适用于RA2的 MIX 文件格式

什么是MIX文件？

MIX文件是存储游戏所使用的文件文件包。

它的结构是什么样子的？

根据现有的资料^[1]描述，它分为两部分，文件头和主体部分。

文件头

MIX 文件有两种变体，没有魔术代码。

offset	type	描述
0x00	uint32	标记 表示这个文件是否有加密或校验和
0x04	uint16	文件数量
0x06	uint32	文件主体大小

Entry

offset	type	描述
0x00	uint32	文件ID
0x04	uint32	偏移位置
0x08	uint32	文件大小

Westwood Studio Key 计算

当 标记 & 0x00020000 == 0x00020000 时，mix内容是被加密的。

文件主体是使用 Blowfish 算法加密的，密钥长度 56 字节。

Blowfish 密钥保存在文件头中，从 0x04 开始，读 80 个字节。

这 80 个字节是两个 RSA 私钥加密的块。

用这个参数解密：
模数 AihRvNoIbTn85FZRYNZRcT+i6KpU+maCsEqr3Q5q+LDB5tH7Tz2qQ38V (base64)
指数 0x10001

...

不想写了 直接贴代码

using System.Buffers;
using System.Buffers.Text;
using System.Diagnostics;
using System.Numerics;

public static class WSKey
{
    private static readonly Lazy<BigInteger> Modulus = new(() => ToBigInteger("AihRvNoIbTn85FZRYNZRcT+i6KpU+maCsEqr3Q5q+LDB5tH7Tz2qQ38V"u8));
    private static readonly Lazy<BigInteger> PublicKeyExponent = new(() => 0x10001u);
    private static readonly Lazy<BigInteger> PrivateKeyExponent = new(() => ToBigInteger("AigKVje8mROcR8QixnxUEF5b29Curkq01DNDWCdOG99XBqH79OaCiTCB"u8));

    private static BigInteger ToBigInteger(ReadOnlySpan<byte> base64)
    {
        var len = Base64.GetMaxDecodedFromUtf8Length(base64.Length);
        Span<byte> data = stackalloc byte[len];
        var status = Base64.DecodeFromUtf8(base64, data, out _, out len);
        Debug.Assert(status is OperationStatus.Done);
        data = data[..len];

        int index = 0;

        if (data[index++] != 0x02)
            throw new FormatException("Expected INTEGER");

        int length = ReadAsn1Length(data, ref index);
        return new(data.Slice(index, length), isBigEndian: true, isUnsigned: true);
    }

    private static int ReadAsn1Length(ReadOnlySpan<byte> data, ref int index)
    {
        byte b = data[index++];
        if ((b & 0x80) == 0) return b;

        int lenBytes = b & 0x7F;
        int length = 0;
        for (int i = 0; i < lenBytes; i++)
            length = (length << 8) | data[index++];
        return length;
    }

    public static void Decrypt(ReadOnlySpan<byte> encrypted, Span<byte> output)
    {
        Debug.Assert(encrypted.Length is 80);
        Debug.Assert(output.Length is 56);

        var modulus = Modulus.Value;
        var exponent = PublicKeyExponent.Value;

        BigInteger cipher1 = new(encrypted[..40], isUnsigned: true, isBigEndian: false);
        BigInteger cipher2 = new(encrypted[40..], isUnsigned: true, isBigEndian: false);

        var plain1 = BigInteger.ModPow(cipher1, exponent, modulus);
        var plain2 = BigInteger.ModPow(cipher2, exponent, modulus);

        plain1.TryWriteBytes(output, out int written1, isUnsigned: true, isBigEndian: false);
        plain2.TryWriteBytes(output[written1..], out int written2, isUnsigned: true, isBigEndian: false);
        Debug.Assert(written1 + written2 is 56);
    }

    public static void Encrypt(ReadOnlySpan<byte> input, Span<byte> encrypted)
    {
        Debug.Assert(input.Length == 56);
        Debug.Assert(encrypted.Length == 80);

        var modulus = Modulus.Value;
        var exponent = PrivateKeyExponent.Value;

        var split = modulus.GetByteCount() - 1;

        BigInteger part1 = new(input[..split], isUnsigned: true, isBigEndian: true);
        BigInteger part2 = new(input[split..], isUnsigned: true, isBigEndian: true);

        BigInteger cipher1 = BigInteger.ModPow(part1, exponent, modulus);
        BigInteger cipher2 = BigInteger.ModPow(part2, exponent, modulus);

        cipher1.TryWriteBytes(encrypted, out int written1, isUnsigned: true, isBigEndian: false);
        cipher2.TryWriteBytes(encrypted[written1..], out int written2, isUnsigned: true, isBigEndian: false);
        Debug.Assert(written1 + written2 is 80);
    }
}

引用

【翻译】MIX 文件格式

---

1. XCC ↩︎