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I'm trying to connect to two different RSS feeds at different addresses on the same server (domain names are slightly different) via Fiddler. One site works properly and returns data as expected. The second site returns a 502 error telling me

The client and server cannot communicate, because they do not possess a common algorithm HTTPS handshake returned error SEC_E_ALGORITHM_MISMATCH

The same problem occurs when I use my code to get at the RSS feeds.

If I go to the non-working site with a web browser it works just fine.

I have Fiddler configured to use tls 1.1 & 1.2

In my code I use 

 ServicePointManager.Expect100Continue = true;
 ServicePointManager.SecurityProtocol = ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12 | SecurityProtocolType.Tls11;
 var reader = XmlReader.Create(url); <Fails here
 feed = SyndicationFeed.Load(reader);

Any suggestions for troubleshooting this?

John S
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  • did you try the solution provided here : https://stackoverflow.com/questions/17595290/fiddler-https-error-because-they-do-not-possess-a-common-algorithm – user9405863 Mar 12 '18 at 22:21
  • What is the point of this? `ServicePointManager.SecurityProtocol = ServicePointManager.SecurityProtocol = ...` Setting something equal to itself is never useful. – itsme86 Mar 12 '18 at 22:52
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    You can use Wireshark to observe the TLS handshake with both endpoints to identify any differences. – ejohnson Mar 13 '18 at 06:58
  • @itsme86 Typo when I cut and pasted my code from VS to here. – John S Mar 13 '18 at 13:16
  • @HazarathChillara Yes tried it. Currently I have Fiddler set to accept SSL3, TLS1.1 & TLS1.2 – John S Mar 13 '18 at 13:25

1 Answers1

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Turns out that the government site I am accessing only supports TLS1.0 and our firewall rules don't allow that protocol through.

Our solution may be to change those rules.

John S
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