aes_cbc_hs.rb in jwe-0.3.1

- old
+ new

@@ -1,7 +1,10 @@
+require 'jwe/enc/cipher'
+
 module JWE
   module Enc
+    # Abstract AES in Block cipher mode, with message signature for different key sizes.
     module AesCbcHs
       attr_accessor :cek
       attr_accessor :iv
       attr_accessor :tag
 
@@ -11,43 +14,47 @@
       end
 
       def encrypt(cleartext, authenticated_data)
         raise JWE::BadCEK.new("The supplied key is invalid. Required length: #{key_length}") if cek.length != key_length
 
-        cipher.encrypt
-        cipher.key = enc_key
-        cipher.iv = iv
+        ciphertext = cipher_round(:encrypt, iv, cleartext)
 
-        ciphertext = cipher.update(cleartext) + cipher.final
-        length = [authenticated_data.length * 8].pack('Q>') # 64bit big endian
+        signature = generate_tag(authenticated_data, iv, ciphertext)
+        self.tag = signature
 
-        to_sign = authenticated_data + iv + ciphertext + length
-        signature = OpenSSL::HMAC.digest(OpenSSL::Digest.new(hash_name), mac_key, to_sign)
-        self.tag = signature[0...mac_key.length]
-
         ciphertext
       end
 
       def decrypt(ciphertext, authenticated_data)
-        raise JWE::BadCEK.new("The supplied key is invalid. Required length: #{key_length}") if cek.length != key_length
+        raise JWE::BadCEK, "The supplied key is invalid. Required length: #{key_length}" if cek.length != key_length
 
-        length = [authenticated_data.length * 8].pack('Q>') # 64bit big endian
-        to_sign = authenticated_data + iv + ciphertext + length
-        signature = OpenSSL::HMAC.digest(OpenSSL::Digest.new(hash_name), mac_key, to_sign)
-        if signature[0...mac_key.length] != tag
-          raise JWE::InvalidData.new('Authentication tag verification failed')
+        signature = generate_tag(authenticated_data, iv, ciphertext)
+        if signature != tag
+          raise JWE::InvalidData, 'Authentication tag verification failed'
         end
 
-        cipher.decrypt
+        cipher_round(:decrypt, iv, ciphertext)
+      rescue OpenSSL::Cipher::CipherError
+        raise JWE::InvalidData, 'Invalid ciphertext or authentication tag'
+      end
+
+      def cipher_round(direction, iv, data)
+        cipher.send(direction)
         cipher.key = enc_key
         cipher.iv = iv
 
-        cipher.update(ciphertext) + cipher.final
-      rescue OpenSSL::Cipher::CipherError
-        raise JWE::InvalidData.new('Invalid ciphertext or authentication tag')
+        cipher.update(data) + cipher.final
       end
 
+      def generate_tag(authenticated_data, iv, ciphertext)
+        length = [authenticated_data.length * 8].pack('Q>') # 64bit big endian
+        to_sign = authenticated_data + iv + ciphertext + length
+        signature = OpenSSL::HMAC.digest(OpenSSL::Digest.new(hash_name), mac_key, to_sign)
+
+        signature[0...mac_key.length]
+      end
+
       def iv
         @iv ||= SecureRandom.random_bytes(16)
       end
 
       def cek
@@ -61,22 +68,21 @@
       def enc_key
         cek[key_length / 2..-1]
       end
 
       def cipher
-        @cipher ||= OpenSSL::Cipher.new(cipher_name)
-      rescue RuntimeError
-        raise JWE::NotImplementedError.new("The version of OpenSSL linked to your Ruby does not support the cipher #{cipher_name}.")
+        @cipher ||= Cipher.for(cipher_name)
       end
 
       def tag
         @tag || ''
       end
 
       def self.included(base)
         base.extend(ClassMethods)
       end
 
+      # Provides availability checks for Key Encryption algorithms
       module ClassMethods
         def available?
           new.cipher
           true
         rescue JWE::NotImplementedError