The package vendor list contains a list of all vendors from whom you wish to authenticate downloaded packages. For each vendor listed, it must contain the corresponding PGP key fingerprint, so that APT can perform signature verification of the release file and subsequent checking of the checksums of each downloaded package. To have authentication enabled, you must add the vendor identification string (see below) enclosed in square braces to the sources.list line for all sites that mirror the repository provided by that vendor.
The format of this file is similar to the one used by apt.conf. It consists of an arbitrary number of blocks of vendors, where each block starts with a string telling the key_type and the vendor_id.
Some vendors may have multiple blocks that define different security policies for their distributions. Debian for instance uses a different signing methodology for stable and unstable releases.
key_type is the type of the check required. Currently, there is only one type available which is simple-key.
vendor_id is the vendor identification string. It is an arbitrary string you must supply to uniquely identifify a vendor that's listed in this file. Example:
This type of verification is used when the vendor has a single secured key that must be used to sign the Release file. The following items should be present
The PGP fingerprint for the key. The fingerprint should be expressed in the standard notion with or without spaces. The --fingerprint option for gpg(1) will show the fingerprint for the selected keys(s).