5 Confidentiality algorithm GEA5

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

5.1 Introduction

The confidentiality algorithm GEA5 is a stream cipher that encrypts/decrypts blocks of data between 1 and 65536 octets in length.

The inputs to the algorithm are given in Table 5.2.1, the output in Table 5.2.2:

Table 5.2.1: GEA5 inputs

Parameter	Size (bits)	Comment
INPUT	32	Frame dependent input INPUT[0]…INPUT[31]
DIRECTION	1	Direction of transmission DIRECTION[0]
FRAMETYPE	8	Input value signifying the type of frame to be protected
KC128	128	Confidentiality key KC128[0]….KC128[127]
M		The number of octets of output required in the range 1 to 65536 inclusive

Table 5.2.2: GEA5 output

Parameter	Size (bits)	Comment
OUTPUT	8M	Keystream octets OUTPUT{0}….OUTPUT{M-1}