Warm-Start Command

Introduction/Additional information:

This ASM implements the Project 25 OTAR Warm Start Command message.

Usage Notes

This message is sent from the Key Management Facility to the Mobile Radio to provide TEKS when the MR has a valid KEK but no TEKs.
Complying with NIST requirements for a separate (non-derived) key for computing the MAC is impossible, as the Project 25 standard calculates the MAC of a Warm Start Message using a key derived from the received TEK.
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 Warm Start Command Message.

This ASM only has an AIS Message 26 variant.

Permitted as from:

12/05/2016

Registrant:

USCG

Physical link:

AIS

Message number (0=VDES-VDE):

DAC or VPFI:

366

FI / Message ID:

Version:

State:

in force

Number of slots (max):

Last modified:

29/01/2021 - 23:19

Used by:

USCG

Details:

Warm Start Command (Message 26, broadcast)

	Parameter	# of Bits	Description
	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 one (structured).
	Destination ID	0	MMSI number of destination station. Not used.
	Spare	0	Not used.

Application Data (unencrypary Datae)	Designated Area Code		10	Designated area code (DAC). This code is based on the maritime identification digits (MID). Set to 366.
	Function Identifier		6	Function identifier. Set to (decimal) 28.
	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 payload encryption algorithm. Set to (hex) 80 = unencrypted.
		Key ID	16	Identifies the TEK used to encrypt the KMM. Set to 0.
		Message Indicator	72	Provides the message indicator to synchronize the encryption of the OTAR KMM. Set to zero.
	OTAR Message ID		8	Identifies the Project 25 “Message ID” type. One of 255 possible values assigned as the message type. Set to (decimal) 32 = Warm Start Command
	Message Length		16	A 16 bit binary number that defines the length (in octets) of the subsequent OTAR fields, including MAC. Set to (decimal) 49.
	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.
	Decryption Instruction Format	Reserved Bit	1	Set to zero (not used).
		Message Indicator Block	1	Set to zero (not used).
		Spare	6	Always zero.
	KEK Algorithm ID		8	The algorithm is used in conjunction with the KeyID to uniquely select the KEK. Set to (hex) 85 = AES-128
	KEK Key ID		16	Identifies the Key ID for the KEK used.
	Message Indicator		0	Optional, not used for AES-ECB wrapped keys.

	Key Length		8	The number of octets to transfer the key. Default = (decimal) 16, however, can be any value.
	Algorithm ID		8	The algorithm to be used for the keyset. Set to (hex) 85 = AES-128
	Key Format	Key Type	1	Set to 0 = TEK
		Spare	1	Not used, set to zero.
		Delete/Rekey	1	Set to 0 = rekey (add new key)
		Key Name Size	5	Set to zero.
	Storage Location Number		16	Identifies one of 65536 possible storage location indices.
	Key ID		16	The Key ID of the warm start TEK.
	Key		128	The warm start TEK, encrypted with already held KEK.
	Key Name		0	Not used.
	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. Set to zero.
		T	1	Not used. Set to zero.
		D	1	Derived Key. Set to one = Derived MAC Key
		R	1	Reserved for future use. Set to zero.
		Version	5	Defines the version of the MAC message body. Set to zero.
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			608	3 Slot Binary Message

Attachment:

eais_idd_v5_4_8may17.pdf [1]