[Python-Dev] RFC: Backport ssl.MemoryBIO and ssl.SSLObject to Python 2.7

Cory Benfield cory at lukasa.co.uk
Thu Jun 1 06:45:14 EDT 2017

> On 1 Jun 2017, at 11:28, Antoine Pitrou <antoine at python.org> wrote:
> Le 01/06/2017 à 12:23, Cory Benfield a écrit :
>> No it can’t.
>> OpenSSL builds chains differently, and disregards some metadata that Windows and macOS store, which means that cert validation will work differently than in the system store. This can lead to pip accepting a cert marked as “untrusted for SSL”, for example, which would be pretty bad.
> Are you claiming that OpenSSL certificate validation is insecure and
> shouldn't be used at all?  I have never heard that claim before.

Of course I’m not.

I am claiming that using OpenSSL certificate validation with root stores that are not intended for OpenSSL can be. This is because trust of a certificate is non-binary. For example, consider WoSign. The Windows TLS implementation will distrust certificates that chain up to WoSign as a root certificate that were issued after October 21 2016. This is not something that can currently be represented as a PEM file. Therefore, the person exporting the certs needs to choose: should that be exported or not? If it is, then OpenSSL will happily trust it even in situations where the system trust store would not.

More generally, macOS allows the administrator to configure graduated trust: that is, to override whether or not a root should be trusted for certificate validation in some circumstances. Again, exporting this to a PEM does not persist this information.


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