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Editorial Team
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Asked: 2026-05-26T19:00:31+00:00

I am trying to export a public key from openssl using python. I have

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I am trying to export a public key from openssl using python. I have the actual key information transferred to the client from the server but the PEM encoding is not transferred so the key on the client is useless. I basically send the public key using send all in python but unfortunately this does not send the PEM encoding. Does anyone know how to transfer the encoding?
I didn’t know that the encoding would not transfer along with the key.

THe code where the string is read in

 import socket

 import M2Crypto as m2c
 import os

 max_transfer_block = 1024
 server_addr = "10.1.1.2"
 dest_port = 3333
 listen_port = 8888
 client_addr =  "10.1.1.3"
 mysocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
 mysocket.connect((server_addr, dest_port))

 #receive the public key from the server
 keysocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
 keysocket.bind((client_addr, listen_port))
 keysocket.listen(1)
 conn, client_addr = keysocket.accept()
 print 'connected by', client_addr
 data = conn.recv(max_transfer_block)
 #FILE = m2c.RSA.save_pub_key(data, "serverPubKey.pem")

 FILE = open("sPub.pem", "w")
 FILE.write(data)
 keysocket.close()     

 #transfer encrypted file
 key = m2c.RSA.load_pub_key('serverPubKey.pem')
 FILE = open("test.txt", "r")

 data = FILE.read()

 encrypted = key.public_encrypt(data, m2c.RSA.pkcs1_padding)

 mysocket.sendall(encrypted)
 mysocket.close()

When I use the line key = m2c.RSA.load_pub_key('serverPubKey.pem') I get an error telling me that there is no starting point.

 raise RSAError, m2.err_reason_error_string(m2.err_get_error()) M2Crypto.RSA.RSAError: no start line

I have figured out that this is because there is not in PEM format. Unfortunately, I don’t know how to put it in that format.

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1 Answer

  1. Editorial Team

    The mistake was that the public/private key pair needs to be created from the same wrapper. What I mean by this is that not all key pairs are the same. My specific problem was that Openssl and the M2Crypto instances of key pairs were not in the same underlying format. Thus creating keys with Openssl and then trying to use M2Crypto to use the keys was wrong. The lesson from all of this is to not import keys from other wrappers. If you do, make sure that they are in the same underlying format like ASCII or Unicode before trying to use them.

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