ETSI EN 300 396-6 V1.6.1 (2016-11)

EUROPEAN STANDARD
Terrestrial Trunked Radio (TETRA);
Direct Mode Operation (DMO);
Part 6: Security
2 ETSI EN 300 396-6 V1.6.1 (2016-11)

Reference
REN/TCCE-06191
Keywords
air interface, data, DMO, security, security mode,
speech, TETRA
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3 ETSI EN 300 396-6 V1.6.1 (2016-11)
Contents
Intellectual Property Rights . 6
Foreword . 6
Modal verbs terminology . 6
1 Scope . 7
2 References . 7
2.1 Normative references . 7
2.2 Informative references . 8
3 Definitions and abbreviations . 8
3.1 Definitions . 8
3.2 Abbreviations . 9
4 DMO security class . 10
4.1 General . 10
4.2 DM-2-A . 11
4.3 DM-2-B . 11
4.4 DM-2-C . 11
5 DMO call procedures . 12
5.1 General . 12
5.1.1 Security profile . 12
5.1.1.0 General . 12
5.1.1.1 Indication of security parameters . 12
5.2 Security class on call setup . 13
5.2.1 General . 13
5.2.2 Normal behaviour . 13
5.2.3 Exceptional behaviour . 13
5.2.3.0 General . 13
5.2.3.1 Call-setup with presence check . 13
5.2.3.2 Call-setup without presence check . 13
5.2.3.3 Behaviour post call-setup . 14
5.3 Security class on call follow-on . 14
5.3.1 General . 14
5.3.2 Normal behaviour . 14
5.3.3 Exceptional behaviour . 14
6 Air interface authentication and key management mechanisms . 15
6.1 Authentication . 15
6.2 Repeater mode operation . 15
6.3 Gateway mode operation . 15
6.4 Air Interface (AI) key management mechanisms . 17
6.4.0 General . 17
6.4.1 Key grouping . 17
6.4.2 Identification of cipher keys in signalling . 20
7 Enable and disable mechanism . 20
8 Air Interface (AI) encryption . 20
8.1 General principles. 20
8.2 Encryption mechanism . 21
8.2.0 General . 21
8.2.1 Allocation of KSS to logical channels . 21
8.3 Application of KSS to specific PDUs. 22
8.3.0 General . 22
8.3.1 Class DM-1 . 22
8.3.2 Class DM-2A . 22
8.3.2.0 General . 22
8.3.2.1 DMAC-SYNC PDU encryption . 22
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4 ETSI EN 300 396-6 V1.6.1 (2016-11)
8.3.2.2 DMAC-DATA PDU encryption . 23
8.3.2.3 DMAC-FRAG PDU encryption . 23
8.3.2.4 DMAC-END PDU encryption . 23
8.3.2.5 DMAC-U-SIGNAL PDU encryption . 24
8.3.2.6 Traffic channel encryption . 24
8.3.3 Class DM-2B . 24
8.3.3.0 General . 24
8.3.3.1 DMAC-SYNC PDU encryption . 25
8.3.3.2 DMAC-DATA PDU encryption . 25
8.3.3.3 DMAC-FRAG PDU encryption . 25
8.3.3.4 DMAC-END PDU encryption . 26
8.3.3.5 DMAC-U-SIGNAL PDU encryption . 26
8.3.3.6 Traffic channel encryption . 26
8.3.4 Class DM-2C . 26
8.3.4.0 General . 26
8.3.4.1 DMAC-SYNC PDU encryption . 27
8.3.4.2 DMAC-DATA PDU encryption . 28
8.3.4.3 DMAC-FRAG PDU encryption . 28
8.3.4.4 DMAC-END PDU encryption . 28
8.3.4.5 DMAC-U-SIGNAL PDU encryption . 28
8.3.4.6 Traffic channel encryption . 29
8.4 Encryption of identities in repeater and gateway presence signal . 29
9 Encryption synchronization . 31
9.1 General . 31
9.1.0 Introduction. 31
9.1.1 Algorithm to establish frame number to increment TVP . 32
9.1.1.1 Master DM-MS operation . 32
9.1.1.2 Slave DM-MS operation . 32
9.2 TVP used for reception of normal bursts . 33
9.3 Synchronization of calls through a repeater . 33
9.3.0 General . 33
9.3.1 Algorithm to establish frame number to increment TVP . 34
9.3.1.1 Master DM-MS operation . 34
9.3.1.2 Slave DM-MS operation . 34
9.4 Synchronization of calls through a gateway . 34
9.5 Synchronization of data calls where data is multi-slot interleaved . 35
9.5.0 General . 35
9.5.1 Recovery of stolen frames from interleaved data . 36
Annex A (normative): Key Stream Generator (KSG) boundary conditions . 37
A.0 General . 37
A.1 Overview . 37
A.2 Use . 38
A.3 Interfaces to the algorithm . 38
A.3.0 General . 38
A.3.1 ECK . 38
A.3.1.0 General . 38
A.3.1.1 Use of ECK in class DM-2-A and DM-2-B . 39
A.3.1.2 Use of ECK in class DM-2-C . 39
A.3.2 Keystream. 39
A.3.3 Time Variant Parameter (TVP) . 39
Annex B (normative): Boundary conditions for cryptographic algorithm TB6 . 40
Annex C (informative): Encryption control in DM-MS . 41
C.0 Introduction . 41
C.1 General . 41
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5 ETSI EN 300 396-6 V1.6.1 (2016-11)
C.2 Service description and primitives . 41
C.2.0 General . 41
C.2.1 DMCC-ENCRYPT primitive . 42
C.2.2 DMC-ENCRYPTION primitive . 44
C.3 Protocol functions . 45
Annex D (informative): Bibliography . 46
Annex E (informative): Change request history . 47
History . 48

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6 ETSI EN 300 396-6 V1.6.1 (2016-11)
Intellectual Property Rights
IPRs essential or potentially essential to the present document may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in
respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web
server (https://ipr.etsi.org/).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web
server) which are, or may be, or may become, essential to the present document.
Foreword
This European Standard (EN) has been produced by ETSI Technical Committee TETRA and Critical Communications
Evolution (TCCE).
The present document is part 6 of a multi-part deliverable covering Direct Mode Operation, as identified below:
Part 1: "General network design";
Part 2: "Radio aspects";
Part 3: "Mobile Station to Mobile Station (MS-MS) Air Interface (AI) protocol";
Part 4: "Type 1 repeater air interface";
Part 5: "Gateway air interface";
Part 6: "Security";
Part 7: "Type 2 repeater air interface";
Part 8: "Protocol Implementation Conformance Statement (PICS) proforma specification";
Part 10: "Managed Direct Mode Operation (M-DMO)".
NOTE: Parts 7, 8 and 10 of this multi-part deliverable are of "historical" status and will not be updated according
to this version of the standard.

