3GPP TS 33.535 V18 — AKMA Security

Q: What does the Scope section cover in 3GPP TS 33.535 V18 — AKMA Security?

The Scope section provides detailed technical specifications, security considerations, and implementation guidance as documented in 3GPP TS 33.535 V18 — AKMA Security. This content is part of the BLACKLABS 3GPP Security Library.

Q: What does the AKMA Architecture section cover in 3GPP TS 33.535 V18 — AKMA Security?

The AKMA Architecture section provides detailed technical specifications, security considerations, and implementation guidance as documented in 3GPP TS 33.535 V18 — AKMA Security. This content is part of the BLACKLABS 3GPP Security Library.

Q: What does the AKMA Key Hierarchy section cover in 3GPP TS 33.535 V18 — AKMA Security?

The AKMA Key Hierarchy section provides detailed technical specifications, security considerations, and implementation guidance as documented in 3GPP TS 33.535 V18 — AKMA Security. This content is part of the BLACKLABS 3GPP Security Library.

Q: What does the AKMA Procedures section cover in 3GPP TS 33.535 V18 — AKMA Security?

The AKMA Procedures section provides detailed technical specifications, security considerations, and implementation guidance as documented in 3GPP TS 33.535 V18 — AKMA Security. This content is part of the BLACKLABS 3GPP Security Library.

Q: What does the Security Analysis section cover in 3GPP TS 33.535 V18 — AKMA Security?

The Security Analysis section provides detailed technical specifications, security considerations, and implementation guidance as documented in 3GPP TS 33.535 V18 — AKMA Security. This content is part of the BLACKLABS 3GPP Security Library.

BLACKLABS

3GPP TS 33.535

Authentication and Key Management for Applications (AKMA) based on 3GPP credentials in 5G

V18.2.0 (2024-06) — Release 18 Security Feature

1. Scope

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Defines the Authentication and Key Management for Applications (AKMA) framework enabling application-layer security using 3GPP credentials (USIM/5G AKA). AKMA allows application functions (AFs) to authenticate UEs and establish application-level keys without requiring separate app credentials.

AKMA in one sentence: It lets applications piggyback on the 5G network authentication (5G-AKA/EAP-AKA') to get per-application session keys — no separate username/password or app-level PKI needed.

2. AKMA Architecture

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┌──────────┐ ┌──────────┐ ┌──────────┐ │ UE │ │ AF │ │ AAnF │ │ (App + │ │(Application │(AKMA │ │ USIM) │ │ Function)│ │ Anchor │ └────┬─────┘ └────┬─────┘ │ Function)│ │ │ └────┬─────┘ │ App Request │ │ │ + A-KID ───────►│ │ │ │── Key Req ────────►│ │ │ (A-KID) │ │ │ │ Lookup K_AF │ │◄── Key Resp ───────│ │ │ (K_AF) │ │ │ │ │◄── Secure Session ─│ │ │ (protected by │ │ │ K_AF) │ │ AAnF derives K_AF from K_AKMA (anchored at AUSF after 5G AKA)

Entity	Role
AAnF	AKMA Anchor Function — stores K_AKMA, derives K_AF per application
AF	Application Function — requests K_AF from AAnF to secure app session
AUSF	Provides K_AKMA derivation material after primary authentication
A-KID	AKMA Key Identifier — presented by UE to AF to identify the AKMA context

3. AKMA Key Hierarchy

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K (USIM permanent key) │ 5G AKA / EAP-AKA' │ ┌────▼─────┐ │ K_AUSF │ (at AUSF — after primary authentication) └────┬─────┘ │ KDF (FC=0x76) ┌────▼─────┐ │ K_AKMA │ (at AAnF — AKMA anchor key) └────┬─────┘ │ KDF (FC=0x77, AF_ID) ┌────▼─────┐ │ K_AF │ (per-application key — at UE + AF) └──────────┘

K_AKMA lifetime tied to K_AUSF — refreshed on re-authentication
K_AF is unique per AF_ID — different applications get different keys
A-KID format: AKMA-KID@HPLMN — contains SUPI derivation info

Privacy: A-KID must not reveal SUPI. It is derived from K_AKMA material and is temporary. UE generates new A-KID after re-authentication.

4. AKMA Procedures

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4.1 AKMA Key Establishment

UE AUSF AAnF │── 5G AKA ────►│ │ │◄── Success ───│ │ │ │ │ │ K_AUSF derived │ │ UE derives K_AKMA │ │ │── K_AKMA ──►│ │ │ (via NEF │ AAnF stores K_AKMA │ │ or direct)│ indexed by A-KID │ │ │

4.2 Application Key Request

UE AF AAnF │ │ │ │── App Req + A-KID ─►│ │ │ │── AKMA Key ──►│ │ │ Req (A-KID) │ │ │ │ Derive K_AF │ │◄── K_AF ──────│ │ │ + expiry │ │ │ │ │◄── Secure Session ──│ │ │ (using K_AF) │ │

5. Security Analysis

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Threat	Description	Mitigation
A-KID Replay	Attacker replays captured A-KID to different AF	A-KID bound to K_AKMA; AF must validate freshness via AAnF
AF Impersonation	Rogue AF requests K_AF for legitimate A-KID	AAnF must authenticate AF identity; K_AF bound to AF_ID
K_AKMA Exposure	Compromise of AAnF exposes all derived K_AF	HSM for K_AKMA storage; key rotation on re-auth
A-KID Linkability	Persistent A-KID enables subscriber tracking	A-KID changes on each primary authentication
Cross-AF Key Reuse	Same K_AF used across multiple AFs	K_AF derivation includes AF_ID — keys are unique per app