TR 33.879
Study on Security enhancements for
Mission Critical Push To Talk (MCPTT) over LTE

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V13.1.0 (Wzip) 2016/06 88 p.

Rapporteur:: Mr. Haigh, Peter
CESG

full Table of Contents for TR 33.879 Word version: 13.1.0

each clause number in 'red' refers to the equivalent title in the Partial Content

Scope p. 8

References p. 8

Definitions and abbreviations p. 9

3.1	Definitions p. 9
3.2	Abbreviations p. 10

Overview of Mission Critical Push-to-Talk (MCPTT) p. 10

4.1

Introduction p. 10

4.2

Architecture p. 11

4.2.1	General p. 11
4.2.2	MCPTT application plane p. 11
4.2.3	MCPTT signalling plane p. 13
4.2.4	Off-network functional model p. 14

4.3

MCPTT identity definition and usage p. 14

List of assets p. 14

Security analysis of MCPTT p. 15

6.1

General security requirements p. 15

6.2

Key Issue # 1: Configuration & service access p. 15

6.2.1	Issue details p. 15
6.2.2	Security threats p. 15
6.2.3	Potential security requirements p. 16

6.3

Key Issue # 2: Group Key Management p. 16

6.3.1	Issue details p. 16
6.3.2	Security threats p. 16
6.3.3	Potential security requirements p. 16

6.4

Key Issue # 3: On-Network Operation: denial of service p. 17

6.4.1	Issue details p. 17
6.4.2	Security threats p. 17
6.4.3	Potential security requirements p. 17

6.5

Key Issue # 4: Ambient Listening p. 17

6.5.1	Key issue details p. 17
6.5.2	Security threats p. 18
6.5.3	Potential security requirements p. 18

6.6

Key Issue # 5: Data communication security between MCPTT network entities p. 18

6.6.1	Issue details p. 18
6.6.2	Security threats p. 18
6.6.3	Potential security requirements p. 18

6.7

Key Issue # 6: On-Network Operation: impersonation p. 18

6.7.1	Issue details p. 18
6.7.2	Security threats p. 19
6.7.3	Potential security requirements p. 19

6.8

Key Issue # 7: On-Network Operation: manipulation p. 19

6.8.1	Issue details p. 19
6.8.2	Security threats p. 19
6.8.3	Potential security requirements p. 19

6.9

Key Issue # 8: On-network operation: traffic analysis p. 20

6.9.1	Issue details p. 20
6.9.2	Security threats p. 20
6.9.3	Potential security requirements p. 20

6.10

Key Issue # 9: On-network operation: interception of user traffic p. 20

6.10.1	Issue details p. 20
6.10.2	Security threats p. 20
6.10.3	Potential security requirements p. 21

6.11

Key Issue # 10: Key Stream Re-use p. 21

6.11.1	Key issue details p. 21
6.11.2	Security threats p. 21
6.11.3	Potential security requirements p. 21

6.12

Key Issue # 11: Late Entry to Group Communication p. 22

6.12.1	Issue details p. 22
6.12.2	Security threats p. 22
6.12.3	Potential security requirements p. 22

6.13

Key Issue # 12: Private Call Confidentiality p. 22

6.13.1	Issue details p. 22
6.13.2	Security threats p. 22
6.13.3	Potential security requirements p. 23

6.14

Key Issue # 13: Off-network operation: denial of service p. 23

6.14.1	Issue details p. 23
6.14.2	Security threats p. 23
6.14.3	Potential security requirements p. 23

6.15

Key Issue # 14: Off-Network Operation: interception of user traffic p. 23

6.15.1	Issue details p. 23
6.15.2	Security threats p. 23
6.15.3	Potential security requirements p. 23

6.16

Key Issue # 15: Off-network operation: impersonation p. 24

6.16.1	Issue details p. 24
6.16.2	Security threats p. 24
6.16.3	Potential security requirements p. 24

6.17

Key Issue # 16: Off-network operation: manipulation p. 24

6.17.1	Issue details p. 24
6.17.2	Security threats p. 24
6.17.3	Potential security requirements p. 24

6.18

Key Issue # 17: Off-network operation: traffic analysis p. 25

6.18.1	Issue details p. 25
6.18.2	Security threats p. 25
6.18.3	Potential security requirements p. 25

6.19

Key Issue #18: Privacy of MCPTT identities p. 25

6.19.1	Issue details p. 25
6.19.2	Security threats p. 25
6.19.3	Potential security requirements p. 26

Proposed Solutions p. 26

7.1

Solution #1: Signalling protection and authentication procedure for MCPTT services p. 26

