Storing/Exporting local keypair

[2-3-5-41]

I want to know if there is a recommended way to export/store a keypair in libp2p. I ask this as my current idea for a project requires a persistent identity for a user/peer even after they restart their client.

I've already looked at the to_protobuf_encoding() and from_protobuf_encoding() functions, however, from_protobuf_encoding() on my system seems to "corrupt" the EdwardsPoint.Z, assuming the Z field isn't supposed to look like this FieldElement51([1, 0, 0, 0, 0]) after getting a keypair from a protobuf encoding.

[thomaseizinger]

however, from_protobuf_encoding() on my system seems to "corrupt" the EdwardsPoint.Z, assuming the Z field isn't supposed to look like this FieldElement51([1, 0, 0, 0, 0]) after getting a keypair from a protobuf encoding.

This sounds like a bug to me. Can you reproduce this with a unit test and open a PR?

I want to know if there is a recommended way to export/store a keypair in libp2p.

It is recommended to use the {to,from}_protobuf_encoding functions because those "tag" the secret key bytes with their type and allow us correctly load them again.

[thomaseizinger]

The easiest way is to derive a public key and then a PeerId and compare those via PartialEq.

[2-3-5-41]

I'm trying to make a unit test for this, but I'm getting this error;

error[E0432]: unresolved import `libp2p_identity::PeerId`
 --> identity/tests/protobuf_encode_decode_api.rs:1:32
  |
1 | use libp2p_identity::{Keypair, PeerId};
  |                                ^^^^^^ no `PeerId` in the root

error[E0599]: no function or associated item named `generate_ed25519` found for struct `Keypair` in the current scope
 --> identity/tests/protobuf_encode_decode_api.rs:5:28
  |
5 |     let keypair = Keypair::generate_ed25519();
  |                            ^^^^^^^^^^^^^^^^ function or associated item not found in `Keypair`

And my code looks like this;

use libp2p_identity::{Keypair, PeerId};

#[test]
fn to_from_protobuf() {
    let keypair = Keypair::generate_ed25519();
    let peer_id_before = PeerId::from(&keypair.public());

    let protobuf_encode = keypair.to_protobuf_encoding().unwrap();
    let keypair_from_protobuf = Keypair::from_protobuf_encoding(&protobuf_encode.as_slice()).unwrap();
    let peer_id_after = PeerId::from(&keypair_from_protobuf.public());

    assert_eq!(peer_id_before, peer_id_after)
}

I'm doing this in the test module folder in the identity crate/workspace member.

[2-3-5-41]

I was able to recreate the unit test in a separate crate that uses libp2p as a dependency, and the test passes, however, I still wonder if that corrupted field affects the private key since we're only testing the PeerId that is derived from the public key.

Unless I have a gross misunderstanding of how the keypairs work.

[thomaseizinger]

The public key is derived from the private key so if the latter is corrupted, you should get a different public key and thus different PeerId.

The error above stems from a missing feature. You'd need to feature-gate your test on the peerid feature.

[2-3-5-41]

I just realized there are already tests doing this in the keypair.rs file.

Anyway, this thread has answered my question, as well as set my mind straight on how keypairs work, thank you.