receiver.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "common.h"
#include "ipc.h"
#include "encryption.h"
#include "integrity.h"
#include "keygen.h"

int main() {
    int shmid, semid;
    struct shared_data *data;
    uint8_t ciphertext[MAX_MESSAGE_SIZE];
    uint8_t plaintext[MAX_MESSAGE_SIZE];
    char master_key[MASTER_KEY_LEN + 1];
    char enc_key[DERIVED_KEY_LEN + 1];
    char hash_key[DERIVED_KEY_LEN + 1];
    unsigned char computed_hash[HASH_SIZE];
    char computed_hash_hex[HASH_SIZE * 2 + 1];

    printf("=== RECEIVER: Secure Message Reception ===\n\n");

    // Get master key from user
    printf("Enter master key: ");
    fgets(master_key, sizeof(master_key), stdin);
    master_key[strcspn(master_key, "\n")] = 0;  // Remove newline

    // Pad or truncate to exact length
    int key_len = strlen(master_key);
    if (key_len < MASTER_KEY_LEN) {
        // Pad with zeros if too short
        for (int i = key_len; i < MASTER_KEY_LEN; i++) {
            master_key[i] = '0';
        }
        master_key[MASTER_KEY_LEN] = '\0';
    } else if (key_len > MASTER_KEY_LEN) {
        // Truncate if too long
        master_key[MASTER_KEY_LEN] = '\0';
    }

    // Derive encryption and hashing keys from master key
    derive_keys(master_key, enc_key, hash_key);

    printf("Key received! Listening for incoming messages...\n");
    printf("\n--- Backend Key Information ---\n");
    printf("Encryption Key: %s\n", enc_key);
    printf("Hash Key: %s\n", hash_key);
    printf("-------------------------------\n\n");

    // Attach to shared memory and semaphore
    shmid = create_shared_memory();
    semid = create_semaphore();
    data = attach_shared_memory(shmid);

    printf("Waiting for message...\n");

    // Wait for data to be ready
    while (data->ready == 0) {
        sleep(1);
    }

    // Lock semaphore
    semaphore_wait(semid);

    // Read encrypted data
    int len = data->message_length;
    memcpy(ciphertext, data->message, len);
    ciphertext[len] = '\0';

    // Display received encrypted text
    printf("\n--- Received Encrypted Text (Hex) ---\n");
    printf("Ciphertext: ");
    for (int i = 0; i < len; i++) {
        printf("%02x", ciphertext[i]);
    }
    printf("\n-------------------------------------\n");

    // Verify integrity
    key_mixed_rolling_hash((char*)ciphertext, len, hash_key, computed_hash, HASH_SIZE);
    to_hex(computed_hash, HASH_SIZE, computed_hash_hex);

    printf("\n--- Hash Verification ---\n");
    printf("Received Hash:  %s\n", data->hash);
    printf("Computed Hash:  %s\n", computed_hash_hex);
    printf("Match: %s\n", (strcmp(data->hash, computed_hash_hex) == 0) ? "YES" : "NO");
    printf("------------------------\n");

    if (strcmp(data->hash, computed_hash_hex) == 0) {
        // Integrity check passed - decrypt and display message
        hybrid_decrypt(ciphertext, plaintext, len, (uint8_t*)enc_key, strlen(enc_key));
        plaintext[len] = '\0';

        printf("\n--- Decrypted Text ---\n");
        printf("Plaintext: %s\n", plaintext);
        printf("----------------------\n");

        printf("\nWow! You got your text:\n");
        printf(">>> %s <<<\n", plaintext);
    } else {
        // Integrity check failed
        printf("\nOops! Sorry, the text was tampered or the key entered is wrong!\n");
    }

    // Mark as consumed
    data->ready = 0;

    // Unlock semaphore
    semaphore_signal(semid);

    // Cleanup
    detach_shared_memory(data);

    printf("\n=== RECEIVER: Reception Complete ===\n");

    return 0;
}