debsig-verify - Verify signatures for a Debian format package
debsig-verify [option...] deb
This program is part of a security model that verifies the source and validity of a Debian format package (commonly referred 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.
- Information about the origin of this policy.
- Rules used to decide if this policy is pertinent to this deb's verification.
- Rules that are used to actually verify the deb.
The policy files will reference OpenPGP keyrings by a filename. These OpenPGP keyrings will be looked for in a subdirectory of the OpenPGP 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, --quiet
- 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, --verbose
- 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, --debug
- Outputs even more info than the -v option. This is mainly for debugging.
- Outputs the usage information for the program.
- Outputs the version information for the program. This includes the policy format version. This option does not require any other arguments.
- 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 policy
- 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 specify 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.
- --policies-dir directory
- Use a different directory when looking up for policies.
- --keyrings-dir directory
- Use a different directory when looking up for OpenPGP keyrings.
- --root directory
- Use a different root directory when looking up for policies and OpenPGP keyrings.
- The requested operation completed successfully.
- General non-success exit value. This occurs for non-verification operations.
- Either no signatures are contained in the deb or no origin signature was found.
- An origin signature was found, but it does not have a corresponding subdirectory in the policies directory.
- The origin was found, and is present. However, no policies were found that passed the selection phase of the process. Thus, no verification was performed.
- The package failed the verification phase of the process. More than likely, this occurs due to a bad signature, or because not all criteria of the verification block of the policy were passed.
- An internal error occurred. This is an unrecoverable error. Either the deb is corrupt, the OpenPGP backend failed abnormally, or some other uncontrollable failure.
- The name (or pathname) of the GnuPG program to use.
- Directory containing the policy (.pol) definitions.
- XML format policy files.
- Directory containing the OpenPGP keyrings (*.pgp) that coincide with the policies.
- OpenPGP format keyrings for use by the policies. Note: The .gpg extensions are the legacy names used due to the prevalence of one of the OpenPGP implementation. These keyrings must be in OpenPGP keyring format, and not some tool specific format (such as GnuPG keybox databases).