verify_dgst.bsh

#!/bin/bash
# ===========================================================
# verify a digial signature (hash) of a file
# ===========================================================

cert=certs/client.cert.pem
file=gettysburg_address.txt
hash=hashes/gettysburg_address.sha256
pub=pubkeys/client.pub

# ---------------------------------------------------------
echo
echo Creating public key from certificate

# does the cert exist?

if [ ! -f $cert ]; then
   echo
   echo "Certificate ($cert) not found"
   echo
   exit 1
else
   echo
   echo Certificate already exists
fi

# does the public key exist?

if [ ! -f $pub ]; then
   echo
   echo "Public key ($pub) not found"
   echo
   exit 1
fi

# create public key

openssl x509 -in certs/client.cert.pem -pubkey \
       -noout > pubkeys/client.pub

# ---------------------------------------------------------
echo
echo Verifying file using public key

# does the file exist?

if [ ! -f $file ]; then
   echo
   echo "File ($file) does no exist"
   echo
   exit 1
fi

# does the file hash exist?

if [ ! -f $hash ]; then
   echo
   echo "Hash ($hash) not found"
   echo
   exit 1
fi

# verify file has not been modified

openssl dgst -sha256 -verify $pub -signature $hash $file