User's Manual

SEL-3022 Transceiver Instruction Manual Date Code 20050615
Wireless Operator Interface Security
The SEL Security Application
C.16
Cryptographic Manual—Do Not Copy
The connection dialog begins with a connection request frame (Frame 1 in Figure C.5)
that is encrypted and authenticated with encryption and authentication keys
programmed into the SEL-5809 Settings Software device image. Upon receiving the
connection request, the SEL-3022 decrypts and authenticates the frame. If the
authentication fails, indicating that the session request came from other than an
authorized user (i.e., a PC programmed with the appropriate AES encryption and
HMAC SHA-1 authentication keys), the SEL-3022 ignores the session request and
remains silent. Note that the initial connection frame must be directed at the correct
User Datagram Protocol (UDP) port on the wireless TCP/IP interface of the SEL-3022
transceiver. Because the UDP protocol does not require a connection handshake, as
does TCP protocol, the SEL-3022 only transmits a TCP/IP frame in response to a fully
authenticated connection request frame. This feature ensures that the SEL-3022 is
immune to traditional port mapping and network reconnaissance techniques such as
ping sweeps, TCP SYN scans, or TCP FIN scans.
If the initial connection request frame passes the authentication process, the SEL-3022
generates a large, random challenge value and transmits it to the PC (Frame 2 in
Figure C.5). Upon receipt of the First Challenge frame, the PC must insert the received
challenge value into a new encrypted and authenticated frame and transmit it to the
SEL-3022 (Frame 3 in Figure C.5). In addition, this First Challenge frame contains the
password information you entered in the SEL-5809 Settings Software session
connection dialog box. When the SEL-3022 receives this frame, it decrypts and
authenticates it. If the authentication fails, again indicating that the session request
came from an unauthorized user, the SEL-3022 terminates the session and resets the
session connection dialog. If the frame passes authentication, the SEL-3022 compares
the transmitted password information with the password value stored in the SEL-3022
settings. It is important to note that if the transmitted password information indicates
that the user entered the wrong password, or if the decrypted challenge value does not
match the challenge value transmitted in Frame 2 of the connection dialog, the
SEL-3022 again terminates the session and resets the connection dialog.
➤ The password you entered in the SEL-5809 Settings Software must
match the password value stored in the SEL-3022 device, or the
session connection will fail. This guarantees that a stolen
maintenance PC programmed with the correct encryption and
authentication keys cannot be used to connect to the SEL-3022
without the user having direct knowledge of the programmed
password value stored in the SEL-3022 (the SEL-5809 Settings
Software never stores the password value on the PC hard drive).
➤ The large, random challenge value that the SEL-3022 formed and
transmitted in Frame 2 of the connection dialog is, with very high
probability, different for every wireless session. Because of this large,
random value, a malicious individual cannot capture a previous
session dialog and use the captured packets to reconnect to the
SEL-3022 (known as a session replay attack). If someone attempted
such an attack, the challenge value transmitted in the First Challenge
Response With Password frame (Frame 3 in Figure C.5) would not
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