Add ActiveSupport::MessageVerifier to aid users who need to store tamper-proof messages in cookies etc.

This is particularly useful for things like remember-me tokens in web applications and auto-unsubscribe links in emails.

1 files changed, 45 insertions, 0 deletions

diff --git a/activesupport/lib/active_support/message_verifier.rb b/activesupport/lib/active_support/message_verifier.rb
new file mode 100644
index 0000000000..f3f905c15e
--- /dev/null
+++ b/activesupport/lib/active_support/message_verifier.rb
@@ -0,0 +1,45 @@
+module ActiveSupport
+  # MessageVerifier makes it easy to generate and verify messages which are signed
+  # to prevent tampering.
+  # 
+  # This is useful for cases like remember-me tokens and auto-unsubscribe links where the
+  # session store isn't suitable or available.
+  #
+  # Remember Me:
+  #   cookies[:remember_me] = @verifier.generate_message([@user.id, 2.weeks.from_now])
+  # 
+  # In the authentication filter:
+  #
+  #   id, time = @verifier.verify_message(cookies[:remember_me])
+  #   if time < Time.now
+  #     self.current_user = User.find(id)
+  #   end
+  # 
+  class MessageVerifier
+    class InvalidSignature < StandardError; end
+    
+    def initialize(secret, digest = 'SHA1')
+      @secret = secret
+      @digest = digest
+    end
+    
+    def verify_message(signed_message)
+      data, digest = signed_message.split("--")
+      if digest != generate_digest(data)
+        raise InvalidSignature
+      else
+        Marshal.load(ActiveSupport::Base64.decode64(data))
+      end
+    end
+    
+    def generate_message(value)
+      data = ActiveSupport::Base64.encode64s(Marshal.dump(value))
+      "#{data}--#{generate_digest(data)}"
+    end
+    
+    private
+      def generate_digest(data)
+        OpenSSL::HMAC.hexdigest(OpenSSL::Digest::Digest.new(@digest), @secret, data)
+      end
+  end
+end
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