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TECHNICAL SPECIFICATION
Digital cellular telecommunications system (Phase 2+) (GSM);
Universal Mobile Telecommunications System (UMTS);
LTE;
Generic Authentication Architecture (GAA);
Generic Bootstrapping Architecture (GBA) Push function
(3GPP TS 33.223 version 15.0.0 Release 15)
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3GPP TS 33.223 version 15.0.0 Release 15 1 ETSI TS 133 223 V15.0.0 (2018-11)
Reference
RTS/TSGS-0333223vf00
Keywords
GSM,LTE,SECURITY,UMTS
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3GPP TS 33.223 version 15.0.0 Release 15 2 ETSI TS 133 223 V15.0.0 (2018-11)
Intellectual Property Rights
Essential patents
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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
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Foreword
This Technical Specification (TS) has been produced by ETSI 3rd Generation Partnership Project (3GPP).
The present document may refer to technical specifications or reports using their 3GPP identities, UMTS identities or
GSM identities. These should be interpreted as being references to the corresponding ETSI deliverables.
The cross reference between GSM, UMTS, 3GPP and ETSI identities can be found under
.
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
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3GPP TS 33.223 version 15.0.0 Release 15 3 ETSI TS 133 223 V15.0.0 (2018-11)
Contents
Intellectual Property Rights . 2
Foreword . 2
Modal verbs terminology . 2
Foreword . 4
Introduction . 4
1 Scope . 5
2 References . 5
3 Definitions, symbols and abbreviations . 6
3.1 Definitions . 6
3.2 Abbreviations . 6
4 GBA Push Architecture . 7
4.1 Introduction . 7
4.1.1 General . 7
4.1.2 GBA-Push system overview . 7
4.2 GBA Push Architecture . 8
4.2.1 Description and Rationale . 8
4.2.2 GBA-Push keying model . 8
4.3 GBA Push Requirements . 9
4.3.1 General GBA Push Requirements . 9
4.3.2 Requirements on HSS and HLR . 9
4.3.3 Requirements on BSF . 9
4.3.4 Requirements on UE . 10
4.3.5 Requirements on Reference Point Upa . 10
4.3.6 Requirements on Reference Point Zh . 10
4.3.7 Requirements on Reference Point Zpn and Zpn' . 10
4.3.8 Requirements on Zn-Proxy . 11
4.3.9 Requirements on Reference Point Ua . 12
4.3.10 Requirements on NAF SA identifiers . 12
4.3.11 Requirements on Reference Point Dz . 12
5 GBA Push Function . 12
5.1 GBA Push Message Flow and Processing . 12
5.1.1 GBA Push Message Flow . 12
5.1.2 NAF processing before issuing GPI request . 14
5.1.3 BSF processing of NAF GPI request . 15
5.1.4 UE processing of GPI . 16
5.2 Data objects . 17
5.2.1 GBA Push Information (GPI) . 17
5.2.2 NAF SA identities . 18
5.2.3 NAF SA . 18
5.3 GPI Integrity and Confidentiality Protection . 19
5.3.1 General considerations . 19
5.3.2 Key material generation . 19
5.3.3 GPI Integrity protection . 20
5.3.4 GPI Confidentiality protection . 20
5.3.5 GPI message format and coding . 20
5.4 Procedures using the NAF SA . 21
Annex A (informative): Rationale behind choice of the Disposable-Ks model . 22
Annex B (normative): GBA-Push UE registration procedure . 23
Annex Z (informative): Change history . 24
History . 25
ETSI
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3GPP TS 33.223 version 15.0.0 Release 15 4 ETSI TS 133 223 V15.0.0 (2018-11)
Foreword
rd
This Technical Specification has been produced by the 3 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.
Introduction
3GPP defined the Generic Authentication Architecture (GAA). The adoption of GAA by other standardization bodies
showed that some services can not make the assumption that the User Equipment (UE) has always the possibility to
connect to the Bootstrapping Server Function (BSF) or that the UE for different reasons has not performed a
bootstrapping procedure directly with the BSF. Hence, this specification introduces and specifies a GBA Push Function.
ETSI
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3GPP TS 33.223 version 15.0.0 Release 15 5 ETSI TS 133 223 V15.0.0 (2018-11)
1 Scope
The present document specifies a Push Function as a functional add-on for the Generic Authentication Architecture
(GAA) [1].
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 TS 33.220: "Generic Authentication Architecture (GAA); Generic bootstrapping
architecture".
[2] 3GPP TR 21.905: "Vocabulary for 3GPP Specifications".
[3] 3GPP TS 33.210: "3G Security; Network Domain Security; IP network layer security".
