keys/scripts/verify.sh

#!/bin/sh

# Verify the signed files in this repo against the pinned [S] subkey
#
# Usage:  ./scripts/verify.sh [FILE...]
#
# FILE defaults to KEYS.md OPENPGP.md ceremonies/*.md AGE.md
#
# A FILE with a FILE.asc next to it is checked as a detached signature,
# any other FILE as a clearsigned document
#
# Also checks the key's expiry, and,
# if KEYS.md or AGE.md is among the FILEs,
# that age-recipient.txt matches the recipient in them
#
# Exits non-zero if any file lacks a valid signature from the pinned key,
# or if the key has expired, or if a cross-check fails

set -eu


# Internal [S] subkey; every file must carry a valid signature from this key
SIGNING_KEY='D6D1989DF1F6B23FD776293DB46EDB4DFC26805D'


# Warn when the key expires within this many days
WARN_DAYS=60


REPO=$(cd "$(dirname "$0")/.." && pwd)


if [ $# -eq 0 ]; then
    set -- \
        "$REPO/KEYS.md" \
        "$REPO/OPENPGP.md" \
        "$REPO"/ceremonies/*.md \
        "$REPO/AGE.md" \
        # Keep this list aligned with the documentation at the top
fi


# Print the fingerprints of all keys that made a valid signature, one per line
signers() {
    gpg \
        --status-fd 1 \
        --verify "$@" \
        2>/dev/null \
        | awk '$2 == "VALIDSIG" { print $3 }'
}


FAILED=0


for FILE; do

    if [ ! -f "$FILE" ]; then
        echo "Error: $FILE not found" >&2
        exit 1
    fi

    if [ -f "$FILE.asc" ]; then
        SIGNERS=$(signers "$FILE.asc" "$FILE")
    else
        SIGNERS=$(signers "$FILE")
    fi

    if printf '%s\n' "$SIGNERS" | grep -qx "$SIGNING_KEY"; then
        echo "OK    $FILE"
    else
        echo "FAIL  $FILE (signed by: $(printf '%s' "${SIGNERS:-nobody}" | tr '\n' ' '))" >&2
        FAILED=1
    fi

done


# Notes:
#  - The 7th field of the pub line is the primary key's expiry in epoch seconds
#  - A subkey resolves to the primary key

EXPIRY=$(gpg --list-keys --with-colons "$SIGNING_KEY" \
         | awk -F: '$1 == "pub" { print $7; exit }')

if [ -z "$EXPIRY" ]; then
    echo "Error: No expiry found for key $SIGNING_KEY" >&2
    exit 1
fi

NOW=$(date -u +%s)

DAYS_LEFT=$(( (EXPIRY - NOW) / 86400 ))


if [ "$EXPIRY" -le "$NOW" ]; then
    echo "FAIL  Key expired $(( (NOW - EXPIRY) / 86400 )) days ago" >&2
    FAILED=1
elif [ "$DAYS_LEFT" -lt "$WARN_DAYS" ]; then
    echo "WARN  Key expires in $DAYS_LEFT days" >&2
else
    echo "OK    Key expires in $DAYS_LEFT days"
fi


# age-recipient.txt is the only unsigned artifact,
# so it must match the recipient in the signed documents
for FILE; do

    case "$FILE" in
        */KEYS.md | KEYS.md | */AGE.md | AGE.md)
            # shellcheck disable=SC2016  # The backticks are literal Markdown
            EXPECTED=$(sed -n 's/^> `\(age1[0-9a-z]*\)`$/\1/p' "$FILE")
            ACTUAL=$(cat "$REPO/age-recipient.txt")
            if [ -z "$EXPECTED" ]; then
                echo "FAIL  No age recipient found in $FILE" >&2
                FAILED=1
            elif [ "$ACTUAL" != "$EXPECTED" ]; then
                echo "FAIL  age-recipient.txt has $ACTUAL, $FILE has $EXPECTED" >&2
                FAILED=1
            fi
            ;;
    esac

done


exit "$FAILED"