CODEWITHSUNDEEP
pythonperlencryptionrsapublic-key
Saqib Ali
Saqib Ali

Reputation: 12585

How can I translate this Perl code for RSA Public key in python?

I have the following JSON object which represents an RSA256 JWK which obtained from a website:

jwk = {
    'e': 'AQAB', 
    'n': 'sAlE_mzYz-2jf_YpxulSJXv_2CGIquflNZWhXUaU1SkJm9P0riLAuzwK7WT5p0Ko3zmQHho70_7D9nqB01rA4ExrMIDKpprE0Qa7NAJN-kgZhd_A25HsdSfpOfpaLvR-mf9fuOTDPLRQCd5HnrjoQKjs3D_XfPmPnT_Ny5erviiky90GSfN9j2DP_5yeDprzWKF-EQ3EDdIWt3snr7AW8rzBcZ1ojyWxckLAeSKDerMXP-zVBUFJE9Kn60HZoGNvmATKaw8LwEbf8DGfrllgSLvhg7mDRMLlbcooQoWAFSfN7t7kFbPSOcvjrpx3Yw_KrEwBZXeUP3260ukmFOx8RQ',
 }

Below is the Perl code showing how a public-key object from the Crypt library can be constructed from the above jwk:

use Crypt::OpenSSL::RSA;
use Crypt::OpenSSL::Bignum;
use MIME::Base64 qw/decode_base64url/;

sub public_key {
    my $rsa = Crypt::OpenSSL::RSA->new_key_from_parameters(
        Crypt::OpenSSL::Bignum->new_from_bin(decode_base64url($jwk->{n})),
        Crypt::OpenSSL::Bignum->new_from_bin(decode_base64url($jwk->{e})),
    );
    return $rsa->get_public_key_x509_string;
}

Two Questions:

How can I translate the above code into Python? The code below failed.

Once I have the public key object in python, how can I use it to verify a JWT signed by the corresponding private key? Please post a snippet showing exactly how it can be done.

>>> from Crypto.PublicKey import RSA
>>> import base64
>>> public_key = RSA.construct((base64.b64decode(jwk['n']), base64.b64decode(jwk['e'])))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "my-virtual-env/lib/python2.7/site-packages/Crypto/PublicKey/RSA.py", line 539, in construct
    key = self._math.rsa_construct(*tup)
  File "my-virtual-env/lib/python2.7/site-packages/Crypto/PublicKey/_slowmath.py", line 84, in rsa_construct
    assert isinstance(n, long)
AssertionError

Upvotes: 2

Views: 305

Answers (1)

llompalles
llompalles

Reputation: 3176

The error is raised because the RSA contructor is expecting 2 long integers and you are using two strings.

The solution is to convert the base64 decoded string into an hexadecimal integer. 

from Crypto.PublicKey import RSA
import base64

n = int(base64.b64decode(jwk['n']).encode('hex'),16)
e = int(base64.b64decode(jwk['e']).encode('hex'),16)
e = long(e)

public_key = RSA.construct((n, e))
print(public_key)

Regarding the second question maybe you can use this method to verify the validity of an RSA signature.

Upvotes: 2

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