How to load a public RSA key into Python-RSA from a file?

Question

I generated a private and a public key using OpenSSL with the following commands:

openssl genrsa -out private_key.pem 512
openssl rsa -in private_key.pem -pubout -out public_key.pem

I then tried to load them with a python script using Python-RSA:

import os
import rsa

with open('private_key.pem') as privatefile:
    keydata = privatefile.read()
privkey = rsa.PrivateKey.load_pkcs1(keydata,'PEM')

with open('public_key.pem') as publicfile:
    pkeydata = publicfile.read()

pubkey = rsa.PublicKey.load_pkcs1(pkeydata)

random_text = os.urandom(8)

#Generate signature
signature = rsa.sign(random_text, privkey, 'MD5')
print signature

#Verify token
try:
    rsa.verify(random_text, signature, pubkey)
except:
    print "Verification failed"

My python script fails when it tries to load the public key:

ValueError: No PEM start marker "-----BEGIN RSA PUBLIC KEY-----" found

Answer 1

Python-RSA uses the PEM RSAPublicKey format and the PEM RSAPublicKey format uses the header and footer lines: openssl NOTES

-----BEGIN RSA PUBLIC KEY-----
-----END RSA PUBLIC KEY-----

Output the public part of a private key in RSAPublicKey format: openssl EXAMPLES

 openssl rsa -in key.pem -RSAPublicKey_out -out pubkey.pem

Answer 2

If on Python3, You also need to open the key in binary mode, e.g:

with open('private_key.pem', 'rb') as privatefile:

Answer 3

To load an OpenSSL generated public key file with python-rsa library, try

with open('public_key.pub', mode='rb') as public_file:
    key_data = public_file.read()
    public_key = rsa.PublicKey.load_pkcs1_openssl_pem(key_data)

Answer 4

You can generate private key by ssh-keygen:

ssh-keygen -t rsa

and generate public key like this:

ssh-keygen -e -m pem -f xxx > pubkey.pem

http://blog.oddbit.com/2011/05/08/converting-openssh-public-keys/