Schweitzer Engineering Laboratories SEL-3022 Instruction Manual Download

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Date Code 20050615

Instruction Manual

SEL-3022 Transceiver

Wireless Operator Interface Security

The SEL Security Application

C.17

Cryptographic Manual—Do Not Copy

match the challenge value the SEL-3022 issued in the First Challenge
frame (Frame 2 in

Figure C.5

), and the SEL-3022 would terminate

the connection attempt.

If the connection dialog succeeds up to this point (i.e., passes all authentication
mechanisms and session replay protection mechanisms described previously), the
SEL-3022 generates another random challenge value, a random session encryption key,
and a random session authentication key and transmits these values in Frame 4 of the
session connection dialog. The SEL-3022 uses these session keys, protected from
interception by SEL Security Application cryptographic mechanisms, described in the
previous sections, to encrypt and authenticate all configuration frames transmitted
between the PC and the SEL-3022 after the five-frame session authentication dialog
succeeds.

Upon receiving the Key Transport and Second Challenge frame, the PC must insert the
transmitted second challenge value into the final frame of the session connection dialog
(Frame 5 in

Figure C.5

) and transmit the frame to the SEL-3022. To complete the

session authentication dialog successfully, the decrypted and authenticated challenge
value the SEL-3022 received in Frame 5 must match the value the SEL-3022 transmits
in Frame 4. This requirement for matching values forms a second, independent layer of
protection against session replay attacks.

If the final frame authenticates correctly and the second challenge values match, the
SEL-3022 opens a wireless operator interface connection with the PC. All
configuration frames transmitted between the two devices after successful completion
of the session authentication dialog previously described will be encrypted and
authenticated through use of the session encryption and authentication keys exchanged
in the dialog.

The SEL-3022 connection authentication provides strong security against a number of
potential threats. We summarize the security features of this connection authentication
dialog as follows:

➤

There are two, independent challenge/response exchanges to prevent
session replay attacks.

➤

There is strong protection against threats posed by maintenance PC
theft. The user must enter from memory, the correct connection
password to successfully authenticate to the SEL-3022 (the
connection password is never stored on the maintenance PC).

➤

Unique session encryption and session authentication key exchanges
limit the number of frames protected by the programmed operator
and security officer role encryption and authentication keys. This
makes the SEL-3022 more resilient to cryptanalytic attacks.

Frame Replay Protection

Every frame in a given wireless operator interface session contains a sequence number
field. The value in this field increments every time a frame is transmitted over the
interface. The SEL-3022 will not accept any frame that contains a sequence number

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