Question
How can I verify that an X.509 certificate is signed by another certificate using PyOpenSSL or Twisted? I want a client to verify that the received server certificate is the one that signed its client certificate.
I've looked through the PyOpenSSL documentation and can't seem to find anything on how to verify a certificate separately from the establishing the SSL connection.
I found a reference to OpenSSL.crypto:X509.verify() in twisted.internet._sslverify:PublicKey.verifyCertificate() , but the twisted method is commented out (in Twisted 13.0) and the X509 method does not exist (in PyOpenSSL 0.13).
pyOpenSSL has no support for verifying a certificate describes a bug for not being able to manually verify a certificate chain, but I'm not entirely sure if that's what I'm trying to do.
Use Case
Certificates:
Generated self-signed CA certificate with openssl.
Generated server certificate signed by CA certificate.
Generated client certificate signed by server certificate.
Setup:
The server is using Twisted's CertificateOptions with its server cert. The CA certs are the CA and server certs to setup a chain where the server cert verifies the received client cert, and the CA cert verifies the server cert (all built-in functionality).
The client is also using CertificateOptions for the client cert. The CA certs only contains the CA cert.
This all works fine (both sides verify each other) but I want to perform an additional step:
In the client set_verify() callback, verify that the client cert is signed by the server cert.
You should be able to do it with something like written here:
http://www.yothenberg.com/validate-x509-certificate-in-python/
which is basically:
load your certificates in PyOpenSSL with load_certificate()
create a X509Store() object
use add_cert() to add your intermediate certificate in the store
create a X509StoreContext() object, initializing it with both your store object and your end certificate
call verify_certificate() on your store context object
In practice, I was unable to make that part, and I think it is for the reasons explained here: https://mail.python.org/pipermail/cryptography-dev/2016-August/000676.html
In short, even in 2016, there still does not seem to be a correct wait to check certificates in PyOpenSSL, which is very sad. Note that the consensus seem to be that if you operate inside a TLS connection, the things are better checked by the connection routine instead of offline through check_certificate()
Related
We have a service that requires a client certificate to be presented with the request or the call will be rejected. For our .NET components, we have the certificate installed in the local Windows cert store. At runtime we can get the certificate by thumbprint and include that with our request.
For our python component, I am able to get the certificate from the store, but only the public data. I can't seem to access the private key. To get around this I have a pem file with the certificate data that python uses. We are cleaning all secrets out of our source repository, so I need to remove this file.
Does anyone have a suggesiton on how I can access the private key for the certificate without checking it in with my code? Things I am exploring are:
Get the private key with the certificate from the windows cert store
Continue to use the pem file, but encrypt it somehow
Something else?
Thanks,
~john
It is given in the documentation of urllib3 that,
In order to enable verification you will need a set of root certificates.
but is there any way to make HTTPS calls by using the SSL certificate of the server itself instead of root certificates.
urllib3 has a property of the PoolManager called assert_fingerprint: this property can be initiated with a string that is the hex-encoded digest of the certificate bytes. When used, this will circumvent the regular chain building logic.
I'm using Python's requests library to perform client side authentication with certificates. The scenario is the following: CA1 has issued a certificate for an intermediate CA (CA2) and CA2 has issued my client's certificate CLIENT. The server I'm connecting to trusts CA1's cert (but does not have CA2's cert). When I use:
requests.get('https:..', cert=('/path/CLIENT.cert', '/path/CLIENT.key'))
I get an error "certificate verify failed". I assumed that's because the server can not retrieve CA2's cert.
However, I'm unable to find a way to send CA2's cert to the server. If I include it in CLIENT, I get an error about private key and cert mismatch. I have also tried to include the chain of certificates in the verify parameter but there does not seem to be any difference on the result (as far as I understand, certs in the verify parameter are used for server side authentication).
Although I think this must be a quite common scenario, I'm unable to find a solution...
PD: If I verify CLIENT's cert with openssl and the full chain of certificates the validation is successful (so there is no problem with the certificates themselves).
Requests recommends using certifi as a CA bundle. Have you tried installing certifi, adding CA1, and passing the certifi bundle path to requests?
I'm running a windows service using python 2.7.9.
As part of it i'm trying to connect to a server using HTTPS.
I'm using requests model (2.7.0) to do it.
I'm also using wincertstore (0.2) model to read windows certificate store and use it as the CA.
the server certificate is singed using an intermediate certificate in the following order -
Root is "Go Daddy Root Certificate Authority - G2"
Intermediate is "Go Daddy Secure Certificate Authority - G2"
The server certificate "*.demoserver.com"
My problem is that the certificate validation fails with the following error - SSLError: [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:581).
Here is the code i'm using:
import requests
import wincertstore
ca = wincertstore.CertFile()
ca.addcerts('ROOT')
ca.addcerts('CA')
requests.get('https://server.demoserver.com', verify=ca.name)
If I open it on Chrome\Firefox\IE the verification is successful.
I did notice the following behavior:
On a fresh OS, if i open the server using a browser for the first time the intermediate certificate ("Go Daddy Secure Certificate Authority - G2") will be added to Windows certificate store, under that user, under Intermediate Certification Authorities.
If then I will run the code above from a python console the validation will work, since the certificate was added to windows store.
However, since my code is run as a service, and that means using SYSTEM user and local machine store, the certificate won't be there and the validation will fail.
My question is how do I make it work? How can I tell python to check the entire chain, I think it checks the server certificate, sees only one level up (the intermediate certificate), doesn't recognizes it and fails, even though the root certificate is found in the system store also.
I also tried using certifi as the CA which also fails
I want to create a Client/Server architecture following the python documentation.
This works well with my self-signed certificates in one pem file. (ca_root root_key ca_intermediate intermediate_key)
So my next plan is to create client certificates which can be revoked by the server if the client isn't trustworthy anymore.
So the way to go is that i create a certificate, signed with the intermediate key, and hand it out to the client.
But i still get
ssl.SSLError: [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:590)
Do i need to export the whole certificate chain to the client? This seems odd to me.
Thanks!
Most likely you're entire chain isn't in your .pem file. Just copy the text from the certificates in the right order into a single .pem file and attempt that. If that doesn't work you may be getting this error because of your server configuration. More information is need thought to provide a better answer.