National transposition dates
Date of adoption of this EN: 1 July 2016
Date of latest announcement of this EN (doa): 31 October 2016
Date of latest publication of new National Standard
or endorsement of this EN (dop/e): 30 April 2017
Date of withdrawal of any conflicting National Standard (dow): 30 April 2017

Modal verbs terminology
In the present document "shall", "shall not", "should", "should not", "may", "need not", "will", "will not", "can" and
"cannot" are to be interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of
provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.
ETSI
7 ETSI EN 300 396-6 V1.6.1 (2016-11)
1 Scope
The present document defines the Terrestrial Trunked Radio system (TETRA) Direct Mode of operation. It specifies the
basic Air Interface (AI), the interworking between Direct Mode Groups via Repeaters and interworking with the
TETRA Trunked system via Gateways. It also specifies the security aspects in TETRA Direct Mode and the intrinsic
services that are supported in addition to the basic bearer and teleservices.
The present document describes the security mechanisms in TETRA Direct Mode. It provides mechanisms for
confidentiality of control signalling and user speech and data at the AI. It also provided some implicit authentication as
a member of a group by knowledge of a shared secret encryption key.
The use of AI encryption gives both confidentiality protection against eavesdropping, and some implicit authentication.
2 References
2.1 Normative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
Referenced documents which are not found to be publicly available in the expected location might be found at
https://docbox.etsi.org/Reference/.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents are necessary for the application of the present document.
[1] ETSI EN 300 392-2: "Terrestrial Trunked Radio (TETRA); Voice plus Data (V+D); Part 2: Air
Interface (AI)".
[2] ISO 7498-2: "Information processing systems -- Open Systems Interconnection -- Basic Reference
Model -- Part 2: Security Architecture".
[3] ETSI EN 300 396-2: "Terrestrial Trunked Radio (TETRA); Technical requirements for Direct
Mode Operation (DMO); Part 2: Radio aspects".
[4] ETSI EN 300 392-7: "Terrestrial Trunked Radio (TETRA); Voice plus Data (V+D);
Part 7: Security".
[5] ETSI EN 300 396-3: "Terrestrial Trunked Radio (TETRA); Technical requirements for Direct
Mode Operation (DMO); Part 3: Mobile Station to Mobile Station (MS-MS) Air Interface (AI)
protocol".
[6] ETSI TS 100 392-15: "Terrestrial Trunked Radio (TETRA); Voice plus Data (V+D);
Part 15: TETRA frequency bands, duplex spacings and channel numbering".
[7] ETSI EN 302 109: "Terrestrial Trunked Radio (TETRA); Security; Synchronization mechanism
for end-to-end encryption".
[8] ETSI EN 300 396-5: "Terrestrial Trunked Radio (TETRA); Technical requirements for Direct
Mode Operation (DMO); Part 5: Gateway air interface".
[9] ETSI EN 300 396-4: "Terrestrial Trunked Radio (TETRA); Technical requirements for Direct
Mode Operation (DMO); Part 4: Type 1 repeater air interface".
[10] ETSI TS 101 053-1: "Rules for the management of the TETRA standard encryption algorithms;
Part 1: TEA1".
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8 ETSI EN 300 396-6 V1.6.1 (2016-11)
[11] ETSI TS 101 053-2: "Security Algorithms Group of Experts (SAGE); Rules for the management
of the TETRA standard encryption algorithms; Part 2: TEA2".
[12] ETSI TS 101 053-3: "Rules for the management of the TETRA standard encryption algorithms;
Part 3: TEA3".
[13] ETSI TS 101 053-4: "Rules for the management of the TETRA standard encryption algorithms;
Part 4: TEA4".
[14] ETSI TS 101 052: "Rules for the management of the TETRA standard authentication and key
management algorithm set TAA1".
2.2 Informative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents are not necessary for the application of the present document but they assist the
user with regard to a particular subject area.
Not applicable.
3 Definitions and abbreviations
3.1 Definitions
For the purposes of the present document, the following terms and definitions apply:
air interface encryption state: status of encryption in a call (on or off)
call transaction: all of the functions associated with a complete unidirectional transmission of information during a call
NOTE: A call is made up of one or more call transactions. In a simplex call these call transactions are sequential.
See ETSI EN 300 396-3 [5].
carrier number: integer, N, used in TETRA to represent the frequency of the RF carrier
NOTE: See ETSI TS 100 392-15 [6].
cipher key: value that is used to determine the transformation of plain text to cipher text in a cryptographic algorithm
cipher text: data produced through the use of encipherment
NOTE: The semantic content of the resulting data is not available (ISO 7498-2 [2]).
decipherment: reversal of a corresponding reversible encipherment
NOTE: See ISO 7498-2 [2].
Direct Mode Operation (DMO): mode of simplex operation where mobile subscriber radio units may communicate
using radio frequencies which may be monitored by, but which are outside the control of, the TETRA TMO network
NOTE: DM operation is performed without intervention of any base station. See ETSI EN 300 396-3 [5].
DMO-net: number of DMO MSs communicating together and using common cryptographic parameters
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9 ETSI EN 300 396-6 V1.6.1 (2016-11)
encipherment: cryptographic transformation of data to produce cipher text
NOTE: See ISO 7498-2 [2].
encryption cipher key: cipher key used as input to the KSG, derived from an address specific cipher key and randomly
varied per channel using algorithm TB6
end-to-end encryption: encryption within or at the source end system, with the corresponding decryption occurring
only within or at the destination end system
explicit authentication: transaction initiated and completed specifically to demonstrate knowledge of a shared secret
where the secret is not revealed
implicit authentication: authenticity demonstrated by proof of knowledge of a shared secret where that demonstration
is a by-product of another function
key stream: pseudo random stream of symbols that is generated by a KSG for encipherment and decipherment
Key Stream Generator (KSG): cryptographic algorithm which produces a stream of binary digits which can be used
for encipherment and decipherment
NOTE: The initial state of the KSG is determined by the initialization value.
Key Stream Segment (KSS): key stream of arbitrary length
plain text: unencrypted source data
NOTE: The semantic content is available.
proprietary algorithm: algorithm which is the intellectual property of a legal entity
SCK set: collective term for the group of 32 SCKs associated with each Individual TETRA Subscriber Identity
SCK-subset: collection of SCKs from an SCK set, with SCKNs in numerical sequence, where every SCK in the subset
is associated with one or more different GSSIs
NOTE: Multiple SCK subsets have corresponding SCKs associated with the same GSSIs.
