original: secondly , it should be computationally infeasible to generate a valid signature for a party who does not possess the private key .
simplifications: it should be infeasible to generate a valid signature for a party who does not possess the private key . secondly , it should be math-based or computer-based incapable of being done to create a valid signature for a party who does not possess the private key . a computer should not generate a valid signature for someone who does not own a private key . secondly , it should be impossible to create a valid signature for a party who does not own the private key . secondly , it should be impossible to make a valid signature for a party who does not have the private key . it should be impossible for someone who does not possess the private key to generate a valid signature . secondly , it should be impractical to gernerate a valid siignature for a party who does not possess the private key , computationally . secondly , it should be computationally infeasible to generate a valid signature for a party who does not possess the private key .