[4] IETF RFC 2246 (1999): "The TLS Protocol Version 1".
[5] Void.
[6] 3GPP TS 33.102: "3G Security; Security architecture".
[7] FIPS PUB 180-2 (2002): "Secure Hash Standard".
[8] IETF RFC 2104 (1997): "HMAC: Keyed-Hashing for Message Authentication".
[9] ISO/IEC 10118-3:2004: "Information Technology – Security techniques – Hash-functions – Part
3: Dedicated hash-functions".
[10] NIST Special Publication 800-38A: "Recommendation for Block Cipher Modes of Operation"
[11] FIPS PUB 197: "Advanced Encryption Standard"
[12] Void
[13] 3GPP TS 33.222 "Access to network application functions using Hypertext Transfer Protocol over
Transport Layer Security (HTTPS)".
[14] 3GPP TS 29.109 "Generic Authentication Architecture (GAA); Zh and Zn Interfaces based on the
Diameter protocol; Stage 3".
[15] 3GPP TS 33.224 "Generic Authentication Architecture (GAA); Generic Bootstrapping
Architecture (GBA) Push Layer".
[15] 3GPP TS 31.101 "UICC-terminal interface; Physical and logical characteristics".
[16] IETF RFC 4330: "Simple Network Time Protocol (SNTP) Version 4 for IPv4, IPv6 and OSI".
ETSI
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3GPP TS 33.223 version 15.0.0 Release 15 6 ETSI TS 133 223 V15.0.0 (2018-11)
3 Definitions, symbols and abbreviations
3.1 Definitions
For the purposes of the present document, the terms and definitions given in TR 21.905 [2], TS 33.220 [1] and the
following apply. A term defined in the present document takes precedence over the definition of the same term, if any,
in TR 21.905 [2].
AUTN(*): In GBA context, GBA_ME relies on AUTN value to verify that the authentication vector is from an
authorised network, while GBA_U relies on AUTN* to perform network authentication as described in [1]. AUTN(*) is
used to refer both to AUTN and AUTN*.
AUTS: Defined in TS 33.102 [6].
Disposable-Ks model: The keying model used in GBA-push. Only one NAF-key is generated per Ks and the Ks cannot
be reused.
GBA_U aware UICC: A UICC which supports GBA_U which means that the Ks will never leave the UICC.
GBA-Push-Info: GBA-Push-Info contains data relevant for key derivation in GBA Push. GBA-Push_Info is sent via
the Upa-reference point from the NAF to the UE.
NAF_Id: The FQDN of the NAF, concatenated with the Ua security protocol identifier,
NAF-key: A NAF-key derived from Ks. It can be used to refer to Ks_(int/ext)_NAF or Ks_NAF.
NAF SA: A security association between a NAF and a UE based on a NAF-key.
Push-message: This is a message that is sent on a Ua-reference point from the NAF to the UE and has applied GBA
keys that were bootstrapped via the Upa-reference point.
Push-NAF: A NAF authorized for using GBA-Push.
UE_Trp: The transport address used for delivery of GPI to the UE.
3.2 Abbreviations
For the purposes of the present document, the abbreviations given in TR 21.905 [2] and the following apply. An
abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in
TR 21.905 [2].
BSF Bootstrapping Server Function
B-TID Bootstrapping Transaction Identifier
FQDN Fully Qualified Domain Name
GAA Generic Authentication Architecture
GBA Generic Bootstrapping Architecture
GBA_ME ME-based GBA
GBA_U GBA with UICC-based enhancements
GPI GBA Push Info
GUSS GBA User Security Settings
HLR Home Location Register
HSS Home Subscriber Server
Ks_NAF NAF-key in GBA_ME mode
Ks_int_NAF UICC internal NAF-key in GBA_U
Ks_ext_NAF UICC external NAF-key in GBA_U
ME Mobile Equipment
NAF Network Application Function
P-TID Push Temporary Identifier
SA Security Association
UE User Equipment
USS User Security Setting
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3GPP TS 33.223 version 15.0.0 Release 15 7 ETSI TS 133 223 V15.0.0 (2018-11)
4 GBA Push Architecture
4.1 Introduction
4.1.1 General
GBA-push is a mechanism to bootstrap the security between a NAF and a UE, without forcing the UE to contact the BSF
to initiate the bootstrapping. GBA-Push is closely related to and builds upon GBA as specified in TS 33.220 [1]. GBA-
Push is aimed for both GBA_U and GBA_ME environments.
4.1.2 GBA-Push system overview
The system overview in this clause gives a high level description of the general ideas behind the GBA-Push system
solution and the features it offers.
