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112 lines
3.5 KiB
112 lines
3.5 KiB
#!/bin/bash
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# Copyright 2018 B. Persson, Bjorn@Rombobeorn.se
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#
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# This material is provided as is, with absolutely no warranty expressed
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# or implied. Any use is at your own risk.
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#
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# Permission is hereby granted to use or copy this shellscript
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# for any purpose, provided the above notices are retained on all copies.
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# Permission to modify the code and to distribute modified code is granted,
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# provided the above notices are retained, and a notice that the code was
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# modified is included with the above copyright notice.
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function print_help {
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cat <<'EOF'
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Usage: gpgverify --keyring=<pathname> --signature=<pathname> --data=<pathname>
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gpgverify is a wrapper around gpgv designed for easy and safe scripting. It
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verifies a file against a detached OpenPGP signature and a keyring. The keyring
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shall contain all the keys that are trusted to certify the authenticity of the
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file, and must not contain any untrusted keys.
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The differences, compared to invoking gpgv directly, are that gpgverify accepts
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the keyring in either ASCII-armored or unarmored form, and that it will not
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accidentally use a default keyring in addition to the specified one.
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Parameters:
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--keyring=<pathname> keyring with all the trusted keys and no others
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--signature=<pathname> detached signature to verify
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--data=<pathname> file to verify against the signature
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EOF
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}
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fatal_error() {
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message="$1" # an error message
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status=$2 # a number to use as the exit code
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echo "gpgverify: $message" >&2
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exit $status
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}
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require_parameter() {
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term="$1" # a term for a required parameter
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value="$2" # Complain and terminate if this value is empty.
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if test -z "${value}" ; then
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fatal_error "No ${term} was provided." 2
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fi
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}
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check_status() {
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action="$1" # a string that describes the action that was attempted
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status=$2 # the exit code of the command
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if test $status -ne 0 ; then
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fatal_error "$action failed." $status
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fi
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}
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# Parse the command line.
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keyring=
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signature=
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data=
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for parameter in "$@" ; do
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case "${parameter}" in
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(--help)
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print_help
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exit
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;;
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(--keyring=*)
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keyring="${parameter#*=}"
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;;
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(--signature=*)
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signature="${parameter#*=}"
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;;
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(--data=*)
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data="${parameter#*=}"
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;;
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(*)
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fatal_error "Unknown parameter: \"${parameter}\"" 2
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;;
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esac
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done
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require_parameter 'keyring' "${keyring}"
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require_parameter 'signature' "${signature}"
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require_parameter 'data file' "${data}"
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# Make a temporary working directory.
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workdir="$(mktemp --directory)"
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check_status 'Making a temporary directory' $?
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workring="${workdir}/keyring.gpg"
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# Decode any ASCII armor on the keyring. This is harmless if the keyring isn't
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# ASCII-armored.
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gpg2 --homedir="${workdir}" --yes --output="${workring}" --dearmor "${keyring}"
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check_status 'Decoding the keyring' $?
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# Verify the signature using the decoded keyring.
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gpgv2 --homedir="${workdir}" --keyring="${workring}" "${signature}" "${data}"
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check_status 'Signature verification' $?
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# (--homedir isn't actually necessary. --dearmor processes only the input file,
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# and if --keyring is used and contains a slash, then gpgv2 uses only that
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# keyring. Thus neither command will look for a default keyring, but --homedir
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# makes extra double sure that no default keyring will be touched in case
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# another version of GPG works differently.)
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# Clean up. (This is not done in case of an error that may need inspection.)
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rm --recursive --force ${workdir}
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