Verify a file with a given public key (best for files signed with "sign.sh")

verify.sh

#!/bin/bash
# Verify a signed file with the specified public key

# Signature file
SRCF=$1

# Public key location
PUBK=$2

# Signature algorithm (defaults to SHA-512)
ALGO=${3:-sha512}

# Algo file
ALGF=$SRCF.$ALGO.sig

# Check for signature file
if [ ! -f "$ALGF" ]; then
	echo "Signature file must be in the same directory"
	exit
fi

if [ -f "$PUBK" ]; then
	if [ -f "$SRCF" ]; then
		openssl dgst -$ALGO -verify $PUBK -signature $ALGF $SRCF
	else
		echo "Source file not found"
	fi
else
	echo "Public key not found"
fi

exit

# To use this, run:
# sh verify.sh /path/to/file.ext /path/to/publickey.pub

# The signature file should be there in "file.ext.sha512.sig" format

# Or if a different algorithm was used, E.G. SHA-256:
# sh verify.sh /path/to/file.ext /path/to/publickey.pub sha256