You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: encryptor.rs
    path of file: ./repos/ockam/implementations/rust/ockam/ockam_identity/src/secure_channel
    
    the code of the file until where you have to start completion: use ockam_core::compat::sync::Arc;
use ockam_core::compat::vec::Vec;
use ockam_core::errcode::{Kind, Origin};
use ockam_core::{Error, Result};
use ockam_vault::{AeadSecretKeyHandle, VaultForSecureChannels};
use tracing
    
    pub async fn encrypt(&mut self, payload: &[u8]) -> Result<Vec<u8>> {
        let current_nonce = self.nonce;
        if current_nonce == u64::MAX {
            return Err(IdentityError::NonceOverflow)?;
        }

        self.nonce += 1;

        if current_nonce > 0 && current_nonce % KEY_RENEWAL_INTERVAL == 0 {
            let new_key = Self::rekey(&self.vault, &self.key).await?;
            let old_key = core::mem::replace(&mut self.key, new_key);
            self.vault.delete_aead_secret_key(old_key).await?;
        }

        let (small_nonce, nonce) = Self::convert_nonce_from_u64(current_nonce);

        let mut cipher_text = self
            .vault
            .aead_encrypt(&self.key, payload, &nonce, &[])
            .await?;

        let mut res = Vec::new();
        res.extend_from_slice(&small_nonce);
        res.append(&mut cipher_text);

        Ok(res)
    }