Return a Ciphertext object

This behaves approximately like a string, at least for many operations
that a ciphertext is likely to have performed on it.  It also supports
encoding to any encoding recognised by RbNaCl

lib/rbnacl.rb

@@ -25,6 +25,7 @@ class LengthError < ArgumentError; end
 require "rbnacl/keys/public_key"
 require "rbnacl/keys/signing_key"
 require "rbnacl/keys/verify_key"
+require "rbnacl/ciphertext"
 require "rbnacl/box"
 require "rbnacl/secret_box"
 require "rbnacl/hash"

lib/rbnacl/ciphertext.rb

@@ -0,0 +1,57 @@
+# encoding: binary
+module Crypto
+  # A Ciphertext returned by the library
+  #
+  # Holds the ciphertext returned by the library.  This acts like a string in
+  # many cases, but also supports interrogating for the primitive used and can
+  # be encoded into a variety of formats.
+  class Ciphertext
+    attr_reader :ciphertext, :primitive
+    attr_accessor :default_encoding
+    def initialize(ciphertext, primitive, default_encoding = :raw)
+      @ciphertext       = ciphertext
+      @primitive        = primitive
+      @default_encoding = default_encoding
+    end
+
+    # Returns the ciphertext string
+    #
+    # Optionally encodes it too
+    #
+    # @param encoding [Symbol] encoding to use
+    #
+    # @return [String] ciphertext
+    def to_str(encoding = default_encoding)
+      Encoder[encoding].encode(ciphertext)
+    end
+
+    alias to_s to_str
+
+
+    def inspect
+      "#<#{self.class}:#{primitive}:#{to_str(:hex)[0,16]}>"
+    end
+
+    # size of the ciphertext in bytes
+    #
+    # This returns the size in the specified encoding, to avoid confusion
+    # in the case of a non-raw default encoding.
+    #
+    # @param encoding [Symbol] encoding to use
+    #
+    # @return [Integer bytesize of encoded ciphertext
+    def bytesize(encoding = default_encoding)
+      to_s(encoding).bytesize
+    end
+
+    # Concatenate a string
+    def +(thing)
+      to_s + thing.to_s
+    end
+
+    # tests for equality by converting a to string
+    def ==(thing)
+      thing.respond_to?(:to_s) ? to_s == thing.to_s : false
+    end
+  end
+end

lib/rbnacl/secret_box/xsalsa20_poly1305.rb

@@ -70,7 +70,8 @@ def box(nonce, message)
         ct  = Util.zeros(msg.bytesize)
 
         NaCl.crypto_secretbox_xsalsa20poly1305(ct, msg, msg.bytesize, nonce, @key) || raise(CryptoError, "Encryption failed")
-        Util.remove_zeros(NaCl::BOXZEROBYTES, ct)
+        ct = Util.remove_zeros(NaCl::BOXZEROBYTES, ct)
+        Ciphertext.new(ct, PRIMITIVE)
       end
       alias encrypt box
 

spec/rbnacl/ciphertext_spec.rb

@@ -0,0 +1,40 @@
+# encoding: binary
+require 'spec_helper'
+
+describe Crypto::Ciphertext do
+  let(:text) { "hello" }
+  let(:primitive) { :test  }
+  let(:ciphertext) { described_class.new(text, primitive) }
+  let(:encoded_ciphertext) { described_class.new(text, primitive, :hex) }
+  it "returns the ciphertext on #to_s" do
+    ciphertext.to_s.should == text
+  end
+
+  it "returns the primitive" do
+    ciphertext.primitive.should be primitive
+  end
+
+  it "interpolates correctly" do
+    "#{ciphertext}".should == text
+  end
+
+  it "packs correctly" do
+    [ciphertext].pack('a*').should == text
+  end
+
+  it "encodes when asked" do
+    ciphertext.to_s(:hex).should == Crypto::Encoder[:hex].encode(text)
+  end
+
+  it "behaves like a string for equality" do
+    ciphertext.should == text
+  end
+
+  it "behaves like a string for addition" do
+    (ciphertext + text).should == text * 2
+  end
+
+  it "accepts a default encoding" do
+    encoded_ciphertext.should == Crypto::Encoder[:hex].encode(text)
+  end
+end