The 51% attack allows more than just reversing some transactions. It allows an attacker to selectively block transactions. It allows an attacker to deny the m

The 51% attack allows more than just reversing some transactions. It allows an attacker to selectively block transactions. It allows an attacker to deny the mining reward to miners. Really though, the point has more to do with formalizing Bitcoin's security. You claim that it relies on the security properties of cryptographic hashes and of digital signatures, but what property of Bitcoin actually reduces to the security of hashes or signatures? What are Bitcoin's security guarantees? When you can at least state some security property Bitcoin achieves, then maybe you can prove that Bitcoin's security depends on hashes and signatures. Without such proof you cannot go about making statements about P vs NP being relevant to Bitcoin's security; indeed, it is hard to speak about "security" for Bitcoin at all.