The NotifyLink key exchange protocol contains a vulnerability that significantly reduces the strength of cryptographic keys used to encrypt mail messages.
Notify Technology NotifyLink Enterprise Server allows users to synchronize e-mail between a PDA and a mail server. The application consists of a PDA-specific client and the NotifyLink server, which acts as a proxy between the client and the mail server(s) the user wants to check. For each e-mail account to be monitored, the user provides mail server credentials that are stored on the NotifyLink server and used to periodically check for mail. When new mail arrives, the NotifyLink server stores a reference to the message ID. Depending on the configuration, the message is either sent to the device via SMS ("Push" mode), or the device periodically checks a link on the NotifyLink web server to retrieve the message ("Poll" mode). The product supports multiple PDA platforms and multiple e-mail servers, including IMAP, POP, Microsoft Exchange, and Novell GroupWise.
NotifyLink uses AES keys to encrypt the mail messages that are exchanged between the PDA and NotifyLink server. These keys are stored on the server in a table named ClientDevices, which is protected from unauthenticated access. If the key is not transferred to the PDA manually, the client can retrieve it from the server using an unauthenticated HTTP post to /hwp/get.asp. When keys are transmitted using this method, the server uses a fixed byte reordering scheme to obfuscate the key. This scheme significantly reduces the strength of the key material, providing protection against only the most casual observer. In addition, any attacker in possession of the source code for get.asp will be able to determine the fixed scheme, making the reversal operation trivial.
This vulnerability significantly reduces the strength of cryptographic keys used to encrypt mail messages.
Use Manual Key Generation
We thank the NOAA NCIRT Lab for their discovery and analysis of this vulnerability.
This document was written by Jeffrey P Lanza and Will Dormann. It is based on analysis provided by the NOAA NCIRT Lab.
|Date First Published:||2005-03-17|
|Date Last Updated:||2005-04-28 15:13 UTC|