convert_debian_to_kali.sh

#!/usr/bin/env bash
set -euo pipefail

export DEBIAN_FRONTEND=noninteractive

### Function to create a default user
create_default_user() {
  local password password_confirm password_hash

  # Check if user exists
  if id "kali" &>/dev/null; then
    echo "User 'kali' already exists. Skipping creation."
    return
  fi

  while true; do
    read -s -r -p "Provide the password for default username (kali): " password
    echo
    read -s -r -p "Confirm the password: " password_confirm
    echo
    if [[ "$password" != "$password_confirm" ]]; then
      echo "Error: Passwords do not match."
      continue
    fi
    if [[ ${#password} -lt 8 || ! "$password" =~ [A-Z] || ! "$password" =~ [a-z] || ! "$password" =~ [0-9] ]]; then
      echo "Error: Password must be at least 8 characters long and contain at least one digit, one uppercase letter, and one lowercase letter."
      continue
    fi
    break
  done

  password_hash=$(openssl passwd -6 "$password")
  sudo useradd --create-home --home "/home/kali" --password "$password_hash" --shell "/bin/bash" --groups sudo kali
  echo "User 'kali' created and added to sudo group."
}

### Function to install necessary packages
install_packages() {
  local packages=(
    tzdata debconf-utils keyboard-configuration
    libncurses5-dev libncursesw5-dev wget gnupg dirmngr
    software-properties-common busybox xrdp lightdm
    bash-completion task-xfce-desktop
  )
  sudo apt update
  sudo apt install -y --no-install-recommends "${packages[@]}"
}

### Function to configure Kali Linux repositories
configure_kali_repos() {
  # Backup existing sources.list
  if [ -f /etc/apt/sources.list ]; then
    sudo mv /etc/apt/sources.list /etc/apt/sources.list.bak
  fi

  # Write official Kali repository
  echo "deb http://http.kali.org/kali kali-rolling main non-free contrib" | sudo tee /etc/apt/sources.list
  echo "deb-src http://http.kali.org/kali kali-rolling main non-free contrib" | sudo tee -a /etc/apt/sources.list

  sudo apt update
}

### Function to install Kali Linux base packages
install_kali_packages() {
  sudo apt install -y libc6
  sudo apt dist-upgrade -y --fix-broken
  sudo apt install -y kali-linux-default kali-desktop-core kali-desktop-xfce spice-vdagent
}

### Function to clean up
clean_up() {
  sudo apt autoremove -y --purge
  sudo apt clean
  echo "Setup completed successfully."
}

### Main script execution
create_default_user
install_packages
configure_kali_repos
install_kali_packages
clean_up

Improving user creation by using openssl to generate a random salt and the password hash, as openssl is typically preinstalled.