6
Encryption Key Loading Guide
© Tait Electronics Limited September 2006
When a radio makes an encrypted call, it includes in the call the Key ID and
the Algorithm ID that it used. If the receiving radio has the same key, it can
decrypt the call. The Key ID that it received tells it what key to use and the
Algorithm ID tells it the encryption algorithm to use.
Entering Encryption Keys
Note
Before encryption keys are entered, your organization should have
developed a policy and procedures for encryption key manage-
ment. This will answer questions such as “How many keys will be
needed?” “How will re-keying occur?” and “How and when will
users change from one key to another?”
Enter into the all the keys that your system will need, following
the instructions for ASTRO 25 operation in the User’s Guide.
Important
Make sure that you follow your organization’s security pol-
icy when handling keys. If encryption information falls into
unauthorized hands, the security of voice communications
could be compromised.
■
The CKR can be any number from 1 to 4095. For example, if all
radios will use the same keys, you can use 1–16 as the CKR
numbers. If you need two groups of keys, use 1–16 for the first
group and 17-32 for the second group.
■
The Key ID can be any hexadecimal number 0–FFFF.
■
For DES encryption, you must select DES-OFB. OFB (Output
Feedback mode) is the only DES mode specified by the P25
common air interface.
■
For DES encryption, the key variable is an 8-octet number, for
example 01 23 45 67 89 AB CD EF. An octet is two hexadecimal
Ke
y I
D =
3
Alg
ori
thm
=
DE
S
CKR 1
KeyID = 3
Alg = DES
Key variable:
**********
**********
**********
CKR 1
KeyID = 3
Alg = DES
Key variable:
**********
**********
**********