alg.go

// Hashing and decryption algorithms used in MPQ files.

package mpq

import (
	"bytes"
	"compress/bzip2"
	"compress/zlib"
	"io"
)

// Different hash types for the hashString() function.
const (
	hashTypeTableOffset = iota << 8
	hashTypeNameA
	hashTypeNameB
	hashTypeFileKey
)

// Converts ASCII characters to uppercase.
// Converts slash (0x2F) to backslash (0x5C)
var asciiToUpperTable = []uint32{
	0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F,
	0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E, 0x1F,
	0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28, 0x29, 0x2A, 0x2B, 0x2C, 0x2D, 0x2E, 0x5C,
	0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3A, 0x3B, 0x3C, 0x3D, 0x3E, 0x3F,
	0x40, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4A, 0x4B, 0x4C, 0x4D, 0x4E, 0x4F,
	0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5A, 0x5B, 0x5C, 0x5D, 0x5E, 0x5F,
	0x60, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4A, 0x4B, 0x4C, 0x4D, 0x4E, 0x4F,
	0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5A, 0x7B, 0x7C, 0x7D, 0x7E, 0x7F,
	0x80, 0x81, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87, 0x88, 0x89, 0x8A, 0x8B, 0x8C, 0x8D, 0x8E, 0x8F,
	0x90, 0x91, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97, 0x98, 0x99, 0x9A, 0x9B, 0x9C, 0x9D, 0x9E, 0x9F,
	0xA0, 0xA1, 0xA2, 0xA3, 0xA4, 0xA5, 0xA6, 0xA7, 0xA8, 0xA9, 0xAA, 0xAB, 0xAC, 0xAD, 0xAE, 0xAF,
	0xB0, 0xB1, 0xB2, 0xB3, 0xB4, 0xB5, 0xB6, 0xB7, 0xB8, 0xB9, 0xBA, 0xBB, 0xBC, 0xBD, 0xBE, 0xBF,
	0xC0, 0xC1, 0xC2, 0xC3, 0xC4, 0xC5, 0xC6, 0xC7, 0xC8, 0xC9, 0xCA, 0xCB, 0xCC, 0xCD, 0xCE, 0xCF,
	0xD0, 0xD1, 0xD2, 0xD3, 0xD4, 0xD5, 0xD6, 0xD7, 0xD8, 0xD9, 0xDA, 0xDB, 0xDC, 0xDD, 0xDE, 0xDF,
	0xE0, 0xE1, 0xE2, 0xE3, 0xE4, 0xE5, 0xE6, 0xE7, 0xE8, 0xE9, 0xEA, 0xEB, 0xEC, 0xED, 0xEE, 0xEF,
	0xF0, 0xF1, 0xF2, 0xF3, 0xF4, 0xF5, 0xF6, 0xF7, 0xF8, 0xF9, 0xFA, 0xFB, 0xFC, 0xFD, 0xFE, 0xFF,
}

// A number table used by the decryption and hashing algorithms.
var cryptTable = make([]uint32, 0x500)

func init() {
	// Initialize/compute the cryptTable:
	// The encryption/decryption and hashing functions use a number table in their procedures.
	// This table must be initialized before the functions are called the first time.

	var seed uint32 = 0x00100001
	var index1, index2 uint32
	var i int

	for ; index1 < 0x100; index1++ {
		for index2, i = index1, 0; i < 5; i, index2 = i+1, index2+0x100 {
			seed = (seed*125 + 3) % 0x2aaaab
			temp := (seed & 0xffff) << 0x10
			seed = (seed*125 + 3) % 0x2aaaab
			cryptTable[index2] = temp | (seed & 0xffff)
		}
	}
}

// decrypt decrypts the given encrypted data with the specified key.
// The same byte slice is used for the result, so the decrypted data will be written back into the input data slice.
func decrypt(data []byte, key uint32) {
	var seed1 = key
	var seed2 = uint32(0xeeeeeeee)
	var ch uint32

	for i, size := 0, len(data); i < size; i += 4 {
		seed2 += cryptTable[0x400+(seed1&0xff)]

		// littleEndian byte order:
		ch = uint32(data[i]) | uint32(data[i+1])<<8 | uint32(data[i+2])<<16 | uint32(data[i+3])<<24
		ch ^= seed1 + seed2

		seed1 = ((^seed1 << 0x15) + 0x11111111) | (seed1 >> 0x0B)
		seed2 = ch + seed2 + (seed2 << 5) + 3

		data[i] = byte(ch)
		data[i+1] = byte(ch >> 8)
		data[i+2] = byte(ch >> 16)
		data[i+3] = byte(ch >> 24)
	}
}

// hashString computes the hash of a string.
func hashString(s string, hashType uint32) uint32 {
	var seed1 uint32 = 0x7fed7fed
	var seed2 uint32 = 0xeeeeeeee

	for i, size := 0, len(s); i < size; i++ {
		ch := asciiToUpperTable[s[i]]

		// Value of hashType is the offset itself
		seed1 = cryptTable[hashType+ch] ^ (seed1 + seed2)
		seed2 = ch + seed1 + seed2 + (seed2 << 5) + 3
	}

	return seed1
}

// FileNameHash returns different hashes of the file name,
// exactly the ones that are needed by MPQ.FileByHash().
func FileNameHash(name string) (h1, h2, h3 uint32) {
	return hashString(name, hashTypeTableOffset),
		hashString(name, hashTypeNameA),
		hashString(name, hashTypeNameB)
}

// decompressMulti decompresses a block which was compressed using the multi compression method (beFlagCompressedMulti).
func decompressMulti(dst, src []byte) error {
	// Check if block is really compressed, some blocks have set the compression flag, but are not compressed.
	if len(src) >= len(dst) {
		// Copy block
		copy(dst, src)
		return nil
	}

	switch src[0] { // The compression flag
	case 0x02: // Flag to indicate zlib compression
		zr, err := zlib.NewReader(bytes.NewReader(src[1:]))
		if err != nil {
			return ErrInvalidArchive
		}
		if _, err := io.ReadFull(zr, dst); err != nil {
			return ErrInvalidArchive
		}
	case 0x10: // Flag to indicate BZip2 compression
		if _, err := io.ReadFull(bzip2.NewReader(bytes.NewReader(src[1:])), dst); err != nil {
			return ErrInvalidArchive
		}
	default: // Compression not supported!
		return ErrInvalidArchive
	}

	return nil
}