The generic use case considered is that a NAF initiate's establishment of a shared Security Association (SA), a NAF
SA, between itself and a UE. This is done by the NAF pushing all information, the so called GBA-Push-Info (GPI),
needed for the UE to set-up the SA. The key in this SA is a NAF-key and the GPI is requested from the BSF. The NAF-
key is generated as defined in GBA, TS 33.220 [1].
After the NAF SA establishment, the NAF can send protected Push-messages to the UE. If a return channel exists and if
defined by the Ua application, the UE can also use the established SA to protect response messages to the initiating
NAF How the NAF SA is used is out of scope for this specification. The NAF SA is identified by downlink and uplink
SA identifiers.
GBA-Push is aimed for both GBA_U and GBA_ME environments. To only establish an external NAF-key with GBA-
Push, the ME-based functionality, GBA_ME, should be used. GBA-Push based on GBA_U will establish both an
internal and external NAF-key.
GBA-Push utilizes a so called Disposable-Ks model. In the Disposable-Ks model, a Ks is only used once to derive a
single set of NAF-keys (and other keying material used to protect the GPI during transport). After the NAF-key
derivation, the Ks is erased or its further usage is denied. A new GBA-Push operation will be needed whenever a new
set of NAF-keys for the same or another NAF is needed.
NOTE 1: A generated NAF-key can be used to protect multiple Push-messages from the NAF to the UE. NAF-keys
from different NAFs can coexist.
With the Disposable-Ks model, existing NAF-keys established as specified in TS 33.220 [1] or by GBA-Push will be
unaffected. GBA_ME based GBA-Push will not interact with GBA_U but a GBA_U based GBA Push will invalidate
an existing Ks on the UICC.
NOTE 2: TS 33.220 [1] specifies that an existing Ks on the UICC will be overwritten when a new GBA_U Ks-
generation procedure is executed. The ME may of course trigger a new bootstrap procedure immediately
after the GBA-Push operation to avoid delays and certain synch problems when the UE operates GBA
according to TS33.220 [1].
The transport method of GPI from a NAF to a UE is not standardized.
NOTE 3: Examples of possible transport methods are SMS, MMS, SIP MESSAGE, UDP or broadcast. For the
transport of GPI to UEs, a NAF needs to know the message transport addresses to use for the chosen
transport method. For SMS and MMS the transport address is the MSISDN, for SIP MESSAGE it is an
IMPU and for UDP an UDP port - IP-address pair. For broadcast delivery the UE transport addresses
could be any public identity associated with a UE or an identity agreed between the NAF and the UE.
Resending of messages is a standard method to get "reliability" for delivery over unreliable channels like e.g. SMS or
broadcast. Hence the GBA-Push shall allow that GPI is retransmitted several times including cases when it is sent every
time a payload is pushed to the UE. Thus the system shall handle retransmissions of GPI efficiently.
The NAF SA defined by the GPI, is based on the use of a particular UICC (USIM/ISIM) application. Sometimes the
transport method / address indicate to the UE which UICC application to use but in other cases it has to be explicitly
signaled. If MSISDN is used as delivery address, then the USIM associated with that MSISDN should be used. This is
so because a SMS will only reach the UE when the USIM corresponding to the MSISDN is active in the UE. When an
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3GPP TS 33.223 version 15.0.0 Release 15 8 ETSI TS 133 223 V15.0.0 (2018-11)
IMPU is used as destination address, the corresponding ISIM should be used. For UDP and broadcast the USIM/ISIM
application to use has to be indicated in the GPI or be agreed upon out of band.
To protect user privacy, parts of the GPI shall be confidentiality protected, in particular the identity of the initiating
NAF when broadcast transport is used. For unlinkability between NAF to UE and UE to NAF messages, a separate SA
identity for UE to NAF security shall be assigned by the NAF and be included in the confidentiality protected part of
the GPI. To help prevent serious effects of DoS attacks and thwart some NAF misuse of GBA-Push, the GPI also needs
to be integrity protected. The integrity protection of GPI will also prevent that incorrect GBA Push security associations
are accepted by the UE as it will detect transmission errors. The keys for confidentiality and integrity protection are
derived from the Ks defined by the GPI.
4.2 GBA Push Architecture
4.2.1 Description and Rationale
The GBA Push functionality builds on the architecture and functionality provided by TS 33.220 [1]. The main
difference from TS 33.220 [1] is the definition of new reference points between the BSF and the NAF and between the
NAF and the UE, as indicated in figure 4.2-1, which is a modified version of figure 4.1 in TS 33.220 [1].
