lib/lockbox.rb in lockbox-0.2.0 vs lib/lockbox.rb in lockbox-0.2.1

@@ -20,10 +20,11 @@
 end
 
 class Lockbox
   class Error < StandardError; end
   class DecryptionError < Error; end
+  class PaddingError < Error; end
 
   class << self
     attr_accessor :default_options
     attr_writer :master_key
   end
@@ -135,9 +136,58 @@
     key
   end
 
   def self.to_hex(str)
     str.unpack("H*").first
+  end
+
+  PAD_FIRST_BYTE = "\x80".b
+  PAD_ZERO_BYTE = "\x00".b
+
+  # ISO/IEC 7816-4
+  # same as Libsodium
+  # https://libsodium.gitbook.io/doc/padding
+  # apply prior to encryption
+  # note: current implementation does not
+  # try to minimize side channels
+  def self.pad(str, size: 16)
+    raise ArgumentError, "Invalid size" if size < 1
+
+    str = str.dup.force_encoding(Encoding::BINARY)
+
+    pad_length = size - 1
+    pad_length -= str.bytesize % size
+
+    str << PAD_FIRST_BYTE
+    pad_length.times do
+      str << PAD_ZERO_BYTE
+    end
+
+    str
+  end
+
+  # note: current implementation does not
+  # try to minimize side channels
+  def self.unpad(str, size: 16)
+    raise ArgumentError, "Invalid size" if size < 1
+
+    if str.encoding != Encoding::BINARY
+      str = str.dup.force_encoding(Encoding::BINARY)
+    end
+
+    i = 1
+    while i <= size
+      case str[-i]
+      when PAD_ZERO_BYTE
+        i += 1
+      when PAD_FIRST_BYTE
+        return str[0..-(i + 1)]
+      else
+        break
+      end
+    end
+
+    raise Lockbox::PaddingError, "Invalid padding"
   end
 
   private
 
   def check_string(str, name)