#!/usr/bin/python3
'''
Verifies signature of a message using RSA public key (possibly generated with rsa_key_gen.py)

Author: Tim Pierson, Dartmouth CS55, Winter 2021
				Based Wenliang Du https://github.com/kevin-w-du/BookCode/tree/master/Public_Key_Cryptography
Usage: 	python3 rsa_verify.py <public key file name>  <signature file name>
		python3 rsa_verify.py public.pem signature.bin
				
'''

from Crypto.Signature import pss
from Crypto.Hash import SHA512
from Crypto.PublicKey import RSA
import sys

message = b'An important message' #same message used in rsa_sign.py

if __name__ == '__main__':
	#usage check: make sure we got a filename to read
	if len(sys.argv) != 3:
		print("Usage: python3 rsa_verify.py <public key file name> <signature file name")
		print("Did you provide these?")
		exit()

	
	print("Reading signature from",sys.argv[2])
	signature= open(sys.argv[2], 'rb').read()

	print("Reading public key from",sys.argv[1])
	key = RSA.import_key(open(sys.argv[1]).read())

	print("Message to verify is:",message)
	print("Hashing message")
	h = SHA512.new(message)

	print("Verifying hash")
	verifier = pss.new(key)
	try:
		verifier.verify(h, signature)
		print("The signature is valid.")
	except (ValueError, TypeError):
		print("The signature is NOT valid.")