ETSI TS 133 122 V17.0.0 (2022-04)

LTE; 5G; Security aspects of Common API Framework (CAPIF) for 3GPP northbound APIs (3GPP TS 33.122 version 17.0.0 Release 17)

RTS/TSGS-0333122vh00

General Information

• Status: Not Published
• Technical Committee: 3GPP SA 3 - Security
• Current Stage: 12 - Completion
• Completion Date: 06-Apr-2022

Standards Content (Sample)

ETSI TS 133 122 V17.0.0 (2022-04)






TECHNICAL SPECIFICATION
LTE;
5G;
Security aspects of Common API Framework (CAPIF)
for 3GPP northbound APIs
(3GPP TS 33.122 version 17.0.0 Release 17)

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3GPP TS 33.122 version 17.0.0 Release 17 1 ETSI TS 133 122 V17.0.0 (2022-04)

Reference
RTS/TSGS-0333122vh00
Keywords
5G,LTE,SECURITY
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ETSI

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3GPP TS 33.122 version 17.0.0 Release 17 2 ETSI TS 133 122 V17.0.0 (2022-04)
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ETSI

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3GPP TS 33.122 version 17.0.0 Release 17 3 ETSI TS 133 122 V17.0.0 (2022-04)
Contents
Intellectual Property Rights . 2
Legal Notice . 2
Modal verbs terminology . 2
Foreword . 5
1 Scope . 6
2 References . 6
3 Definitions, symbols and abbreviations . 6
3.1 Definitions . 6
3.2 Symbols . 6
3.3 Abbreviations . 7
4 Security requirements . 7
4.1 General . 7
4.2 Common security requirements . 7
4.3 Security requirements on the CAPIF-1/1e reference points . 7
4.4 Security requirements on the CAPIF-2/2e reference points . 8
4.5 Security requirements on the CAPIF-3/4/5 reference points . 8
4.6 Security requirements on the CAPIF-3e/4e/5e reference points . 9
4.7 Security requirements on the CAPIF-7/7e reference points . 9
5 Functional security model . 9
6 Security procedures . 10
6.1 Security procedures for API invoker onboarding . 10
6.2 Security procedures for CAPIF-1 reference point . 12
6.3 Security procedures for CAPIF-1e reference point . 12
6.3.1 Authentication and authorization . 12
6.3.1.1 General . 12
6.3.1.2 Security method negotiation. 12
6.3.1.3 API discovery . 13
6.3.1.4 Topology hiding . 13
6.4 Security procedures for CAPIF-2 reference point . 13
6.5 Security procedures for CAPIF-2e reference point . 14
6.5.1 General . 14
6.5.2 Authentication and authorization . 14
6.5.2.1 Method 1 – Using TLS-PSK . 14
6.5.2.2 Method 2 – Using PKI . 15
6.5.2.3 Method 3 – TLS with OAuth token . 16
6.6 Security procedures for CAPIF-3/4/5 reference points . 18
6.7 Security procedures for updating security method . 18
6.8 Security procedure for API invoker offboarding . 18
6.9 Security procedures for CAPIF-7/7e reference points . 20
6.10 Security procedures for CAPIF-3e/4e/5e reference points . 20
Annex A (normative): Key derivation functions . 21
A.1 AEFPSK derivation function. 21
Annex B (informative): Security flows . 22
B.1 Onboarding . 22
B.2 Authentication and authorization . 23
Annex C (normative): Access token profile for ‘Method 3 - TLS with OAuth token’ . 26
C.1 General . 26
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3GPP TS 33.122 version 17.0.0 Release 17 4 ETSI TS 133 122 V17.0.0 (2022-04)
C.2 Access token profile . 26
C.2.1 General . 26
C.2.2 Token claims . 26
C.3 Obtaining tokens . 27
C.3.1 General . 27
C.3.2 Access token request . 27
C.3.3 Access token response . 28
C.4 Refreshing an access token . 28
C.5 Using the token to access API exposing functions . 28
C.6 . Token
revocation . 28
C.7 Token validation . 29
C.7.1 Access token validation . 29
Annex D (informative): Change history . 30
History . 31