Static Cipher Key (SCK): predetermined cipher key that may be used to provide confidentiality in class DM-2-A,
DM-2-B and DM-2-C systems with a corresponding algorithm
synchronization value: sequence of symbols that is transmitted to the receiving terminal to synchronize the KSG in the
receiving terminal with the KSG in the transmitting terminal
synchronous stream cipher: encryption method in which a cipher text symbol completely represents the
corresponding plain text symbol
NOTE: The encryption is based on a key stream that is independent of the cipher text. In order to synchronize the
KSGs in the transmitting and the receiving terminal synchronization data is transmitted separately.
TETRA algorithm: mathematical description of a cryptographic process used for either of the security processes
authentication or encryption
Trunked Mode Operation (TMO): Operations of TETRA specified in ETSI EN 300 392-2 [1].
3.2 Abbreviations
For the purposes of the present document, the following abbreviations apply:
ACK ACKnowledgement
AI Air Interface
CK Cypher Key
CN Carrier Number
DM Direct Mode
DMAC Direct Mode Media Access Control
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10 ETSI EN 300 396-6 V1.6.1 (2016-11)
DMC A layer 2 Service Access Point (DMC-SAP)
DMCC Direct Mode Call Control
DMO Direct Mode Operation
DSB Direct Mode Synchronisation Burst
ECK Encryption Cipher Key
EDSI Encrypted Direct-mode Short Identity
EDSI-URTC Encrypted DMO Short Identity-Usage Restriction Type Confidentiality
EUIV EDSI-URTC Initialisation Vector
FN Frame Number
GSSI Group Short Subscriber Identity
GTSI Group TETRA Subscriber Identity
KAG Key Association Group
KSG Key Stream Generator
KSS Key Stream Segment
MAC Medium Access Control
MDE Message Dependent Elements
MNC Mobile Network Code
MNI Mobile Network Identity
MS Mobile Station
OTAR Over The Air Rekeying
PDU Protocol Data Unit
PICS Protocol Implementation Conformance Statement
REP REPeater
RF Radio Frequency
SAP Service Access Point
SCH Signalling CHannel
SCH/F Full SCH
SCH/H Half SCH
SCH/S Synchronization SCH
SCK Static Cipher Key
SCKN Static Cipher Key Number
SCK-VN SCK-Version Number
SDS Short Data Service
SDU Service Data Unit
SSI Short Subscriber Identity
STCH STolen CHannel
SwMI Switching and Management Infrastructure
SYNC SYNChronization
TCH Traffic CHannel
TCH/S Speech Traffic CHannel
TDMA Time Division Media Access
TMO Trunked Mode Operation
TN Timeslot Number
TSI TETRA Subscriber Entity
TVP Time Variant Parameter
U-PLANE User-PLANE
URT Usage Restriction Type
URTC Usage Restriction Type Confidentiality
V+D Voice + Data
XOR eXclusive OR
4 DMO security class
4.1 General
TETRA security is defined in terms of class. DMO security offers 4 classes defined in table 4.1.
NOTE: DMO offers equivalence to TMO security class 1 (no encryption enabled) and to TMO security class 2
(SCK encryption supported).
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11 ETSI EN 300 396-6 V1.6.1 (2016-11)
Table 4.1: Direct Mode security class
DMO security class Remark
DM-1 No encryption applied.
DM-2-A The DM-SDU and any related traffic is AI encrypted. Addresses are not encrypted.
DM-2-B The destination address (SSI), DM-SDU and any related traffic are AI encrypted.
DM-2-C In the DMAC-SYNC PDU, the PDU is encrypted from destination address element and
onwards except for source address type element, and any related traffic is AI encrypted. In
the DMAC-DATA PDU, the PDU is encrypted from the destination address type element and
onwards.
NOTE 1: Except in DMAC-DATA PDUs for class DM-2-C the destination and source address type elements are never
encrypted.
NOTE 2: DM-1 is considered the lowest level of security.
NOTE 3: DM-2-A through DM-2-B to DM-2-C provide progressively increased levels of security by encrypting more of
the signalling content.
The security class is identified in DMAC-SYNC PDUs by the AI encryption state element (see table 4.2).
Table 4.2: AI encryption state element encoding
Information element Length Value Class
Air Interface encryption state 2 00 DM-1
10 DM-2-A
DM-2-B
01 DM-2-C
On establishing a call the first master shall establish the security class of the call. The security class should be
maintained for the duration of the call.
4.2 DM-2-A
The purpose of security class DM-2-A is to provide confidentiality of user traffic and signalling in applications where it
is not necessary to hide the addressing information.
In addition security class DM-2-A allows calls to be made through a repeater where the repeater is not provided with
the capability to encrypt or decrypt messages by maintaining the layer 2 (MAC) elements of any signalling in clear.
Addresses identified by the Usage Restriction Type (URT) field in repeaters, gateways and combined
repeater-gateways, shall be in clear (i.e. the Encrypted DMO Short Identity-Usage Restriction Type Confidentiality
(EDSI-URTC) shall not apply).
4.3 DM-2-B
The purpose of security class DM-2-B is to provide confidentiality of user traffic and signalling.
Security class DM-2-B extends the confidentiality applied to signalling over that provided in class DM-2-A to encrypt
parts of the MAC header. The encryption allows repeater operation to be made without requiring the repeater to be able
to encrypt and decrypt transmissions unless it wishes to check the validity of the destination address. In class DM-2-B
because the source address is in clear, a pre-emptor can identify the pre-emption slots and hence the call can be
pre-empted even if the pre-emptor does not have the encryption key being used by the call master.
Addresses identified by the URT field in repeaters, gateways and combined repeater-gateways, should be encrypted
(i.e. EDSI-URTC should apply).
4.4 DM-2-C
The purpose of security class DM-2-C is to provide confidentiality of user traffic and signalling including all identities
other than those of repeaters and gateways.
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12 ETSI EN 300 396-6 V1.6.1 (2016-11)
In addition in class DM-2-C the bulk of the MAC header elements are encrypted. Where repeaters are used, the repeater
requires the ability to encrypt and decrypt all transmissions. In class DM-2-C calls can only be pre-empted by an MS
which has the SCK in use by the call master.
Addresses identified by the URT field in repeaters, gateways and combined repeater-gateways, should be encrypted
(i.e. EDSI-URTC should apply).
5 DMO call procedures
5.1 General
5.1.1 Security profile
5.1.1.0 General
An MS should maintain a security profile for each destination address. The security profile should contain at least the
following for each destination address:
• KSG, as identified by its KSG-identifier;
• current SCK, as identified by SCKN, for transmission;
• valid SCKs, as identified by SCKN, for reception;
• the preferred, and minimum, security class to be applied to calls for transmission;
• the minimum security class to be applied to calls for reception; and
• the minimum security class that a master will accept in a pre-emption request.
