Data Encryption Standard (DES)
Data Encryption Standard (DES) is an encryption method that uses a secret key. It is
so hard to break (it provides 72 quadrillion possible keys) that the U.S. government
forbids its exportation to other countries. It is tough to break because the key is
randomly chosen from an enormous pool.
DES applies a 56-bit key to each 64-bit block of data. This is considered strong
encryption. Of course strong is a relative term, and if someone is really determined and
has the resources, it is possible to crack DES. Many organizations employ triple DES,
which applies three keys in succession.
Advanced Encryption Standard (AES)
Advanced Encryption Standard (AES) is poised to become the de facto encryption
standard. AES applies 128-, 192-, or 256-bit keys to 128-, 192-, or 256-bit blocks of
data.
As of 2004, there had been no reported cracks of AES, and it is the first time that the
U.S. Government’s National Security Agency (NSA) authorized an encryption tool for
transmission of top-secret, classified information.
Other Resources
• University of California, Berkeley Internet Security, Applications,
Authentication and Cryptography (ISAAC) Report on WEP insecurity
http://www.isaac.cs.berkeley.edu/isaac/wep-faq.html
• Wi-Fi Alliance
http://www.wi-fi.org/
• National Institute of Standards and Technology
http://www.nist.gov
IT Certification CCIE,CCNP,CCIP,CCNA,CCSP,Cisco Network Optimization and Security Tips
WPA2
WPA2
As you might deduce from its name, WPA2 is the second and latest version of WPA.
The most important difference between the two is the method of encryption. WPA uses
RC4, whereas WPA2 uses AES. Not only is the AES encryption method much stronger,
it is also a requirement for some government and industry users.
WPA2 is backward compatible with WPA, and many WPA-certified products can be
upgraded with software to WPA2. However, some products might require hardware
upgrades. WPA was designed to be a software upgrade to WEP. However, WPA2 didn’t
have such a design goal. As such, in many cases a hardware upgrade will be necessary
to update to WPA2.
Other Resources 79
Encryption
Scrambling a WLAN’s data as it leaves the AP, and then unscrambling it when it arrives
at the client, requires an encryption method. The popular RC4 has already been
discussed, but sturdier, stronger encryption methods are out there and in use in WLAN
systems, as described next.
As you might deduce from its name, WPA2 is the second and latest version of WPA.
The most important difference between the two is the method of encryption. WPA uses
RC4, whereas WPA2 uses AES. Not only is the AES encryption method much stronger,
it is also a requirement for some government and industry users.
WPA2 is backward compatible with WPA, and many WPA-certified products can be
upgraded with software to WPA2. However, some products might require hardware
upgrades. WPA was designed to be a software upgrade to WEP. However, WPA2 didn’t
have such a design goal. As such, in many cases a hardware upgrade will be necessary
to update to WPA2.
Other Resources 79
Encryption
Scrambling a WLAN’s data as it leaves the AP, and then unscrambling it when it arrives
at the client, requires an encryption method. The popular RC4 has already been
discussed, but sturdier, stronger encryption methods are out there and in use in WLAN
systems, as described next.
Wi-Fi Protected Access (WPA)
Wi-Fi Protected Access (WPA)
Another means of WLAN security comes in the form of Wi-Fi Protected Access
(WPA). WPA was introduced in 2003 by the Wi-Fi Alliance, a nonprofit association
that certifies WLAN product interoperability based on IEEE 802.11 specifications.
Two versions of WPA exist: WPA and WPA2. They are described in the sections that
follow.
WPA
WPA was designed as a replacement for WEP. The Temporal Key Integrity Protocol
(TKIP) is an improvement over WEP. It causes keys to automatically change, and when
used in conjunction with a larger initialization vector (IV), it makes discovering keys
highly unlikely.
Credentials
Used
Digital
certificate
Windows
password
Clients:
Windows,
Novell NDS,
LDAP password,
and OTP
or token.
Server: Digital
certificate
Windows
password
Server: Digital
certificate
Windows
password,
LDAP user
ID and
password
PAC
Single Sign-On
Using
Windows
Login?
Yes Yes No Yes Yes
Password
Expiration and
Change?
– No No Yes Yes
Fast Secure
Roaming
Compatible?
No Yes No No Yes
WPA
Compatible?
