rpgmv_decryptor/src/main.rs

use anyhow::{anyhow, Context, Result};
use clap::{App, Arg};
use std::fs::File;
use std::io::{Read, Write};
use std::path::Path;

/// # RPGMV Decryptor
///
fn main() -> Result<()> {
    let matches = App::new("RPGMV Decoder")
        .version("0.1.0")
        .author("paoda <musukarekai@gmail.com>")
        .about("Decodes .rpgmvp, .rpgmvm and .rpgmvo files")
        .arg(
            Arg::with_name("path")
                .index(1)
                .value_name("FILE")
                .help("Path to the file which will be decrypted")
                .takes_value(true)
                .required(true),
        )
        .arg(
            Arg::with_name("key")
                .short("k")
                .long("key")
                .value_name("KEY")
                .help("The Encryption Key (look in www/data/System.json or www/js/rpg_core.js")
                .takes_value(true)
                .required(true),
        )
        .get_matches();

    let path_string = matches.value_of("path").context("No file path provided")?;
    let key_string = matches.value_of("key").context("No key provided")?;

    let path = Path::new(path_string);
    let key = get_key_bytes(key_string)?;

    // let default_rpgmv_header: [u8; 16] = [
    //     0x52, 0x50, 0x47, 0x4d, 0x56, 0x00, 0x00, 0x00, 0x00, 0x3, 0x1, 0x00, 0x00, 0x00, 0x00,
    //     0x00,
    // ];

    let file_buf = get_file_data(path)?;
    let decrypted = decrypt(file_buf, key);

    let mut file;

    let filename = path
        .file_stem()
        .context("Unable to determine file stem")?
        .to_str()
        .context("Unable to convert file stem to UTF-8 string")?;

    match detect_original_extension(path)? {
        RPGFile::Photo => file = File::create(format!("{}.png", filename))?, // .rpgmvps are .pngs
        RPGFile::Video => file = File::create(format!("{}.m4a", filename))?, // .rpgmvms are .m4as
        RPGFile::Audio => file = File::create(format!("{}.ogg", filename))?, // .rpgmvos are .oggs
    }

    file.write_all(&decrypted)?;

    Ok(())
}

/// Determines the original file type for the encrypted .rpgmv* file
fn detect_original_extension<P: AsRef<Path>>(path: P) -> Result<RPGFile> {
    match path.as_ref().extension() {
        Some(ext) => {
            let ext = ext
                .to_str()
                .context("File extension was not UTF-8 Compatible")?;

            match ext {
                "rpgmvp" => Ok(RPGFile::Photo),
                "rpgmvm" => Ok(RPGFile::Video),
                "rpgmvo" => Ok(RPGFile::Audio),
                _ => Err(anyhow!("File was lacking a supported file extension")),
            }
        }
        None => Err(anyhow!("File is lacking a file extension")),
    }
}

/// get_key_bytes takes a 32-character hexadecimal string and interperets
/// every two characters as an unsined 8-bit integer.
///
/// # Examples
/// `71e7bdd9b28010980c2a4e8a1386e100` will be split up as:
///
/// `0x71`, `0xe7`, `0xbd`, `0xd9`, `0xb2`, `0x80`, `0x10`, `0x98`, `0x0c`, `0x2a`, `0x4e`, `0x8a`, `0x13`, `0x86`, `0xe1`, and `0x00`
fn get_key_bytes(key: &str) -> Result<Vec<u8>> {
    let sub_len = 2;

    let mut key_buf = Vec::with_capacity(key.len() / 2);

    let mut chars = key.chars();
    let sub_strings = (0..)
        .map(|_| chars.by_ref().take(sub_len).collect::<String>())
        .take_while(|s| !s.is_empty())
        .collect::<Vec<_>>();

    for string in sub_strings {
        key_buf.push(u8::from_str_radix(&string, 16)?);
    }

    Ok(key_buf)
}

/// get_file_data returns a buffer containing a data of a file which is on disk.
fn get_file_data<P: AsRef<Path>>(path: P) -> Result<Vec<u8>> {
    let mut buf = Vec::new();

    let mut file = File::open(path.as_ref())?;
    file.read_to_end(&mut buf)?;

    Ok(buf)
}

fn _encrypt(_bytes: Vec<u8>, _key: Vec<u8>) -> Vec<u8> {
    unimplemented!();
}

/// Decrypts a RPGMV media file
///
/// The only part of the data that is actually encrypted (read: has a cipher applied to it)
/// is the header of the original file, which is bytes 17 -> 33 (16 bytes). Our key provides us with
/// 16 values which we can use to perform a bitwise XOR. The bitwise XOR will undo the cipher, returning the header to
/// it's original position. At this point, byte #17 -> end of file will now be recognized as their respected unencrypted
// file formats.
fn decrypt(bytes: Vec<u8>, key: Vec<u8>) -> Vec<u8> {
    let mut decrypted = bytes[16..].to_owned(); // Throw out the first 16 bytes (the RPGMV Header)

    for i in 0..16 as usize {
        decrypted[i as usize] = decrypted[i] ^ key[i];
    }

    decrypted
}

/// An enum that represents the types of supported RPGMV media files.
enum RPGFile {
    Photo,
    Video,
    Audio,
}