[Python] How to convert a key string back into a pycrypto key object? (Python)

I am replicating a TCP client-server secure handshake in python using the pycrypto module. When the "server" sends the public key over the socket, I am forced to convert the public key to a string. The "client" then receives the public key as a string, which cannot be encrypted according the pycrypto module.

I get the error:

AttributeError: 'str' object has no attribute 'encrypt' in reference to enc_data = public_key.encrypt(secret_piece, 12) on the client side.
​

How do convert the string public_key back to its original value when it was first generated by the RSA module?

Server Code:

def main():
host = '127.0.0.1'
port = 5000

s = socket.socket()
s.bind((host,port))

s.listen(1)
c, addr = s.accept()
print "Connection from: "+str(addr)
while True:
data = c.recv(1024)
if not data:
break
print "from connected user: "+str(data)

print "Start the SSL Handshake..."
a = raw_input('Press enter to generate the key pair. ')

key = RSA.generate(1024, random_generator)
public_key = key.publickey()

print "Key pair generated"
a = raw_input('Press enter to send public key to client ')

print "Sending key..."

if c.send(str(public_key)):
print "Public Key Sent"

print "Waiting for secret list..."

if c.recv(1024):
print "List received."

secret_list = c.recv(1024)

a = raw_input('Press enter to check the information from the list. ')

decrypted_info = key.decrypt(secret_list.enc_data)

match_or_not = SHA256.new(decrypted_info).digest() == secret_list.hash_value

if match_or_not:
print "Info Matches. Sending the ciphertext..."

info_to_be_encrypted = "It seems all secure. Let's talk!"
aes = AES.new(Random.get_random_bytes(16), AES.MODE_ECB)
cipher_text = aes.encrypt(info_to_be_encrypted)

if c.send(cipher_text):
print "Ciphertext sent."


Client Code

def main():
host = '127.0.0.1'
port = 5000

s = socket.socket()
s.connect((host,port))



message = raw_input("-> ")
while message != 'q':
s.send(message)
public_key = s.recv(1024)
print 'Received from server: '+str(public_key)

message = raw_input("->Press enter to verify the public key.")
print "Public Key verified!"
message = raw_input("-> Press enter to prepare the secret list.")
print "Client prepares the secret list."

secret_piece = Random.get_random_bytes(16)
enc_data = public_key.encrypt(secret_piece, 12)
hash_value = SHA256.new(secret_piece).digest()
L = [enc_data, hash_value]

print "List is ready."
message = raw_input("-> Press enter to send the list")

s.send(str(L))
print "List sent."
print "Waiting for ciphertext from the server..."

if s.recv(1024):
print "Ciphertext recieved."

cipher_text = s.recv(1024)

print "The encrypted message is: " + cipher_text
print "The decrypted message is: " + aes.decrypt(cipher_text)




s.close()

Continue reading...