tls: add --tls-cipher-list command line switch

doc/api/tls.markdown

@@ -77,6 +77,44 @@ handshake extensions allowing you:
   * SNI - to use one TLS server for multiple hostnames with different SSL
     certificates.
 
+## Modifying the Default TLS Cipher suite
+
+Node.js is built with a default suite of enabled and disabled TLS ciphers.
+Currently, the default cipher suite is:
+
+    ECDHE-RSA-AES128-GCM-SHA256:
+    ECDHE-ECDSA-AES128-GCM-SHA256:
+    ECDHE-RSA-AES256-GCM-SHA384:
+    ECDHE-ECDSA-AES256-GCM-SHA384:
+    DHE-RSA-AES128-GCM-SHA256:
+    ECDHE-RSA-AES128-SHA256:
+    DHE-RSA-AES128-SHA256:
+    ECDHE-RSA-AES256-SHA384:
+    DHE-RSA-AES256-SHA384:
+    ECDHE-RSA-AES256-SHA256:
+    DHE-RSA-AES256-SHA256:
+    HIGH:
+    !aNULL:
+    !eNULL:
+    !EXPORT:
+    !DES:
+    !RC4:
+    !MD5:
+    !PSK:
+    !SRP:
+    !CAMELLIA
+
+This default can be overriden entirely using the `--tls-cipher-list` command
+line switch. For instance, the following makes
+`ECDHE-RSA-AES128-GCM-SHA256:!RC4` the default TLS cipher suite:
+
+    node --tls-cipher-list="ECDHE-RSA-AES128-GCM-SHA256:!RC4"
+
+Note that the default cipher suite included within Node.js has been carefully
+selected to reflect current security best practices and risk mitigation.
+Changing the default cipher suite can have a significant impact on the security
+of an application. The `--tls-cipher-list` switch should by used only if
+absolutely necessary.
 
 ## Perfect Forward Secrecy
 
@@ -138,7 +176,7 @@ automatically set as a listener for the [secureConnection][] event.  The
   - `crl` : Either a string or list of strings of PEM encoded CRLs (Certificate
     Revocation List)
 
-  - `ciphers`: A string describing the ciphers to use or exclude, seperated by
+  - `ciphers`: A string describing the ciphers to use or exclude, separated by
     `:`. The default cipher suite is:
 
         ECDHE-RSA-AES128-GCM-SHA256:

doc/iojs.1

@@ -64,6 +64,9 @@ and servers.
 
   --v8-options           print v8 command line options
 
+  --tls-cipher-list=list use an alternative default TLS cipher list
+                         (available only when Node.js is built with
+                         OpenSSL and crypto support enabled)
 
 .SH ENVIRONMENT VARIABLES
 

lib/tls.js

@@ -5,6 +5,7 @@ const url = require('url');
 const util = require('util');
 const binding = process.binding('crypto');
 const Buffer = require('buffer').Buffer;
+const constants = require('constants');
 
 // Allow {CLIENT_RENEG_LIMIT} client-initiated session renegotiations
 // every {CLIENT_RENEG_WINDOW} seconds. An error event is emitted if more
@@ -15,29 +16,7 @@ exports.CLIENT_RENEG_WINDOW = 600;
 
 exports.SLAB_BUFFER_SIZE = 10 * 1024 * 1024;
 
-exports.DEFAULT_CIPHERS = [
-  'ECDHE-RSA-AES128-GCM-SHA256',
-  'ECDHE-ECDSA-AES128-GCM-SHA256',
-  'ECDHE-RSA-AES256-GCM-SHA384',
-  'ECDHE-ECDSA-AES256-GCM-SHA384',
-  'DHE-RSA-AES128-GCM-SHA256',
-  'ECDHE-RSA-AES128-SHA256',
-  'DHE-RSA-AES128-SHA256',
-  'ECDHE-RSA-AES256-SHA384',
-  'DHE-RSA-AES256-SHA384',
-  'ECDHE-RSA-AES256-SHA256',
-  'DHE-RSA-AES256-SHA256',
-  'HIGH',
-  '!aNULL',
-  '!eNULL',
-  '!EXPORT',
-  '!DES',
-  '!RC4',
-  '!MD5',
-  '!PSK',
-  '!SRP',
-  '!CAMELLIA'
-].join(':');
+exports.DEFAULT_CIPHERS = constants.defaultCipherList;
 
 exports.DEFAULT_ECDH_CURVE = 'prime256v1';
 

src/node.cc

@@ -3111,6 +3111,9 @@ static void PrintHelp() {
          "  --track-heap-objects  track heap object allocations for heap "
          "snapshots\n"
          "  --v8-options          print v8 command line options\n"
+#if HAVE_OPENSSL
+         "  --tls-cipher-list=val use an alternative default TLS cipher list\n"
+#endif
 #if defined(NODE_HAVE_I18N_SUPPORT)
          "  --icu-data-dir=dir    set ICU data load path to dir\n"
          "                        (overrides NODE_ICU_DATA)\n"
@@ -3242,6 +3245,10 @@ static void ParseArgs(int* argc,
     } else if (strcmp(arg, "--v8-options") == 0) {
       new_v8_argv[new_v8_argc] = "--help";
       new_v8_argc += 1;
+#if HAVE_OPENSSL
+    } else if (strncmp(arg, "--tls-cipher-list=", 18) == 0) {
+      default_cipher_list = arg + 18;
+#endif
 #if defined(NODE_HAVE_I18N_SUPPORT)
     } else if (strncmp(arg, "--icu-data-dir=", 15) == 0) {
       icu_data_dir = arg + 15;

src/node_constants.cc

@@ -24,6 +24,10 @@ namespace node {
 using v8::Handle;
 using v8::Object;
 
