User's Manual

Date Code 20091009 SEL-3031 Instruction Manual
SEL-3044 Encryption Card
Theory of Operation—SEL Protocol
B.5
NOTE: Both SEL-3044 transceivers that communicate with
each other must share the same system key.
AES Overview
The AES encryption function uses a 256-bit-long secret key and scrambles the contents
of each frame prior to transmission to provide cryptographically strong data
confidentiality.
Encryption is the process of transforming a digital message from its original form into
a form that an unauthorized individual cannot interpret. The output of the encryption
process is a function of the message and an encryption key (see Figure B.3).
Figure B.3 Operation of the AES Encryption Function
This encryption process must be completely reversible by an authorized individual
with access to the secret decryption key. Authority to read a message is only granted by
sharing knowledge of the secret decryption key. Ideally, only individuals with
knowledge of the decryption key can reverse the encryption operation and interpret the
protected message. There are two main classes of encryption functions. Symmetric key
encryption relies on the same secret key value, K, to perform both the encryption and
decryption transformations. Asymmetric key encryption, on the other hand, uses a
different key for encryption and decryption for example, asymmetric encryption might
use K1 for encryption and K2 for decryption. The AES encryption algorithm the
SEL-3044 uses is a symmetric block cipher with an encryption/decryption key size of
256 bits.
The AES is the latest encryption standard adopted by NIST. In 1997, NIST challenged
the cryptographic community to develop the next generation encryption algorithm to
replace the aging DES and 3DES encryption standards. In 2000, NIST chose the
Rijndael encryption algorithm as the AES encryption standard. During the evaluation
of candidates for the AES standard, some of the world’s best cryptanalysts analyzed
and approved Rijndael. Since its adoption in 2001, AES has proven to be very effective
against known attacks, very efficient, and simple to implement.
Encryption Key Decryption Key
Hi Bob!
*4gu>g
aIL8}2=h
AES
Encrypt
Hi Bob!
AES
Decrypt