dh

dh.c

+/* A simple client program for server.c
+
+   To compile: gcc client.c -o client
+
+   To run: start the server, then the client */
+#include <stdbool.h>
+
+#include <sys/types.h>
+
+#include <sys/socket.h>
+
+#include <netinet/in.h>
+
+#include <unistd.h>
+
+#include <arpa/inet.h>
+
+#include <netdb.h>
+
+#include <unistd.h>
+
+#include <signal.h>
+
+#include <stdio.h>
+
+#include <string.h>
+
+#include <fcntl.h>
+
+#include <errno.h>
+
+#include <sys/time.h>
+
+#include <stdlib.h>
+
+#include <memory.h>
+
+#include <ifaddrs.h>
+
+#include <net/if.h>
+
+#include <stdarg.h>
+
+// https://www.techiedelight.com/c-program-demonstrate-diffie-hellman-algorithm/
+
+int compute(int g, int b, int p) {
+  int r;
+  int y = 1;
+
+  while (b > 0) {
+    r = b % 2;
+
+    // fgst exponention
+    if (r == 1)
+      y = (y * g) % p;
+    g = g * g % p;
+
+    b = b / 2;
+  }
+
+  return y;
+}
+
+int main(int argc, char ** argv) {
+  int sockfd, portno, n, b, f;
+  struct sockaddr_in serv_addr;
+  struct hostent * server;
+  portno = 7800;
+  char buffer[256];
+
+  b = atoi(argv[1]);
+
+  bzero((char * ) & serv_addr, sizeof(serv_addr));
+  /* Translate host name into peer's IP address ;
+   * This is name translation service by the operating system
+   */
+  server = gethostbyname("172.26.37.44");
+
+  if (server == NULL) {
+    fprintf(stderr, "ERROR, no such host\n");
+    exit(0);
+  }
+
+  /* Building data structures for socket */
+
+  bzero((char * ) & serv_addr, sizeof(serv_addr));
+
+  serv_addr.sin_family = AF_INET;
+
+  bcopy(server->h_addr_list[0], (char *)&serv_addr.sin_addr.s_addr, server->h_length);
+
+  serv_addr.sin_port = htons(portno);
+
+  /* Create TCP socket -- active open
+   * Preliminary steps: Setup: creation of active open socket
+   */
+
+  sockfd = socket(AF_INET, SOCK_STREAM, 0);
+
+  if (sockfd < 0) {
+    perror("ERROR opening socket");
+    exit(0);
+  } else {
+    printf("Socket connection successful\n");
+  }
+
+  if (connect(sockfd, (struct sockaddr * ) & serv_addr, sizeof(serv_addr)) < 0) {
+    perror("ERROR");
+    exit(0);
+  }
+
+  bool protocol = true;
+  char * message_phase[] = {
+    "send_username",
+    "send_gb_mod_p",
+    "send_ga_mod_p",
+    "success",
+    "end"
+  };
+  char * current_phase = "send_username";
+
+  printf("Send Usename");
+  char * username = "achattaraj\n";
+  bzero(buffer, 256);
+  sprintf(buffer, username);
+  n = write(sockfd, buffer, strlen(buffer));
+  current_phase = message_phase[1];
+
+  printf("send gb mod p \n");
+  bzero(buffer, 256);
+  b = compute(15, atoi(argv[1]), 97);
+  sprintf(buffer, "%d\n", b);
+  n = write(sockfd, buffer, strlen(buffer));
+  current_phase = message_phase[2];
+
+  printf("send ga mod p \n");
+  bzero(buffer, 256);
+  n = read(sockfd, buffer, 255);
+  int a = atoi(buffer);
+  bzero(buffer, 256);
+  a = compute(a, atoi(argv[1]), 97);
+  sprintf(buffer, "%d\n", a);
+  n = write(sockfd, buffer, strlen(buffer));
+
+  n = 0;
+  while (strstr(buffer, "Success") == NULL) {
+    n = read(sockfd, buffer, 255);
+
+    current_phase = "end";
+    buffer[n] = 0;
+    printf("%s\n", buffer);
+
+    close(sockfd);
+    return 0;
+
+  }
+}