C.2 Null-scheme

33.5013GPPRelease 18Security architecture and procedures for 5G SystemTS

The null-scheme shall be implemented such that it returns the same output as the input, which applies to both encryption and decryption.

When using the null-scheme, the SUCI does not conceal the SUPI and therefore the newly generated SUCIs do not need to be fresh.

NOTE 1: The reason for mentioning the non-freshness is that, normally, in order to attain unlinkability (i.e., to make it infeasible for over-the-air attacker to link SUCIs together), it is necessary for newly generated SUCIs to be fresh. But, in case of the null-scheme, the SUCI does not conceal the SUPI. So unlinkability is irrelevant.

NOTE 2: The null-scheme provides no privacy protection.