ETSI

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3GPP TS 33.122 version 17.0.0 Release 17 5 ETSI TS 133 122 V17.0.0 (2022-04)
Foreword
This Technical Specification has been produced by the 3rd Generation Partnership Project (3GPP).
The contents of the present document are subject to continuing work within the TSG and may change following formal
TSG approval. Should the TSG modify the contents of the present document, it will be re-released by the TSG with an
identifying change of release date and an increase in version number as follows:
Version x.y.z
where:
x the first digit:
1 presented to TSG for information;
2 presented to TSG for approval;
3 or greater indicates TSG approved document under change control.
y the second digit is incremented for all changes of substance, i.e. technical enhancements, corrections,
updates, etc.
z the third digit is incremented when editorial only changes have been incorporated in the document.
ETSI

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3GPP TS 33.122 version 17.0.0 Release 17 6 ETSI TS 133 122 V17.0.0 (2022-04)
1 Scope
The present document specifies the security architecture i.e., the security features and the security mechanisms for the
common API framework (CAPIF) as per the architecture and procedures defined in 3GPP TS 23.222 [3].
2 References
The following documents contain provisions which, through reference in this text, constitute provisions of the present
document.
- References are either specific (identified by date of publication, edition number, version number, etc.) or
non-specific.
- For a specific reference, subsequent revisions do not apply.
- For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including
a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same
Release as the present document.
[1] 3GPP TR 21.905: "Vocabulary for 3GPP Specifications".
[2] 3GPP TS 33.310: "Network Domain Security (NDS); Authentication Framework (AF)".
[3] 3GPP TS 23.222: "Common API Framework for 3GPP Northbound APIs".
[4] IETF RFC 6749: "The OAuth 2.0 Authorization Framework".
[5] IETF RFC 6750: "The OAuth 2.0 Authorization Framework: Bearer Token Usage".
[6] IETF RFC 7519: "JSON Web Token (JWT)".
[7] IETF RFC 7515: "JSON Web Signature (JWS)".
[8] 3GPP TS 33.220: "Generic Authentication Architecture (GAA); Generic Bootstrapping
Architecture (GBA)".
[9] Void
[10] 3GPP TS 33.210: "3G security; Network Domain Security (NDS); IP network layer security".
3 Definitions, symbols and abbreviations
3.1 Definitions
For the purposes of the present document, the terms and definitions given in 3GPP TR 21.905 [1] and the following
apply. A term defined in the present document takes precedence over the definition of the same term, if any, in 3GPP
TR 21.905 [1].
3.2 Symbols
For the purposes of the present document, the following symbols apply:
AEF Pre-Shared Key for AEF
PSK

