On 5/13/2020 2:11 PM, Sean Mullan wrote:
It is not expected to use this extension regularly.
Please let me know if you still prefer to use "enableCAExtension".
Also, it is a bit unfortunate that we have to have a system
property to enable it. Can we not enable it based on whether the
configured X509TrustManager.getAcceptedIssuers returns a non-empty
list?
We can do that on server side, but there are compatibility impact on
client behavior if we did it in client side. See #2 in the
"Specification" section.
But doesn't the default JDK PKIX TrustManager throw a fatal exception
and close the connection if the server's certificate cannot be
validated? Could we check if the PKIX TrustManager is being used?
Yes, the trust manager could throw a fatal exception and close the
connection if the trust cannot be established. The fallback mechanism
is implemented in the customized trust manager, that if users accept
the cert, the cert is trusted, and no exception and the handshaking
continued. It is too later to fallback after the connection closed.
If a client wants to accept self-signed or untrusted server
certificates, I would have expected them to have to use a custom
X509TrustManager that allows that, and that getAcceptedIssuers()
should return an empty List. Is that not is what is typically done in
practice?
Yes, customized trust manager is used to accept users manually
selection. As the users may also want to accept normal certificate
without manually involved, so getAcceptedIssuers() should respect
those CA as well.
I see. Out of curiosity, have you checked how other implementations
handle this extension? For web browsers, they typically give the user
the option of proceeding if the server certificate is not trusted. Seems
to be a bit of a configuration dilemma as you may want this extension
enabled for certain sites that have multiple certificates, but not as a
general default because then you wouldn't be able to connect to
untrusted sites (at your own risk of course). I wonder if it would have
been better for the RFC to allow the server to treat this extension more
as a hint, and still return its chain if an acceptable certificate could
not be found.
If it is treated as a hint, then it might be better no have this extension.
I checked with browsers, the extension is not present in ClientHello.
For JDK, I would not expect a lot use of this extension in client side.
It is just designed to workaround a few cases, just as you mentioned above.
Xuelei
