Security procedures for 5G system


KDF interface (33.501 Annexe A)

AUSF
Authentication Server Function
SEAF
Security Anchor Function
XOR
||
String concatenation
KDF input parameter construction
Key Parameters
KAUSF KEY The input key KEY shall be equal to the concatenation CK || IK of CK and IK
FC 0x6A
P0 serving network name (33.501 ยง6.1.1.4)
L0 length of the serving network name (variable length as specified in 24.501)
P1 SQN ⊕ AK
L1 length of SQN ⊕ AK (i.e. 0x00 0x06)
RES* and XRES* KEY The input key KEY shall be equal to the concatenation CK || IK of CK and IK
FC 0x6B
P0 serving network name
L0 length of the serving network name (variable length as specified in 24.501)
P1 RAND
L1 length of RAND (i.e. 0x00 0x10)
P2 RES or XRES
L2 length RES or XRES (i.e. variable length between 0x00 0x04 and 0x00 0x10)
KSEAF KEY The input key KEY shall be KAUSF
FC 0x6C
P0 serving network name
L0 length of the serving network name (variable length as specified in 24.501)
KAMF KEY The input key KEY shall be the 256-bit KSEAF
FC 0x6D
P0 SUPI
L0 P0 length - number of octets in P0
P1 ABBA parameter (0x0000)
L1 P1 length - number of octets in P1
KgNb KEY The input key KEY shall be the 256-bit KAMF
FC 0x6E
P0 Uplink NAS COUNT
L0 length of uplink NAS COUNT (i.e. 0x00 0x04)
P1 Access type distinguisher (3GPP access = 0x01)
L1 length of Access type distiguisher (i.e. 0x00 0x01)

Generic key derivation function (KDF)

All key derivations (including input parameter encoding) for 5GC shall be performed using the key derivation function (KDF)
Input string = FC || P0 || L0 || P1 || L1 || P2 || L2 || P3 || L3 || ... || Pn || Ln
33.220 Annexe B : Derived key = HMAC-SHA-256 ( Secret Key , Input string )

 digits
 bits
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Security architecture for 5G system

NR Keys