ETSI

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3GPP TS 33.122 version 17.0.0 Release 17 7 ETSI TS 133 122 V17.0.0 (2022-04)
3.3 Abbreviations
For the purposes of the present document, the abbreviations given in 3GPP TR 21.905 [1] and the following apply. An
abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in
3GPP TR 21.905 [1].
AEF API Exposing Function
API Application Programming Interface
CAPIF Common API Framework
JSON JavaScript Object Notation
JWT JSON Web Token
KDF Key Derivation Function
PKI Public Key Infrastructure
PSK Pre-Shared Key
TLS Transport Layer Security
4 Security requirements
4.1 General
Architectural requirements pertaining to CAPIF security are found in 3GPP TS 23.222 [3]. The following are CAPIF
derived security requirements.
4.2 Common security requirements
Security requirements that are applicable to all CAPIF entities are:
- [CAPIF-SEC-4.2-a] The CAPIF shall provide mechanisms to hide the topology of the PLMN trust domain from
the API invokers accessing the service APIs from outside the PLMN trust domain.
- [CAPIF-SEC-4.2-b] The CAPIF shall provide mechanisms to hide the topology of the 3rd party API provider
trust domain from the API invokers accessing the service APIs from outside the 3rd party API provider trust
domain.
- [CAPIF-SEC-4.2-c] The CAPIF shall provide authorization mechanism for service APIs from the 3rd party API
providers.
- [CAPIF-SEC-4.2-d] The CAPIF shall support a common security mechanism for all API implementations to
provide confidentiality and integrity protection.
- [CAPIF-SEC-4.2-e] API invoker authentication and authorization shall support all deployment models listed in
3GPP TS 23.222 [3].
- [CAPIF-SEC-4.2-f] The API invoker and CAPIF should enforce the result of the authentication for the duration
of communications (e.g. by integrity protection or implicit authentication by encryption with a key that is
derived from the authentication and is unknown to the adversary).
4.3 Security requirements on the CAPIF-1/1e reference points
The CAPIF-1/1e reference points between the API invoker and the CAPIF core function shall fulfil the following
requirements:
- [CAPIF-SEC-4.3-a] Mutual authentication between the API invoker and the CAPIF Core function shall be
supported.
- [CAPIF-SEC-4.3-b] The transport of messages over the CAPIF-1 and CAPIF-1e reference points shall be
integrity protected.
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3GPP TS 33.122 version 17.0.0 Release 17 8 ETSI TS 133 122 V17.0.0 (2022-04)
- [CAPIF-SEC-4.3-c] The transport of messages over the CAPIF-1 and CAPIF-1e reference points shall be
protected from replay attacks.
- [CAPIF-SEC-4.3-d] The transport of messages over the CAPIF-1 and CAPIF-1e reference points shall be
confidentiality protected.
- [CAPIF-SEC-4.3-e] Privacy of the 3GPP user over the CAPIF-1 and CAPIF-1e reference points shall be
protected.
- [CAPIF-SEC-4.3-f] The CAPIF core function shall authorize the API invoker prior to the API invoker accessing
the AEF.
- [CAPIF-SEC-4.3-g] The CAPIF core function shall authorize the API invoker prior to accessing the discover
service API.
- [CAPIF-SEC-4.3-h] The CAPIF core function shall authenticate the API invoker's onboarding request.
- [CAPIF-SEC-4.3-i] The CAPIF core function shall authenticate the API invoker's offboarding request.
4.4 Security requirements on the CAPIF-2/2e reference points
The CAPIF-2/2e reference points between the API invoker and API exposing function shall fulfil the following
requirements:
- [CAPIF-SEC-4.4-a] Mutual authentication between the API invoker and the API exposing function shall be
supported.
- [CAPIF-SEC-4.4-b] The transport of messages over the CAPIF-2 and CAPIF-2e reference points shall be
integrity protected.
- [CAPIF-SEC-4.4-c] The transport of messages over the CAPIF-2 and CAPIF-2e reference points shall be
protected from replay attacks.
- [CAPIF-SEC-4.4-d] The transport of messages over the CAPIF-2 and CAPIF-2e reference points shall be
confidentiality protected.
- [CAPIF-SEC-4.4-e] Privacy of the 3GPP user over the CAPIF-2 and CAPIF-2e reference points shall be
protected.
- [CAPIF-SEC-4.4-f] The API exposing function shall determine whether API invoker is authorized to access
service API.
4.5 Security requirements on the CAPIF-3/4/5 reference points
The security requirements for CAPIF-3/4/5 reference points are:
- [CAPIF-SEC-4.5-a] The transport of messages over the CAPIF-3/4/5 reference points shall be integrity
protected.
- [CAPIF-SEC-4.5-b] The transport of messages over the CAPIF-3/4/5 reference points shall be confidentiality
protected.
- [CAPIF-SEC-4.5-c] The transport of messages over the CAPIF-3/4/5 reference points shall be protected from
replay attacks.
- [CAPIF-SEC-4.5-d] The CAPIF core function shall be able to authenticate the service API publishers to publish
and manage the service API information.
- [CAPIF-SEC-4.5-e] The CAPIF core function shall be able to authorize the service API publishers to publish
and manage the service API information.
- [CAPIF-SEC-4.5-f] The CAPIF core function shall be able to request explicit grant of new API invoker’s
onboarding.
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3GPP TS 33.122 version 17.0.0 Release 17 9 ETSI TS 133 122 V17.0.0 (2022-04)
- [CAPIF-SEC-4.5-g] The CAPIF core function shall be able to authenticate the API Management function’s
registration request for API Provider domain functions.
- [CAPIF-SEC-4.5-h] The CAPIF core function shall be able to authenticate the API Management function’s
registration update request for API provider domain functions.
4.6 Security requirements on the CAPIF-3e/4e/5e reference
points
The security requirements for CAPIF-3e/4e/5e reference points are:
- [CAPIF-SEC-4.6 -a] The transport of messages over the CAPIF-3e/4e/5e reference points shall be integrity
protected.
- [CAPIF-SEC-4. 6 -b] The transport of messages over the CAPIF-3e/4e/5e reference points shall be
confidentiality protected.
- [CAPIF-SEC-4. 6 -c] The transport of messages over the CAPIF-3e/4e/5e reference points shall be protected
from replay attacks.
- [CAPIF-SEC-4. 6 -d] The CAPIF core function shall be able to authenticate the service API publishers to
publish and manage the service API information.
- [CAPIF-SEC-4. 6 -e] The CAPIF core function shall be able to authorize the service API publishers to publish
and manage the service API information.
- [CAPIF-SEC-4. 6 -f] The CAPIF core function shall be able to request explicit grant of new API invoker’s
onboarding.
- [CAPIF-SEC-4.6-g] The CAPIF core function shall be able to authenticate the API Management function’s
registration request for API Provider domain functions.
- [CAPIF-SEC-4.6-h] The CAPIF core function shall be able to authenticate the API Management function’s
registration update request for API provider domain functions.
4.7 Security requirements on the CAPIF-7/7e reference points
The security requirements for CAPIF-7/7e reference points are:
- [CAPIF-SEC-4.7-a] The transport of messages over the CAPIF-7 and CAPIF-7e reference points shall be
integrity protected.
- [CAPIF-SEC-4.7-b] The transport of messages over the CAPIF-7 and CAPIF-7e reference points shall be
protected from replay attacks.
- [CAPIF-SEC-4.7-c] The transport of messages over the CAPIF-7 and CAPIF-7e reference points shall be
confidentiality protected.
- [CAPIF-SEC-4.7-d] Privacy of the 3GPP user over the CAPIF-7 and CAPIF-7e reference points shall be
protected.
- [CAPIF-SEC-4.7-e] The API exposing function (destination AEF handling service API) shall determine whether
AEF that is topology hiding entity, is authorized to access service API.

