Implementing-cryptography-using-python

274 Chapter 9 ■ Mastering Cryptography Using Python
def generateSharedSecret(self, privateKey, receiverPublicKey):
"""
Generates the shared secret after checking if receiverPublicKey
is valid.
"""
prime)
if (self.testReceiverPublicKey(receiverPublicKey) == True):
sharedSecret = pow (receiverPublicKey, privateKey, self.
return sharedSecret
else:
raise Exception ("Invalid public key.")
def generateSharedKey (self, receiverPublicKey):
"""
Gets shared secret, then hash it to obtain the shared key.
"""
self.sharedSecret = self.generateSharedSecret(self.privateKey,
receiverPublicKey)
try:
_sharedSecretBytes = self.sharedSecret.to_bytes(self.
sharedSecret.bit_length() // 8 + 1, byteorder="big")
except AttributeError:
_sharedSecretBytes = str(self.sharedSecret)
shared = hashlib.sha256()
shared.update(bytes(_sharedSecretBytes))
self.key = shared.digest()
def getSharedKey (self):
"""
Return shared secret Key
"""
return self.key
def displayParameters (self):
"""
Display parameters used on the DH agreement.
"""
print(">>>>>>> Parameters:")
print("Prime[{0}]: {1}\n".format(self.prime.bit_length(), self.
prime))
print("Generator:", self.generator, "\n")