+#if HAVE_OPENSSL
+const char* default_cipher_list = DEFAULT_CIPHER_LIST_CORE;
+#endif
+
 void DefineErrnoConstants(Handle<Object> target) {
 #ifdef E2BIG
   NODE_DEFINE_CONSTANT(target, E2BIG);
@@ -1108,13 +1112,25 @@ void DefineUVConstants(Handle<Object> target) {
   NODE_DEFINE_CONSTANT(target, UV_UDP_REUSEADDR);
 }
 
+void DefineCryptoConstants(Handle<Object> target) {
+#if HAVE_OPENSSL
+  NODE_DEFINE_STRING_CONSTANT(target,
+                              "defaultCoreCipherList",
+                              DEFAULT_CIPHER_LIST_CORE);
+  NODE_DEFINE_STRING_CONSTANT(target,
+                              "defaultCipherList",
+                              default_cipher_list);
+#endif
+}
+
 void DefineConstants(Handle<Object> target) {
   DefineErrnoConstants(target);
   DefineWindowsErrorConstants(target);
   DefineSignalConstants(target);
   DefineOpenSSLConstants(target);
   DefineSystemConstants(target);
   DefineUVConstants(target);
+  DefineCryptoConstants(target);
 }
 
 }  // namespace node

src/node_constants.h

@@ -4,7 +4,36 @@
 #include "node.h"
 #include "v8.h"
 
+#if HAVE_OPENSSL
+#define DEFAULT_CIPHER_LIST_CORE "ECDHE-RSA-AES128-GCM-SHA256:"     \
+                                 "ECDHE-ECDSA-AES128-GCM-SHA256:"   \
+                                 "ECDHE-RSA-AES256-GCM-SHA384:"     \
+                                 "ECDHE-ECDSA-AES256-GCM-SHA384:"   \
+                                 "DHE-RSA-AES128-GCM-SHA256:"       \
+                                 "ECDHE-RSA-AES128-SHA256:"         \
+                                 "DHE-RSA-AES128-SHA256:"           \
+                                 "ECDHE-RSA-AES256-SHA384:"         \
+                                 "DHE-RSA-AES256-SHA384:"           \
+                                 "ECDHE-RSA-AES256-SHA256:"         \
+                                 "DHE-RSA-AES256-SHA256:"           \
+                                 "HIGH:"                            \
+                                 "!aNULL:"                          \
+                                 "!eNULL:"                          \
+                                 "!EXPORT:"                         \
+                                 "!DES:"                            \
+                                 "!RC4:"                            \
+                                 "!MD5:"                            \
+                                 "!PSK:"                            \
+                                 "!SRP:"                            \
+                                 "!CAMELLIA"
+#endif
+
 namespace node {
+
+#if HAVE_OPENSSL
+extern const char* default_cipher_list;
+#endif
+
 void DefineConstants(v8::Handle<v8::Object> target);
 }  // namespace node
 

src/node_internals.h

@@ -12,6 +12,22 @@
 
 struct sockaddr;
 
+// Variation on NODE_DEFINE_CONSTANT that sets a String value.
+#define NODE_DEFINE_STRING_CONSTANT(target, name, constant)                   \
+  do {                                                                        \
+    v8::Isolate* isolate = target->GetIsolate();                              \
+    v8::Local<v8::String> constant_name =                                     \
+        v8::String::NewFromUtf8(isolate, name);                               \
+    v8::Local<v8::String> constant_value =                                    \
+        v8::String::NewFromUtf8(isolate, constant);                           \
+    v8::PropertyAttribute constant_attributes =                               \
+        static_cast<v8::PropertyAttribute>(v8::ReadOnly | v8::DontDelete);    \
+    target->ForceSet(isolate->GetCurrentContext(),                            \
+                     constant_name,                                           \
+                     constant_value,                                          \
+                     constant_attributes);                                    \
+  } while (0)
+
 namespace node {
 
 // Forward declaration

test/parallel/test-tls-cipher-list.js

@@ -0,0 +1,32 @@
+'use strict';
+const common = require('../common');
+
+if (!common.hasCrypto) {
+  console.log('1..0 # Skipped: missing crypto');
+  return;
+}
+
+const assert = require('assert');
+const spawn = require('child_process').spawn;
+const defaultCoreList = require('constants').defaultCoreCipherList;
+
+function doCheck(arg, check) {
+  var out = '';
+  var arg = arg.concat([
+    '-pe',
+    'require("constants").defaultCipherList'
+  ]);
+  spawn(process.execPath, arg, {}).
+    on('error', assert.fail).
+    stdout.on('data', function(chunk) {
+      out += chunk;
+    }).on('end', function() {
+      assert.equal(out.trim(), check);
+    }).on('error', assert.fail);
+}
+
+// test the default unmodified version
+doCheck([], defaultCoreList);
+
+// test the command line switch by itself
+doCheck(['--tls-cipher-list=ABC'], 'ABC');