5 Functional security model
Figure 5-1 shows the functional security model for the CAPIF architecture. The interfaces CAPIF-1, CAPIF-1e,
CAPIF-2, CAPIF-2e, CAPIF-3, CAPIF-4, CAPIF-5, CAPIF-3e, CAPIF-4e, CAPIF-5e, CAPIF-7 and CAPIF-7e are
defined in 3GPP TS 23.222 [3] and support the CAPIF functionality defined in 3GPP TS 23.222 [3]. CAPIF-1, CAPIF-
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3GPP TS 33.122 version 17.0.0 Release 17 10 ETSI TS 133 122 V17.0.0 (2022-04)
2, CAPIF-3, CAPIF-4, CAPIF-5 and CAPIF-7 are interfaces that lie within the PLMN trust domain while the CAPIF-1e
, CAPIF-2e, CAPIF-3e, CAPIF-4e, CAPIF-5e and CAPIF-7e interfaces are CAPIF core and AEF access points for API
Invokers outside of the PLMN trust domain.
Security for the CAPIF-1, CAPIF-2, CAPIF-3, CAPIF-4, CAPIF-5 and CAPIF-7 interfaces support TLS and are
defined in subclauses 6.2, 6.4 and 6.6 of the present document. Security for the CAPIF-1e, CAPIF-2e and CAPIF-7e
interfaces support TLS, and are defined in subclause 6.3, subclause 6.5, and subclause 6.9 respectively.
Security for the CAPIF-3e, CAPIF-4e and CAPIF-5e interfaces support NDS/IP security to secure communication
between different IP security domains. This avoids multiple secure connections between API provider domain and
CAPIF core domain by leveraging the NDS/IP security procedures specified in TS 33.210 [2].
Authentication and authorization are required for both API invokers that lie within the PLMN trust domain and API
invokers that lie outside of the PLMN trust domain. For an API invoker that is outside of the PLMN trust domain, the
CAPIF core function in coordination with the API exposing function utilizes the CAPIF-1e, CAPIF-2e and the CAPIF-3
interfaces to onboard, authenticate and authorize the API invoker prior to granting access to CAPIF services. Security
flow diagrams for onboarding security, CAPIF-1e security and CAPIF-2e security can be found in Annex B. When the
API invoker is within the PLMN trust domain, the CAPIF core function in coordination with the API exposing function
perform authentication and authorization of the API invoker via the CAPIF-1, the CAPIF-2 and the CAPIF-3 interfaces
prior to granting access to CAPIF services. Authentication and authorization of API invokers (both internal and external
to the PLMN trust domain) is specified in clause 6 of the present document.
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