crypt.c

/* crypt.c -- base code for traditional PKWARE encryption
   Version 1.2.0, September 16th, 2017

   Copyright (C) 2012-2017 Nathan Moinvaziri
     https://github.com/nmoinvaz/minizip
   Copyright (C) 1998-2005 Gilles Vollant
     Modifications for Info-ZIP crypting
     http://www.winimage.com/zLibDll/minizip.html
   Copyright (C) 2003 Terry Thorsen

   This code is a modified version of crypting code in Info-ZIP distribution

   Copyright (C) 1990-2000 Info-ZIP.  All rights reserved.

   This program is distributed under the terms of the same license as zlib.
   See the accompanying LICENSE file for the full text of the license.

   This encryption code is a direct transcription of the algorithm from
   Roger Schlafly, described by Phil Katz in the file appnote.txt. This
   file (appnote.txt) is distributed with the PKZIP program (even in the
   version without encryption capabilities).

   If you don't need crypting in your application, just define symbols
   NOCRYPT and NOUNCRYPT.
*/

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <time.h>

#ifdef _WIN32
#  include <windows.h>
#  include <wincrypt.h>
#else
#  include <sys/stat.h>
#  include <fcntl.h>
#  include <unistd.h>
#endif

#include "zlib.h"

#include "crypt.h"

/***************************************************************************/

#define CRC32(c, b) ((*(pcrc_32_tab+(((uint32_t)(c) ^ (b)) & 0xff))) ^ ((c) >> 8))

/***************************************************************************/

uint8_t decrypt_byte(uint32_t *pkeys)
{
    unsigned temp;  /* POTENTIAL BUG:  temp*(temp^1) may overflow in an
                     * unpredictable manner on 16-bit systems; not a problem
                     * with any known compiler so far, though */

    temp = ((uint32_t)(*(pkeys+2)) & 0xffff) | 2;
    return (uint8_t)(((temp * (temp ^ 1)) >> 8) & 0xff);
}

uint8_t update_keys(uint32_t *pkeys, const z_crc_t *pcrc_32_tab, int32_t c)
{
    (*(pkeys+0)) = (uint32_t)CRC32((*(pkeys+0)), c);
    (*(pkeys+1)) += (*(pkeys+0)) & 0xff;
    (*(pkeys+1)) = (*(pkeys+1)) * 134775813UL + 1;
    {
        register int32_t keyshift = (int32_t)((*(pkeys + 1)) >> 24);
        (*(pkeys+2)) = (uint32_t)CRC32((*(pkeys+2)), keyshift);
    }
    return c;
}

void init_keys(const char *passwd, uint32_t *pkeys, const z_crc_t *pcrc_32_tab)
{
    *(pkeys+0) = 305419896UL;
    *(pkeys+1) = 591751049UL;
    *(pkeys+2) = 878082192UL;
    while (*passwd != 0)
    {
        update_keys(pkeys, pcrc_32_tab, *passwd);
        passwd += 1;
    }
}

/***************************************************************************/

#ifndef NOCRYPT
int cryptrand(unsigned char *buf, unsigned int len)
{
#ifdef _WIN32
    HCRYPTPROV provider;
    unsigned __int64 pentium_tsc[1];
    int rlen = 0;
    int result = 0;


    if (CryptAcquireContext(&provider, NULL, NULL, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT | CRYPT_SILENT))
    {
        result = CryptGenRandom(provider, len, buf);
        CryptReleaseContext(provider, 0);
        if (result)
            return len;
    }

    for (rlen = 0; rlen < (int)len; ++rlen)
    {
        if (rlen % 8 == 0)
            QueryPerformanceCounter((LARGE_INTEGER *)pentium_tsc);
        buf[rlen] = ((unsigned char*)pentium_tsc)[rlen % 8];
    }

    return rlen;
#else
    arc4random_buf(buf, len);
    return len;
#endif
}

int crypthead(const char *passwd, uint8_t *buf, int buf_size, uint32_t *pkeys,
              const z_crc_t *pcrc_32_tab, uint8_t verify1, uint8_t verify2)
{
    uint8_t n = 0;                      /* index in random header */
    uint8_t header[RAND_HEAD_LEN-2];    /* random header */
    uint16_t t = 0;                     /* temporary */

    if (buf_size < RAND_HEAD_LEN)
        return 0;

    init_keys(passwd, pkeys, pcrc_32_tab);

    /* First generate RAND_HEAD_LEN-2 random bytes. */
    cryptrand(header, RAND_HEAD_LEN-2);

    /* Encrypt random header (last two bytes is high word of crc) */
    init_keys(passwd, pkeys, pcrc_32_tab);

    for (n = 0; n < RAND_HEAD_LEN-2; n++)
        buf[n] = (uint8_t)zencode(pkeys, pcrc_32_tab, header[n], t);

    buf[n++] = (uint8_t)zencode(pkeys, pcrc_32_tab, verify1, t);
    buf[n++] = (uint8_t)zencode(pkeys, pcrc_32_tab, verify2, t);
    return n;
}
#endif

/***************************************************************************/