The preferred security class is the security class to be used for transmission when the MS is acting as a call master. The
minimum security class for transmission is the lowest security class that the MS shall use to transmit responses to other
signalling.
NOTE 1: Minimum may be the same as preferred.
NOTE 2: A default profile may be maintained in addition to a profile for specific addresses.
NOTE 3: A profile should exist for received individual calls (i.e. for calls where destination address is that of the
receiving MS).
NOTE 4: If the preferred security class to be applied to calls for transmission is DM-2-C the minimum security
class that a master will accept in a pre-emption request should be set to class DM-2-C MS.
5.1.1.1 Indication of security parameters
In call setup procedures the DMAC-SYNC PDU found in logical channel SCH/S shall contain the parameters required
to identify the security class of the call, the encryption algorithm and the identity of the key in use, in addition to the
current value of the Time Variant Parameter used to synchronize the encryption devices (see also annex A).
The DMAC-SYNC PDU is defined in clause 9 of ETSI EN 300 396-3 [5] and contains the security elements identified
in table 5.1.
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13 ETSI EN 300 396-6 V1.6.1 (2016-11)
Table 5.1: Security elements of DMAC-SYNC PDU contents in SCH/S
Information element Length Value Remark
Air interface encryption state 2 Security class (see note 1)
Time Variant Parameter 29 Any
Reserved 1 0 Default value is 0
KSG number 4
Encryption key number 5 Identifies SCKN (see note 2)
NOTE 1: If set to DM-1 the other security elements shall not be present.
NOTE 2: The encoding is such that 00000 indicates SCKN = 1, 11111 indicates SCKN = 32.
2 2
5.2 Security class on call setup
5.2.1 General
On establishing a call the first master shall establish the security class of the call by setting the Air Interface (AI)
encryption state element of DMAC-SYNC PDU using data contained in the master's security profile.
Once an SCK has been established for a call transaction the master shall make no changes to the ciphering parameters
(key, algorithm, class) within that call transaction.
The security class and algorithm should be maintained for the duration of the call. The key may be different in different
transactions because each MS may have a different definition of which SCKN is current.
5.2.2 Normal behaviour
On receipt of call setup the DM-MS shall extract the ciphering parameters from the DMAC-SYNC PDU. These
parameters shall be compared with the DM-MS's predefined security profile associated with the destination address.
If the parameters match the security profile (i.e. KSG-id identical, SCKN belongs to the KAG specified for the address,
security class is equal to or greater than the minimum required for the destination address) the call may be accepted
(i.e. speech or data path opened).
5.2.3 Exceptional behaviour
5.2.3.0 General
On receipt of call setup the slave DM-MS shall extract the ciphering parameters from the DMAC-SYNC PDU. These
parameters shall be compared with the DM-MS's predefined security profile associated with the destination address.
5.2.3.1 Call-setup with presence check
If the parameters do not match the security profile (i.e. KSG-id is not identical, or SCKN does not belong to the KAG
specified for the address, or security class is not equal to or greater than the minimum required for the destination
address) the slave should ignore or reject the call (i.e. speech or data path closed) with reason "security parameter
mismatch".
5.2.3.2 Call-setup without presence check
If the parameters do not match the security profile (i.e. KSG-id is not identical, or SCKN does not belong to the KAG
specified for the address, or security class is not equal to or greater than the minimum required for the destination
address), the slave should ignore the call (i.e. speech or data path closed).
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14 ETSI EN 300 396-6 V1.6.1 (2016-11)
5.2.3.3 Behaviour post call-setup
Once an SCK has been established for a call transaction the master shall make no changes to the ciphering parameters
(key, algorithm, class) within that call transaction. If the slave DM-MS perceives that such a change is being attempted
the slave DM-MS (receiver) shall ignore the change and maintain the original parameters for the remainder of that call
transaction.
5.3 Security class on call follow-on
5.3.1 General
NOTE 1: The mechanisms in this clause apply to security classes 2A, 2B and 2C for slave, DM-GATE and idle
MSs.
The slave or idle DM-MS shall have a method of determining the preferred security class to be applied to calls for
transmission (see clause 5.1.1). The MS shall use this preferred security class when the MS becomes the call master in
the follow on case.
If the follow on transaction is sent to the same address, the new call master shall select the SCKN from KAG associated
with that address that it considers to be the current key (which may be different to the SCKN used by the previous call
master).
NOTE 2: The new call master may be either a DM-MS or a DM-GATE.
Random access requests (e.g. pre-emption, changeover, timing adjust), should be sent in a manner that the current call
master can understand but shall not use a lower security class than its minimum security class as defined in the security
profile (see clause 5.1.1). If a slave or idle DM-MS uses class 2C security to send a random access request to the master
of a call, the requesting DM-MS should encrypt the request using the SCK being used by the current call master or may
use the SCK that it considers current in the associated KAG.
NOTE 3: The term "slave or idle DM-MS" includes gateways and repeaters (although it is noted that a DM-REP
does not generate random access requests).
If a random access request is received using a different class to that of the call being pre-empted, any response to the
pre-emption request shall be sent using the lower of the two security classes.
NOTE 4: A master may ignore a random access request (without sending a response) if the security class used for
the random access request is insufficient.
The master shall respond to any random access request using the SCKN that it considers to be the current SCK for the
ongoing call (as indicated by the security profile for the ongoing call). This shall be the same SCKN that the master was
using for the call transaction prior to receiving the request.
5.3.2 Normal behaviour
When making an attempt to follow on a pre-existing call the new call master shall establish a new independent TVP.
On receipt of call setup the DM-MS shall extract the encryption parameters from the DMAC-SYNC PDU. These
parameters shall be compared with the predefined security profile associated with the destination address. If the
parameters match in full the call may be accepted (i.e. speech or data path opened).
5.3.3 Exceptional behaviour
On receipt of call setup the DM-MS shall e
...

