SENA STS Series - Manual (Page 57)

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Padding
The padding is a standard block cipher. The pad value is the total number of pad bytes in the
padding(1~8).
In 3DES algorithm in STS Series, key and initial vector, which are used in generating encrypted data
packet, is derived from key block. And key block is generated by using user configured key string.
Figure 4-13 shows key derivation process.
Key Block(32-byte)
Key (24-byte) IV(8-byte)
Figure 4-13 Key derivation
The key block is defined as:
Key_Block = MD5(KEY_STRING) + MD5(MD5(KEY_STRING)+KEY_STRING)
= (16 bytes) + (16 bytes)
Key = first 24bytes of Key Block
IV(Initial Vector) = last 8 bytes of Key block
4.2.7.3. RC4 Cryptography Method
By setting the cryptography method as RC4, the STS Series can communicate with other STS Series
device in RC4 encrypted sessions. In RC4 encryption mode, STS Series will encrypt/decrypt all the
TCP stream with the user configured key string, and there is no header and no padding. RC4 is faster
than 3DES.
4.2.8. Filter Application
The STS Series supports user manipulation of raw data between remote host and serial device
connected serial port. Filter application configuration can be used for this purpose. If user makes his
own filter application program, he can upload it to STS Series and configure name of the program and
its arguments through filter application configuration menu. For more detail information about making
filter application, please refer to 9.4. Making And Running User’s Own Code section.