The notion of identity has confounded philosophers and thinkers for centuries. "You can never visit the same river twice" the saying goes, because it streams away.
Is there identity -- per se, or all that we have is a collection of attributes conveniently bundled into an owner identity.
If an entity splits, do both splits carry the same identity? When you lose a tooth -- is this tooth you?
If you observe n attributes to ascertain identity, how many m < n attributes will have to be off, for you to determine that you deal with an imposter?
The philosophical dilemma regarding the concept of identity spills into the cryptographic burden.