Checking a Package's Signature
If you wish to verify that a package has not been corrupted or tampered with, examine only the md5sum by typing the following command at a shell prompt (replace coolapp with the filename of your RPM package):
rpm --checksig --nogpg coolapp-1.1-1.rpm |
On the other hand, how trustworthy is the developer who created the package? If the package is signed with the developer's GnuPG key, you'll know that the developer really is who they say they are.
An RPM package can be signed using Gnu Privacy Guard (or GnuPG), to help you make certain your downloaded package is trustworthy.
GnuPG is a tool for secure communication; it is a complete and free replacement for the encryption technology of PGP, an electronic privacy program. With GnuPG, you can authenticate the validity of documents, and encrypt/decrypt data to and from other recipients. GnuPG is capable of decrypting and verifying PGP 5.x files, as well.
During the installation of Red Hat Linux, GnuPG is installed by default. That way you can immediately start using GnuPG to verify any packages that you receive from Red Hat. First, you will need to import Red Hat's public key.
Importing Keys
When you import a public key, you add that key to your keyring (a file in which public and secret keys are kept). Then, when you download a document or file from that entity, you can check the validity of that document against the key you added to your keyring.
To import a key, use the --import option. To demonstrate, download and import Red Hat's public key. That way, any time you want to validate a package from Red Hat, you will be able to check it against the key you retrieved.
You can find Red Hat's key at http://www.redhat.com/about/contact.html. Using
your browser, download the key by pressing the
gpg --import redhat2.asc |
The resulting message tells you that the key was processed. To check that the key was added, type gpg --list-keys. You'll see the key you just downloaded from Red Hat, as well as your own keys.
[newuser@localhost newuser]$ gpg --list-keys /home/newuser/.gnupg/pubring.gpg ----------------------------------------- pub 1024D/DB42A60E 1999-09-23 Red Hat, Inc <security@redhat.com> sub 2048g/961630A2 1999-09-23 |
 | Keys Do Not Have to be Links |
|---|---|
Sometimes, you will not be able to download a key from a link. Keys are text files, so they can be moved to your machine in any way a regular text file can be saved. As long as you know the name and location of the file you saved, you can import it to your keyring. |
Verifying Packages
To check the GnuPG signature of an RPM file after importing the builder's GnuPG key, use the following command (replace coolapp with the filename of your RPM package):
rpm --checksig coolapp-1.1-1.rpm |
More about GnuPG
For more information about GnuPG, see Appendix B.