Comtech EF Data CDM-570/L Vipersat Parameter Editor - Manual (Page 79)

Chapter 2 - Using Parameter Editor 2-63
Admin
Figure 2-43 Triple DES dialog
Using Key1 as an example, 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 of 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 entry will not be accepted and the alert message Each
Segment Must Be Unique will appear. Also, the least significant bit of each
byte in a 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