Merge pull request chicks#2 from a1exsh/padding-option

Padding option

Author: chicks

README.rdoc

@@ -33,6 +33,21 @@ Usage:
  AES.decrypt(plain, key, {:format => :plain})
   => "A super secret message" 
 
+ # By default data is padded to the nearest 16 bytes block.  To turn
+ # this off, you may use the :padding => false (or nil) option.
+ #
+ # In this mode however, the caller is required to pad the data.  In
+ # the following example the message is exactly 16 bytes long, so no
+ # error aries.
+ msg = AES.encrypt("A secret message", key, {:padding => false})
+  => "SnD+WIfEfjZRrl+WAM/9pw==$89sGGZsu973j8Gl6aXC8Uw=="
+
+ # Be sure to pass the same padding option when decrypting the
+ # message, as it will fail if you try to decrypt unpadded data and
+ # didn't specify :padding => false.
+ AES.decrypt(msg, key, {:padding => false})
+  => "A secret message"
+
 == Contributing to aes
 
 * Check out the latest master to make sure the feature hasn't been implemented or the bug hasn't been fixed yet

lib/aes/aes.rb

@@ -122,11 +122,13 @@ def _encrypt
       # Merge init options with defaults
       def merge_options(opts)
         @options = {
-          :format => :base_64,
-          :cipher => "AES-256-CBC",
-          :iv     => nil,
+          :format  => :base_64,
+          :cipher  => "AES-256-CBC",
+          :iv      => nil,
+          :padding => true, # use cipher padding by default
         }.merge! opts
         _handle_iv
+        _handle_padding
       end
 
       def _handle_iv
@@ -139,12 +141,18 @@ def _handle_iv
         end
       end
 
+      def _handle_padding
+        # convert value to what OpenSSL module format expects
+        @options[:padding] = @options[:padding] ? 1 : 0
+      end
+      
       # Create a new cipher using the cipher type specified
       def _setup(action)
         @cipher ||= OpenSSL::Cipher::Cipher.new(@options[:cipher]) 
         # Toggles encryption mode
         @cipher.send(action)
+        @cipher.padding = @options[:padding]
         @cipher.key = @key.unpack('a2'*32).map{|x| x.hex}.pack('c'*32)
       end
   end
-end
+end

test/test_aes.rb

@@ -19,6 +19,17 @@ class TestAES < Test::Unit::TestCase
     enc2 = AES.encrypt(msg, key, {:iv => iv})
     assert_equal enc1, enc2
   end
+    
+  should "handle padding option" do
+    key = "01234567890123456789012345678901"
+    msg = "This is a message that nobody should ever see"
+    # unpadded message length should be a multiple of cipher block
+    # length (16 bytes)
+    msg += " "*(16 - (msg.length % 16))
+
+    enc = AES.encrypt(msg, key, {:padding => false})
+    assert_equal msg, AES.decrypt(enc, key, {:padding => false})
+  end
 
   should "generate a new key when AES#key" do
     assert_equal 32, AES.key.length