quakespasm/launcher/crypt.h

/* crypt.h -- base code for traditional PKWARE encryption
   Version 1.01e, February 12th, 2005

   Copyright (C) 1998-2005 Gilles Vollant
   Modifications for Info-ZIP crypting
     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.

   See the Info-ZIP LICENSE file version 2000-Apr-09 or later for terms of use
   which also may be found at: ftp://ftp.info-zip.org/pub/infozip/license.html

   The encryption/decryption parts of this source code (as opposed to the
   non-echoing password parts) were originally written in Europe. The
   whole source package can be freely distributed, including from the USA.
   (Prior to January 2000, re-export from the US was a violation of US law.)

   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.
   
   Mar 8th, 2016 - Lucio Cosmo 
   Fixed support for 64bit builds for archives with "PKWARE" password.
   Changed long, unsigned long, unsigned to unsigned int in 
   access functions to crctables and pkeys

*/

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

/***********************************************************************
 * Return the next byte in the pseudo-random sequence
 */
static int decrypt_byte(unsigned int* 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 = ((unsigned int)(*(pkeys+2)) & 0xffff) | 2;
    return (unsigned int)(((temp * (temp ^ 1)) >> 8) & 0xff);
}

/***********************************************************************
 * Update the encryption keys with the next byte of plain text
 */
static int update_keys(unsigned int* pkeys,const unsigned int* pcrc_32_tab,int c)
{
    (*(pkeys+0)) = CRC32((*(pkeys+0)), c);
    (*(pkeys+1)) += (*(pkeys+0)) & 0xff;
    (*(pkeys+1)) = (*(pkeys+1)) * 134775813L + 1;
    {
        register int keyshift = (int)((*(pkeys+1)) >> 24);
        (*(pkeys+2)) = CRC32((*(pkeys+2)), keyshift);
    }
    return c;
}


/***********************************************************************
 * Initialize the encryption keys and the random header according to
 * the given password.
 */
static void init_keys(const char* passwd,unsigned int* pkeys,const unsigned int* pcrc_32_tab)
{
    *(pkeys+0) = 305419896L;
    *(pkeys+1) = 591751049L;
    *(pkeys+2) = 878082192L;
    while (*passwd != 0)
    {
        update_keys(pkeys,pcrc_32_tab,(int)*passwd);
        passwd++;
    }
}

#define zdecode(pkeys,pcrc_32_tab,c) \
    (update_keys(pkeys,pcrc_32_tab,c ^= decrypt_byte(pkeys)))

#define zencode(pkeys,pcrc_32_tab,c,t) \
    (t=decrypt_byte(pkeys), update_keys(pkeys,pcrc_32_tab,c), t^(c))

#ifdef INCLUDECRYPTINGCODE_IFCRYPTALLOWED

#define RAND_HEAD_LEN  12
   /* "last resort" source for second part of crypt seed pattern */
#  ifndef ZCR_SEED2
#    define ZCR_SEED2 3141592654UL     /* use PI as default pattern */
#  endif

static int crypthead(const char* passwd,      /* password string */
                     unsigned char* buf,      /* where to write header */
                     int bufSize,
                     unsigned int* pkeys,
                     const unsigned int* pcrc_32_tab,
                     unsigned int crcForCrypting)
{
    int n;                                  /* index in random header */
    int t;                                  /* temporary */
    int c;                                  /* random byte */
    unsigned char header[RAND_HEAD_LEN-2];  /* random header */
    static unsigned calls = 0;              /* ensure different random header each time */

    if (bufSize < RAND_HEAD_LEN)
        return 0;

    /* First generate RAND_HEAD_LEN-2 random bytes. We encrypt the
     * output of rand() to get less predictability, since rand() is
     * often poorly implemented.
     */
    if (++calls == 1)
    {
        srand((unsigned)(time(NULL) ^ ZCR_SEED2));
    }
    init_keys(passwd, pkeys, pcrc_32_tab);
    for (n = 0; n < RAND_HEAD_LEN-2; n++)
    {
        c = (rand() >> 7) & 0xff;
        header[n] = (unsigned char)zencode(pkeys, pcrc_32_tab, c, t);
    }
    /* 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] = (unsigned char)zencode(pkeys, pcrc_32_tab, header[n], t);
    }
    buf[n++] = (unsigned char)zencode(pkeys, pcrc_32_tab, (int)(crcForCrypting >> 16) & 0xff, t);
    buf[n++] = (unsigned char)zencode(pkeys, pcrc_32_tab, (int)(crcForCrypting >> 24) & 0xff, t);
    return n;
}

#endif