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I am getting this warning on mobile devices, the full warning is:

The connection uses TLS 1.2 The connection is encrypted using AES_256_CBC, with HMAC-SHA1 for message authentication and ECDHE_RSA as the key exchange.

I am using a dedicated VPS for the website and I have used IISCrypto with best practices applied.

You can see the results of the site scanner with the link below.

Qualys Scan Results

The Schannels I am using are below:

Schannel configuration

Chipher Suit Configuration

The Server is Windows 2012 r2 with IIS

Any help would be very grateful.

Paul.

user2006049
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1 Answers1

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To cite from the Chromium documentation what you need to do to make this warning go away:

... prioritize an ECDHE cipher suite with AES_128_GCM or CHACHA20_POLY1305. Most servers will wish to negotiate TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256.

Looking at what Windows Server 2012 R2 actually supports on ciphers you'll find that it does not support CHACHA20_POLY1305 and that it supports GCM ciphers only with ECC certificates, i.e. it implements ciphers like TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256_P256 but not ciphers like TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256.

But, you are using an RSA certificate and not an ECC certificate which means that none of the GCM ciphers supported by your OS can be used with your certificate. The ciphers you need are only supported with Windows Server 2016.

Steffen Ullrich
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  • Thank you Steffen, are you saying that there is nothing I can do on Windows 2012 and that I need to use 2016 to make the warnings go away? – user2006049 Jul 26 '18 at 06:40
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    @user2006049: you get an ECDSA cert (which might lock-out other clients especially any older ones) or https://serverfault.com/questions/683697/change-key-exchange-mechanism-in-iis-8/683705#683705 says there's a patch with 'issues' that can get you GCM with DHE_RSA (but apparently DHE-1024, which is not very good). – dave_thompson_085 Jul 26 '18 at 07:27