DRY decrypt code

Author: xdmnl

lib/xmlenc.js

@@ -123,58 +123,30 @@ function decrypt(xml, options, callback) {
   if (!options.key)
     return callback(new Error('key option is mandatory and you should provide a valid RSA private key'));
 
-  var decrypted;
-
   try {
     var doc = typeof xml === 'string' ? new xmldom.DOMParser().parseFromString(xml) : xml;
 
     var symmetricKey = decryptKeyInfo(doc, options);
     var encryptionMethod = xpath.select("//*[local-name(.)='EncryptedData']/*[local-name(.)='EncryptionMethod']", doc)[0];
     var encryptionAlgorithm = encryptionMethod.getAttribute('Algorithm');
 
-    var algorithm;
-    var ivLength;
     var encryptedContent = xpath.select("//*[local-name(.)='EncryptedData']/*[local-name(.)='CipherData']/*[local-name(.)='CipherValue']", doc)[0];
 
     var encrypted = new Buffer(encryptedContent.textContent, 'base64');
 
     switch (encryptionAlgorithm) {
       case 'http://www.w3.org/2001/04/xmlenc#aes128-cbc':
-        algorithm = 'aes-128-cbc';
-        ivLength = 16;
-        break;
+        return callback(null, decryptWithAlgorithm('aes-128-cbc', symmetricKey, 16, encrypted));
       case 'http://www.w3.org/2001/04/xmlenc#aes256-cbc':
-        algorithm = 'aes-256-cbc';
-        ivLength = 16;
-        break;
+        return callback(null, decryptWithAlgorithm('aes-256-cbc', symmetricKey, 16, encrypted));
       case 'http://www.w3.org/2001/04/xmlenc#tripledes-cbc':
-        algorithm = 'des-ede3-cbc';
-        ivLength = 8;
-        break;
+        return callback(null, decryptWithAlgorithm('des-ede3-cbc', symmetricKey, 8, encrypted));
       default:
         return callback(new Error('encryption algorithm ' + encryptionAlgorithm + ' not supported'));
     }
-
-    var decipher = crypto.createDecipheriv(algorithm, symmetricKey, encrypted.slice(0,ivLength));
-    decipher.setAutoPadding(false);
-
-    decrypted = decipher.update(encrypted.slice(ivLength), null, 'binary') + decipher.final('binary');
-
-    // Remove padding bytes equal to the value of the last byte of the returned data.
-    var padding = decrypted.charCodeAt(decrypted.length - 1);
-    if (1 <= padding && padding <= ivLength) {
-      decrypted = decrypted.substr(0, decrypted.length - padding);
-    } else {
-      callback(new Error('padding length invalid'));
-      return;
-    }
-
-    decrypted = new Buffer(decrypted, 'binary').toString('utf8');
   } catch (e) {
     return callback(e);
   }
-
-  callback(null, decrypted);
 }
 
 function decryptKeyInfo(doc, options) {
@@ -233,6 +205,24 @@ function encryptWithAlgorithm(algorithm, symmetricKey, ivLength, content, encodi
   });
 }
 
+function decryptWithAlgorithm(algorithm, symmetricKey, ivLength, content) {
+  var decipher = crypto.createDecipheriv(algorithm, symmetricKey, content.slice(0,ivLength));
+  decipher.setAutoPadding(false);
+
+  var decrypted = decipher.update(content.slice(ivLength), null, 'binary') + decipher.final('binary');
+
+  // Remove padding bytes equal to the value of the last byte of the returned data.
+  var padding = decrypted.charCodeAt(decrypted.length - 1);
+  if (1 <= padding && padding <= ivLength) {
+    decrypted = decrypted.substr(0, decrypted.length - padding);
+  } else {
+    callback(new Error('padding length invalid'));
+    return;
+  }
+
+  return new Buffer(decrypted, 'binary').toString('utf8');
+}
+
 exports = module.exports = {
   decrypt: decrypt,
   encrypt: encrypt,