Quick script to prepare SSHFP DNS records on a host

sshfp_gen.sh

#!/bin/sh

# https://www.iana.org/assignments/dns-sshfp-rr-parameters/dns-sshfp-rr-parameters.xhtml

set_sha() {
    if [ "`uname -s`" = "Linux" ]; then
        sha="sha${fp_algo}sum"
    else
        sha="sha${fp_algo}"
    fi
}

gen_fp() {
    pk_algo=$1
    fp_algo=$2
    case $pk_algo in
        "rsa") pk_value=1 ;;
        "ecdsa") pk_value=3 ;;
        "ed25519") pk_value=4 ;;
    esac

    case $fp_algo in
        1) fp_value=1 ;;
        256) fp_value=2 ;;
    esac

    file="/etc/ssh/ssh_host_${pk_algo}_key.pub"
    echo -n "SSHFP $pk_value $fp_value "
    set_sha
    awk '{ print $2 }' $file | openssl base64 -d -A | $sha | tr '[:lower:]' '[:upper:]' | awk '{ print $1 }'
}

for pk_algo in rsa ecdsa ed25519 ; do
    for fp_algo in 1 256 ; do
        gen_fp $pk_algo $fp_algo
    done
done

% ./sshfp_gen.sh
SSHFP 1 1 D10F1CC9E07D171F8B0B55199A9E3C0D0C822947
SSHFP 1 2 BBDC17DBB63EE907FEA0186A60C7B7CA734F74D92D9859511D954CF40ED70464
SSHFP 3 1 C41BED2EF5FFB70C63B7C3E4177FE3B664919A4D
SSHFP 3 2 952467625840FB4B3EB425CAB57D7B2B7E8CD03F4184884C7D0DF68015B25671
SSHFP 4 1 C1959C036FB22C22E745A2DFD6845613C4F623CB
SSHFP 4 2 5EEFABA44BDB36FEA1DA3C1F68B969F5C717ECE25A09959CD304C50C8B8E53A4