How does Windows Server negotiate cipher suite?

N

Nathaniel B

I'm trying to find an official answer on how Windows Server handles picking a TLS cipher suite from a client's list of preferred ciphers. In addition I am looking for the equivalent option to Apache's SSLHonorCipherOrder which forces the web service to follow the client order or to instead pick the strongest cipher from what client and server have in common.

One such example: A fully patched Windows 2016 server has only the strongest TLS 1.2 ciphers enabled:

TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256_P384
TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256_P256
TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384
TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256
TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384
TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384

If a session is started by a client with:

Cipher Suite: TLS_RSA_WITH_AES_128_CBC_SHA256 (0x003c)
Cipher Suite: TLS_RSA_WITH_AES_128_CBC_SHA (0x002f)
Cipher Suite: TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256 (0xc027)
Cipher Suite: TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA (0xc013)
Cipher Suite: TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA (0xc014)
Cipher Suite: TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 (0xc02b)
Cipher Suite: TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA384 (0xc024)
Cipher Suite: TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA (0xc009)
Cipher Suite: TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA (0xc00a)
Cipher Suite: TLS_DHE_DSS_WITH_AES_128_CBC_SHA256 (0x0040)
Cipher Suite: TLS_DHE_DSS_WITH_AES_128_CBC_SHA (0x0032)

What will be the result of the agreed upon cipher? I would think going down the list the first match is TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 (0xc02b) but instead the server actually resets the connection because no match is found. How did the server determine that?

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