lib/slosilo/symmetric.rb in slosilo-1.1.0 vs lib/slosilo/symmetric.rb in slosilo-2.0.0

@@ -1,33 +1,54 @@
 module Slosilo
   class Symmetric
+    VERSION_MAGIC = 'G'
+    TAG_LENGTH = 16
+
     def initialize
-      @cipher = OpenSSL::Cipher.new 'AES-256-CBC'
+      @cipher = OpenSSL::Cipher.new 'aes-256-gcm' # NB: has to be lower case for whatever reason.
     end
-    
+
+    # This lets us do a final sanity check in migrations from older encryption versions
+    def cipher_name
+      @cipher.name
+    end
+
     def encrypt plaintext, opts = {}
       @cipher.reset
       @cipher.encrypt
-      @cipher.key = opts[:key]
+      @cipher.key = (opts[:key] or raise("missing :key option"))
       @cipher.iv = iv = random_iv
-      ctxt = @cipher.update(plaintext)
-      iv + ctxt + @cipher.final
+      @cipher.auth_data = opts[:aad] || "" # Nothing good happens if you set this to nil, or don't set it at all
+      ctext = @cipher.update(plaintext) + @cipher.final
+      tag = @cipher.auth_tag(TAG_LENGTH)
+      "#{VERSION_MAGIC}#{tag}#{iv}#{ctext}"
     end
-    
+
     def decrypt ciphertext, opts = {}
+      version, tag, iv, ctext = unpack ciphertext
+
+      raise "Invalid version magic: expected #{VERSION_MAGIC} but was #{version}" unless version == VERSION_MAGIC
+
       @cipher.reset
       @cipher.decrypt
       @cipher.key = opts[:key]
-      @cipher.iv, ctxt = ciphertext.unpack("a#{@cipher.iv_len}a*")
-      ptxt = @cipher.update(ctxt)
-      ptxt + @cipher.final
+      @cipher.iv = iv
+      @cipher.auth_tag = tag
+      @cipher.auth_data = opts[:aad] || ""
+      @cipher.update(ctext) + @cipher.final
     end
     
     def random_iv
       @cipher.random_iv
     end
     
     def random_key
       @cipher.random_key
+    end
+
+    private
+    # return tag, iv, ctext
+    def unpack msg
+      msg.unpack "aa#{TAG_LENGTH}a#{@cipher.iv_len}a*"
     end
   end
 end