Provide more utility methods for conversion between basic pubkey/secret key types

[sanket1729]

Similar motivation for the first commit of #372

Add method KeyPair::public_key
Currently to get the XOnlyPublicKey from a KeyPair users must do
XOnlyPublicKey::from_keypair(&kp). While this does the job we can make
the lib more ergonomic by providing a method directly on KeyPair that
calls through to XOnlyPublicKey::from_keypair.

I think we should have more conversion methods

• KeyPair:

  • secret_key() -> SecretKey
  • x_only_pub_key() -> XOnlyPublicKey
  • pub_key() -> PublicKey See(389abdd#r831616364)

• SecretKey:

  • keypair() -> KeyPair
  • x_only_pub_key() -> XOnlyPublicKey
  • pub_key() -> PublicKey

• XonlyPublicKey:

  • pub_key() -> PublicKey

• PublicKey:

  • x_only_pub_key() -> (XonlyPublicKey, Parity)

I would like to call these methods pubkey instead of pub_key, but I think because of #372 (comment) it might be difficult.

[tcharding]

I like pubkey better too, don't know why I used public_key.

By far the most important reason for favouring pubkey is that my editor does not catch the annoyingly common typo 'pubic key`.

[sanket1729]

Sorry, I meant to highlight this comment, not the commit. #372 (comment)

[apoelstra]

I'd prefer to use pubkey over pub_key, but otherwise I agree with you @sanket1729.

I wouldn't mind pushing out a quick major release to fix these.

[sanket1729]

If you don't mind quick breaking changes, my preference would be:

1. public_key()
2. pubkey()
3. pub_key()

I am not too picky on these, feel free to choose any of them. But we should be consistent in the naming throughout.

[apoelstra]

I agree with your ranking.

[tcharding]

I'll hack it up!

[tcharding]

We currently have PublicKey::from_secret_key_global do we want more of these _global functions for all the conversion functions that take a secp parameter?

[sanket1729]

We currently have PublicKey::from_secret_key_global do we want more of these _global functions for all the conversion functions that take a secp parameter?

I have never used them downstream. But, I would not complain we have those. No strong opinions on this.

In the near future, we will have static contexts in upstream libsecp, so we can later update our APIs to remove the secp param altogether.

[tcharding]

In the near future, we will have static contexts in upstream libsecp, so we can later update our APIs to remove the secp param altogether.

With that in mind I won't add _global versions then.