Introduce SecretKeyGenerator for more secure session secrets than...

Introduce SecretKeyGenerator for more secure session secrets than CGI::Session's pseudo-random id generator. Consider extracting to Active Support later. Closes #10286.


git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@8229 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

railties/CHANGELOG

 *SVN*
 
+* Introduce SecretKeyGenerator for more secure session secrets than CGI::Session's pseudo-random id generator. Consider extracting to Active Support later.  #10286 [Hongli Lai]
+
 * RAILS_GEM_VERSION may be set to any valid gem version specifier.  #10057 [Chad Woolley, Chu Yeow]
 
 * Load config/preinitializer.rb, if present, before loading the environment.  #9943 [Chad Woolley]

railties/lib/rails_generator/generators/applications/app/app_generator.rb

 require 'rbconfig'
 require 'digest/md5' 
+require 'rails_generator/secret_key_generator'
 
 class AppGenerator < Rails::Generator::Base
   DEFAULT_SHEBANG = File.join(Config::CONFIG['bindir'],
@@ -33,6 +34,9 @@ def manifest
     md5 << String($$)
     md5 << @app_name
 
+    # Do our best to generate a secure secret key for CookieStore
+    secret = Rails::SecretKeyGenerator.new(@app_name).generate_secret
+
     record do |m|
       # Root directory and all subdirectories.
       m.directory ''
@@ -61,7 +65,7 @@ def manifest
 
       # Environments
       m.file "environments/boot.rb",    "config/boot.rb"
-      m.template "environments/environment.rb", "config/environment.rb", :assigns => { :freeze => options[:freeze], :app_name => @app_name, :app_secret => md5.hexdigest }
+      m.template "environments/environment.rb", "config/environment.rb", :assigns => { :freeze => options[:freeze], :app_name => @app_name, :app_secret => secret }
       m.file "environments/production.rb",  "config/environments/production.rb"
       m.file "environments/development.rb", "config/environments/development.rb"
       m.file "environments/test.rb",        "config/environments/test.rb"