Yes Yes Yes Yes Yes
Table 4-1 Comparing 802.1X Authentication Methods (Continued)
78 Wi-Fi Protected Access (WPA)
NOTE: An IV is a block of bits added to the first block of data of a block cipher. This block
is added—or hashed—with the base key and is used with other types of ciphers. This block
strengthens security because the same transmissions with the same key yield the same
output. As a result, attackers can notice the similarities and derive both the messages and
the keys being used.
On top of authentication and encryption improvements, WPA secures the payload
better than in WEP. With WEP, cyclic redundancy checks (CRC) are used to ensure
packet integrity. However, it is possible to alter the payload and update the message
CRC without knowing the WEP key because the CRC is not encrypted. WPA uses
message integrity checks (MIC) to ensure packet integrity. The MICs also employ a
frame counter, which prevents replay attacks.
NOTE: Replay attacks occur when an attacker intercepts a transmission, and then
rebroadcasts that transmission at a later time. For example, if a password is intercepted, the
attacker does not need to know how to read the message; he can simply rebroadcast it later,
and then gain access using the victim’s credentials.
NOTE: MICs are often called Michael in Wi-Fi parlance.
Breaking into a WLAN using WPA is more difficult than WEP because the IVs are
larger, there are more keys in use, and there is a sturdier message verification system.
Another means of WLAN security comes in the form of Wi-Fi Protected Access
(WPA). WPA was introduced in 2003 by the Wi-Fi Alliance, a nonprofit association
that certifies WLAN product interoperability based on IEEE 802.11 specifications.
Two versions of WPA exist: WPA and WPA2. They are described in the sections that
follow.
WPA
WPA was designed as a replacement for WEP. The Temporal Key Integrity Protocol
(TKIP) is an improvement over WEP. It causes keys to automatically change, and when
used in conjunction with a larger initialization vector (IV), it makes discovering keys
highly unlikely.
Credentials
Used
Digital
certificate
Windows
password
Clients:
Windows,
Novell NDS,
LDAP password,
and OTP
or token.
Server: Digital
certificate
Windows
password
Server: Digital
certificate
Windows
password,
LDAP user
ID and
password
PAC
Single Sign-On
Using
Windows
Login?
Yes Yes No Yes Yes
Password
Expiration and
Change?
– No No Yes Yes
Fast Secure
Roaming
Compatible?
No Yes No No Yes
WPA
Compatible?
Yes Yes Yes Yes Yes
Table 4-1 Comparing 802.1X Authentication Methods (Continued)
78 Wi-Fi Protected Access (WPA)
NOTE: An IV is a block of bits added to the first block of data of a block cipher. This block
is added—or hashed—with the base key and is used with other types of ciphers. This block
strengthens security because the same transmissions with the same key yield the same
output. As a result, attackers can notice the similarities and derive both the messages and
the keys being used.
On top of authentication and encryption improvements, WPA secures the payload
better than in WEP. With WEP, cyclic redundancy checks (CRC) are used to ensure
packet integrity. However, it is possible to alter the payload and update the message
CRC without knowing the WEP key because the CRC is not encrypted. WPA uses
message integrity checks (MIC) to ensure packet integrity. The MICs also employ a
frame counter, which prevents replay attacks.
NOTE: Replay attacks occur when an attacker intercepts a transmission, and then
rebroadcasts that transmission at a later time. For example, if a password is intercepted, the
attacker does not need to know how to read the message; he can simply rebroadcast it later,
and then gain access using the victim’s credentials.
NOTE: MICs are often called Michael in Wi-Fi parlance.
Breaking into a WLAN using WPA is more difficult than WEP because the IVs are
larger, there are more keys in use, and there is a sturdier message verification system.
Comparison of 802.1X Authentication Methods
Comparison of 802.1X Authentication Methods
There are a lot of differences among PEAP, Cisco Wireless EAP, EAP-TLS, and EAPFAST.
To help sort the attributes of these protocols, Table 4-1 compares the various
features of these different authentication methods.
Table 4-1 Comparing 802.1X Authentication Methods
Characteristics EAP-TLS
Cisco
Wireless
EAP
PEAP Version 1
(with Generic
Token Card)
PEAP Version 0
(with MS-CHAP
Version 2) EAP-FAST
User
Authentication
Database and
Server
OTP
LDAP
Novell NDS
Windows NT
Domains
Active
Directory
Windows
NT
Domains
Active
Directory
OTP
LDAP
Novell NDS
Windows NT
Domains
Active
Directory
Windows NT
Domains
Active
Directory
Windows
NT Domains
Active
Directory
LDAP
Server
Certificates
Required?
