clearsign - Signs a single file using GnuPG (gpg)

#!/bin/bash
#
# clearsign - Signs a single file using GnuPG (gpg)
# in clearsign mode (non-detached, ASCII-armored)
# Uses zenity for GUI. Nautilus-scripts compatible.
#
#    Copyright (C) 2011 Rodrigo Silva - <[email protected]>
#
#    This program is free software: you can redistribute it and/or modify
#    it under the terms of the GNU General Public License as published by
#    the Free Software Foundation, either version 3 of the License, or
#    (at your option) any later version.
#
#    This program is distributed in the hope that it will be useful,
#    but WITHOUT ANY WARRANTY; without even the implied warranty of
#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#    GNU General Public License for more details.
#
#    You should have received a copy of the GNU General Public License
#    along with this program.  If not, see <http://www.gnu.org/licenses/>.
#
# Huge thanks to all the gurus and friends in <irc://irc.freenet.org/#bash>
# and the contributors of <http://mywiki.wooledge.org/>
#
# Usage: clearsign FILE
#
# TODO: add more output options:
#        Detached binary (file.ext.sig) - "gpg --detach-sign"
#        Detached text   (file.ext.asc) - "gpg --detach-sign --armor"
#    Non-Detached binary (file.ext.gpg) - "gpg --sign"
#    Non-Detached binary-to-text (file.ext.asc) - "gpg --sign --armor"
#
# TODO: add help, usage, verbose, debug, force, etc
# TODO: test if zenity and gpg avaliable
# TODO: allow multiple files and directories
# TODO: update common lib and use it
# TODO: read (and pre-select) default key from searhorse
# TODO: use proper icon
# FIXME: gnupg creates blank dir.asc if file is actually a dir


# User input
FILE="$1"            # globs not allowed.. for now
OUTPUT="${FILE}.asc" # user may only change if already exists

# Constants
SELF="${0##*/}"
SELF_GUI="Sign file"
WIDTH_MAX=790
WIDTH_BASE=250
WIDTH_UNIT=8    #char

HEIGHT_MAX=600
HEIGHT_BASE=130
HEIGHT_UNIT=25  #line

# Variables
max_chars=0
window_width=0
window_height=0


# Functions

fatal() { : ; }

fatalgui()
{
    local message="$1"
    local errorcode="${2:-1}"
    local dump="$3"

    [[ -n "$dump"    ]] && echo "$dump" >&2
    [[ -n "$message" ]] && echo "$SELF: ${message/%['!''.'':']/}" >&2

    zenity --error --title="$SELF_GUI" \
           --text="${message:+$message\n\n}${dump:+$dump\n\n}" #"Exiting with error code ${errorcode}"

    exit $errorcode
}

min() { (( $1 < $2 )) && printf %d "$1" || printf %d "$2"; }
max() { (( $1 > $2 )) && printf %d "$1" || printf %d "$2"; }


# =========================================== MAIN

# Check input file
[[ -r "$FILE" ]] || fatalgui "File to sign is missing or is not readable."

# Check more than 1 file
[[ $# = 1 ]] || {
    zenity --question --title="Multiple files" \
        --text="Multiple files were selected, but only this will be signed:\n\n${FILE}\n\nProceed?" \
    || exit 0
}

# Grab the list of keys
keys=$(
    gpg --list-keys --with-colons --keyid-format short 2>&1
) || fatalgui "Error when retrieving list of keys:" $? "$keys"

# Empy array to hold the keys
array=()

# Loop the list
while IFS=":" read -r -s keyType _ keySize _ keyId keyDate _ _ _ keyUser _ keyFlags _ ; do

    # Check for (pub)lic keys that are able to (s)ign and are not (D)isabled
    if [[ "$keyType" = "pub" && "$keyFlags" = *s* && ! "$keyFlags" = *D* ]] ; then

        # populate the array
        array+=("$keyId" "$keyUser" "${keyId:(-8)}" "$keyDate" "$keySize")

        # Save the number of chars of the longest user string
        (( ${#keyUser} > $max_chars )) && max_chars=${#keyUser}

        #DEBUG echo "$keyType|$keySize|${keyId:(-8)}|$keyDate|${#keyUser}|$max_chars|$keyUser"
    fi

done <<< "$keys"

# Check if suitable keys were found
[[ ${#array[@]} = 0 ]] && fatalgui "No suitable keys for signing were found."

# Set window height and weight
window_width=$(  min  $WIDTH_MAX $(( $WIDTH_BASE +  $WIDTH_UNIT * $max_chars    )) )
window_height=$( min $HEIGHT_MAX $(($HEIGHT_BASE + $HEIGHT_UNIT * ${#array[@]}/5)) )

# Choose key
key=$(
    zenity --list --title="Choose Signer" --text="Sign file as:" --hide-column=1        \
           --width=$window_width --height=$window_height                                \
           --window-icon="/usr/share/pixmaps/seahorse-plugins/22x22/seahorse-key.png"   \
           --column="id" --column="User" --column="Key" --column="Date" --column="Size" \
           "${array[@]}"
) || exit 0


# default output already exists?
[[ -f "$OUTPUT" ]] && {

    # prompt for another output file
    OUTPUT=$(
        zenity --file-selection --save --filename="$OUTPUT"                               \
               --window-icon="/usr/share/pixmaps/seahorse-plugins/22x22/seahorse-key.png" \
               --title="Choose Signed File Name for ${FILE##*/}"                          \
               --confirm-overwrite --file-filter "*.asc"
    ) || exit 0
}


# Do it! :D
dump=$(
    gpg --clearsign --batch --yes --default-key="$key" --output="$OUTPUT" "$FILE" 2>&1
) || fatalgui "Error when signing $FILE:" $? "$dump"


exit 0