authnz-u2f 0.2.8

use bytes::Buf;
use serde::Serialize;
use std::io::Cursor;

use crate::register::sha256;
use crate::u2ferror::U2fError;

/// The `Result` type used in this crate.
type Result<T> = ::std::result::Result<T, U2fError>;

#[derive(Serialize, Clone)]
#[serde(rename_all = "camelCase")]
pub struct Authorization {
  pub counter: u32,
  pub user_presence: bool,
}

pub fn parse_sign_response(app_id: String, client_data: Vec<u8>, public_key: Vec<u8>, sign_data: Vec<u8>) -> Result<Authorization> {
  if sign_data.len() <= 5 {
    return Err(U2fError::InvalidSignatureData);
  }

  let user_presence_flag = &sign_data[0];
  let counter = &sign_data[1..=4];
  let signature = &sign_data[5..];

  // Let's build the msg to verify the signature
  let app_id_hash = sha256(&app_id.into_bytes());
  let client_data_hash = sha256(&client_data[..]);

  let mut msg = vec![];
  msg.extend_from_slice(app_id_hash.as_ref());
  msg.push(*user_presence_flag);
  msg.extend_from_slice(counter);
  msg.extend_from_slice(client_data_hash.as_ref());

  let public_key = super::crypto::NISTP256Key::from_bytes(&public_key)?;

  // The signature is to be verified by the relying party using the public key obtained during registration.
  let verified = public_key.verify_signature(signature, msg.as_ref())?;
  if !verified {
    return Err(U2fError::BadSignature);
  }

  let authorization = Authorization {
    counter: get_counter(counter),
    user_presence: true,
  };

  Ok(authorization)
}

fn get_counter(counter: &[u8]) -> u32 {
  let mut buf = Cursor::new(counter);
  buf.get_u32_be()
}