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Terrestrial Trunked Radio (TETRA) - Direct Mode Operation (DMO) - Part 6: Security33.070.10Prizemni snopovni radio (TETRA)Terrestrial Trunked Radio (TETRA)ICS:Ta slovenski standard je istoveten z:ETSI EN 300 396-6 V1.6.1 (2016-11)SIST EN 300 396-6 V1.6.1:2017en01-januar-2017SIST EN 300 396-6 V1.6.1:2017SLOVENSKI
STANDARD
EUROPEAN STANDARD SIST EN 300 396-6 V1.6.1:2017

ETSI ETSI EN 300 396-6 V1.6.1 (2016-11) 2
Reference REN/TCCE-06191 Keywords air interface, data, DMO, security, security mode, speech, TETRA ETSI 650 Route des Lucioles F-06921 Sophia Antipolis Cedex - FRANCE
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DECTTM, PLUGTESTSTM, UMTSTM and the ETSI logo are Trade Marks of ETSI registered for the benefit of its Members. 3GPPTM and LTE™ are Trade Marks of ETSI registered for the benefit of its Members and of the 3GPP Organizational Partners. GSM® and the GSM logo are Trade Marks registered and owned by the GSM Association. SIST EN 300 396-6 V1.6.1:2017

ETSI ETSI EN 300 396-6 V1.6.1 (2016-11) 3 Contents Intellectual Property Rights . 6 Foreword . 6 Modal verbs terminology . 6 1 Scope . 7 2 References . 7 2.1 Normative references . 7 2.2 Informative references . 8 3 Definitions and abbreviations . 8 3.1 Definitions . 8 3.2 Abbreviations . 9 4 DMO security class . 10 4.1 General . 10 4.2 DM-2-A . 11 4.3 DM-2-B . 11 4.4 DM-2-C . 11 5 DMO call procedures . 12 5.1 General . 12 5.1.1 Security profile . 12 5.1.1.0 General . 12 5.1.1.1 Indication of security parameters . 12 5.2 Security class on call setup . 13 5.2.1 General . 13 5.2.2 Normal behaviour . 13 5.2.3 Exceptional behaviour . 13 5.2.3.0 General . 13 5.2.3.1 Call-setup with presence check . 13 5.2.3.2 Call-setup without presence check . 13 5.2.3.3 Behaviour post call-setup . 14 5.3 Security class on call follow-on . 14 5.3.1 General . 14 5.3.2 Normal behaviour . 14 5.3.3 Exceptional behaviour . 14 6 Air interface authentication and key management mechanisms . 15 6.1 Authentication . 15 6.2 Repeater mode operation . 15 6.3 Gateway mode operation . 15 6.4 Air Interface (AI) key management mechanisms . 17 6.4.0 General . 17 6.4.1 Key grouping . 17 6.4.2 Identification of cipher keys in signalling . 20 7 Enable and disable mechanism . 20 8 Air Interface (AI) encryption . 20 8.1 General principles. 20 8.2 Encryption mechanism . 21 8.2.0 General . 21 8.2.1 Allocation of KSS to logical channels . 21 8.3 Application of KSS to specific PDUs. 22 8.3.0 General . 22 8.3.1 Class DM-1 . 22 8.3.2 Class DM-2A . 22 8.3.2.0 General . 22 8.3.2.1 DMAC-SYNC PDU encryption . 22 SIST EN 300 396-6 V1.6.1:2017

ETSI ETSI EN 300 396-6 V1.6.1 (2016-11) 4 8.3.2.2 DMAC-DATA PDU encryption . 23 8.3.2.3 DMAC-FRAG PDU encryption . 23 8.3.2.4 DMAC-END PDU encryption . 23 8.3.2.5 DMAC-U-SIGNAL PDU encryption . 24 8.3.2.6 Traffic channel encryption . 24 8.3.3 Class DM-2B . 24 8.3.3.0 General . 24 8.3.3.1 DMAC-SYNC PDU encryption . 25 8.3.3.2 DMAC-DATA PDU encryption . 25 8.3.3.3 DMAC-FRAG PDU encryption . 25 8.3.3.4 DMAC-END PDU encryption . 26 8.3.3.5 DMAC-U-SIGNAL PDU encryption . 26 8.3.3.6 Traffic channel encryption . 26 8.3.4 Class DM-2C . 26 8.3.4.0 General . 26 8.3.4.1 DMAC-SYNC PDU encryption . 27 8.3.4.2 DMAC-DATA PDU encryption . 28 8.3.4.3 DMAC-FRAG PDU encryption . 28 8.3.4.4 DMAC-END PDU encryption . 28 8.3.4.5 DMAC-U-SIGNAL PDU encryption . 28 8.3.4.6 Traffic channel encryption . 29 8.4 Encryption of identities in repeater and gateway presence signal . 29 9 Encryption synchronization . 31 9.1 General . 31 9.1.0 Introduction. 31 9.1.1 Algorithm to establish frame number to increment TVP . 32 9.1.1.1 Master DM-MS operation . 32 9.1.1.2 Slave DM-MS operation . 32 9.2 TVP used for reception of normal bursts . 33 9.3 Synchronization of calls through a repeater . 33 9.3.0 General . 33 9.3.1 Algorithm to establish frame number to increment TVP . 34 9.3.1.1 Master DM-MS operation . 34 9.3.1.2 Slave DM-MS operation . 34 9.4 Synchronization of calls through a gateway . 34 9.5 Synchronization of data calls where data is multi-slot interleaved . 35 9.5.0 General . 35 9.5.1 Recovery of stolen frames from interleaved data . 36 Annex A (normative): Key Stream Generator (KSG) boundary conditions . 37 A.0 General . 37 A.1 Overview . 37 A.2 Use . 38 A.3 Interfaces to the algorithm . 38 A.3.0 General . 38 A.3.1 ECK . 38 A.3.1.0 General . 38 A.3.1.1 Use of ECK in class DM-2-A and DM-2-B . 39 A.3.1.2 Use of ECK in class DM-2-C . 39 A.3.2 Keystream. 39 A.3.3 Time Variant Parameter (TVP) . 39 Annex B (normative): Boundary conditions for cryptographic algorithm TB6 . 40 Annex C (informative): Encryption control in DM-MS . 41 C.0 Introduction . 41 C.1 General . 41 SIST EN 300 396-6 V1.6.1:2017

ETSI ETSI EN 300 396-6 V1.6.1 (2016-11) 5 C.2 Service description and primitives . 41 C.2.0 General . 41 C.2.1 DMCC-ENCRYPT primitive . 42 C.2.2 DMC-ENCRYPTION primitive . 44 C.3 Protocol functions . 45 Annex D (informative): Bibliography . 46 Annex E (informative): Change request history . 47 History . 48
ETSI ETSI EN 300 396-6 V1.6.1 (2016-11) 6 Intellectual Property Rights IPRs essential or potentially essential to the present document may have been declared to ETSI. The information pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web server (https://ipr.etsi.org/). Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web server) which are, or may be, or may become, essential to the present document. Foreword This European Standard (EN) has been produced by ETSI Technical Committee TETRA and Critical Communications Evolution (TCCE). The present document is part 6 of a multi-part deliverable covering Direct Mode Operation, as identified below: Part 1: "General network design"; Part 2: "Radio aspects"; Part 3: "Mobile Station to Mobile Station (MS-MS) Air Interface (AI) protocol"; Part 4: "Type 1 repeater air interface"; Part 5: "Gateway air interface"; Part 6: "Security"; Part 7: "Type 2 repeater air interface"; Part 8: "Protocol Implementation Conformance Statement (PICS) proforma specification"; Part 10: "Managed Direct Mode Operation (M-DMO)". NOTE: Parts 7, 8 and 10 of this multi-part deliverable are of "historical" status and will not be updated according to this version of the standard.
National transposition dates Date of adoption of this EN: 1 July 2016 Date of latest announcement of this EN (doa): 31 October 2016 Date of latest publication of new National Standard or endorsement of this EN (dop/e):
30 April 2017 Date of withdrawal of any conflicting National Standard (dow): 30 April 2017
Modal verbs terminology In the present document "shall", "shall not", "should", "should not", "may", "need not", "will", "will not", "can" and "cannot" are to be interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of provisions). "must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation. SIST EN 300 396-6 V1.6.1:2017

