is it possible to replace the cryptography and public key algorithms in Bitcoin? Is it possible to replace the cryptographic algorithms used in Bitcoin, such as the hash algorithms and the elliptic curve public key cryptography?

Does this require a soft fork or a hard fork?
Is it possible to replace the cryptographic algorithms used in Bitcoin, such as the hash algorithms and the elliptic curve public key cryptography in Bitcoin?


Yes.


  Does this require a soft fork or a hard fork?


It'll definitely be a hard fork since older clients will not be able to process the new transactions that require different cryptographic algorithms, especially sighashing.