how to add tag/additionalData

[nbari]

I am trying to migrate this from go to rust

// Encrypt AES-256 GCM
func Encrypt(password, message, additionalData []byte) ([]byte, error) {
	if len(password) != 32 {
		return nil, fmt.Errorf("key size %d != 32", len(password))
	}

	c, err := aes.NewCipher(password)
	if err != nil {
		return nil, err
	}

	gcm, err := cipher.NewGCM(c)
	if err != nil {
		return nil, err
	}

	nonce, err := crypto.GenerateNonce(gcm.NonceSize())
	if err != nil {
		return nil, err
	}

	out := gcm.Seal(nonce, nonce, message, additionalData)
	return out, nil
}

From my understanding the AdditionalData is the tag, I am using this in rust:

fn encrypt(password: &[u8,32], data : &Vec<u8>)-> Result<Vec<u8>> { 
   let key = GenericArray::from_slice(password);
    let cipher = Aes256Gcm::new(key);
    let nonce = Aes256Gcm::generate_nonce(&mut OsRng);
    cipher.encrypt(&nonce, data.as_ref()).map_or_else(
        |_| Err(anyhow!("Failed to encrypt data")),
        |ciphertext| {
            let mut encrypted_data = nonce.to_vec();
            encrypted_data.extend_from_slice(&ciphertext);
            Ok(encrypted_data)
        },
    )
}

But how do you pass the additionalData/Tag ?

[tarcieri]

Instead of data.as_ref(), pass an aead::Payload instead: https://docs.rs/aead/latest/aead/struct.Payload.html

[nbari]

Hi, many thanks, just in case I soved using:

 let key = GenericArray::from_slice(password);
    let cipher = Aes256Gcm::new(key);
    let nonce = Aes256Gcm::generate_nonce(&mut OsRng);
    let payload = Payload {
        msg: data.as_ref(),
        aad: additional_data.as_bytes(),
    };
    cipher.encrypt(&nonce, payload).map_or_else(
        |_| Err(anyhow!("Failed to encrypt data")),
        |ciphertext| {
            let mut encrypted_data = nonce.to_vec();
            encrypted_data.extend_from_slice(&ciphertext);
            Ok(encrypted_data)
        },
    )