google_arts_tile_decrypte_reverse_engineering.rs

pub fn decrypt(mut input_buf: Vec<u8>) -> Result<Vec<u8>, InvalidEncryptedImage> {
    if get_int(&input_buf, 0) != 0x0A_0A_0A_0A { return Ok(input_buf); }
    let header_size = get_int(&input_buf, input_buf.len() as u32 - 4);
    let encrypted_size_pos = header_size + 4;
    let encrypted_pos = encrypted_size_pos + 4;
    let encrypted_size = get_int(&input_buf, encrypted_size_pos);
    let encrypted_end_pos = encrypted_pos + encrypted_size;
    let footer_size = input_buf.len() as u32 - 4 - encrypted_end_pos;
    let encrypted = input_buf.get(encrypted_pos as usize..(encrypted_pos + encrypted_size) as usize).unwrap();
    let mut encrypted_copy = Vec::from(encrypted);
    let decrypted = aes_decrypt_buffer(&mut encrypted_copy)?;
    let output_size = header_size + decrypted.len() as u32;
    let final_size = header_size + output_size + footer_size;
    let mut output_buf = Vec::with_capacity(final_size as usize);
    output_buf.write_all(&input_buf[4..(4 + header_size) as usize])?;
    output_buf.write_all(decrypted)?;
    output_buf.write_all(&input_buf[encrypted_end_pos as usize..(encrypted_end_pos + footer_size) as usize])?;
    Ok(output_buf)
}

fn get_int(buf: &[u8], pos: u32) -> u32 {
    let i = pos as usize;
    let mut bytes = [0u8; 4];
    bytes.copy_from_slice(&buf[i..i + 4]);
    u32::from_le_bytes(bytes)
}