Well Timed Authentication

#include <unistd.h>
#include <time.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <string.h>

void printwelcomemessage();
void generatesessionids();

long authuser();
long passwdauth();
long sessionauth();

void runmyterminal();

void authwait();
void printtime();

const char* users[3] = {"TrueGrit", "root", "guest"};
#define users_len (sizeof (users) / sizeof (const char *))
#define TRUEGRIT 0
#define ROOT 1
#define GUEST 2
long sessionID[users_len];

int main(){
    setbuf(stdin, 0);
    printwelcomemessage();
    generatesessionids();
    while(1){
        int userid = authuser();
        if(userid < 0){
            printf("Could not authenticate. Goodbye.\n");
            exit(0);
        }
        runmyterminal(userid);
    }
}

void generatesessionids(){
    time_t curtime;
    struct tm * timeinfo;
    time(&curtime);
    srand(curtime);
    for(int i = 0; i < users_len; i++){
        sessionID[i] = (rand() ^ rand());
    }
}

void runmyterminal(int userid){
    while(1){
        printf("%s@umbc$ ", users[userid]);
        char command[64];
        memset(&command, 0, 64);
        fgets(command, 64, stdin);

        if(strncmp(command, "help", 4) == 0){
            printf("Available commands: ls, whoami, sid, dog, flag, time\n");
        }else if(strncmp(command, "ls", 2) == 0){
            system("ls");
        }else if(strncmp(command, "whoami", 4) == 0){
            printf("%s\n", users[userid]);
        }else if(strncmp(command, "sid", 3) == 0){
            printf("Session ID: %ld\n", sessionID[userid]);
        }else if(strncmp(command, "dog", 3) == 0){
            system("cat dog.txt");
        }else if(strncmp(command, "flag", 4) == 0){
            if(userid <= 1){
                system("cat flag.txt");
                sleep(2);
                exit(0);
            }else{
                printf("cat: flag.txt: Permission denied\n");
            }
        }else if(strncmp(command, "time", 4) == 0){
            printtime();
        }else if(strncmp(command, "logout", 6) == 0){
            printf("Logging out...\n");
            return;
        }else{
            printf("Unknown command.\nAvailable commands: ls, whoami, sid, dog, flag, time\n");
        }
    }
}

long authuser(){
    printf("(L)ogin normally or use (S)ession id? (L/S): ");
    char loginType = getchar();
    getchar(); // Consume newline

    if(loginType == 'l' || loginType == 'L')
        return passwdauth(); // Login using username and password

    if(loginType == 's' || loginType == 'S')
        return sessionauth(); // Login using session ID

    printf("Invalid option.\n");
    exit(0);
}

void printwelcomemessage(){
    system("cat dog.txt");
    printf("Welcome! Please login!\n");
}

long sessionauth(){
    char session[20];
    printf("Enter session ID: "); // Prompt session ID
    fgets(session, 20, stdin);
    long result = atol(session);
    int uid = -1;
    for(int i = 0; i < users_len; i++){
        if(sessionID[i] == result){
            uid = i;
        }
    }
    authwait();
    return uid;

}

long passwdauth(){
    int uid = -1;
    char username[64];
    char passwd[64];
    printf("login as: "); // Prompt username
    fgets(username, 64, stdin);
    username[strnlen(username, 64)-1] = 0; // null terminate
    if(strncmp(username, "guest", 64) == 0)// Guest doesn't need login
        return GUEST;

    printf("%s's password: ", username); // Prompt password
    fgets(passwd, 64, stdin);

    for(int i = 0; i < users_len; i++){ // Get user id
        if(!strncmp(username, users[i], 64)){
            uid = i;
            break;
        }
    }
    authwait();

    if(uid == -1){
        return -1;
    }

    FILE *fp = fopen("/dev/random", "r");
    if(fp == NULL){
        return -1;
    }
    char* line = NULL;
    size_t len = 64;
    getline(&line, &len, fp);
    if(line == NULL){
        return -1;
    }

    if(strncmp(passwd, line, 64) != 0){
        return -1;
    }else{
        return uid;
    }

}

void authwait(){
    printf("Authenticating");
    fflush(stdout);
    for(int i = 0; i < 3; i++){
        sleep(1);
        printf(".");
        fflush(stdout);
    }
    sleep(1);
    printf("\n");
}

void printtime(){
    time_t t = time(NULL);
    struct tm tm = *localtime(&t);
    printf("Today's date and time is: %d-%d-%d %d:%d:%d\n", tm.tm_year + 1900, tm.tm_mon + 1,tm.tm_mday, tm.tm_hour, tm.tm_min, tm.tm_sec);
}

// compiled under WSL

//  nemo@marshmallow-laptop /mnt/e/Users/xiong/Documents/CPP/vsc-playground ./a.out
// 1586610253
// 2110040916
// 1207701983
// 2003440833

#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <stdbool.h>
#include <time.h>

#define INPUT_BUFFER_LENGTH 256
#define OUTPUT_BUFFER_LENGTH 4096
#define TEMP_BUFFER_LENGTH 64

long sessionID[3] = {0};

void generatesessionids(){
    time_t curtime;
    time(&curtime);
    srand(curtime);
    printf("%ld\n", curtime);
    for(int i = 0; i < 3; i++){
        sessionID[i] = (rand() ^ rand());
    }
}

int main(void)
{
    generatesessionids();
    printf("%ld\n%ld\n%ld", sessionID[0], sessionID[1], sessionID[2]);
    return 0;
}

✘ nemo@marshmallow-laptop  /mnt/c/Users/nemo  nc ctf.umbccd.io 5600
           __
      (___()'`;
      /,    /`
      \\"--\\
          Welcome! Please login!
(L)ogin normally or use (S)ession id? (L/S): L
login as: guest
guest@umbc$ sid
Session ID: 2003440833
guest@umbc$ logout
Logging out...
(L)ogin normally or use (S)ession id? (L/S): S
Enter session ID: 2110040916
Authenticating...
TrueGrit@umbc$ flag
DawgCTF{ps3ud0_r4nd0m_1s_n0t_tru3_r4nd0m}