Function write_link_proof_wire_packet 

pub fn write_link_proof_wire_packet(
    link_id: &LinkId,
    packet_hash: &PacketHash,
    signature: &Ed25519Signature,
    buf: &mut [u8],
) -> Result<usize, WireError>

Unencrypted per the reference. RNS 1.4.2 Packet.pack exemption (“packet proofs over links are not encrypted”).