sign.sh

#!/usr/bin/env sh
filepath=${1}
signature=${2:-"signature.txt"}
privkey=${3:-"private_key.pem"}
pubkey=${4:-"public_key.pem"}
binsgn="${signature}.bin"

openssl genrsa -out $privkey 2048
openssl rsa -in $privkey -pubout -out $pubkey
openssl dgst -sign $privkey \
  -out $binsgn $filepath
openssl base64 -in $binsgn \
  -out $signature
rm -f $binsgn

usage.md

# Sign:
$ ./sign.sh mylabs.zip

# Verify:
$ ./verify.sh mylabs.zip signature.txt

verify.sh

#!/usr/bin/env sh
filepath=${1}
signature=${2:-"signature.txt"}
pubkey=${3:-"public_key.pem"}
binsgn="${signature}.bin"

openssl base64 -d -in $signature -out $binsgn
openssl dgst -verify $pubkey \
  -signature $binsgn $filepath
rm -f $binsgn