diff --git a/Dockerfile b/Dockerfile
index 06e3a27..cc1a3d6 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -4,6 +4,7 @@ RUN apt-get update
 RUN apt-get install -y \
 	android-tools-adb \
 	android-tools-fastboot
+RUN pip3 install protobuf
 COPY . /magisk
 WORKDIR /magisk
 CMD bash reinstall-magisk-on-lineageos
diff --git a/reinstall-magisk-on-lineageos b/reinstall-magisk-on-lineageos
index dc6f563..085fc40 100755
--- a/reinstall-magisk-on-lineageos
+++ b/reinstall-magisk-on-lineageos
@@ -45,6 +45,15 @@ get_build_url() {
         head -1
 }
 
+check_exists_latest_lineageos_build() {
+    # The --location lets curl follow the redirection.
+    curl --location "$(get_build_url)?sha256" --output /tmp/lineageos.sha256
+    hash1=$( awk '{print $1}' lineageos.sha256 )
+    hash2=$( sha256sum lineageos.zip | awk '{print $1}' )
+    [[ "$hash1" =~ "$hash2" ]]
+    return
+}
+
 download_latest_lineageos_build() {
     # The --location lets curl follow the redirection.
     curl --location "$(get_build_url)" --output /tmp/lineageos.zip
@@ -66,10 +75,6 @@ extract_boot_image_from_file_based_ota() {
     exit 1
 }
 
-install_python_protobuf() {
-    sudo python3 -m pip install protobuf
-}
-
 extract_payload_from_payload_based_ota() {
     unzip -od /tmp /tmp/lineageos.zip payload.bin
 }
@@ -79,11 +84,10 @@ generate_random_alnum_string_of_length_6() {
 }
 
 extract_boot_image_from_payload_file() {
-    install_python_protobuf
     # For cases in which the repo has already been cloned, I prefer to create a random directory name to clone into, instead of deleting any file or directory on the user's machine.
     scripts_directory_name="scripts_$(generate_random_alnum_string_of_length_6)"
     git clone https://github.com/LineageOS/scripts /tmp/$scripts_directory_name
-    python /tmp/$scripts_directory_name/update-payload-extractor/extract.py --partitions boot --output_dir /tmp/ /tmp/payload.bin
+    python3 /tmp/$scripts_directory_name/update-payload-extractor/extract.py --partitions boot --output_dir /tmp/ /tmp/payload.bin
 }
 
 extract_boot_image_from_payload_based_ota() {
@@ -142,8 +146,22 @@ reboot_phone() {
     fastboot -s "$PHONE_ADB_SERIAL_NUMBER" reboot
 }
 
-check_magisk_folder() {
-    adb -s "$PHONE_ADB_SERIAL_NUMBER" shell ls /data/adb/magisk/
+check_magisk_app() {
+    magisk_package_name="com.topjohnwu.magisk"
+    magisk_package_name_count=$(adb -s "$PHONE_ADB_SERIAL_NUMBER" shell pm list packages "$magisk_package_name" | wc -l)
+    if [ "${magisk_package_name_count}" -eq 1 ]
+    then
+        print_message " [OK] Magisk app seems to be installed on selected phone"
+    elif [ "${magisk_package_name_count}" -eq 0 ]
+    then
+        print_message " [ERROR] Magisk app seems not installed on selected phone. Exiting."
+        exit -1
+    else
+        print_message " [ERROR] More than one Magisk app entry is present:"
+        adb -s "$PHONE_ADB_SERIAL_NUMBER" shell pm list packages "$magisk_package_name"
+        print_message "Exiting."
+        exit -1
+    fi
 }
 
 is_rooted_debugging_enabled() {
@@ -155,10 +173,14 @@ main() {
     check_phone_is_connected
     print_message "Checking on phone if rooted debugging is enabled"
     is_rooted_debugging_enabled
-    print_message "Checking on phone if Magisk folder is present listing /data/adb/magisk/"
-    check_magisk_folder
-    print_message "Downloading build archive from $(get_build_url)"
-    download_latest_lineageos_build
+    print_message "Checking on phone if Magisk is installed"
+    check_magisk_app
+    if check_exists_latest_lineageos_build; then
+        print_message "Build archive already exists, skipping download"
+    else
+        print_message "Downloading build archive from $(get_build_url)"
+        download_latest_lineageos_build
+    fi
     print_message "Extracting 'boot.img' from build archive in /tmp/boot.img"
     extract_boot_image
     print_message "Copying from PC to phone the boot image in /sdcard/Download/boot.img"