ETSI ETSI EN 300 396-6 V1.6.1 (2016-11) 7 1 Scope The present document defines the Terrestrial Trunked Radio system (TETRA) Direct Mode of operation. It specifies the basic Air Interface (AI), the interworking between Direct Mode Groups via Repeaters and interworking with the TETRA Trunked system via Gateways. It also specifies the security aspects in TETRA Direct Mode and the intrinsic services that are supported in addition to the basic bearer and teleservices. The present document describes the security mechanisms in TETRA Direct Mode. It provides mechanisms for confidentiality of control signalling and user speech and data at the AI. It also provided some implicit authentication as a member of a group by knowledge of a shared secret encryption key. The use of AI encryption gives both confidentiality protection against eavesdropping, and some implicit authentication.
2 References 2.1 Normative references References are either specific (identified by date of publication and/or edition number or version number) or non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the referenced document (including any amendments) applies. Referenced documents which are not found to be publicly available in the expected location might be found at https://docbox.etsi.org/Reference/. NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee their long term validity. The following referenced documents are necessary for the application of the present document. [1] ETSI EN 300 392-2: "Terrestrial Trunked Radio (TETRA); Voice plus Data (V+D); Part 2: Air Interface (AI)". [2] ISO 7498-2: "Information processing systems -- Open Systems Interconnection -- Basic Reference Model -- Part 2: Security Architecture". [3] ETSI EN 300 396-2: "Terrestrial Trunked Radio (TETRA); Technical requirements for Direct Mode Operation (DMO); Part 2: Radio aspects". [4] ETSI EN 300 392-7: "Terrestrial Trunked Radio (TETRA); Voice plus Data (V+D); Part 7: Security". [5] ETSI EN 300 396-3: "Terrestrial Trunked Radio (TETRA); Technical requirements for Direct Mode Operation (DMO); Part 3: Mobile Station to Mobile Station (MS-MS) Air Interface (AI) protocol". [6] ETSI TS 100 392-15: "Terrestrial Trunked Radio (TETRA); Voice plus Data (V+D); Part 15: TETRA frequency bands, duplex spacings and channel numbering". [7] ETSI EN 302 109: "Terrestrial Trunked Radio (TETRA); Security; Synchronization mechanism for end-to-end encryption". [8] ETSI EN 300 396-5: "Terrestrial Trunked Radio (TETRA); Technical requirements for Direct Mode Operation (DMO); Part 5: Gateway air interface". [9] ETSI EN 300 396-4: "Terrestrial Trunked Radio (TETRA); Technical requirements for Direct Mode Operation (DMO); Part 4: Type 1 repeater air interface". [10] ETSI TS 101 053-1: "Rules for the management of the TETRA standard encryption algorithms; Part 1: TEA1". SIST EN 300 396-6 V1.6.1:2017

ETSI ETSI EN 300 396-6 V1.6.1 (2016-11) 8 [11] ETSI TS 101 053-2: "Security Algorithms Group of Experts (SAGE); Rules for the management of the TETRA standard encryption algorithms; Part 2: TEA2". [12] ETSI TS 101 053-3: "Rules for the management of the TETRA standard encryption algorithms; Part 3: TEA3". [13] ETSI TS 101 053-4: "Rules for the management of the TETRA standard encryption algorithms; Part 4: TEA4". [14] ETSI TS 101 052: "Rules for the management of the TETRA standard authentication and key management algorithm set TAA1". 2.2 Informative references References are either specific (identified by date of publication and/or edition number or version number) or non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the referenced document (including any amendments) applies. NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee their long term validity. The following referenced documents are not necessary for the application of the present document but they assist the user with regard to a particular subject area. Not applicable. 3 Definitions and abbreviations 3.1 Definitions For the purposes of the present document, the following terms and definitions apply: air interface encryption state: status of encryption in a call (on or off) call transaction: all of the functions associated with a complete unidirectional transmission of information during a call NOTE: A call is made up of one or more call transactions. In a simplex call these call transactions are sequential. See ETSI EN 300 396-3 [5]. carrier number: integer, N, used in TETRA to represent the frequency of the RF carrier
NOTE: See ETSI TS 100 392-15 [6]. cipher key: value that is used to determine the transformation of plain text to cipher text in a cryptographic algorithm cipher text: data produced through the use of encipherment NOTE: The semantic content of the resulting data is not available (ISO 7498-2 [2]). decipherment: reversal of a corresponding reversible encipherment
NOTE: See ISO 7498-2 [2]. Direct Mode Operation (DMO): mode of simplex operation where mobile subscriber radio units may communicate using radio frequencies which may be monitored by, but which are outside the control of, the TETRA TMO network NOTE: DM operation is performed without intervention of any base station. See ETSI EN 300 396-3 [5]. DMO-net: number of DMO MSs communicating together and using common cryptographic parameters SIST EN 300 396-6 V1.6.1:2017

