debsig-verify - Verify signatures for a Debian format package

debsig-verify [options] <deb>

This program is part of a security model that verifies the source and validity of a Debian format package (commonly refered to as a deb).

This program implements the verification specs defined in the document, "Package Verification with dpkg: Implementation", which is a more complete reference for the verification procedure.

The program generally takes one argument, the deb file to be verified. It will then check the origin signature of the deb, find its Public Key ID (long format), and use that as the name for a policy subdirectory. If this subdirectory does not exist, then the verification fails immediately.

In this subdirectory, the program finds one or more files named with the .pol file extension, which signifies an XML format policy definition. This file contains three main parts.

Origin

Information about the origin of this policy.

Selection

Rules used to decide if this policy is pertinent to this deb's verification.

Verification

Rules that are used to actually verify the deb.

The policy files will reference keyrings by a filename. These keyrings will be looked for in a subdirectory of the keyring directory. The subdirectory has the same name as the policy subdirectory (previously determined by the Origin's Public Key ID).

The program will, after first parsing the entire file, check the Origin ID against the Public Key ID of the origin signature in the deb. If these match (which they should, else something is really wrong), then it will proceed to the Selection rules.

The Selection rules decide whether this policy is suitable for verifying this deb. If these rules fail, then the program will proceed to the next policy. If it passes, then the program commits to using this policy for verification, and no other policies will be referenced.

The last verification step relies on the Verification rules. These are similar in format to the Selection rules, but are usually more constrained. If these rules fail, the program exits with a non-zero status. If they pass, then it exits with a zero status.

-q

Causes the program to send no output, other than fatal errors. This is useful when being called from another program, where you rely on the exit value only.

-v

Causes the program to send more output on execution, so as to follow the steps it is taking while trying to verify the deb.

-d

Outputs even more info than the -v option. This is mainly for debugging.

--version

Outputs the version information for the program. This includes the policy format version. This option does not require any other arguments.

--list-policies

Outputs a list of the policies that passed the Selection phase of the verification process. In other words, those that could potentially verify the deb. The output is one line showing the directory selected by the origin signature, and then a single line for any policy files in that directory that pass the Selection rules. This option will NOT verify the deb.

--use-policy <pol>

This option takes one argument, which is the name of the policy file (as shown by the --list-policies option). Note, this is just a file, and not a full path. You cannot specifiy arbitrary policies. This option is useful if more than one policy applies to potentially verifying the deb. The program will then use this policy, and only this policy, to try and verify the deb.

/etc/debsig/policies/

Directory containing the policy (.pol) definitions.

/etc/debsig/policies/*/*.pol

XML format policy files.

/usr/share/debsig/keyrings/

Directory containing the keyrings that coincide with the policies.

/usr/share/debsig/keyrings/*/*.gpg

GPG format keyrings for use by the policies.

deb(5),

Ben Collins <bcollins@debian.org>