Implementing-cryptography-using-python

Chapter 9 ■ Mastering Cryptography Using Python 273
(https://en.wikipedia.org/wiki/Cryptographically_secure_pseudorandom_
number_generator)
"""
randomNumber = 0
_bytes = bits // 8 + 8
while (randomNumber.bit_length() < bits):
randomNumber = int.from_bytes(random_function(_bytes),
byteorder='big')
return randomNumber
def generatePrivateKey(self, bits):
"""
Generate the private key
"""
return self.generateRandomNumber(bits)
def generatePublicKey(self):
"""
Generate public key with generator ** privateKey % prime
"""
return pow(self.generator, self.privateKey, self.prime)
def testReceiverPublicKey (self, receiverPublicKey):
"""
Checks receiver Public Key to make sure it's valid.
Since a safe prime is used, verify that the Euler's Criterion
for the Legendre Symbol == 1
Not super trustworthy tho, it has its limitations.
(https://en.wikipedia.org/wiki/Legendre_symbol)
(https://www.youtube.com/watch?v=o23itWTcEYw)
"""
if (receiverPublicKey > 2 and receiverPublicKey < self.prime - 1):
if(pow(receiverPublicKey, (self.prime - 1)//2, self.prime) == 1):
#if it's a quadratic residue
return True
return False