cisco's encryption algorithm can be easily broken


Subject: Security Notice: cisco Systems password encryption update

Date: Fri, 17 Mar 1995 12:21:27 -0800

From: David Carrel 



In recent postings, member(s) of this audience noted details of the

password "encryption" scheme utilized on cisco products.  These postings

note cisco's encryption algorithm can be easily broken.  This posting will

also explain the risks involved, what actions we're taking and what you can

do.  If you have any further questions after reading this posting, please

contact us through your normal support channel.



1) What is cisco's password protection/encryption legacy?



	cisco routers and access servers utilize passwords for

authentication.  Our products can perform authentication in several ways,

some of which require cleartext passwords.  For example, PPP-CHAP and ARAP

both require the cisco router to have access to a cleartext password.  A

strong one-way encryption algorithm is not an option for storing these

passwords.  Originally, all passwords were stored in cleartext.  Later, we

implemented a reversible algorithm with the intent of hiding passwords from

the casual observer.  Nothing more complex was ever intended, and we have

made this clear on this and other lists from time to time.



2) What are the risks with cisco's password protection/encryption scheme?



	Risks exist if an attacker can gain access to your configuration

with the encrypted strings.  Since our encryption can be reversed, access

to the encrypted strings can provide access to cleartext passwords.  If you

store configurations on a network server (either using tftp or rcp from the

router) there is some risk if an attacker has access to the networks

between the cisco router and the server, or if the attacker has access to

the server.  You may also be at risk if you view the configuration over a

networks session (such as telnet) and an intruder can gain access to those

network segments.



3) How can you protect your router passwords from unauthorized access?



        - First, consider upgrading your cisco software to get the latest

	  security enhancements.  These are described in the next section.

        - Next, protect your configurations.  Use Access lists and

	  Firewalls to help provide protection.  cisco can help you in both

	  of these areas.  If you must write configurations to a network

	  server, do your best to protect the network and the server.

        - Use rcp instead of tftp if possible.  Rcp is far from perfect,

	  but it is more secure that Tftp.  Tftp is completely

	  unauthenticated.

        - Use a console whenever possible for configuring a router.

	  Hardwiring a console means configuration data doesn't cross the

	  network.

        - Use TACACS to help keep a minimum number of passwords stored on

	  the router.  TACACS provides far superior authentication

	  mechanisms including one-time password systems.



4) Encryption enhancements are now available from cisco



        To address this encryption problem, we have implemented a stronger

one-way encryption algorithm. The algorithm is based on the MD5 hashing

function.  Remember, many passwords on the router must be reversible, so this

new algorithm is only used for the enable passwords. Using the new algorithm

and TACACS, users will be able to remove all weakly encrypted passwords from

the router.



	cisco has made new software images available on CIO (for registered

users: http://www.cisco.com or telnet/terminal access cio.cisco.com

408-526-8070 N81) or customers with Software Maintenance contracts may call

the Cisco Technical Assistance Center [800-553-2447, tac@cisco.com] to

request the software.



This code is available to customers in the following releases::



        Interim         Date            Maintenance     Date

        Release         Available       Release         Available

--------------------------------------------------------------------------

        10.0(8.1)*       NOW             10.0(9)         scheduled FCS 4/10

        10.2(4.4)*       NOW             10.2(5)         scheduled FCS 3/27

        10.3(1.2)*       NOW             10.3(2)         scheduled FCS 4/3



*the interim releases are only available via TAC.



        In addition, cisco is developing several additional security

enhancement projects.  Please continue to monitor our WWW homepage as some

of these will be available in the very near future.





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David Carrel				|  E-mail:  carrel@cisco.com

Security Development, cisco Systems	|  phone:   (408) 526-5207

170 W. Tasman Drive			|  fax:     (408) 526-4952

San Jose, CA 95134-1706			|  

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-- 

Paul Ferguson                                           ||        ||

cisco Systems                                           ||        ||

Consulting Engineering                                 ||||      ||||

Reston, Virginia USA                               ..:||||||:..:||||||:..

e-mail: pferguso@cisco.com                         c i s c o S y s t e m s