user59757: 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?

user31586: 
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.

59757: <p>Is it possible to replace the cryptographic algorithms used in Bitcoin, such as the hash algorithms and the elliptic curve public key cryptography?</p>

<p>Does this require a soft fork or a hard fork?</p>
 31586: <blockquote>
  <p>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?</p>
</blockquote>

<p>Yes.</p>

<blockquote>
  <p>Does this require a soft fork or a hard fork?</p>
</blockquote>

<p>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.</p>