ETSI ETSI EN 300 396-6 V1.6.1 (2016-11) 9 encipherment: cryptographic transformation of data to produce cipher text NOTE: See ISO 7498-2 [2]. encryption cipher key: cipher key used as input to the KSG, derived from an address specific cipher key and randomly varied per channel using algorithm TB6 end-to-end encryption: encryption within or at the source end system, with the corresponding decryption occurring only within or at the destination end system explicit authentication: transaction initiated and completed specifically to demonstrate knowledge of a shared secret where the secret is not revealed implicit authentication: authenticity demonstrated by proof of knowledge of a shared secret where that demonstration is a by-product of another function key stream: pseudo random stream of symbols that is generated by a KSG for encipherment and decipherment Key Stream Generator (KSG): cryptographic algorithm which produces a stream of binary digits which can be used for encipherment and decipherment NOTE: The initial state of the KSG is determined by the initialization value.
Key Stream Segment (KSS): key stream of arbitrary length plain text: unencrypted source data NOTE: The semantic content is available. proprietary algorithm: algorithm which is the intellectual property of a legal entity SCK set: collective term for the group of 32 SCKs associated with each Individual TETRA Subscriber Identity SCK-subset: collection of SCKs from an SCK set, with SCKNs in numerical sequence, where every SCK in the subset is associated with one or more different GSSIs NOTE: Multiple SCK subsets have corresponding SCKs associated with the same GSSIs. Static Cipher Key (SCK): predetermined cipher key that may be used to provide confidentiality in class DM-2-A, DM-2-B and DM-2-C systems with a corresponding algorithm synchronization value: sequence of symbols that is transmitted to the receiving terminal to synchronize the KSG in the receiving terminal with the KSG in the transmitting terminal synchronous stream cipher: encryption method in which a cipher text symbol completely represents the corresponding plain text symbol NOTE: The encryption is based on a key stream that is independent of the cipher text. In order to synchronize the KSGs in the transmitting and the receiving terminal synchronization data is transmitted separately. TETRA algorithm: mathematical description of a cryptographic process used for either of the security processes authentication or encryption Trunked Mode Operation (TMO): Operations of TETRA specified in ETSI EN 300 392-2 [1]. 3.2 Abbreviations For the purposes of the present document, the following abbreviations apply: ACK ACKnowledgement AI Air Interface CK Cypher Key CN Carrier Number DM Direct Mode DMAC Direct Mode Media Access Control SIST EN 300 396-6 V1.6.1:2017

ETSI ETSI EN 300 396-6 V1.6.1 (2016-11) 10 DMC A layer 2 Service Access Point (DMC-SAP) DMCC Direct Mode Call Control DMO Direct Mode Operation DSB Direct Mode Synchronisation Burst ECK Encryption Cipher Key EDSI Encrypted Direct-mode Short Identity EDSI-URTC Encrypted DMO Short Identity-Usage Restriction Type Confidentiality EUIV EDSI-URTC Initialisation Vector FN Frame Number GSSI Group Short Subscriber Identity GTSI Group TETRA Subscriber Identity KAG Key Association Group KSG Key Stream Generator KSS Key Stream Segment MAC Medium Access Control MDE Message Dependent Elements MNC Mobile Network Code MNI Mobile Network Identity MS Mobile Station OTAR Over The Air Rekeying PDU Protocol Data Unit PICS Protocol Implementation Conformance Statement REP REPeater RF Radio Frequency SAP Service Access Point SCH Signalling CHannel SCH/F Full SCH SCH/H Half SCH SCH/S Synchronization SCH SCK Static Cipher Key SCKN Static Cipher Key Number SCK-VN SCK-Version Number SDS Short Data Service SDU Service Data Unit SSI Short Subscriber Identity STCH STolen CHannel SwMI Switching and Management Infrastructure SYNC SYNChronization TCH Traffic CHannel TCH/S Speech Traffic CHannel TDMA Time Division Media Access TMO Trunked Mode Operation TN Timeslot Number TSI TETRA Subscriber Entity TVP Time Variant Parameter U-PLANE User-PLANE URT Usage Restriction Type URTC Usage Restriction Type Confidentiality V+D Voice + Data XOR eXclusive OR 4 DMO security class 4.1 General TETRA security is defined in terms of class. DMO security offers 4 classes defined in table 4.1. NOTE: DMO offers equivalence to TMO security class 1 (no encryption enabled) and to TMO security class 2 (SCK encryption supported).
ETSI ETSI EN 300 396-6 V1.6.1 (2016-11) 11 Table 4.1: Direct Mode security class DMO security class Remark DM-1 No encryption applied. DM-2-A The DM-SDU and any related traffic is AI encrypted. Addresses are not encrypted. DM-2-B The destination address (SSI), DM-SDU and any related traffic are AI encrypted. DM-2-C In the DMAC-SYNC PDU, the PDU is encrypted from destination address element and onwards except for source address type element, and any related traffic is AI encrypted. In the DMAC-DATA PDU, the PDU is encrypted from the destination address type element and onwards. NOTE 1: Except in DMAC-DATA PDUs for class DM-2-C the destination and source address type elements are never encrypted. NOTE 2: DM-1 is considered the lowest level of security.
NOTE 3: DM-2-A through DM-2-B to DM-2-C provide progressively increased levels of security by encrypting more of the signalling content.
The security class is identified in DMAC-SYNC PDUs by the AI encryption state element (see table 4.2). Table 4.2: AI encryption state element encoding Information element Length Value Class Air Interface encryption state 2 002 DM-1
102 DM-2-A
112 DM-2-B
012 DM-2-C
On establishing a call the first master shall establish the security class of the call. The security class should be maintained for the duration of the call. 4.2 DM-2-A The purpose of security class DM-2-A is to provide confidentiality of user traffic and signalling in applications where it is not necessary to hide the addressing information.
In addition security class DM-2-A allows calls to be made through a repeater where the repeater is not provided with the capability to encrypt or decrypt messages by maintaining the layer 2 (MAC) elements of any signalling in clear. Addresses identified by the Usage Restriction Type (URT) field in repeaters, gateways and combined repeater-gateways, shall be in clear (i.e. the Encrypted DMO Short Identity-Usage Restriction Type Confidentiality (EDSI-URTC) shall not apply). 4.3 DM-2-B The purpose of security class DM-2-B is to provide confidentiality of user traffic and signalling.
Security class DM-2-B extends the confidentiality applied to signalling over that provided in class DM-2-A to encrypt parts of the MAC header. The encryption allows repeater operation to be made without requiring the repeater to be able to encrypt and decrypt transmissions unless it wishes to check the validity of the destination address. In class DM-2-B because the source address is in clear, a pre-emptor can identify the pre-emption slots and hence the call can be pre-empted even if the pre-emptor does not have the encryption key being used by the call master. Addresses identified by the URT field in repeaters, gateways and combined repeater-gateways, should be encrypted (i.e. EDSI-URTC should apply). 4.4 DM-2-C The purpose of security class DM-2-C is to provide confidentiality of user traffic and signalling including all identities other than those of repeaters and gateways. SIST EN 300 396-6 V1.6.1:2017

