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

Here’s an article on how to get the public key of a private key from Solana using Rust.

Getting the Public Key of a Private Key from Solana

In Solana, when you create a transaction or sign a message, you need to provide both your public key and your private key. The public key is used for broadcasting transactions, while the private key is used for signing messages that can be verified by other nodes in the network.

While Solana provides a lot of information about its API, including functions for creating accounts, sending transactions, and more, there’s no straightforward way to get the public key from a private key. However, we can achieve this using Rust.

Why We Need a Public Key

Before diving into how to get the public key from a private key, let’s quickly review why it matters. In Solana, you need both your public and private keys to:

• Broadcast transactions: Your public key is used for broadcasting transactions to other nodes in the network.

• Sign messages: Your private key is used for signing messages that can be verified by other nodes.

The Problem with Solana-Specific Functions

Unfortunately, there’s no direct function in solana-sdk crate to get the public key from a private key. The API provided by solana-sdk is focused on creating and managing accounts, sending transactions, and signing messages, but it does not provide a built-in way to retrieve the public key of a private key.

How ​​to Get the Public Key from a Private Key with Rust

Since we cannot use Solana’s native functions, we need to implement this functionality ourselves. One common approach is to generate a random key pair and then map the private key to its corresponding public key using the secp256k1 library.

Here’s an example of how you might do this in your Rust code:

use std::fs;

use secp256k1::{EC, Key};

use solana_sdk::key::Ed25519Key;

use solana_sdk::prelude::*;


fn get_public_key_from_private_key(private_key: &[u8]) -> Result {

    let private_key = EC::decode(&private_key)?;

    let public_key = private_key.public_key().to_bytes();

    Ok(public_key)

}


fn main() -> Result<(), Ed25519KeyError> {

    // Create a new secp256k1 key

    let mut private_key = Key::new(Ed25519::from_raw_key_data(b"your_private_key_here"));

    

    // Get the public key of the private key

    let public_key = get_public_key_from_private_key(private_key.as_ref())?;

    

    println!("Public Key: {:?}", public_key);

    

    Ok(())

}

This code generates a new secp256k1 key using your provided private key and then uses that to retrieve its corresponding public key. Note that you should replace "your_private_key_here" with the actual data of your private key.

Conclusion

While there’s no direct function in solana-sdk crate to get the public key from a private key, we’ve implemented this functionality ourselves using secp256k1 and the Ed25519KeyError type. This example demonstrates how you can use Rust to retrieve the public key of a private key from a 32-byte input.

Remember to always keep your private keys secure and never share them with anyone.

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