Delete Key Command (encrypted)
This ASM implements the Project 25 OTAR Delete Key Command message.
Usage Notes
- This message is sent from the Key Management Facility to the Mobile Radio to delete keys on the MR.
- The “Number of Unique Key IDs” field is limited to 23 per message, in order to remain within the AIS limit of five slot messages.
- This message is broadcast as a non-addressed message, with repeat disabled, to reduce the message size, and to avoid issues from a relocated RSI to a different MMSI.
Version 0:
This is an RTCM compliant implementation of the Project 25 OTAR Delete Key Command Message.
This ASM only has an AIS Message 26 variant
Delete Key Command (Message 26, broadcast)
|
|
|
Parameter |
# of Bits |
Description |
|
|
|
|||
|
Standard Message Header |
Message ID |
6 |
Identifier for Message 26; always (decimal) 26. |
|
|
Repeat Indicator |
2 |
Indicates how many times a message has been repeated. 0 – 3; 0 = default; 3 = do not repeat any more. Set to zero (default). |
||
|
Source MMSI |
30 |
MMSI number of source station. Varies according to the transmitter ID. |
||
|
Destination Indicator |
1 |
0 = broadcast (no Destination ID field) 1 = Addressed (30 bit Destination ID field). Set to zero (broadcast). |
||
|
Binary Data Flag |
1 |
0 = unstructured binary data (no Application Identifier bits used) 1 = binary data coded as defined by the 16-bit AI. Set to 1 (structured). |
||
|
Destination ID |
0 |
MMSI number of destination station. Not used. |
||
|
Spare |
0 |
Not used. |
|
|
Binary Data |
Designated Area Code |
10 |
Designated area code (DAC). Set to 366. |
||
|
Function Identifier |
6 |
Function identifier. Set to (decimal) 31. |
||||
|
KMM Preamble |
Reserved |
3 |
Reserved for future use. Set to 0. |
|||
|
Version |
5 |
Version of KMM Preamble Message Body. Set to 0. |
||||
|
MFID |
8 |
Manufacturer’s ID, indicates conformance to standard. Set to 0. |
||||
|
Algorithm ID |
8 |
Identifies the algorithm used to encrypt payload. Set to (hex) 85 = AES-128. |
||||
|
Key ID |
16 |
Identifies the TEK used to encrypt the KMM. |
||||
|
Message Indicator |
72 |
Provides the message indicator to synchronize the encryption of the OTAR KMM. |
||||
|
Encrypted Payload |
OTAR Message ID |
8 |
Identifies the Project 25 “Message ID” type. One of 255 possible values assigned as the message type. Set to (decimal) 8 = Delete Key Command |
|||
|
Message Length |
16 |
A 16 bit binary number that defines the length (in octets) of the subsequent OTAR fields, including MAC. (decimal) 26 – 92. |
||||
|
Message Format |
RSP |
2 |
Response Kind defines acknowledgment to be returned to the sender of the KMM. 00 =Rsp Kind 1, 01 = Rsp Kind 2, 10 = Rsp Kind 3 and 11 is undefined. |
|||
|
MN |
2 |
Message Number defines the size of the Message Number field in the KMM. 00 = no message number, 10 = a 2 octet message number. Set to (binary) 10 |
||||
|
MAC Processing |
2 |
Defines the type of MAC processing performed over the entire KMM. Set to (binary) 11 = Type 3 MAC |
||||
|
Spare |
1 |
Set to zero. |
||||
|
Done |
1 |
Indicates if KMM is last in a series. 1 = More to follow (Not Done), 0 = done. |
||||
|
Destination RSI |
24 |
Radio Set Identifier number |
||||
|
Source RSI |
24 |
Radio Set Identifier Number |
||||
|
KMF Message Number |
16 |
A rolling sequence number to prevent message playback. Binary number representing values from 0 – 65535. |
||||
|
Number of Unique Key IDs |
8 |
Number of keys to be deleted. (decimal) 1 – 23. |
||||
|
Algorithm ID |
8 |
The algorithm is used in conjunction with the KeyID to uniquely select a key. Set to (hex) 85 = AES-128 |
||||
|
Key ID |
16 |
Identifies the Key ID to be deleted. |
||||
|
Subsequent Key Items |
0 - 528 |
Subsequent items are 24 bits apiece, Algorithm ID and Key ID repeated for each item. |
||||
|
|
Binary Data |
Encrypted Payload |
Message Authentication Code |
MAC |
64 |
OTAR Message authentication code, concatenated to key length/2. Calculated per paragraph 13.5.2 of TIA 102.AACA-A, September 2014. |
|
MAC Length |
8 |
Length of message authentication code in octets. Set to (decimal) 8 |
||||
|
MAC Algorithm ID |
8 |
Used with MAC Key ID to uniquely determine key to used to produce MAC. Set to (hex) 85 = AES-128. |
||||
|
MAC Key ID |
16 |
Identifies the Key to be used to compute the MAC |
||||
|
T |
1 |
Not used. Set to zero. |
||||
|
D |
1 |
Derived Key. Set to zero = Dedicated MAC Key |
||||
|
R |
1 |
Reserved for future use. Set to zero. |
||||
|
Version |
5 |
Defines the version of the MAC message body. Set to zero. |
||||
|
Encryption Bit Padding |
Variable |
Sufficient spare bits to ensure that the binary data is a multiple of 128 bits for block encryption (256, 384, 512, 640, 768). Set to zero. |
||||
|
Checksum |
16 |
16-bit CRC calculated as per EAIS Specification |
||||
|
Footer |
Spare |
4 |
Four extra bits to ensure the message ends on a byte boundary. Set to zero. |
|||
|
Communications State Selector |
1 |
0 = SOTDMA communication state follows 1 = ITDMA communication state follows |
||||
|
Communications State |
19 |
SOTDMA communication state (see ITU 1371-5 § 3.3.7.2.1, Annex 2), if communication state selector flag is set to 0, or ITDMA communication state (§ 3.3.7.3.2, Annex 2), if communication state selector flag is set to 1. |
||||
|
Total bits |
464 – 976 |
3 - 5 Slot Binary Message |
||||
