Transcript A Roaming Authentication Solution for Wifi using IPSec

A Roaming Authentication Solution for
Wifi using IPSec VPNs with client
certificates
Carlos Ribeiro
[email protected]
Fernando Silva
[email protected]
André Zúquete
[email protected]
Goals
 Primary goal
– To provide user authentication, data encryption
and automatic roaming on wifi networks.
– e-U initiative
 The solution should be:
– deliverable on most computers and wifi access
points (APs);
– simple to deploy;
– simple to use by clients;
– scalable to many users and networks.
TNC2004 Carlos Ribeiro, Fernando Silva, André Zúquete
Overview of the solution
 Virtual Private Networks (VPNs), provide:
– data encryption;
– and Peer/data authentication;
 IPSec VPNs
– Standard;
– Well-tested.
– Available in most platforms.
 Authentication with client (hereafter supplicants)
certificates
– Authentication servers are able to check certificates
issued by other institutions.
TNC2004 Carlos Ribeiro, Fernando Silva, André Zúquete
Architecture
Local supplicants
access only
Open subnet
Laptop computer
Laptop computer
Laptop computer
VPN Gateway &
Firewall
Generic traffic
blocked by the firewall
Internet
Traffic carried
by the VPN
Radio tower
Radio tower
Radio tower
Internal
Network
Wifi
VLAN
External
Firewall
VPN Traffic
Redirected
HTTP/HTTPS
Traffic
LDAP Server
HTTP/HTTPS
Server
TNC2004 Carlos Ribeiro, Fernando Silva, André Zúquete
Supplicant certificates
 Often avoided due to the complexity of
Public Key Infrastructures (PKIs)
 To avoid PKIs, supplicant certificates:
– Cannot be used for irrevocable identification
(sign);
– Must have a short/medium validity period.
 Instead of a PKI, supplicant credentials are:
– distributed by HTTPS server;
– Kept in a directory server (LDAP, SQL, AD)
TNC2004 Carlos Ribeiro, Fernando Silva, André Zúquete
Supplicant credentials
 Credentials are generated and kept in the directory
server.
– Credentials = private
key; supplicant certificate; and
other certificates.
– Supplicants do not need
to generate the credentials
themselves.
– Can be supplied more
then once to end users.
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Directory Server
 Certificates have short validity periods
– Certification Revocation Lists are not necessary
TNC2004 Carlos Ribeiro, Fernando Silva, André Zúquete
HTTPS server
Roaming
 Each institution acts has a certification entity for
their users.
– It has a private key and a self-signed certificate.
– Generates private keys and certificates for their users.
– There is no need for a central certification entity.
 Roaming agreements can be put in place
incrementally
– Without modifying or reissuing local certificates.
– Bilateral agreements.
– Multilateral, hierarchical agreements.
 Local certificates issued before the roaming
agreement, become valid roaming certificates
transparently.
TNC2004 Carlos Ribeiro, Fernando Silva, André Zúquete
Local authentication
Institution A
Supplicant
Institution A
Gateway
stablishing a Gateway
Authentication
ession key
Supplicant
authentication
Supplicant
Send
InstA
Supplicant
InstA
Verify Certificate
Extract
InstA
Supplicant
Private key
Send
Supplicant
Public key
Gateway
InstA
Gateway
Public key
Gateway
Private key
TNC2004 Carlos Ribeiro, Fernando Silva, André Zúquete
InstA
Supplicant
authentication
Roaming authentication
Supplicant
InstA
Send
Supplicant
Verify Certificate
InstA
Extract
InstB
Supplicant
Private key
Supplicant
Public key
The only difference between local and roaming
authentication is in the certificate verification phase.
• Bilateral agreements
• Multilateral/Hierarchical agreements
TNC2004 Carlos Ribeiro, Fernando Silva, André Zúquete
InstB
Roaming Certificate Verification
Bilateral Agreements
Supplicant
InstA
InstA
Certificates in
InstA supplicant
InstA
InstA
Certificates in
InstB gateway
InstB
InstB
InstB
InstA
InstB
Gateway
InstB
TNC2004 Carlos Ribeiro, Fernando Silva, André Zúquete
Roaming Verification of signature
Multilateral (hierarchical) Agreements
Supplicant
InstA
InstA
InstT
InstA
Certificates in
InstA supplicant
InstA
InstT
Certificates in
InstB gateway
InstB
InstB
InstT
InstB
InstB
InstA
 Each institution signs T public key
 T signs every institution public key
Gateway
InstT
InstT
InstX
InstX
InstT
 The chains may have more levels, reproducing a multi-
hierarchical structure:
– e.g. Regional, national, international.
TNC2004 Carlos Ribeiro, Fernando Silva, André Zúquete
InstB
Additional features
 Visitors not included in roaming agreements:
– Can be easily provided with temporary
certificates.
– Temporary certificate management can be easily
delegated to some class of users (e.g.
Professors).
 Authentication is transparent.
– Even after long periods of disconnection there is
no need for an explicit authentication.
TNC2004 Carlos Ribeiro, Fernando Silva, André Zúquete
Discussion
 Stability and Longevity
– IPSec is a mature standard which ensures stability for the present and longevity.
 Ubiquity
– The proposed solution does not depend on special authentication features of the host
APs.
– Only mandatory IPSec features promotes maximum compatibility.
• Currently: Windows 2000, Windows XP, Linux, MacOS X.
 Roaming
– Lightweight roaming infrastructure.
– Certificate chains do not need to be checked online.
– The solution does not require a full-featured PKI.
 Other Features
– The authentication process is fast and transparent.
– Offers a simple method to allow limited-time access to foreign visitors.
 The current implementation is completely free.
TNC2004 Carlos Ribeiro, Fernando Silva, André Zúquete