Comtech EF Data CDM-IP 300L - Manual (Page 172)

CDM-IP 300L IP-Centric Satellite Modem Rev. 1
CD/CDMIP300L.IOM
146
Receive Decrypt Enabled Read
Only
Displays feature status. This field updates via the
Features Configuration menu.
Transmit Key 1 - 8 1
through
8
These 3xDES keys are used to encrypt traffic being
sent over the Satellite Interface.
The key is entered in HEX (48 digits max)
Receive Key 1 - 8 A
through
H
These 3xDES keys are used to decrypt traffic being
received from the Satellite Interface.
The key is entered in HEX (48 digits max)
Save Parameters S This option allows a user to save the current
configuration of the CDM-IP to permanent storage.
This configuration will be restored on each successive
power cycle of the CDM-IP.
Exit X This option allows a user to exit the current menu and
return to its parent menu.
IMPORTANT
A 24 Byte [192-bit] 3xDES key is actually a combination of 3 single DES keys of 8
Bytes [64-bits]. The CLI will display the Key with a space separating the Key into 3
sections. In the screen capture above, Transmit Key 1 is displayed 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 and then decrypted with Key1B and again
encrypted with Key1C. So if a user specifies 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 back the original data and then when encrypted with Key1C results in a total effect
of single DES key.
Because of this, the user is required to enter unique 64-bit keys. If any 2 sections
of the Key match, the CDM-IP will respond
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 will have all
the corresponding bit positions masked. So a Key entry of:
1111111133333333 5555555577777777 99999999BBBBBBBB
becomes
1010101032323232 5454545476767676 98989898BABABABA