add AES256-SHA as a default cipher for TLS 1.2

[kevinAlbs]

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Summary

Add AES256-SHA as a default cipher suite for TLS 1.2.

Motivation

The current default TLS 1.2 cipher suites do not intersect with the default cipher suites in the Golang TLS library. Golang TLS 1.2 default ciphers are listed under cipherSuitesPreferenceOrder here.

KMIP 1.4 Profiles section 3.2.2 notes:

Conformant KMIP servers and clients MAY support the cipher suites specified as MAY in Basic Authentication Cipher Suites (3.1.2) of the Basic Authentication Suite

TLS_RSA_WITH_AES_256_CBC_SHA is listed in section 3.1.2.

Reproducing

To reproduce, run a PyKMIP server with TLS 1.2:

% cd /path/to/PyKMIP/bin
% ./create_certificates.py
% cat server.cfg 
[server]
hostname=127.0.0.1
port=5696
certificate_path=./server_certificate.pem
key_path=./server_key.pem
ca_path=./root_certificate.pem
auth_suite=TLS1.2
database_path=./pykmip.db
% pykmip-server --config_path ./server.cfg --log_path ./pykmip.log --logging_level=DEBUG

Then, use a Go TLS client to connect. Here is a runnable example. The relevant bit is:

conn, err := tls.Dial("tcp", "localhost:5696", &tls.Config{
		Certificates:       []tls.Certificate{cert},
		InsecureSkipVerify: true, // Do not verify hostname or server certificate signature.
	})
	if err != nil {
		panic("failed to connect: " + err.Error())
	}

This fails with panic: failed to connect: remote error: tls: handshake failure. The PyKMIP server logs:

Traceback (most recent call last):
  File "/Users/kevin.albertson/.venv/lib/python3.9/site-packages/kmip/services/server/session.py", line 102, in run
    self._connection.do_handshake()
  File "/usr/local/Cellar/[email protected]/3.9.7_1/Frameworks/Python.framework/Versions/3.9/lib/python3.9/ssl.py", line 1309, in do_handshake
    self._sslobj.do_handshake()
ssl.SSLError: [SSL: NO_SHARED_CIPHER] no shared cipher (_ssl.c:1129)

[kevinAlbs]

@PeterHamilton is it possible this could get reviewed soon? PyKMIP has been very helpful in testing the MongoDB Go driver with KMIP support. Thank you!

[kevinAlbs]

@arp102 is this OK to be merged?

[arp102]

@arp102 is this OK to be merged?

For security reasons, I don't think we want to add AES256-SHA to the default cipher set for TLS12AuthenticationSuite.

Have you tried using the BasicAuthenticationSuite instead? You can set auth_suite=Basic in the config files, and AES256-SHA will be one of the available ciphers.

If that doesn't work and code changes are required, then we should find another way to support your use-case without compromising security for the default TLS12 configuration.