I’m trying to implement a virtual UART using socat command for send and receive a string that is encrypted using XOR cipher on sending and decrpyted while receiving using c program.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <termios.h>

#define BUFFER_SIZE 256
#define UART_DEVICE_TX "./ttyV0"  // Transmit end
#define UART_DEVICE_RX "./ttyV1"  // Receive end

// XOR cipher for encryption and decryption
void xor_cipher(char *data, size_t length, char key) {
    for (size_t i = 0; i < length; ++i) {
        data[i] ^= key;
    }
}

// Configure the UART device
int configure_uart(const char *device) {
    int uart_fd = open(device, O_RDWR | O_NOCTTY);
    if (uart_fd < 0) {
        perror("Failed to open UART device");
        return -1;
    }

    struct termios options;
    tcgetattr(uart_fd, &options);

    // Set baud rate to 9600, 8 data bits, no parity, 1 stop bit
    cfsetispeed(&options, B9600);
    cfsetospeed(&options, B9600);
    options.c_cflag = (options.c_cflag & ~CSIZE) | CS8;  // 8 data bits
    options.c_cflag |= (CLOCAL | CREAD);                 // Enable receiver
    options.c_cflag &= ~(PARENB | CSTOPB);               // No parity, 1 stop bit
    options.c_iflag &= ~(IXON | IXOFF | IXANY);          // Disable flow control
    options.c_lflag = 0;                                 // Raw input mode
    options.c_oflag = 0;                                 // Raw output mode

    tcsetattr(uart_fd, TCSANOW, &options);
    return uart_fd;
}

int main() {
    const char key = 0x5A;          // XOR encryption key
    char original_message[] = "Hello, UART!";  // Original message
    char encrypted_message[BUFFER_SIZE];
    char received_message[BUFFER_SIZE];

    printf("Original message: %sn", original_message);

    // Copy the original message and encrypt it
    strcpy(encrypted_message, original_message);
    xor_cipher(encrypted_message, strlen(encrypted_message), key);

    // Configure UART devices
    int uart_fd_tx = configure_uart(UART_DEVICE_TX);  // Transmit end
    int uart_fd_rx = configure_uart(UART_DEVICE_RX);  // Receive end
    if (uart_fd_tx < 0 || uart_fd_rx < 0) {
        return EXIT_FAILURE;
    }

    // Send the encrypted message to the TX port (master)
    write(uart_fd_tx, encrypted_message, strlen(encrypted_message));
    printf("Encrypted message sent: %sn", encrypted_message);

    // Receive the encrypted message from the RX port (slave)
    memset(received_message, 0, BUFFER_SIZE);
    int bytes_read = read(uart_fd_rx, received_message, BUFFER_SIZE - 1);
    if (bytes_read < 0) {
        perror("Failed to read from UART device");
        close(uart_fd_tx);
        close(uart_fd_rx);
        return EXIT_FAILURE;
    }

    // Decrypt the received message
    xor_cipher(received_message, bytes_read, key);
    printf("Decrypted message: %sn", received_message);

    // Check if the original and decrypted messages match
    if (strcmp(original_message, received_message) == 0) {
        printf("Decryption successful: Messages match.n");
    } else {
        printf("Decryption failed: Messages do not match.n");
    }

    // Clean up
    close(uart_fd_tx);
    close(uart_fd_rx);
    return EXIT_SUCCESS;
}

for creating virtual uart driver in the working directory i used this command:
socat -d -d PTY,link=./ttyV0,raw,echo=0 PTY,link=./ttyV1,raw,echo=0

after compilation and running the c file the encryption parting running and iam getting the encrypted data on tty1(cat ./ttyV1)

but the decryption part is not working.. i need help to figure this out.

when i tried without looking on the devices its working fine

Original message: Hello, UART!

Encrypted message sent: ?665vz

Encrypted message received: ?665vz

Decrypted message: Hello, UART!

Decryption successful: Messages match.

when i start cat ./ttyV1 in one terminal and run the program it will display like this

Original message: Hello, UART!

Encrypted message sent: ?665vz

not doing the decryption part

but the key can be seen in the other terminal that runs cat ./ttyV1

why this happening?