railties/lib/rails_generator/secret_key_generator.rb

+# A class for creating random secret keys. This class will do its best to create a
+# random secret key that's as secure as possible, using whatever methods are
+# available on the current platform. For example:
+#
+#   generator = Rails::SecretKeyGenerator("some unique identifier, such as the application name")
+#   generator.generate_secret     # => "f3f1be90053fa851... (some long string)"
+
+module Rails
+  class SecretKeyGenerator
+    GENERATORS = [ :secure_random, :win32_api, :urandom, :openssl, :prng ].freeze
+
+    def initialize(identifier)
+      @identifier = identifier
+    end
+
+    # Generate a random secret key with the best possible method available on
+    # the current platform.
+    def generate_secret
+      generator = GENERATORS.find do |g|
+        self.class.send("supports_#{g}?")
+      end
+      send("generate_secret_with_#{generator}")
+    end
+
+    # Generate a random secret key by using the Win32 API. Raises LoadError
+    # if the current platform cannot make use of the Win32 API. Raises
+    # SystemCallError if some other error occured.
+    def generate_secret_with_win32_api
+      # Following code is based on David Garamond's GUID library for Ruby.
+      require 'Win32API'
+
+      crypt_acquire_context = Win32API.new("advapi32", "CryptAcquireContext",
+                                           'PPPII', 'L')
+      crypt_gen_random = Win32API.new("advapi32", "CryptGenRandom",
+                                      'LIP', 'L')
+      crypt_release_context = Win32API.new("advapi32", "CryptReleaseContext",
+                                         'LI', 'L')
+      prov_rsa_full       = 1
+      crypt_verifycontext = 0xF0000000
+
+      hProvStr = " " * 4
+      if crypt_acquire_context.call(hProvStr, nil, nil, prov_rsa_full,
+                                    crypt_verifycontext) == 0
+        raise SystemCallError, "CryptAcquireContext failed: #{lastWin32ErrorMessage}"
+      end
+      hProv, = hProvStr.unpack('L')
+      bytes = " " * 64
+      if crypt_gen_random.call(hProv, bytes.size, bytes) == 0
+        raise SystemCallError, "CryptGenRandom failed: #{lastWin32ErrorMessage}"
+      end
+      if crypt_release_context.call(hProv, 0) == 0
+        raise SystemCallError, "CryptReleaseContext failed: #{lastWin32ErrorMessage}"
+      end
+      bytes.unpack("H*")[0]
+    end
+
+    # Generate a random secret key with Ruby 1.9's SecureRandom module.
+    # Raises LoadError if the current Ruby version does not support
+    # SecureRandom.
+    def generate_secret_with_secure_random
+      require 'securerandom'
+      return SecureRandom.hex(64)
+    end
+
+    # Generate a random secret key with OpenSSL. If OpenSSL is not
+    # already loaded, then this method will attempt to load it.
+    # LoadError will be raised if that fails.
+    def generate_secret_with_openssl
+      require 'openssl'
+      if !File.exist?("/dev/urandom")
+        # OpenSSL transparently seeds the random number generator with
+        # data from /dev/urandom. On platforms where that is not
+        # available, such as Windows, we have to provide OpenSSL with
+        # our own seed. Unfortunately there's no way to provide a
+        # secure seed without OS support, so we'll have to do with
+        # rand() and Time.now.usec().
+        OpenSSL::Random.seed(rand(0).to_s + Time.now.usec.to_s)
+      end
+      data = OpenSSL::BN.rand(2048, -1, false).to_s
+      return OpenSSL::Digest::SHA512.new(data).hexdigest
+    end
+
+    # Generate a random secret key with /dev/urandom.
+    # Raises SystemCallError on failure.
+    def generate_secret_with_urandom
+      return File.read("/dev/urandom", 64).unpack("H*")[0]
+    end
+
+    # Generate a random secret key with Ruby's pseudo random number generator,
+    # as well as some environment information.
+    #
+    # This is the least cryptographically secure way to generate a secret key,
+    # and should be avoided whenever possible.
+    def generate_secret_with_prng
+      require 'digest/sha2'
+      sha = Digest::SHA2.new(512)
+      now = Time.now
+      sha << now.to_s
+      sha << String(now.usec)
+      sha << String(rand(0))
+      sha << String($$)
+      sha << @identifier
+      return sha.hexdigest
+    end
+
+    private
+      def lastWin32ErrorMessage
+        # Following code is based on David Garamond's GUID library for Ruby.
+        get_last_error = Win32API.new("kernel32", "GetLastError", '', 'L')
+        format_message = Win32API.new("kernel32", "FormatMessageA",
+                                      'LPLLPLPPPPPPPP', 'L')
+        format_message_ignore_inserts  = 0x00000200
+        format_message_from_system     = 0x00001000
+
+        code = get_last_error.call
+        msg = "\0" * 1024
+        len = format_message.call(format_message_ignore_inserts +
+                                  format_message_from_system, 0,
+                                  code, 0, msg, 1024, nil, nil,
+                                  nil, nil, nil, nil, nil, nil)
+        msg[0, len].tr("\r", '').chomp
+      end
+
+      def self.supports_secure_random?
+        begin
+          require 'securerandom'
+          true
+        rescue LoadError
+          false
+        end
+      end
+
+      def self.supports_win32_api?
+        return false unless RUBY_PLATFORM =~ /(:?mswin|mingw)/
+        begin
+          require 'Win32API'
+          true
+        rescue LoadError
+          false
+        end
+      end
+
+      def self.supports_urandom?
+        File.exists?('/dev/urandom')
+      end
+
+      def self.supports_openssl?
+        begin
+          require 'openssl'
+          true
+        rescue LoadError
+          false
+        end
+      end
+
+      def self.supports_prng?
+        true
+      end
+  end
+end

railties/test/secret_key_generation_test.rb

+require 'test/unit'
+
+# Must set before requiring generator libs.
+if defined?(RAILS_ROOT)
+  RAILS_ROOT.replace "#{File.dirname(__FILE__)}/fixtures"
+else
+  RAILS_ROOT = "#{File.dirname(__FILE__)}/fixtures"
+end
+
+$LOAD_PATH.unshift "#{File.dirname(__FILE__)}/../lib"
+
+require 'rails_generator'
+require 'rails_generator/secret_key_generator'
+require 'rails_generator/generators/applications/app/app_generator'
+
+class SecretKeyGenerationTest < Test::Unit::TestCase
+  SECRET_KEY_MIN_LENGTH = 128
+  APP_NAME = "foo"
+
+  def setup
+    @generator = Rails::SecretKeyGenerator.new(APP_NAME)
+  end
+
+  def test_secret_key_generation
+    assert @generator.generate_secret.length >= SECRET_KEY_MIN_LENGTH
+  end
+
+  Rails::SecretKeyGenerator::GENERATORS.each do |generator|
+    if Rails::SecretKeyGenerator.send("supports_#{generator}?")
+      define_method("test_secret_key_generation_with_#{generator}") do
+        assert @generator.send("generate_secret_with_#{generator}").length >= SECRET_KEY_MIN_LENGTH
+      end
+    end
+  end
+end