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

I think the problem is the format of the public key. If you look closely, the header on the openssl generated public key is, "-----BEGIN PUBLIC KEY-----". The format is X509 SubjectPublicKeyInfo. The method you are using is looking for PKCS1 format with a header of "-----BEGIN RSA PUBLIC KEY-----". — gtrig
– gtrig, Commented Jun 19, 2013 at 21:04

Kimvais · Accepted Answer · 2014-04-01 08:44:57Z

15

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

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

answered Apr 1, 2014 at 8:44

Kimvais

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1 Comment

KdPisda Over a year ago

Damm! The saviour :P

jww · Accepted Answer · 2019-06-24 23:33:48Z

9

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

edited Jun 24, 2019 at 23:33

jww

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answered Feb 17, 2014 at 12:40

Googuez

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1 Comment

Tumble Jan 22 at 14:56

Brilliant, thank you - hadn't spotted the difference until I saw this and had been going round the houses

haiyizxx · Accepted Answer · 2019-02-06 15:53:02Z

7

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)

edited Feb 6, 2019 at 15:53

answered Feb 6, 2019 at 15:24

haiyizxx

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Comments

Logovskii Dmitrii · Accepted Answer · 2022-10-04 10:01:16Z

3

from cryptography.hazmat.primitives import serialization
from cryptography.hazmat.backends import default_backend


def load_keys(public_key_path, private_key_path):
    with open(public_key_path, "rb") as f:
        public = serialization.load_pem_public_key(
            f.read(), backend=default_backend()
        )
    with open(private_key_path, "rb") as f:
        private = serialization.load_pem_private_key(
            f.read(), None, backend=default_backend()
        )
    return private, public

edited Oct 4, 2022 at 10:01

answered Nov 14, 2019 at 13:54

Logovskii Dmitrii

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Comments

thinker3 · Accepted Answer · 2017-12-27 06:57:02Z

1

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/

answered Dec 27, 2017 at 6:57

thinker3

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