Converting RSA encryption code from php to python - php

Question

I'm trying to connect to a api in my python app .
so the api documentations comes with php and asp sample code but no python
I'm pretty good with php but have no experience with encryption ... I'm trying to re-write python code for the api using php sample .
They use this class for RSA
https://github.com/AlaFalaki/Pclass/blob/master/libraries/rsa.class.php
(Since its a RSA lib im guessing python RSA lib would take care of this part ) :
static function rsa_sign($message, $private_key, $modulus, $keylength) {
$padded = RSA::add_PKCS1_padding($message, false, $keylength / 8);
$number = RSA::binary_to_number($padded);
$signed = RSA::pow_mod($number, $private_key, $modulus);
$result = RSA::number_to_binary($signed, $keylength / 8);
return $result;
}
Here is the problem php sign function takes 4 arguments uses some internal functions ... But python rsa has 3 and one of them is just the hash method !
rsa.sign(message, priv_key, hash)
Parameters:
message – the message to sign. Can be an 8-bit string or a file-like object. If message has a read() method, it is assumed to be a file-like object.
priv_key – the rsa.PrivateKey to sign with
hash – the hash method used on the message. Use ‘MD5’, ‘SHA-1’, ‘SHA-256’, ‘SHA-384’ or ‘SHA-512’.
i've tried little experiment to see if i get same output
so i've singed a simple text string in php
echo base64_encode(RSA::rsa_sign(sha1("test"),$private_key,$modulus,$key_length));
i got
something like
dKt+4CocMNdIrtYCUr8aZykR8CpfmYUEEVONMuAPlM5mR70AoyzMhGjcEGB9fKLVC4rr5xt66w2ZmHqWO+p834rJmo9Fj57udRSY5wFs0VokMF2S2SMFn5WTYYmMBuWciRzZybWnfXcSIyp9Ibi28cdwl5hXJOMpXEJrNQLFy2s=
next i extracted private_key , public_key , modulus from a xml file that they gave me with api containing my keys ( using the same RSA class ) like
$xmlObj = simplexml_load_string($xmlRsakey);
$this->modulus = RSA::binary_to_number(base64_decode($xmlObj->Modulus));
$this->public_key = RSA::binary_to_number(base64_decode($xmlObj->Exponent));
$this->private_key = RSA::binary_to_number(base64_decode($xmlObj->D));
$this->key_length = strlen(base64_decode($xmlObj->Modulus))*8;
i made a python dictionary with them
def keys():
obj = {
'modulus' : "14417185111734127374105962730273......." ,
'public_key' : "61111" ,
'private_key' : "3739752306322843055980611965983321761993....." ,
'key_length' : 1024 ,
}
return obj
and i've tried to sign a string in python
def sign(request):
api = keys()
message = 'test'
crypto = rsa.sign(message.encode('utf-8'), api['private_key'] , 'SHA-1')
b64 = base64.b64encode(crypto)
return HttpResponse(b64)
but i get :
'str' object has no attribute 'n'
and that was my failed experiment
As i said i dont have any experience with encryption or rsa .... i want some advice from someone who worked with this stuff .
Should i give up and use php to encrypt/decrypt ?

Answer 1

They use this class for RSA
https://github.com/AlaFalaki/Pclass/blob/master/libraries/rsa.class.php
My advice: Run away screaming.
RSA is a mine field of security issues. There are a lot of things that you can screw up. So when someone implements the primitives in PHP using the BC extension, that's the security equivalent of standing naked in front of a firing squad and expecting to have no holes.
Encrypting with PKCS1 padding allows near-trivial message decryption
Screwing up your parameters can completely remove all security from your crypto
Home-grown RSA is ripe with side-channel attacks
Recommendation: Use Libsodium Instead
There are both PHP and Python bindings available for libsodium.
If RSA is Unavoidable...
If you really want RSA and not modern cryptography, check out phpseclib.
<?php
use
$rsa = new RSA();
// HIGHLY RECOMMENDED FOR SECURITY:
$rsa->setEncryptionMode(RSA::ENCRYPTION_OAEP);
$rsa->setMGFHash('sha256');
$rsa->loadKey($yourPEMencodedRSAPublicKey);
$ciphertext = $rsa->encrypt($plaintext);
If you're going to encrypt with RSA, you must follow these cryptography rules. If your library doesn't let you follow these rules, it's time to switch to libsodium.
Also note that encrypting large messages with RSA is both slow and dangerous: There's usually nothing preventing messages from being reordered, which can be really bad.
The solution here is: Use symmetric-key authenticated encryption and use RSA to encrypt the public key. That's what EasyRSA does, although I'm not aware of any Python equivalents, so I can't recommend that as a solution.
Of course, if you use libsodium's crypto_box API you don't have to worry about that!