Struggling with secp256k1

help
1

Hi everyone,
As my first project on Rust i'm trying to build a simple blockchain, but i'm stumbling into some stones along the way hahaha.
I've created a struct:

pub struct Output {
    pub sender: String,
    pub receiver: String,
    pub amount: u64,
    pub signature: String,
    pub spent: Cell<bool>,
}

but when i'm trying to make the signature, the unwrap() method always fails on me:

Error:

thread 'main' panicked at src\output.rs:32:79:
called `Result::unwrap()` on an `Err` value: InvalidMessage

//signs the message
    fn sign(&mut self, secret_key: &SecretKey) {
        let secp = Secp256k1::new();
        let message = self.create_message();
        let signature = secp.sign_ecdsa(&Message::from_digest_slice(&message).unwrap(), secret_key); //error happens here
        
        self.signature = signature.to_string();
    }

    //creates a message in bytes
    fn create_message(&self) -> Vec<u8> {
        let mut bytes = Vec::new();
        bytes.extend(self.sender.as_bytes());
        bytes.extend(self.receiver.as_bytes());
        bytes.extend(self.amount.to_le_bytes());
        bytes
    }

i'm not quite getting why. Sorry for any newbie stuff, i'm actually newbie.

2

Hi,
According to the document secp256k1, you need to create digest using sha256 hash before you can sign it.

use secp256k1::hashes::{sha256, Hash};
use secp256k1::rand::rngs::OsRng;
use secp256k1::{Message, Secp256k1, SecretKey};


  // other code 
  fn sign(&mut self, secret_key: &SecretKey) {
    // message created above
    let digest = sha256::Hash::hash(&message);
    let signature = secp.sign_ecdsa(
        &Message::from_digest_slice(&digest.to_byte_array()).unwrap(),
        secret_key,
    );
    // rest of code
  }

Remember to enable features
secp256k1 = {version="0.29.0", features=["rand-std", "hashes-std"] }

3

It's unworthy to use ECC any more, you should use Lattice-based asymmetric-key cryptography, Lattice-based ciphers can be post-quantum. NSA suggests using Kyber and Dilithium.

1 Like
4

Thank you! The problem was enabling the features, documentation was not very clear about that (or maybe I missed it).

1 Like
5

Thanks for the tip, will take a look on that. Since it's only for learning purposes i'm ok, but always good to learn the right way.

6

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