1/* crypt.h -- base code for crypt/uncrypt ZIPfile
  2
  3
  4   Version 1.01e, February 12th, 2005
  5
  6   Copyright (C) 1998-2005 Gilles Vollant
  7
  8   This code is a modified version of crypting code in Infozip distribution
  9
 10   The encryption/decryption parts of this source code (as opposed to the
 11   non-echoing password parts) were originally written in Europe.  The
 12   whole source package can be freely distributed, including from the USA.
 13   (Prior to January 2000, re-export from the US was a violation of US law.)
 14
 15   This encryption code is a direct transcription of the algorithm from
 16   Roger Schlafly, described by Phil Katz in the file appnote.txt.  This
 17   file (appnote.txt) is distributed with the PKZIP program (even in the
 18   version without encryption capabilities).
 19
 20   If you don't need crypting in your application, just define symbols
 21   NOCRYPT and NOUNCRYPT.
 22
 23   This code support the "Traditional PKWARE Encryption".
 24
 25   The new AES encryption added on Zip format by Winzip (see the page
 26   http://www.winzip.com/aes_info.htm ) and PKWare PKZip 5.x Strong
 27   Encryption is not supported.
 28*/
 29
 30#define CRC32(c, b) ((*(pcrc_32_tab+(((int)(c) ^ (b)) & 0xff))) ^ ((c) >> 8))
 31
 32/***********************************************************************
 33 * Return the next byte in the pseudo-random sequence
 34 */
 35static int decrypt_byte(unsigned long* pkeys, const z_crc_t* pcrc_32_tab)
 36{
 37    unsigned temp;  /* POTENTIAL BUG:  temp*(temp^1) may overflow in an
 38                     * unpredictable manner on 16-bit systems; not a problem
 39                     * with any known compiler so far, though */
 40
 41    temp = ((unsigned)(*(pkeys+2)) & 0xffff) | 2;
 42    return (int)(((temp * (temp ^ 1)) >> 8) & 0xff);
 43}
 44
 45/***********************************************************************
 46 * Update the encryption keys with the next byte of plain text
 47 */
 48static int update_keys(unsigned long* pkeys,const z_crc_t* pcrc_32_tab,int c)
 49{
 50    (*(pkeys+0)) = CRC32((*(pkeys+0)), c);
 51    (*(pkeys+1)) += (*(pkeys+0)) & 0xff;
 52    (*(pkeys+1)) = (*(pkeys+1)) * 134775813L + 1;
 53    {
 54      register int keyshift = (int)((*(pkeys+1)) >> 24);
 55      (*(pkeys+2)) = CRC32((*(pkeys+2)), keyshift);
 56    }
 57    return c;
 58}
 59
 60
 61/***********************************************************************
 62 * Initialize the encryption keys and the random header according to
 63 * the given password.
 64 */
 65static void init_keys(const char* passwd,unsigned long* pkeys,const z_crc_t* pcrc_32_tab)
 66{
 67    *(pkeys+0) = 305419896L;
 68    *(pkeys+1) = 591751049L;
 69    *(pkeys+2) = 878082192L;
 70    while (*passwd != '\0') {
 71        update_keys(pkeys,pcrc_32_tab,(int)*passwd);
 72        passwd++;
 73    }
 74}
 75
 76#define zdecode(pkeys,pcrc_32_tab,c) \
 77    (update_keys(pkeys,pcrc_32_tab,c ^= decrypt_byte(pkeys,pcrc_32_tab)))
 78
 79#define zencode(pkeys,pcrc_32_tab,c,t) \
 80    (t=decrypt_byte(pkeys,pcrc_32_tab), update_keys(pkeys,pcrc_32_tab,c), t^(c))
 81
 82#ifdef INCLUDECRYPTINGCODE_IFCRYPTALLOWED
 83
 84#define RAND_HEAD_LEN  12
 85   /* "last resort" source for second part of crypt seed pattern */
 86#  ifndef ZCR_SEED2
 87#    define ZCR_SEED2 3141592654UL     /* use PI as default pattern */
 88#  endif
 89
 90static int crypthead(const char* passwd,      /* password string */
 91                     unsigned char* buf,      /* where to write header */
 92                     int bufSize,
 93                     unsigned long* pkeys,
 94                     const z_crc_t* pcrc_32_tab,
 95                     unsigned long crcForCrypting)
 96{
 97    int n;                       /* index in random header */
 98    int t;                       /* temporary */
 99    int c;                       /* random byte */
100    unsigned char header[RAND_HEAD_LEN-2]; /* random header */
101    static unsigned calls = 0;   /* ensure different random header each time */
102
103    if (bufSize<RAND_HEAD_LEN)
104      return 0;
105
106    /* First generate RAND_HEAD_LEN-2 random bytes. We encrypt the
107     * output of rand() to get less predictability, since rand() is
108     * often poorly implemented.
109     */
110    if (++calls == 1)
111    {
112        srand((unsigned)(time(NULL) ^ ZCR_SEED2));
113    }
114    init_keys(passwd, pkeys, pcrc_32_tab);
115    for (n = 0; n < RAND_HEAD_LEN-2; n++)
116    {
117        c = (rand() >> 7) & 0xff;
118        header[n] = (unsigned char)zencode(pkeys, pcrc_32_tab, c, t);
119    }
120    /* Encrypt random header (last two bytes is high word of crc) */
121    init_keys(passwd, pkeys, pcrc_32_tab);
122    for (n = 0; n < RAND_HEAD_LEN-2; n++)
123    {
124        buf[n] = (unsigned char)zencode(pkeys, pcrc_32_tab, header[n], t);
125    }
126    buf[n++] = (unsigned char)zencode(pkeys, pcrc_32_tab, (int)(crcForCrypting >> 16) & 0xff, t);
127    buf[n++] = (unsigned char)zencode(pkeys, pcrc_32_tab, (int)(crcForCrypting >> 24) & 0xff, t);
128    return n;
129}
130
131#endif