The GetDownloadOriginalKey method generates a download key for downloading password-protected originals. This method is new in API version 1.2.
string GetDownloadOriginalKey( long photoIds, string password )
A download key that should be provided as a query parameter in the download URL to authenticate the request. See Downloading Photos for more details.
The return value of this method is valid for a limited time. As a general rule, applications should issue a download request immediately after calling this method. Applications should not issue more than one download request per GetDownloadOriginalKey invocation.