Yes No Yes Yes No
Client
Certificates
Required?
Yes No No No No
Operating
Systems
Windows XP/
2000/CE
Other OSes
supported
with thirdparty
utility.
Windows
98/2000/
NT/ME/
XP/CE
Mac OS
Linux
DOS
Windows XP/
2000/CE
Other OSes
supported with
third-party
utility.
Windows XP/
2000/CE
Other OSes
supported with
third-party
utility.
Windows
XP/2000/CE
Other OSes
supported
with thirdparty
utility.
Characteristics
EAP-TLS
Cisco
Wireless
EAP
PEAP Version 1
(with Generic
Token Card)
PEAP Version 0
(with MS-CHAP
Version 2) EAP-FAST
Wi-Fi Protected Access (WPA) 77
Wi-Fi Protected Access (WPA)
Another means of WLAN security comes in the form of Wi-Fi Protected Access
(WPA). WPA was introduced in 2003 by the Wi-Fi Alliance, a nonprofit association
that certifies WLAN product interoperability based on IEEE 802.11 specifications.
Two versions of WPA exist: WPA and WPA2. They are described in the sections that
follow.
WPA
WPA was designed as a replacement for WEP. The Temporal Key Integrity Protocol
(TKIP) is an improvement over WEP. It causes keys to automatically change, and when
used in conjunction with a larger initialization vector (IV), it makes discovering keys
highly unlikely.
Credentials
Used
Digital
certificate
Windows
password
Clients:
Windows,
Novell NDS,
LDAP password,
and OTP
or token.
Server: Digital
certificate
Windows
password
Server: Digital
certificate
Windows
password,
LDAP user
ID and
password
PAC
Single Sign-On
Using
Windows
Login?
Yes Yes No Yes Yes
Password
Expiration and
Change?
– No No Yes Yes
Fast Secure
Roaming
Compatible?
No Yes No No Yes
WPA
Compatible?
Yes Yes Yes Yes Yes
There are a lot of differences among PEAP, Cisco Wireless EAP, EAP-TLS, and EAPFAST.
To help sort the attributes of these protocols, Table 4-1 compares the various
features of these different authentication methods.
Table 4-1 Comparing 802.1X Authentication Methods
Characteristics EAP-TLS
Cisco
Wireless
EAP
PEAP Version 1
(with Generic
Token Card)
PEAP Version 0
(with MS-CHAP
Version 2) EAP-FAST
User
Authentication
Database and
Server
OTP
LDAP
Novell NDS
Windows NT
Domains
Active
Directory
Windows
NT
Domains
Active
Directory
OTP
LDAP
Novell NDS
Windows NT
Domains
Active
Directory
Windows NT
Domains
Active
Directory
Windows
NT Domains
Active
Directory
LDAP
Server
Certificates
Required?
Yes No Yes Yes No
Client
Certificates
Required?
Yes No No No No
Operating
Systems
Windows XP/
2000/CE
Other OSes
supported
with thirdparty
utility.
Windows
98/2000/
NT/ME/
XP/CE
Mac OS
Linux
DOS
Windows XP/
2000/CE
Other OSes
supported with
third-party
utility.
Windows XP/
2000/CE
Other OSes
supported with
third-party
utility.
Windows
XP/2000/CE
Other OSes
supported
with thirdparty
utility.
Characteristics
EAP-TLS
Cisco
Wireless
EAP
PEAP Version 1
(with Generic
Token Card)
PEAP Version 0
(with MS-CHAP
Version 2) EAP-FAST
Wi-Fi Protected Access (WPA) 77
Wi-Fi Protected Access (WPA)
Another means of WLAN security comes in the form of Wi-Fi Protected Access
(WPA). WPA was introduced in 2003 by the Wi-Fi Alliance, a nonprofit association
that certifies WLAN product interoperability based on IEEE 802.11 specifications.
Two versions of WPA exist: WPA and WPA2. They are described in the sections that
follow.
