Implement and integrate a PoW blockchain logic in users' credentials.

[MavrosOplarxigos]

By integrating blockchain logic into the credentials of the user (be it pseudonymous or non-pseudonymous) the scheme becomes more resilient against Sybil attacks since PoW (proof-of-work) can be used to as a means to make such attacks more difficult.

In turn, Sybil attack from the LBS provider itself an become difficult this way since it would have to constantly dedicate computational power for every Sybil identity it maintains.