ETSI ETSI EN 300 396-6 V1.6.1 (2016-11) 12 In addition in class DM-2-C the bulk of the MAC header elements are encrypted. Where repeaters are used, the repeater requires the ability to encrypt and decrypt all transmissions. In class DM-2-C calls can only be pre-empted by an MS which has the SCK in use by the call master. Addresses identified by the URT field in repeaters, gateways and combined repeater-gateways, should be encrypted (i.e. EDSI-URTC should apply). 5 DMO call procedures 5.1 General 5.1.1 Security profile 5.1.1.0 General An MS should maintain a security profile for each destination address. The security profile should contain at least the following for each destination address:
• KSG, as identified by its KSG-identifier; • current SCK, as identified by SCKN, for transmission;
• valid SCKs, as identified by SCKN, for reception; • the preferred, and minimum, security class to be applied to calls for transmission; • the minimum security class to be applied to calls for reception; and • the minimum security class that a master will accept in a pre-emption request. The preferred security class is the security class to be used for transmission when the MS is acting as a call master. The minimum security class for transmission is the lowest security class that the MS shall use to transmit responses to other signalling. NOTE 1: Minimum may be the same as preferred. NOTE 2: A default profile may be maintained in addition to a profile for specific addresses. NOTE 3: A profile should exist for received individual calls (i.e. for calls where destination address is that of the receiving MS). NOTE 4: If the preferred security class to be applied to calls for transmission is DM-2-C the minimum security class that a master will accept in a pre-emption request should be set to class DM-2-C MS. 5.1.1.1 Indication of security parameters In call setup procedures the DMAC-SYNC PDU found in logical channel SCH/S shall contain the parameters required to identify the security class of the call, the encryption algorithm and the identity of the key in use, in addition to the current value of the Time Variant Parameter used to synchronize the encryption devices (see also annex A). The DMAC-SYNC PDU is defined in clause 9 of ETSI EN 300 396-3 [5] and contains the security elements identified in table 5.1. SIST EN 300 396-6 V1.6.1:2017

ETSI ETSI EN 300 396-6 V1.6.1 (2016-11) 13 Table 5.1: Security elements of DMAC-SYNC PDU contents in SCH/S Information element Length Value Remark Air interface encryption state 2
Security class (see note 1) Time Variant Parameter 29 Any
Reserved 1 0 Default value is 0 KSG number 4
Encryption key number 5
Identifies SCKN (see note 2) NOTE 1: If set to DM-1 the other security elements shall not be present. NOTE 2: The encoding is such that 000002 indicates SCKN = 1, 111112 indicates SCKN = 32.
5.2 Security class on call setup 5.2.1 General On establishing a call the first master shall establish the security class of the call by setting the Air Interface (AI) encryption state element of DMAC-SYNC PDU using data contained in the master's security profile. Once an SCK has been established for a call transaction the master shall make no changes to the ciphering parameters (key, algorithm, class) within that call transaction. The security class and algorithm should be maintained for the duration of the call. The key may be different in different transactions because each MS may have a different definition of which SCKN is current. 5.2.2 Normal behaviour On receipt of call setup the DM-MS shall extract the ciphering parameters from the DMAC-SYNC PDU. These parameters shall be compared with the DM-MS's predefined security profile associated with the destination address.
If the parameters match the security profile (i.e. KSG-id identical, SCKN belongs to the KAG specified for the address, security class is equal to or greater than the minimum required for the destination address) the call may be accepted (i.e. speech or data path opened). 5.2.3 Exceptional behaviour 5.2.3.0 General On receipt of call setup the slave DM-MS shall extract the ciphering parameters from the DMAC-SYNC PDU. These parameters shall be compared with the DM-MS's predefined security profile associated with the destination address. 5.2.3.1 Call-setup with presence check If the parameters do not match the security profile (i.e. KSG-id is not identical, or SCKN does not belong to the KAG specified for the address, or security class is not equal to or greater than the minimum required for the destination address) the slave should ignore or reject the call (i.e. speech or data path closed) with reason "security parameter mismatch".
5.2.3.2 Call-setup without presence check If the parameters do not match the security profile (i.e. KSG-id is not identical, or SCKN does not belong to the KAG specified for the address, or security class is not equal to or greater than the minimum required for the destination address), the slave should ignore the call (i.e. speech or data path closed). SIST EN 300 396-6 V1.6.1:2017

ETSI ETSI EN 300 396-6 V1.6.1 (2016-11) 14 5.2.3.3 Behaviour post call-setup Once an SCK has been established for a call transaction the master shall make no changes to the ciphering parameters (key, algorithm, class) within that call transaction. If the slave DM-MS perceives that such a change is being attempted the slave DM-MS (receiver) shall ignore the change and maintain the original parameters for the remainder of that call transaction. 5.3 Security class on call follow-on 5.3.1 General NOTE 1: The mechanisms in this clause apply to security classes 2A, 2B and 2C for slave, DM-GATE and idle MSs. The slave or idle DM-MS shall have a method of determining the preferred security class to be applied to calls for transmission (see clause 5.1.1). The MS shall use this preferred security class when the MS becomes the call master in the follow on case. If the follow on transaction is sent to the same address, the new call master shall select the SCKN from KAG associated with that address that it considers to be the current key (which may be different to the SCKN used by the previous call master). NOTE 2: The new call master may be either a DM-MS or a DM-GATE. Random access requests (e.g. pre-emption, changeover, timing adjust), should be sent in a manner that the current call master can understand but shall not use a lower security class than its minimum security class as defined in the security profile (see clause 5.1.1). If a slave or idle DM-MS uses class 2C security to send a random access request to the master of a call, the requesting DM-MS should encrypt the request using the SCK being used by the current call master or may use the SCK that it considers current in the associated KAG. NOTE 3: The term "slave or idle DM-MS" includes gateways and repeaters (although it is noted that a DM-REP does not generate random access requests). If a random access request is received using a different class to that of the call being pre-empted, any response to the pre-emption request shall be sent using the lower of the two security classes. NOTE 4: A master may ignore a random access request (without sending a response) if the security class used for the random access request is insufficient. The master shall respond to any random access request using the SCKN that it considers to be the current SCK for the ongoing call (as indicated by the security profile for the ongoing call). This shall be the same SCKN that the master was using for the call transaction prior to receiving the request. 5.3.2 Normal behaviour When making an attempt to follow on a pre-existing call the new call master shall establish a new independent TVP. On receipt of call setup the DM-MS shall extract the encryption parameters from the DMAC-SYNC PDU. These parameters shall be compared with the predefined security profile associated with the destination address. If the parameters match in full the call may be accepted (i.e. speech or data path opened). 5.3.3 Exceptional behaviour On receipt of call setup the DM-MS shall extract the encryption parameters from the DMAC-SYNC PDU. These parameters shall be compared with the predefined security profile associated with the destination address. If the parameters do not match the security profile (i.e. KSG-id is not identical, SCKN does not belong the KAG specified for the address, or security class is not equal to or greater than the minimum required for the destination address) the call should be rejected (i.e. speech or data pa
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