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 (where <rpm-file> is the file name of the RPM package): 

rpm -K --nosignature <rpm-file>

The message <rpm-file>: md5 OK is displayed. This brief message means that the file was not corrupted by the download. To see a more verbose message, replace -K with -Kvv in the command.

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 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 installation, GnuPG is installed by default. That way you can immediately start using GnuPG to verify any packages that you receive from CentOS. Before doing so, you must first import CentOS's public key.

Importing Keys

To verify CentOS packages, you must import the CentOS GPG key. To do so, execute the following command at a shell prompt: 

rpm --import /etc/pki/rpm-gpg/RPM-GPG-KEY-redhat-release

To display a list of all keys installed for RPM verification, execute the command: 

rpm -qa gpg-pubkey*

For the CentOS key, the output includes: 

gpg-pubkey-37017186-45761324

To display details about a specific key, use rpm -qi followed by the output from the previous command: 

rpm -qi gpg-pubkey-37017186-45761324

Verifying Signature of Packages

To check the GnuPG signature of an RPM file after importing the builder's GnuPG key, use the following command (replace <rpm-file> with the filename of the RPM package): 

rpm -K <rpm-file>

If all goes well, the following message is displayed: md5 gpg OK. This means that the signature of the package has been verified, and that it is not corrupt.