6 Integrity algorithm GIA5

3GPP55.251GEA5 and GIA5 algorithm specificationSpecification of the GEA5 and GIA5 encryption algorithms for General Packet Radio Service (GPRS)TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

6.1 Introduction

The integrity algorithm GIA5 computes a Message Authentication Code (MAC) on an input message under an integrity key KI128. The message may be between 1 and 65536 octets long.

For ease of implementation the algorithm is based on the same stream cipher (SNOW 3G) [2] as is used by the confidentiality algorithm GEA5.

6.2 Inputs and outputs

The inputs to the algorithm are given in table 6.2.1, the output in table 6.2.2:

Table 6.2.1: GIA5 inputs

Parameter	Size (bits)	Comment
INPUT-I	32	Frame dependent input INPUT-I[0]…INPUT-I[31]
M		The length of MESSAGE in octets (1-65536)
MESSAGE	8M	Input octet stream MESSAGE{0}….MESSAGE{M-1}
DIRECTION	1	Direction of transmission DIRECTION[0]
FRAMETYPE	8	Input value signifying the type of frame to be protected
KI128	128	Integrity key KI128[0]…KI128[127]

Table 6.2.2: GIA5 output

Parameter	Size (bits)	Comment
MAC	32	Message authentication code MAC[0]…MAC[31]

6.3 Components and architecture

6.4 Initialization

This clause only available under licence.
See http://www.etsi.org/about/what-we-do/security-algorithms-and-codes/cellular-algorithm-licences.

6.5 Calculation

This clause only available under licence.
See http://www.etsi.org/about/what-we-do/security-algorithms-and-codes/cellular-algorithm-licences.

Annex A (informative):
Mathematical background of some operations of the GIA5 Algorithm

6.1 Introduction

6.2 Inputs and outputs

6.3 Components and architecture

6.3.1 SNOW 3G

6.3.2 MULx

6.3.3 MULxPOW

6.3.4 MUL

6.4 Initialization

6.5 Calculation