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/*
* Q2Crypt.c
* The Lemon Man (C) 2010
*
* gcc -O3 -Wall Q2Crypt.c md5.c -o Q2Crypt
*
*/

#include <stdio.h>
#include <string.h>
#include <assert.h>
#include "md5.h"

#define HEADER_LEN 0x34
#define MD5_DIGEST_LEN 0x10
#define DATA_BLOCK_LEN 128

static unsigned char xorTable[DATA_BLOCK_LEN] = {
    0xA3,0x04,0xB9,0xCD,0x34,0x13,0x4A,0x19,0x19,0x35,0xDF,0xBB,0x8F,0x3D,0x7F,0x09,
    0x42,0x3C,0x96,0xC6,0x41,0xA9,0x95,0xF1,0xD0,0xAC,0x16,0x37,0x57,0x1F,0x28,0xE7,
    0x0B,0xC2,0x12,0x09,0x39,0x42,0xD2,0x96,0xF5,0x00,0xD2,0x23,0xA4,0x24,0xE2,0x8E,
    0x50,0x3C,0x6E,0x23,0xEB,0x68,0xED,0x31,0xB7,0xEE,0xC0,0xC7,0x09,0xF8,0x0E,0x9D,
    0x51,0xED,0x17,0x95,0x64,0x09,0xE0,0xF9,0xF0,0xEF,0x86,0xC0,0x04,0x46,0x89,0x8A,
    0x6E,0x27,0x69,0xDE,0xC7,0x9D,0x1E,0xEE,0x3C,0x3F,0x17,0x05,0x44,0xBB,0xBB,0x1D,
    0x3D,0x5D,0x6E,0xF2,0xCF,0x15,0xD6,0x3C,0xCC,0x7D,0x67,0x1A,0xB8,0xD2,0x1B,0x54,
    0x97,0xA2,0x58,0x58,0xF7,0x4E,0x5E,0x50,0x42,0x69,0xDC,0xE7,0x3A,0x87,0x2E,0x22
};

static unsigned char updateHeader[HEADER_LEN+4] = {
    0x53,0x41,0x4D,0x53,0x55,0x4E,0x47,0x20,0x59,0x45,0x50,0x50,0x00,0x00,0x00,0x00,
    0x39,0x2E,0x39,0x39,0x00,0x00,0x00,0x00,0x45,0x55,0x00,0x00,0x00,0x00,0x00,0x00,
    0x59,0x50,0x2D,0x51,0x32,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
    0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00
};

void xorBlock (unsigned char *block)
{
    int bPos = 0;

    for (bPos = 0; bPos < DATA_BLOCK_LEN; bPos++)
    {
        block[bPos] ^= xorTable[bPos];
    }
}

int createUpdate (char *dest, char *updateArchivePath)
{
    FILE * updateDat = NULL;
    FILE * updateArk = NULL;

    unsigned char updateBlock [DATA_BLOCK_LEN];
    md5_byte_t digest [MD5_DIGEST_LEN];

    int updateSz;

    md5_state_t hashState;

    md5_init(&hashState);

    updateDat = fopen(dest, "w+b");
    updateArk = fopen(updateArchivePath, "rb");

    assert(updateDat);
    assert(updateArk);

    printf("Write header...\n");

    fwrite(updateHeader, 1, 0x38, updateDat);

    printf("Encrypting and hashing blob blocks...\n");

    while (fread(updateBlock, 1, DATA_BLOCK_LEN, updateArk) == DATA_BLOCK_LEN)
    {
        xorBlock(updateBlock);
        md5_append(&hashState, (const md5_byte_t *)updateBlock, DATA_BLOCK_LEN);
        fwrite(updateBlock, 1, DATA_BLOCK_LEN, updateDat);
    }

    md5_finish(&hashState, digest);

    printf("Writing the hash...\n");

    fwrite(digest, 1, MD5_DIGEST_LEN, updateDat);

    printf("Adjusting size...\n");

    updateSz = ftell(updateDat);
    updateSz -= 0x4; /* Size tag */
    updateSz -= HEADER_LEN;
    updateSz -= MD5_DIGEST_LEN;

    fseek(updateDat, 0x34, SEEK_SET);

    printf("Writing the size...\n");

    fwrite(&updateSz, 1, 4, updateDat);

    fclose(updateDat);
    fclose(updateArk);

    return updateSz;
}

int decryptUpdate (char *dest, char *updateDat)
{
    FILE * encFile = NULL;
    FILE * decFile = NULL;

    int updateSz;
    int totalRead;
    unsigned char updateBlock [DATA_BLOCK_LEN];
    md5_byte_t md5Digest [MD5_DIGEST_LEN];
    md5_byte_t myDigest [MD5_DIGEST_LEN];
    md5_state_t hashState;

    encFile = fopen(updateDat, "rb");
    decFile = fopen(dest, "w+b");

    assert(encFile);
    assert(decFile);

    md5_init(&hashState);

    fseek(encFile, HEADER_LEN, SEEK_SET);

    printf("Reading update size...\n");

    fread(&updateSz, 1, 4, encFile);

    fseek(encFile, 0, SEEK_END);

    if (ftell(encFile) != (HEADER_LEN + 4 + updateSz + MD5_DIGEST_LEN))
    {
        printf("Size mismatch, unpack action aborted.\n");

        fclose(encFile);
        fclose(decFile);

        return 0;
    }

    fseek(encFile, HEADER_LEN + 4, SEEK_SET);

    totalRead = 0;

    printf("Decrypting and hashing updater blocks...\n");

    while (totalRead < updateSz)
    {
        totalRead += fread(updateBlock, 1, DATA_BLOCK_LEN, encFile);
        md5_append(&hashState, (const md5_byte_t *)updateBlock, DATA_BLOCK_LEN);
        xorBlock(updateBlock);
        fwrite(updateBlock, 1, DATA_BLOCK_LEN, decFile);
    }

    md5_finish(&hashState, myDigest);

    printf("Checking for hash mismatches...\n");

    fread(&md5Digest, 1, MD5_DIGEST_LEN, encFile);

    if (!memcmp(md5Digest, myDigest, MD5_DIGEST_LEN))
        printf("MD5 hash are matching!\n");
    else
        printf("MD5 hash mismatch, *DO NOT FLASH* this image\n");

    if (ftell(encFile) != (HEADER_LEN + 4 + updateSz + MD5_DIGEST_LEN))
    {
        printf("Not at the EOF, wtf?\n");
        exit(0);
    }

    fclose(encFile);
    fclose(decFile);

    return 1;
}

int main (int argc, char *argv[])
{
    printf("** Q2Crypt for SAMSUNG YP-Q2 **\nThe Lemon Man (C) 2010\nUsage:\n\tQ2Crypt -enc/-dec infile outfile\n\n");

    if (argc < 3)
        return 0;

    if (!strcmp(argv[1], "-dec"))
        decryptUpdate(argv[3], argv[2]);
    else if (!strcmp(argv[1], "-enc"))
        createUpdate(argv[3], argv[2]);
    else
        return 0;

    return 1;
}
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