R&D: WAMP CRA

[om26er]

Need code to sign cra challenge

[asimfarooq5]

Arduino WAMPCRA Signing

Create the WAMPCRAAuthenticator Class

WAMPCRAAuthenticator.h

#ifndef WAMPCRAAuthenticator_h
#define WAMPCRAAuthenticator_h

#include <Arduino.h>
#include <mbedtls/md.h>  // For HMAC

class WAMPCRAAuthenticator {
public:
    WAMPCRAAuthenticator(const String& secret);
    String signChallenge(const String& challenge);

private:
    String secret;
};

#endif

WAMPCRAAuthenticator.cpp

#include "WAMPCRAAuthenticator.h"

// Constructor to initialize the secret
WAMPCRAAuthenticator::WAMPCRAAuthenticator(const String& secret) {
    this->secret = secret;
}

// Function to compute HMAC-SHA256
String WAMPCRAAuthenticator::signChallenge(const String& challenge) {
    const size_t key_length = secret.length();
    const size_t challenge_length = challenge.length();
    unsigned char hmac_result[32];  // HMAC-SHA256 generates a 32-byte output

    mbedtls_md_context_t ctx;
    mbedtls_md_type_t md_type = MBEDTLS_MD_SHA256;

    // Initialize the context for HMAC
    mbedtls_md_init(&ctx);
    mbedtls_md_setup(&ctx, mbedtls_md_info_from_type(md_type), 1);
    mbedtls_md_hmac_starts(&ctx, (const unsigned char*)secret.c_str(), key_length);
    mbedtls_md_hmac_update(&ctx, (const unsigned char*)challenge.c_str(), challenge_length);
    mbedtls_md_hmac_finish(&ctx, hmac_result);
    mbedtls_md_free(&ctx);

    // Convert the result into a hex string
    String hmac_hex_str = "";
    for (int i = 0; i < 32; i++) {
        char hex[3];
        sprintf(hex, "%02x", hmac_result[i]);
        hmac_hex_str += hex;
    }

    return hmac_hex_str;  // Return the hex string
}

Example Usage

WAMPCRAAuthenticator.ino

#include <Arduino.h>
#include "WAMPCRAAuthenticator.h"

// Define the secret
const String secret = "662844e29567480a1c7e37cad65dc10161f6490793109adfea1bf02afec1fa91";

WAMPCRAAuthenticator authenticator(secret);

void setup() {
    Serial.begin(115200);
    Serial.println("Setup started");
}

void loop() {
    delay(500);

    String challenge = "2KWqh/ScQM3L1apZGBPmg==";
    String signed_challenge = authenticator.signChallenge(challenge);

    Serial.println("Signed Challenge: " + signed_challenge);
}

Usage Instructions

Create the Class Files:

Create two files in your Arduino project: WAMPCRAAuthenticator.h and WAMPCRAAuthenticator.cpp.
Paste the class definitions into these files.
Include the Class:

In your main sketch (WAMPCRAAuthenticator.ino), include the class by adding #include "WAMPCRAAuthenticator.h".

Upload the Sketch:

Upload the sketch to your Arduino board, and it will compute and print the signed challenge in hexadecimal format.

[muzzammilshahid]

The code works as expected. I have tested it using wampproto cli. However, instead of passing the secret to the constructor, we should pass it to the function, as we do in our other projects(example) and few other adjustments also needed in code.