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Date: Tue, 29 Mar 2011 10:41:55 +1100
From: Patrick Barnes <mrtrick@gmail.com>
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To: user@couchdb.apache.org
Subject: Re: Question about validator functions and replication
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On 29/03/2011 2:38 AM, Nebu Pookins wrote:
>> If you have some secure data floating around in your db, encryption can
>> >  still be a good idea. Parts of one of my databases are encrypted, because
>> >  users need to be able to see some documents in the db but not others.
> I'm curious as how you've implemented encryption in your DB. Was it
> pure JavaScript, or did you use native libraries? Elsewhere in this
> thread, I've started a new "branch" where I've started outlining my
> concerns with a pure JavaScript solution and wondered if cryptography
> could be included as a core feature of CouchDB.

I'm using couchdb as a database, not to serve up pages directly to 
users. As a consequence, a 'user' is a web application, and multiple 
applications have differing levels of access to the database.

Each application is allowed to store it's own 'application data' 
documents and I override two methods in my document class to allow 
transparent decryption/encryption of those docs when read/written. (see 
below)

The reason I implemented encryption is that there's no per-doc read 
access control in couchdb, so without encryption, I'm not able to 
prevent applications from accessing another application's document. It's 
not as good a solution as proper access control.

-Patrick


	/**
	 * Given an object - load all the attributes from it into the document 
- displacing existing attributes.
      * If the data field is encrypted, attempts to decrypt it.
	 * @param stdClass $obj : An object with the desired attributes.
	 **/
	public function loadFromObject(stdClass $obj) {
         parent::loadFromObject($obj);
         if ($this->doc_type != 'appdata') throw new 
InvalidArgumentException("Wrong object type - Cgm_Appdata is for appdata 
only");

         //Does the data section need to be decrypted?
         if (isset($this->encrypted) and $this->encrypted == true) {
             // Check that decryption info is stored
             $conf = Cgm_Document_Gateway::getAppConfig($this->source);
             if (!$conf->decrypt) throw new LogicException("Cannot load 
document - no decryption is configured, and the document is encrypted.");

             // Decrypt and decode the data
             $decryptor = new Zend_Filter_Decrypt($conf->decrypt);

             $raw = base64_decode($this->data);
             $plain_json = trim($decryptor->filter($raw));
             $plain = json_decode($plain_json);

             if ($plain === NULL) throw new LogicException("Cannot load 
document - decryption configuration is incorrect.");

             // Store the plain data within the object, in the same way 
as a non-encrypted object.
             $this->data = $plain;
             unset($this->encrypted);
         }
	}

     /**
      * Export to an object.
      * If encryption is configured, attempts to encrypt the data field.
      * @return stdClass $obj
      */
     public function exportToObject() {
         $obj = parent::exportToObject();

         //Should the data section be encrypted?
         $conf = Cgm_Document_Gateway::getAppConfig($this->source);
         if ($conf->encrypt) {
             $encryptor = new Zend_Filter_Encrypt($conf->encrypt);
             $cryptdata = base64_encode( $encryptor->filter( 
Zend_Json::encode($obj->data) ) );
             $obj->data = $cryptdata;
             $obj->encrypted = true;
         }
         //Was it encrypted before? - ensure that the flag is cleared
         elseif (isset($obj->encrypted)) {
             $obj->encrypted = false;
         }

         return $obj;
     }