How to generate an Ethereum public key from a private key using rust-secp256k1?

Question

I found rust-secp256k1 and it seems to be what I need, but there are no examples in the documentation.

I tried to use this crate in my code:

extern crate secp256k1;

use secp256k1::key::SecretKey;

fn main() {
    let context = secp256k1::Secp256k1::without_caps();

    let private_key: String = String::from("d500266f7d37f0957564e4ce1a1dcc8bb3408383634774a2f4a94a35f4bc53e0");

    let secret_key = SecretKey::new(&context, &mut private_key);

    println!("{:?}", secret_key);
}

I got an error:

error[E0277]: the trait bound `std::string::String: secp256k1::rand::Rng` is not satisfied
  --> src/main.rs:10:22
   |
10 |     let secret_key = SecretKey::new(&context, &mut private_key);
   |                      ^^^^^^^^^^^^^^ the trait `secp256k1::rand::Rng` is not implemented for `std::string::String`
   |
   = note: required by `secp256k1::key::SecretKey::new`

Answer 1

The following code generates a public key from a private key:

extern crate secp256k1;
extern crate hex;

use secp256k1::key::{SecretKey, PublicKey};

fn main() {
    let context = secp256k1::Secp256k1::new();

    let private_key: &[u8] = "d500266f7d37f0957564e4ce1a1dcc8bb3408383634774a2f4a94a35f4bc53e0".as_bytes();

    let secret_key = SecretKey::from_slice(&hex::decode(private_key).unwrap());

    let public_key = PublicKey::from_secret_key(&context, &secret_key.unwrap());

    println!("{:?}", public_key.unwrap()); // PublicKey(a423c05d32e3385bb2930e42ebbf104567215761e166c3ae3dd91d9c8bee0adcfc4f9e4ec43998eae8000de6b166014c5921c6d4545675f4f9205e7bc3d4401e)
}

Instead of using SecretKey::new, which expects a random number generator as the second parameter, I needed to use SecretKey::from_slice. from_slice takes a 32-byte key, which I can parse from my string into a compatible slice of bytes.