Remove ciphersuites without Lucky13 countermeasures

SHA-256 variants of the CBC ciphersuites don't implement any Lucky13
countermeasures. See http://www.isg.rhul.ac.uk/tls/Lucky13.html and
https://www.imperialviolet.org/2013/02/04/luckythirteen.html.

authority/config/tls_options.go

@@ -22,18 +22,19 @@ var (
 	}
 	// ApprovedTLSCipherSuites smallstep approved ciphersuites.
 	ApprovedTLSCipherSuites = CipherSuites{
-		"TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA",
-		"TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256",
+		// AEADs w/ ECDHE
 		"TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256",
-		"TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA",
+		"TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256",
 		"TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384",
+		"TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384",
 		"TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256",
+		"TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256",
+
+		// CBC w/ ECDHE
+		"TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA",
+		"TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA",
 		"TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA",
-		"TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256",
-		"TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256",
 		"TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA",
-		"TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384",
-		"TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256",
 	}
 	// DefaultTLSOptions represents the default TLS version as well as the cipher
 	// suites used in the TLS certificates.
@@ -146,8 +147,8 @@ var cipherSuites = map[string]uint16{
 	"TLS_CHACHA20_POLY1305_SHA256": tls.TLS_CHACHA20_POLY1305_SHA256,
 
 	// Legacy names.
-	"TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305":   tls.TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305,
-	"TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305": tls.TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305,
+	"TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305":   tls.TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256,
+	"TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305": tls.TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256,
 }
 
 // TLSOptions represents the TLS options that can be specified on *tls.Config