A Roaming Authentication Solution for Wifi using IPSec VPNs with client certificates Carlos Ribeiro Fernando Silva André Zúquete

TNC2004 Carlos Ribeiro, Fernando Silva, André Zúquete 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

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.  Certificates have short validity periods –Certification Revocation Lists are not necessary

TNC2004 Carlos Ribeiro, Fernando Silva, André Zúquete 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 InstA Supplicant Private key InstA Supplicant Send Verify Certificate Supplicant Public key Extract Supplicant authentication Establishing a Session key Gateway Public key Gateway Private key Gateway Authentication Send Institution A Gateway Institution A Supplicant InstA Gateway

TNC2004 Carlos Ribeiro, Fernando Silva, André Zúquete Roaming authentication InstB InstA Supplicant Private key InstA Supplicant Send Verify Certificate Supplicant Public key Extract Supplicant authentication 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 Roaming Certificate Verification InstA Supplicant InstB InstA InstB Gateway InstA InstB Certificates in InstA supplicant Certificates in InstB gateway Bilateral Agreements

TNC2004 Carlos Ribeiro, Fernando Silva, André Zúquete Roaming Verification of signature  Each institution signs T public key  T signs every institution public key  The chains may have more levels, reproducing a multi- hierarchical structure: –e.g. Regional, national, international. InstA Supplicant InstB InstT InstB Gateway InstA InstT Certificates in InstA supplicant Certificates in InstB gateway Multilateral (hierarchical) Agreements InstT InstA InstT InstB InstT InstX InstT

TNC2004 Carlos Ribeiro, Fernando Silva, André Zúquete 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.