7.2

Solution #2: MCPTT User authentication and registration based on OpenID Connect p. 28

7.2.0

Introduction p. 28

7.2.1

OpenID Connect (OIDC) p. 30

7.2.1.0	General p. 30
7.2.1.1	OpenID Connect Authorization Code flow using Proof Key for Code Exchange p. 30

7.2.2

Detailed flow for MCPTT User Authentication and Registration using OpenID Connect p. 31

7.3

Solution #3: Addition of KMS function and interfaces p. 32

7.3.1

General p. 32

7.3.2

Functional model for the MCPTT KMS p. 32

7.3.2.0	Introduction p. 32
7.3.2.1	Reference point CSC-8 (between key management client and key management server) p. 33
7.3.2.2	Reference point CSC-9 (between the key management server and the MCPTT Server) p. 33
7.3.2.3	Reference point CSC-10 (between the key management server and a group management server) p. 33

7.3.3

Security Procedures p. 33

7.3.4

Key material provisioned to support Solution #4 and #5 p. 34

7.4

Solution #4: Distribution of a group security context p. 35

7.4.1

General p. 35

7.4.2

Security procedures for GMK provisioning p. 36

7.4.3

Group keying for media protection and floor control p. 37

7.4.4

Group creation procedure p. 38

7.4.5

Dynamic Group Keying p. 38

7.4.5.1	General p. 38
7.4.5.2	Group regrouping procedures (within a single MCPTT system) p. 38
7.4.5.3	Group regrouping procedures (involving multiple MCPTT systems) p. 38

7.4.6

Derivation of SRTP/SRTCP master keys p. 39

7.5

Solution #5: Private call security p. 40

7.5.1	General p. 40
7.5.2	Security procedures (on-network) p. 41
7.5.3	Off-network security procedures p. 42
7.5.4	Media stream protection p. 43

7.6

Solution #6: End-to-end protection for private call in on-network p. 44

7.6.1

General p. 44

7.6.2

End-to-end protection using SDES p. 44

7.6.3

End-to-access edge using SDES p. 46

7.6.4

End-to-end protection using KMS p. 46

7.6.5

Feasibility analysis of SDES and KMS mechanism p. 47

7.6.5.1	SDES and KMS mechanisms p. 47
7.6.5.2	MCPTT media plane security p. 47
7.6.5.3	Feasibility of SDES and KMS p. 48
7.6.5.4	Conclusion p. 48

7.7

Solution #7: Media stream protection p. 48

7.7.1	General p. 48
7.7.2	Security procedures for media stream protection p. 49

7.8

Solution #8: Protection of floor control signalling (SRTCP) p. 50

7.8.1	General p. 50
7.8.3	Floor control protection (SRTCP) p. 50
7.8.4	Security procedures for floor control protection p. 51

7.9

Solution #9: GCSE based security for MCPTT service p. 52

7.9.1

Introduction p. 52

7.9.2

Potential GCSE based security solutions for MCPTT p. 52

7.9.2.0	Introduction p. 52
7.9.2.1	Security for unicast delivery mode p. 52
7.9.2.2	Security for multicast delivery mode p. 52

7.10

Solution #10: Inter/Intra domain protection for MCPTT service p. 53

7.11

Solution #11: HTTP-1 interface protection p. 53

7.11.1	General p. 53
7.11.2	Authentication for Common Service Core (CSC) access p. 53
7.11.3	HTTP-1 interface security p. 53

7.12

Solution #12: Using S/MIME to protect MCPTT Application plane messaging in SIP messages p. 54

7.12.1	General p. 54
7.12.2	Cryptographic Message Syntax (CMS) p. 54
7.12.3	S/MIME p. 55
7.12.4	Confidentiality and integrity protection of MCPTT application information using asymmetric keys p. 55
7.12.5	Confidentiality protection of MCPTT application information p. 58