WPA
WPA was designed as a replacement for WEP. The Temporal Key Integrity Protocol
(TKIP) is an improvement over WEP. It causes keys to automatically change, and when
used in conjunction with a larger initialization vector (IV), it makes discovering keys
highly unlikely.
Credentials
Used
Digital
certificate
Windows
password
Clients:
Windows,
Novell NDS,
LDAP password,
and OTP
or token.
Server: Digital
certificate
Windows
password
Server: Digital
certificate
Windows
password,
LDAP user
ID and
password
PAC
Single Sign-On
Using
Windows
Login?
Yes Yes No Yes Yes
Password
Expiration and
Change?
– No No Yes Yes
Fast Secure
Roaming
Compatible?
No Yes No No Yes
WPA
Compatible?
Yes Yes Yes Yes Yes
PEAP
PEAP
PEAP was developed by Cisco, Microsoft, and RSA Security. PEAP allows
authentication of WLAN clients without requiring certificates. This protocol simplifies
the architecture of WLAN security.
PEAP Overview
PEAP, like the competing tunneled transport layer security (TTLS), uses transport
layer security (TLS). Think of it as a stronger version of SSL, the protocol used to
secure HTTP sessions. TLS establishes an end-to-end tunnel to transmit the client’s
credentials. A certificate is required on the server.
There are two phases to PEAP functionality:
• Phase 1—Server-side TLS authentication starts, and an encrypted tunnel is
created. This creates a server-side authentication system, such as the kind used to
authenticate using SSL. When this phase is completed, all authentication data is
encrypted.
• Phase 2—The client is authenticated using either MS-CHAP Version 2 or other
authentication schemes (which are explained in the next section, “PEAP Version
0 and Version 1”).
Figure 4-4 shows how PEAP works.
Client 1 2
3
4
5
6
Access Point
RADIUS Server
74 IEEE 802.1X Authentication
Figure 4-4 The PEAP Authentication Process
The PEAP authentication process is as follows:
1. The client associates with the AP.
2. The AP blocks the client from accessing the network.
3. The client verifies the RADIUS server’s certificate.
4. The RADIUS server authenticates the client using MS-CHAP or other means,
such as an OTP.
5. The RADIUS server and the client agree on the WEP key.
6. A secure tunnel is established between the client and the server.
An organization can use Windows logins and passwords if it has not issued certificates
to every station. RADIUS servers that support EAP-TTLS and PEAP can check LAN
access requests with Windows domain controllers, Active Directories, and other
existing user databases.
PEAP Version 0 and Version 1
There are two versions of PEAP:
• PEAP Version 0 (also known as Microsoft PEAP)
• PEAP Version 1 (also known as Cisco PEAP)
Each version supports a different method of client authentication through its TLS
tunnel. Version 0 authenticates clients using MS-CHAP Version 2. This limits user
databases to those supporting MS-CHAP Version 2, such as Active Directory.
1 2
3
4
5
6
Client
Access Point Switch
RADIUS Server
IEEE 802.1X Authentication 75
Version 1 (Cisco PEAP) authenticates clients using OTPs and logon passwords, which
allow OTP support from vendors and logon password databases in addition to
Microsoft databases.
In addition, Version 1 enables users to hide name identities until the TLS tunnel is
created. This ensures that usernames are not broadcast during the authentication phase.
EAP-FAST
EAP-FAST is like EAP-TLS in that it uses a certificate-like Protected Access
Credential (PAC) file for authentication, and it is like PEAP in that it authenticates the
station using a username and password via an encrypted TLS tunnel. EAP-FAST is
unique in that it is designed to speed re-authentication as stations roam among APs.
EAP-TLS and PEAP require lengthy message exchanges between the station and the
server, taking several seconds to re-authenticate. Applications that are not latency
sensitive do not need to worry much about this; however, applications that are sensitive
to latency (such as voice over IP) suffer if re-authentication takes more than a few
milliseconds.
EAP-FAST uses shared secret keys to accelerate the re-authentication process. Public
keys are convenient because the station and AP can authenticate each other without
having to know each other in advance. (Public keys are used when connecting to a
secure website, for instance.) Secret keys are faster, but require that both the station and
the AP already have the secret key. Figure 4-5 shows how EAP-FAST works.
