How to get the public key of a private key with Rust?

Question

I've got a 32-bytes private key. I want to calculate the corresponding public key of this private key. How can I achieve this with Rust? I can't find such a function in solana-sdk crate.

Answer 1

If you look at the keypair module in solana-sdk, you'll find keypair_from_seed to do exactly what you want: https://docs.rs/solana-sdk/latest/solana_sdk/signer/keypair/fn.keypair_from_seed.html. With the keypair, you can get the public key:

let keypair = keypair_from_seed(<YOUR_PRIVATE_KEY_BYTES_HERE>).unwrap();
let public_key = keypair.pubkey();

Answer 2

To calculate the corresponding public key from a 32-byte private key in Rust, you won’t directly find this functionality in the solana-sdk crate. However, Solana uses Ed25519 for cryptographic signing, which means you can use the popular Rust crate called ed25519-dalek for this purpose.

• Install the ed25519-dalek crate: This crate provides all the necessary tools to generate a public key from a private key using the Ed25519 signature scheme.
• Use the ed25519-dalek::Keypair::from_bytes function to convert the 32-byte private key into a keypair, and then extract the public key from it.

In your Cargo.toml, include this dependency [dependencies] ed25519-dalek = "1.0"

try out this Rust code to convert a 32-byte private key into a corresponding public key

use ed25519_dalek::{Keypair, SecretKey, PublicKey};
use ed25519_dalek::Signer;

fn main() {
    // Your 32-byte private key
    let private_key_bytes: [u8; 32] = [/* Your 32-byte private key here */];

    // Convert the private key bytes to a SecretKey object
    let secret_key = SecretKey::from_bytes(&private_key_bytes).expect("Invalid private key");

    // Generate the corresponding PublicKey
    let public_key: PublicKey = (&secret_key).into();

    // Print out the public key in bytes
    println!("Public key: {:?}", public_key.to_bytes());
}

SecretKey is the 32-byte private key wrapped in the SecretKey type from ed25519-dalek. PublicKey: The public key is derived from the private key by using (&secret_key).into(), which automatically converts the secret key into its corresponding public key. public_key.to_bytes() gives you the byte representation of the public key.