7.13

Solution #13: KMS managed Content Encryption Key (CEK) for S/MIME p. 58

7.13.0	Introduction p. 58
7.13.1	Authorizing the distribution of the Content Encryption Key (CEK) p. 58
7.13.2	Creation and distribution of the Content Encryption Key (CEK) p. 58
7.13.3	Key management of the Content Encryption Key (CEK) p. 60

7.14

Solution #14: Identity based cryptography managed Content Encryption Key (CEK) for S/MIME p. 63

7.14.0	Introduction p. 63
7.14.1	Authorizing the distribution of the Content Encryption Key (CEK) p. 63
7.14.2	Creation and distribution of the Content Encryption Key (CEK) p. 63
7.14.3	Key management of the Content Encryption Key (CEK) p. 63
7.14.4	Transfer of the Content Encryption Key (CEK) p. 64

7.15

Solution #15: Using content indirection and XCAP to hide MCPTT sensitive application information in SIP messages p. 65

7.15.1	General p. 65
7.15.2	Content indirection p. 66
7.15.3	XCAP URIs p. 67
7.15.4	Contact list organisation p. 67

7.16

Solution #16: Protecting the location object p. 68

7.16.1	General p. 68
7.16.2	Cryptographic Message Syntax (CMS) p. 68
7.16.3	MCPTT client signing and encrypting the location object p. 69
7.16.4	MCPTT server retrieving the location object p. 70

7.17

Solution #17: Protection of sensitive application data based on xmlsec p. 71

7.17.1	General p. 71
7.17.2	Protected content p. 71
7.17.3	Key agreement p. 72
7.17.3a	Confidentiality protection using XML encryption (xmlenc) p. 72
7.17.4	Integrity protection using XML signature (xmlsig) p. 72
7.17.5	Calculation of keys for application data protection p. 73

Evaluation of solutions p. 73

8.1

Signaling protection and IMS authentication p. 74

8.1.0	Introduction p. 74
8.1.0a	Potential requirements relating to application layer security p. 74
8.1.1	S/MIME CEK Key management p. 74
8.1.2	Evaluation of sensitive application signalling p. 75

8.2

MCPTT User authentication and authorisation p. 75

8.2.1	Introduction p. 75
8.2.2	MCPTT requirements relating to user authentication and authorisation p. 76
8.2.3	Evaluation of user authentication and authorisation solutions p. 76

8.3

Group call key distribution solutions p. 77

8.3.1	General p. 77
8.3.2	Potential requirements relating to group call security p. 77
8.3.3	Evaluation of solution #4 against requirements p. 77
8.3.4	System impact evaluation p. 78
8.3.5	Summary of evaluation p. 78

8.4

Private call key distribution solutions p. 78

8.4.1	General p. 78
8.4.2	Potential requirements relating to private call security p. 79
8.4.3	Evaluation of key distribution solutions against requirements p. 79
8.4.4	System impact evaluation p. 81
8.4.5	Summary of evaluation p. 81

8.5

Media and floor control protection p. 81

8.5.1	General p. 81
8.5.2	Potential sequirements relating to media and floor control p. 81
8.5.3	Comparison of solutions p. 82
8.5.4	Choice of algorithm p. 82
8.5.5	Summary of evaluation p. 82

Conclusion p. 82

9.1

Signaling protection and IMS authentication p. 83

9.1.0	Introduction p. 83
9.1.1	S/MIME CEK key management p. 83
9.1.2	Sensitive application signalling protection p. 83

9.2

MCPTT User authentication and registration p. 83

9.3

Group call key distribution solutions p. 83

9.4

Private call key distribution solutions p. 83

9.5

Media and floor control protection p. 83

Authentication call-flows p. 84

A.1	MCPTT service authentication call-flow example-1 p. 84
A.2	MCPTT service authentication call-flow example-2 p. 86

Change History p. 88

TR 33.879 Study on Security enhancements for Mission Critical Push To Talk (MCPTT) over LTE

full Table of Contents for TR 33.879 Word version: 13.1.0

TR 33.879
Study on Security enhancements for
Mission Critical Push To Talk (MCPTT) over LTE