Use openssl with ed448 keys, to sign & verify shake256 digests

_openssl_keys

# will prompt for passphrase on stdin
openssl genpkey -out skey.pem -verbose -pass stdin -aes-256-cbc -algorithm ed448

openssl ec -in skey.pem -pubout -out pub.pem

# create hash
openssl shake256 -xoflen 64 -out dgst thefile

openssl pkeyutl -sign -inkey skey.pem -rawin -in dgst -out dgst.sig
openssl pkeyutl -verify -rawin -inkey pub.pem -pubin -sigfile dgst.sig -in dgst

linux.sh

# extract only checksum from digest
cat dgst | awk 'BEGIN { FS="=" } {print $2}' | cut -c2-

windows.ps1

# extract only checksum from digest
(gc file.dgst) | % {$_.substring(($_.IndexOf('=') + 2))}