verification failed
        std::cout << "Server verification failed" << std::endl; // Print error message
    } else { // If server verification succeeded
        // Otherwise, verify the proof using client signature
        bool clientVerification = clientObject.verify(token, clientSignature, proof.proof);
        if (!clientVerification) { // Check if client verification failed
            std::cout << "Client verification failed" << std::endl; // Print error message
        } else { // If client verification succeeded
            std::cout << "Authentication successful" << std::endl; // Print success message
        }
    }

    return 0; // Return 0 to indicate successful execution
}

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Example 3

#include "src/ZeroKnowledge/core/base.h" // Include the header file for ZeroKnowledge class
#include "src/HMAC/core/base.h" // Include the header file for HMAC_Client functionality
#include "src/SeedGeneration/core/base.h" // Include the header file for SeedGenerator functionality
#include <iostream> // Include the input/output stream standard header
#include <thread> // Include the thread standard header
#include <queue> // Include the queue standard header
#include <string> // Include the string standard header

constexpr bool DEBUG = true; // Define a constexpr boolean variable DEBUG with value true

void print_msg(const std::string &who, const std::string &message) { // Define a function to print messages
    if (DEBUG) { // Check if debugging is enabled
        std::cout << "[" << who << "] " << message << std::endl; // Print the message with source identifier
    }
}

bool check_if_queue_empty(std::queue<std::string> &socket) { // Define a function to check if a queue is empty
    while (true) { // Infinite loop
        if (!socket.empty()) { // Check if the queue is not empty
            return true; // Return true if the queue is not empty
        }
    }
}

std::string get_content_from_socket(std::queue<std::string> &socket) { // Define a function to get content from a socket (queue)
    if (check_if_queue_empty(socket)) { // Check if the queue is not empty
        std::string val = socket.front(); // Get the front element of the queue
        socket.pop(); // Remove the front element from the queue
        return val; // Return the retrieved value
    }
}

void client(std::queue<std::string> &client_socket, std::queue<std::string> &server_socket) { // Define the client function
    // Generating the main seed
    SeedGenerator seed_generator("job"); // Create an instance of SeedGenerator
    std::vector<unsigned char> main_seed = seed_generator.generate(); // Generate the main seed

    // Creating an instance of HMAC_Client for encrypting messages
    print_msg("client", "first");
    HMAC_Client obj("sha256", main_seed, 1); // Create an instance of HMAC_Client

    // Sending the main seed to the server
    server_socket.emplace(main_seed.begin(), main_seed.end()); // Convert the main seed vector to a string and send it to the server
    print_msg("client", "after obj");

    // Checking if the server has successfully received the seed
    if (get_content_from_socket(client_socket) == obj.encrypt_message("")) { // Check if the server received the seed
        print_msg("client", "after if");

        // If successful, send a message to the server
        std::string message = "hello"; // Define the message to be sent
        server_socket.push(obj.encrypt_message_by_chunks(message)); // Encrypt and send the message to the server
        print_msg("client", "client sent message " + message);

        // Checking if the server has successfully decrypted the message
        if (get_content_from_socket(client_socket) == obj.encrypt_message(message)) { // Check if the server decrypted the message
            print_msg("client", "server has decrypted message");
        }
    }
}

void server(std::queue<std::string> &server_socket, std::queue<std::string> &client_socket) { // Define the server function
    // Receiving the main seed from the client
    std::string main_seed = get_content_from_socket(server_socket); // Receive the main seed from the client

    // Creating an instance of HMAC_Client for encrypting messages
    HMAC_Client obj("sha256", std::vector<unsigned char>(main_seed.begin(), main_seed.end()), 1); // Create an instance of HMAC_Client

    // Sending an empty message to the client as acknowledgment
    client_socket.push(obj.encrypt_message("")); // Encrypt and send an empty message to the client as acknowledgment

    // Receiving the encrypted message from the client
    std::string msg = get_content_from_socket(server_socket); // Receive the encrypted message from the client
    print_msg("server", "message encrypted: " + msg);

    // Decrypting the message
    print_msg("server", "before decrypt ");
    std::string msg_raw = obj.decrypt_message_by_chunks(msg); // Decrypt the received message
    print_msg("server", "message raw: " + msg_raw);

    // Sending the encrypted message back to the client
    client_socket.push(obj.encrypt_message(msg_raw)); // Encrypt and send the decrypted message back to the client
}

void init_talking() { // Define a function to initialize client-server communication
    std::queue<std::string> client_socket, server_socket; // Create queues for client and server sockets
    std::thread client_thread(client, std::ref(client_socket), std::ref(server_socket)); // Create a thread for the client function
    std::thread server_thread(server, std::ref(server_socket), std::ref(client_socket)); // Create a thread for the server function

    // Joining the threads to wait for their completion
    client_thread.join(); // Wait for the client thread to finish
    server_thread.join(); // Wait for the server thread to finish
}

int main() { // Main function

    // Creating a ZeroKnowledge object for the client with specified curve and hash algorithm
    ZeroKnowledge clientObject = ZeroKnowledge::createNew("secp256k1", "sha3_256");

    // Creating a ZeroKnowledge object for the server with specified curve and hash algorithm
    ZeroKnowledge serverObject = ZeroKnowledge::createNew("secp384r1", "sha3_512");

    // Setting the server password
    std::string serverPassword = "SecretServerPassword";

    // Creating a signature for the server password
    ZeroKnowledgeSignature serverSignature = serverObject.createSignature(serverPassword);

    // Creating a signature for the client identity
    std::string identity = "John";
    ZeroKnowledgeSignature clientSignature = clientObject.createSignature(identity);
    std::cout << "before\n";

    // Generating a token signed by the server for the client
    std::cout << clientObject.token() << "\n";

    ZeroKnowledgeData token = serverObject.sign(serverPassword, clientObject.token());
    std::cout << "after\n";

    // Generating proof using client identity and token
    ZeroKnowledgeData proof = clientObject.sign(identity, token.data);

    // Verifying the received proof
    bool serverVerification = serverObject.verify(token, serverSignature);
    if (!serverVerification) { // Check if server verification failed
        std::cout << "Server verification failed" << std::endl; // Print error message
    } else { // If server verification succeeded
        // Otherwise, verify the proof using client signature
        bool clientVerification = clientObject.verify(token, clientSignature, proof.proof);
        if (!clientVerification) { // Check if client verification failed
            std::cout << "Client verification failed" << std::endl; // Print error message
        } else { // If client verification succeeded
            std::cout << "Authentication successful" << std::endl; // Print success message
            init_talking(); // Initialize client-server communication

        }
    }

    return 0; // Return 0 to indicate successful execution
}