HSS
Dz
Zh Zpn
BSF
SLF
NAF
Upa Ua
UE
Figure 4.2-1: Simple network model for pushed bootstrapping via NAF
The GBA Push architecture outlined in figure 4.2-1 is based on the following rationales:
- The Ua reference point protection shall be unaffected i.e. it should not make any difference for Ua-protocols
whether the GBA-keys used for protection are UE-initiated or push-initiated.
- In viewpoint of the BSF, the NAF is still the initiating entity of a key retrieval, but now in situations where the
NAF has no B-TID (but the UE may have a valid GBA session). A Zpn reference point is introduced, based on
the Zn-reference point protocols defined by TS 33.220 [1].
- A new reference point Upa is introduced between the NAF and the UE. All messages over Upa are network
initiated. Upa defines the GBA-Push-Info.
- The NAF receives the GBA-Push-Info intended for the UE from the BSF over the Zpn reference point and
forwards it over Upa.
4.2.2 GBA-Push keying model
The Disposable-Ks model is the keying model used in GBA-Push. In the Disposable-Ks model, a Ks is only used once
to derive a single set of NAF-keys (and other keying material used to protect the GPI during transport, see clause 5.3).
After the NAF-key derivation, the Ks is erased or its further use is denied implicitly, which means that there will be no
generally usable Ks established.
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To only establish an external NAF-key with GBA-Push, GBA_ME can and should always be used. This functionality
does not require a GBA_U aware UICC. GBA-Push based on GBA_U will establish both an internal and an external
NAF-key. NAF-keys are derived as specified in TS 33.220 [1].
In GBA_ME based GBA-Push bootstrapping, a Ks, generated by a bootstrapping according to TS 33.220 [1], will be
unaffected.
In GBA_U based GBA Push bootstrapping, a GBA_U Ks generated by bootstrapping according to TS 33.220 [1] will
be invalidated. A new GBA_U Ks needs to be established using normal GBA if an application requires GBA_U NAF-
keys after GBA_U based GBA-Push bootstrapping. Applications can continue using NAF-keys derived from such an
invalidated Ks, i.e. applications already using NAF-keys are unaffected of the GBA-Push bootstrapping run.
GBA-Push only supports generation of so called NAF SAs, shared by a UE and a NAF. A NAF SA contains a NAF-
key, key life-time and other information as defined in clause 5.2.3.
4.3 GBA Push Requirements
4.3.1 General GBA Push Requirements
The following general requirements are applicable to enable GBA Push:
- A network entity, a so called Push NAF, shall be able to securely trigger the generation of a NAF SA between
itself and a UE.
- A Push-NAF shall be able to use channels with deferred delivery of messages when triggering the generation of
a NAF SA.
- A Push-NAF shall be able to use public identities when referencing a UE in a request towards the BSF.
- When a public identifier is used for GBA push it shall correspond uniquely to a single private identity.
- ME based GBA Push shall be used when only ME based NAF keys are needed, i.e. Ks is established in the ME.
UICC based GBA Push shall be used only when UE contains a GBA aware UICC (GBA_U), and when UICC
and ME based NAF keys are needed or when only UICC based NAF keys are needed, i.e. Ks is established in
the UICC.
- The generation of the NAF SA in the UE is triggered by the reception of a message pushed to the UE from the
Push-NAF.
- The UE should not have to contact any network entity to be able to correctly generate the NAF SA.
- The UE and the NAF shall be able to use bootstrapped NAF-keys on Ua reference point independent on whether
the bootstrapping has been performed via Ub or Upa reference point.
NOTE: When a GBA-push mechanism is used to create a NAF SA between the UE and the NAF, the NAF is not
restricted to use the derived security association for network initiated protocols only. Analogously, the fact
that UE initiated GBA was used does not restrict a NAF to use the derived security association for UE-
initiated protocols only (Ua reference point).
- The mechanism to generate keys for confidentially and integrity protection of GPI shall be based on GBA-
principles in order to avoid pre-configuration of keys.
- The NAF shall be unable to obtain or generate the keys that protect GPI.
4.3.2 Requirements on HSS and HLR
The requirements for HSS and HLR are in TS 33.220 [1].
4.3.3 Requirements on BSF
In addition to the BSF requirements in clause 4.2.1 of TS 33.220 [1] following requirements apply:
- The BSF shall be able to find the private identity corresponding to a public identity.
- The BSF shall index existing Ks's based on private user identity.
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3GPP TS 33.223 version 15.0.0 Release 15 10 ETSI TS 133 223 V15.0.0 (2018-11)
- The BSF shall generate GPI based on a fresh Ks.
- The BSF shall integri
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