Figure 4-5 The EAP-FAST Authentication Process
The EAP-FAST authentication process is as follows:
1. The client associates with the AP.
1 2
3
4
5
6
Client
Access Point Switch
RADIUS Server
76 IEEE 802.1X Authentication
2. The AP blocks the client from accessing the network.
3. The client verifies the RADIUS server’s credentials with the shared secret key.
4. The RADIUS server authenticates the client with the shared secret key.
5. The RADIUS server and the client agree on the WEP key.
6. A secure connection is established.
PEAP was developed by Cisco, Microsoft, and RSA Security. PEAP allows
authentication of WLAN clients without requiring certificates. This protocol simplifies
the architecture of WLAN security.
PEAP Overview
PEAP, like the competing tunneled transport layer security (TTLS), uses transport
layer security (TLS). Think of it as a stronger version of SSL, the protocol used to
secure HTTP sessions. TLS establishes an end-to-end tunnel to transmit the client’s
credentials. A certificate is required on the server.
There are two phases to PEAP functionality:
• Phase 1—Server-side TLS authentication starts, and an encrypted tunnel is
created. This creates a server-side authentication system, such as the kind used to
authenticate using SSL. When this phase is completed, all authentication data is
encrypted.
• Phase 2—The client is authenticated using either MS-CHAP Version 2 or other
authentication schemes (which are explained in the next section, “PEAP Version
0 and Version 1”).
Figure 4-4 shows how PEAP works.
Client 1 2
3
4
5
6
Access Point
RADIUS Server
74 IEEE 802.1X Authentication
Figure 4-4 The PEAP Authentication Process
The PEAP authentication process is as follows:
1. The client associates with the AP.
2. The AP blocks the client from accessing the network.
3. The client verifies the RADIUS server’s certificate.
4. The RADIUS server authenticates the client using MS-CHAP or other means,
such as an OTP.
5. The RADIUS server and the client agree on the WEP key.
6. A secure tunnel is established between the client and the server.
An organization can use Windows logins and passwords if it has not issued certificates
to every station. RADIUS servers that support EAP-TTLS and PEAP can check LAN
access requests with Windows domain controllers, Active Directories, and other
existing user databases.
PEAP Version 0 and Version 1
There are two versions of PEAP:
• PEAP Version 0 (also known as Microsoft PEAP)
• PEAP Version 1 (also known as Cisco PEAP)
Each version supports a different method of client authentication through its TLS
tunnel. Version 0 authenticates clients using MS-CHAP Version 2. This limits user
databases to those supporting MS-CHAP Version 2, such as Active Directory.
1 2
3
4
5
6
Client
Access Point Switch
RADIUS Server
IEEE 802.1X Authentication 75
Version 1 (Cisco PEAP) authenticates clients using OTPs and logon passwords, which
allow OTP support from vendors and logon password databases in addition to
Microsoft databases.
In addition, Version 1 enables users to hide name identities until the TLS tunnel is
created. This ensures that usernames are not broadcast during the authentication phase.
EAP-FAST
EAP-FAST is like EAP-TLS in that it uses a certificate-like Protected Access
Credential (PAC) file for authentication, and it is like PEAP in that it authenticates the
station using a username and password via an encrypted TLS tunnel. EAP-FAST is
unique in that it is designed to speed re-authentication as stations roam among APs.
EAP-TLS and PEAP require lengthy message exchanges between the station and the
server, taking several seconds to re-authenticate. Applications that are not latency
sensitive do not need to worry much about this; however, applications that are sensitive
to latency (such as voice over IP) suffer if re-authentication takes more than a few
milliseconds.
EAP-FAST uses shared secret keys to accelerate the re-authentication process. Public
keys are convenient because the station and AP can authenticate each other without
having to know each other in advance. (Public keys are used when connecting to a
secure website, for instance.) Secret keys are faster, but require that both the station and
the AP already have the secret key. Figure 4-5 shows how EAP-FAST works.
Figure 4-5 The EAP-FAST Authentication Process
The EAP-FAST authentication process is as follows:
1. The client associates with the AP.
1 2
3
4
5
6
Client
Access Point Switch
RADIUS Server
76 IEEE 802.1X Authentication
2. The AP blocks the client from accessing the network.
3. The client verifies the RADIUS server’s credentials with the shared secret key.
4. The RADIUS server authenticates the client with the shared secret key.
5. The RADIUS server and the client agree on the WEP key.
6. A secure connection is established.
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