Comtech EF Data CDD-562AL - Manual (Page 115)

CDD-562AL/564A/L Multi-Channel Demodulator Revision 0
Telnet and CLI Operation MN-CDD562AL564AL
9–13
• These 3xDES keys are used to decrypt traffic being received from the Satellite Interface. The key
is entered in HEX format (48 digits max).
• The keys specified for one receive channel are completely independent for the 3xDES keys
specified for other receive channels.
NOTE: On the bottom of each CLI Menu, the Demod Select number shows the
receive channel for which you are setting parameters.
A 24 Byte [192-bit] 3xDES key is actually a combination of 3 single DES keys of 8 Bytes [64-bits]. The
CLI shows the Key with a space separating the Key into 3 sections.
In the screen example, Transmit Key 1 is shown as:
2222222222222222 4444444444444444 6666666666666666
Consider the first section as Key1A, the second as Key1B, and the third as Key1C. Data is first encrypted
with Key1A, then decrypted with Key1B, and encrypted again with Key1C.
If you set all the three Keys the same, (like 48 ‘1's OR all the characters in DES key the same) the
cumulative effect of 3xDES is just a single DES. When data is first encrypted with Key1A, and decrypted
with Key1B, we get the original data. When encrypted again with Key1C, the result is a total effect of a
single DES key.
Because of this possibility, you must enter unique, 64-bit keys. If any two sections of the Key match, the
demodulator responds with this message:
Invalid Key - Please Re-enter
Also, the least significant bit of each byte in a 24-Byte [192-bit] 3xDES key is reserved for the DES
Algorithm for parity. Entries of 1, 3, 5, 7, 9, B, D or F have all the corresponding bit positions masked.
So, a Key entry of this:
1111111133333333 5555555577777777 99999999BBBBBBBB
becomes this:
1010101032323232 5454545476767676 98989898BABABABA