To ensure that only trusted packages are installed, Kali Linux uses GPG (GNU Privacy Guard) for package signing. This allows developers to sign their packages using a private key, which can be verified by anyone who has access to the corresponding public key. Here’s how you can download and verify signed packages in Kali Linux:
1. First, make sure that your system is configured with GPG keys. You can do this by running the following command:
# This line updates the list of available packages and their versions from the repositories.
apt-get update
# This line installs the gnupg package, which is necessary for verifying signed packages.
apt-get install gnupg
2. Next, add the official Kali Linux signing key to your system’s trusted list using the following command:
# Downloads the Kali Linux signing key from the specified URL and saves it as "archive-key.asc"
wget -q https://archive.kali.org/archive-key.asc
# Adds the downloaded key to the system's list of trusted keys using the "apt-key" command with the "add" option
sudo apt-key add archive-key.asc
3. Now, you can download and install packages from Kali Linux’s official repositories using the `apt` command. For example:
# This script updates the package list and upgrades the nmap package from Kali Linux's official repositories using the `apt` command.
# Update the package list using `apt update` command
sudo apt update
# Upgrade the nmap package using `apt upgrade` command
sudo apt upgrade nmap
4. To verify that a package has been signed by an authorized developer, use the following command:
# This script is used to verify if a package has been signed by an authorized developer.
# It uses the apt-get download command to download the specified package and then uses gpg to verify the signature.
# The sudo command is used to run the following command as a superuser, allowing for necessary permissions.
sudo apt-get download <package_name> | gpg --verify -a
# The apt-get download command downloads the specified package.
# The | symbol is used to pipe the output of the previous command to the next command.
# The gpg command is used to verify the signature of the downloaded package.
# The --verify flag tells gpg to verify the signature.
# The -a flag tells gpg to use ASCII armor format for the signature.
# This ensures that the signature can be read and verified by gpg.
5. This will display information about the signature and whether it is valid or not. If everything looks good, you can proceed with installing the package using `sudo apt-get install`.
6. To view a list of all signed packages in Kali Linux’s official repositories, use the following command:
# This script checks the validity of a package signature and retrieves the package version number.
# It is intended to be used in Kali Linux's official repositories.
# The first command uses apt-cache to display information about the specified package.
# The output is then piped to grep to search for the line containing the word 'Candidate'.
# The output of grep is then piped to awk to print the second column, which contains the package version number.
# Finally, the output is piped to cut to extract the version number from the third field, delimited by '/'.
sudo apt-cache policy <package_name> | grep 'Candidate' | awk '{print $2}' | cut -d '/' -f 3
7. This will display the version number and signature status of the package. If it says “OK” next to the signature, then you can trust that the package has not been tampered with during distribution.
By following these steps, you can ensure that only trusted packages are installed on your Kali Linux system, which helps protect against malware and other security threats.