librespot/audio/src/decrypt.rs

use std::io;

use aes_ctr::Aes128Ctr;
use aes_ctr::stream_cipher::{
    NewStreamCipher, SyncStreamCipher, SyncStreamCipherSeek
};
use aes_ctr::stream_cipher::generic_array::GenericArray;

use core::audio_key::AudioKey;

const AUDIO_AESIV: [u8; 16] = [
    0x72, 0xe0, 0x67, 0xfb, 0xdd, 0xcb, 0xcf, 0x77,
    0xeb, 0xe8, 0xbc, 0x64, 0x3f, 0x63, 0x0d, 0x93,
];

pub struct AudioDecrypt<T: io::Read> {
    cipher: Aes128Ctr,
    reader: T,
}

impl<T: io::Read> AudioDecrypt<T> {
    pub fn new(key: AudioKey, reader: T) -> AudioDecrypt<T> {
        let cipher = Aes128Ctr::new(
            &GenericArray::from_slice(&key.0),
            &GenericArray::from_slice(&AUDIO_AESIV),
        );
        AudioDecrypt { cipher, reader }
    }
}

impl<T: io::Read> io::Read for AudioDecrypt<T> {
    fn read(&mut self, output: &mut [u8]) -> io::Result<usize> {
        let len = try!(self.reader.read(output));

        self.cipher.apply_keystream(&mut output[..len]);

        Ok(len)
    }
}

impl<T: io::Read + io::Seek> io::Seek for AudioDecrypt<T> {
    fn seek(&mut self, pos: io::SeekFrom) -> io::Result<u64> {
        let newpos = try!(self.reader.seek(pos));

        self.cipher.seek(newpos);

        Ok(newpos)
    }
}