D.2 Ciphering algorithms

33.5013GPPRelease 18Security architecture and procedures for 5G SystemTS

D.2.1 128-bit Ciphering algorithms

D.2.1.1 Inputs and outputs

The input parameters to the ciphering algorithm are a 128-bit cipher key named KEY, a 32-bit COUNT, a 5-bit bearer identity BEARER, the 1-bit direction of the transmission i.e. DIRECTION, and the length of the keystream required i.e. LENGTH. The DIRECTION bit shall be 0 for uplink and 1 for downlink.

Figure D.2.1.1-1 illustrates the use of the ciphering algorithm NEA to encrypt plaintext by applying a keystream using a bit per bit binary addition of the plaintext and the keystream. The plaintext may be recovered by generating the same keystream using the same input parameters and applying a bit per bit binary addition with the ciphertext.

Figure D.2.1.1-1: Ciphering of data

Based on the input parameters the algorithm generates the output keystream block KEYSTREAM which is used to encrypt the input plaintext block PLAINTEXT to produce the output ciphertext block CIPHERTEXT.

The input parameter LENGTH shall affect only the length of the KEYSTREAM BLOCK, not the actual bits in it.

D.2.1.2 128-NEA1

128-NEA1 is identical to 128-EEA1 as specified in Annex B of TS 33.401 [10].

D.2.1.3 128-NEA2

128-NEA2 is identical to 128-EEA2 as specified in Annex B of TS 33.401 [10].

D.2.1.4 128-NEA3

128-NEA3 is identical to 128-EEA3 as specified in Annex B of TS 33.401 [10].