How to use public key to encrypt data and use base64 encode it in python?

Question

I want to implement the following function using python, it uses public key to encrypt the password and then using base64 to encode it. I have searched many answers but I didn't find a solution, I think probably I didn't understand them. Would you please give me some advice?

// # java code
public static String encryptRSA(String password, String publicKey) {
        try {
            byte[] decoded = Base64.decode(publicKey);
            RSAPublicKey pubKey = (RSAPublicKey) KeyFactory.getInstance("RSA")
                    .generatePublic(new X509EncodedKeySpec(decoded));
            Cipher cipher = Cipher.getInstance("RSA");
            cipher.init(Cipher.ENCRYPT_MODE, pubKey);
            String outStr = Base64.encode(cipher.doFinal(password.getBytes("UTF-8")));
            return outStr;
        } catch (Exception e) {
        }
        return null;
    }

I use the following code, but it raises error M2Crypto.RSA.RSAError.

# python code
import base64

import M2Crypto

pub = "MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQClnY+3rAf/az9t2bxC80TObpZ2ZCH1xSjPt9QtXl6k6UtD7mQcI2CWSwnDgKJr2m2WnM1kR6X+oOL61lXO0gSuuD8tWOx/knZA2VaSTLdsHBDLOX3e6Fo/O3CtoLVwO5FYFBIFHXMoikPkR8tFIOLWsX0y3slLQQShwSJAHytP4QIDAQAB"
password = 123


def public_encrypt(public_key, password):
    rsa_pub = M2Crypto.RSA.load_key_string(public_key.encode('utf-8'))
    ctxt_pub = rsa_pub.public_encrypt(password.encode(), M2Crypto.RSA.pkcs1_padding)
    ctxt64_pub = base64.b64encode(ctxt_pub).decode()
    return ctxt64_pub


res = public_encrypt(pub, password)
print('res:', res)

user_9014097 · Answer

The full error message is: M2Crypto.RSA.RSAError: no start line, indicating that the key is imported incorrectly.

load_key_string() requires a PEM-encoded private key in PKCS#1 or PKCS#8 format, but no public key. A PEM encoded public key in X.509/SPKI format can be imported with load_pub_key_bio().

From the posted X.509/SPKI key a PEM encoded key can be created by adding a newline after every 64 characters and adding a corresponding header and footer:

import M2Crypto

x509 = '''-----BEGIN PUBLIC KEY-----
MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQClnY+3rAf/az9t2bxC80TObpZ2
ZCH1xSjPt9QtXl6k6UtD7mQcI2CWSwnDgKJr2m2WnM1kR6X+oOL61lXO0gSuuD8t
WOx/knZA2VaSTLdsHBDLOX3e6Fo/O3CtoLVwO5FYFBIFHXMoikPkR8tFIOLWsX0y
3slLQQShwSJAHytP4QIDAQAB
-----END PUBLIC KEY-----'''

bio = M2Crypto.BIO.MemoryBuffer(x509)
rsa_pub = M2Crypto.RSA.load_pub_key_bio(bio)

Another issue is that there is no encode() defined for an integer, but presumably password is supposed to be a string and this is just a copy/paste error.

With these changes the code works.

Note that a 1024 bits RSA key (like yours) is insecure nowadays, instead the length should be >= 2048 bits.

How to use public key to encrypt data and use base64 encode it in python?

1 Answers