Print weak signatures of your PGP keys (with GnuPG)

weak-gpg-sigs

#!/bin/bash

# source: https://www.gnupg.org/documentation/manuals/gpgme/Hash-Algorithms.html
digests=(
    nil
    MD5
    SHA1
    RMD160
    MD2
    TIGER
    HAVAL
    SHA256
    SHA384
    SHA512
    SHA224
    MD4
    CRC32
    CRC32_RFC1510
    CRC24_RFC2240
)

# read preferred digests
while read -r option_name option_value; do
    [[ $option_name == personal-digest-preferences ]] || continue
    preferred_digests=($option_value)
done < ~/.gnupg/gpg.conf

read -rp 'Key ID: ' key_id

# see description in /usr/share/doc/gnupg/DETAILS (Org mode; in Emacs: uncollapse headings with TAB)
# shellcheck disable=SC2034
gpg --list-sigs --with-colons -- "$key_id" | while IFS=: read -r record_type validity key_length public_key_algorithm key_id creation_date expiration_date hash ownertrust user_id signature_class key_capabilities fingerprint flags token hash_algo curve_name; do
    [[ $record_type == sig ]] || continue
    digest_name=${digests[$hash_algo]}
    for ((i=0; i<${#preferred_digests[@]}; i++)); do
        if [[ $digest_name == "${preferred_digests[$i]}" ]]; then
            continue 2
        fi
    done
    printf '%16s %s\n' "$digest_name" "$user_id"
done