Initial commit with length-hiding middleware and railtie

.gitignore

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+*.gem
+*.rbc
+.bundle
+.config
+.yardoc
+Gemfile.lock
+InstalledFiles
+_yardoc
+coverage
+doc/
+lib/bundler/man
+pkg
+rdoc
+spec/reports
+test/tmp
+test/version_tmp
+tmp

Gemfile

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+source 'https://rubygems.org'
+
+# Specify your gem's dependencies in breach-mitigation-rails.gemspec
+gemspec

LICENSE.txt

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+Copyright (c) 2013 BBA, Inc.
+
+MIT License
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

README.md

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+# breach-mitigation-rails
+
+Makes Rails applications less susceptible to the BREACH / CRIME
+attacks. See [breachattack.com](http://breachattack.com/) for details.
+
+## How it works
+
+This gem implements two of the suggestion mitigation strategies from
+the paper:
+
+*Masking Secrets*: The Rails CSRF token is 'masked' by encrypting it
+with a 32-byte one-time pad, and the pad and encrypted token are
+returned to the browser, instead of the "real" CSRF token. This only
+protects the CSRF token from an attacker; it does not protect other
+data on your pages (see the paper for details on this).
+
+*Length Hiding*: The BreachMitigation::LengthHiding middleware
+appends an HTML comment up to 2k in length to the end of all HTML
+documents served by your app. As noted in the paper, this does not
+prevent plaintext recovery, but it can slow the attack and it's
+relatively inexpensive to implement. Unlike the CSRF token masking,
+length hiding protects the entire page body from recovery.
+
+## Warning!
+
+BREACH and CRIME are **complicated and wide-ranging attacks**, and this
+gem offers only partial protection for Rails applications. If you're
+concerned about the security of your web app, you should review the
+BREACH paper and look for other, application-specific things you can
+do to prevent or mitigate this class of attacks.
+
+## Installation
+
+Add this line to your Rails Gemfile:
+
+    gem 'breach-mitigation-rails'
+
+And then execute:
+
+    $ bundle
+
+TODO And then?
+
+## Contributing
+
+Pull requests are welcome, either to enhance the existing mitigation
+strategies or to add new ways to mitigate against the attack.
+
+## License
+
+MIT - see LICENSE.txt

Rakefile

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+require "bundler/gem_tasks"

breach-mitigation-rails.gemspec

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+# coding: utf-8
+lib = File.expand_path('../lib', __FILE__)
+$LOAD_PATH.unshift(lib) unless $LOAD_PATH.include?(lib)
+require 'breach_mitigation/version'
+
+Gem::Specification.new do |spec|
+  spec.name          = "breach-mitigation-rails"
+  spec.version       = BreachMitigation::VERSION
+  spec.authors       = ["Bradley Buda"]
+  spec.email         = ["[email protected]"]
+  spec.description   = %q{Mitigates the BREACH and CRIME attacks on TLS in Rails applications}
+  spec.summary       = %q{Uses length-hiding and CSRF token masking to make it more difficult for an attacker to recover plaintext from HTTP responses. See README.md for details.}
+  spec.homepage      = "https://github.com/meldium/breach-mitigation-rails"
+  spec.license       = "MIT"
+
+  spec.files         = `git ls-files`.split($/)
+  spec.executables   = spec.files.grep(%r{^bin/}) { |f| File.basename(f) }
+  spec.test_files    = spec.files.grep(%r{^(test|spec|features)/})
+  spec.require_paths = ["lib"]
+
+  spec.add_development_dependency "bundler", "~> 1.3"
+  spec.add_development_dependency "rake"
+end

lib/breach-mitigation-rails.rb

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+require 'breach_mitigation/railtie' if defined?(Rails)

lib/breach_mitigation/length_hiding.rb

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+module BreachMitigation
+  class LengthHiding
+    def initialize(app)
+      @app = app
+    end
+
+    def call(env)
+      status, headers, body = @app.call(env)
+
+      # Only pad HTML documents
+      if headers['Content-Type'] =~ /text\/html/
+        # Copy the existing response to a new object
+        response = Rack::Response.new(body, status, headers)
+
+        # Append to that response
+        response.write random_html_comment
+
+        body.close if body.respond_to? :close
+        response.finish
+      else
+        [status, headers, body]
+      end
+    end
+
+    private
+
+    # Append a comment from 0 to MAX_LENGTH bytes in size to the
+    # response body. See section 3.1 of "BREACH: Reviving the CRIME
+    # attack". This should make BREACH attacks take longer, but does
+    # not fully protect against them. The longer MAX_LENGTH is, the
+    # more effective the mitigation is, however longer lengths mean
+    # more time spent in this middleware and more data on the wire.
+
+    MAX_LENGTH = 2048
+    ALPHABET = ('a'..'z').to_a
+
+    def random_html_comment
+      # The length of the padding should be strongly random, but the
+      # data itself doesn't need to be strongly random; it just needs
+      # to be resistant to compression
+      length = SecureRandom.random_number(1024)
+
+      # TODO make this faster
+      junk = ''
+      length.times { junk << ALPHABET.sample }
+
+      "\n<!-- This is a random-length HTML comment: #{junk} -->"
+    end
+  end
+end

lib/breach_mitigation/railtie.rb

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+require 'breach_mitigation/length_hiding'
+
+module BreachMitigation
+  class Railtie < Rails::Railtie
+    initializer "breach-mitigation-rails.insert_middleware" do |app|
+      app.config.middleware.use "BreachMitigation::LengthHiding"
+    end
+  end
+end

lib/breach_mitigation/version.rb

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+module BreachMitigation
+  VERSION = "0.0.1"
+end