Chris@4: /* crypt.h -- base code for crypt/uncrypt ZIPfile
Chris@4: 
Chris@4: 
Chris@4:    Version 1.01e, February 12th, 2005
Chris@4: 
Chris@4:    Copyright (C) 1998-2005 Gilles Vollant
Chris@4: 
Chris@4:    This code is a modified version of crypting code in Infozip distribution
Chris@4: 
Chris@4:    The encryption/decryption parts of this source code (as opposed to the
Chris@4:    non-echoing password parts) were originally written in Europe.  The
Chris@4:    whole source package can be freely distributed, including from the USA.
Chris@4:    (Prior to January 2000, re-export from the US was a violation of US law.)
Chris@4: 
Chris@4:    This encryption code is a direct transcription of the algorithm from
Chris@4:    Roger Schlafly, described by Phil Katz in the file appnote.txt.  This
Chris@4:    file (appnote.txt) is distributed with the PKZIP program (even in the
Chris@4:    version without encryption capabilities).
Chris@4: 
Chris@4:    If you don't need crypting in your application, just define symbols
Chris@4:    NOCRYPT and NOUNCRYPT.
Chris@4: 
Chris@4:    This code support the "Traditional PKWARE Encryption".
Chris@4: 
Chris@4:    The new AES encryption added on Zip format by Winzip (see the page
Chris@4:    http://www.winzip.com/aes_info.htm ) and PKWare PKZip 5.x Strong
Chris@4:    Encryption is not supported.
Chris@4: */
Chris@4: 
Chris@4: #define CRC32(c, b) ((*(pcrc_32_tab+(((int)(c) ^ (b)) & 0xff))) ^ ((c) >> 8))
Chris@4: 
Chris@4: /***********************************************************************
Chris@4:  * Return the next byte in the pseudo-random sequence
Chris@4:  */
Chris@4: static int decrypt_byte(unsigned long* pkeys, const unsigned long* pcrc_32_tab)
Chris@4: {
Chris@4:     unsigned temp;  /* POTENTIAL BUG:  temp*(temp^1) may overflow in an
Chris@4:                      * unpredictable manner on 16-bit systems; not a problem
Chris@4:                      * with any known compiler so far, though */
Chris@4: 
Chris@4:     temp = ((unsigned)(*(pkeys+2)) & 0xffff) | 2;
Chris@4:     return (int)(((temp * (temp ^ 1)) >> 8) & 0xff);
Chris@4: }
Chris@4: 
Chris@4: /***********************************************************************
Chris@4:  * Update the encryption keys with the next byte of plain text
Chris@4:  */
Chris@4: static int update_keys(unsigned long* pkeys,const unsigned long* pcrc_32_tab,int c)
Chris@4: {
Chris@4:     (*(pkeys+0)) = CRC32((*(pkeys+0)), c);
Chris@4:     (*(pkeys+1)) += (*(pkeys+0)) & 0xff;
Chris@4:     (*(pkeys+1)) = (*(pkeys+1)) * 134775813L + 1;
Chris@4:     {
Chris@4:       register int keyshift = (int)((*(pkeys+1)) >> 24);
Chris@4:       (*(pkeys+2)) = CRC32((*(pkeys+2)), keyshift);
Chris@4:     }
Chris@4:     return c;
Chris@4: }
Chris@4: 
Chris@4: 
Chris@4: /***********************************************************************
Chris@4:  * Initialize the encryption keys and the random header according to
Chris@4:  * the given password.
Chris@4:  */
Chris@4: static void init_keys(const char* passwd,unsigned long* pkeys,const unsigned long* pcrc_32_tab)
Chris@4: {
Chris@4:     *(pkeys+0) = 305419896L;
Chris@4:     *(pkeys+1) = 591751049L;
Chris@4:     *(pkeys+2) = 878082192L;
Chris@4:     while (*passwd != '\0') {
Chris@4:         update_keys(pkeys,pcrc_32_tab,(int)*passwd);
Chris@4:         passwd++;
Chris@4:     }
Chris@4: }
Chris@4: 
Chris@4: #define zdecode(pkeys,pcrc_32_tab,c) \
Chris@4:     (update_keys(pkeys,pcrc_32_tab,c ^= decrypt_byte(pkeys,pcrc_32_tab)))
Chris@4: 
Chris@4: #define zencode(pkeys,pcrc_32_tab,c,t) \
Chris@4:     (t=decrypt_byte(pkeys,pcrc_32_tab), update_keys(pkeys,pcrc_32_tab,c), t^(c))
Chris@4: 
Chris@4: #ifdef INCLUDECRYPTINGCODE_IFCRYPTALLOWED
Chris@4: 
Chris@4: #define RAND_HEAD_LEN  12
Chris@4:    /* "last resort" source for second part of crypt seed pattern */
Chris@4: #  ifndef ZCR_SEED2
Chris@4: #    define ZCR_SEED2 3141592654UL     /* use PI as default pattern */
Chris@4: #  endif
Chris@4: 
Chris@4: static int crypthead(const char* passwd,      /* password string */
Chris@4:                      unsigned char* buf,      /* where to write header */
Chris@4:                      int bufSize,
Chris@4:                      unsigned long* pkeys,
Chris@4:                      const unsigned long* pcrc_32_tab,
Chris@4:                      unsigned long crcForCrypting)
Chris@4: {
Chris@4:     int n;                       /* index in random header */
Chris@4:     int t;                       /* temporary */
Chris@4:     int c;                       /* random byte */
Chris@4:     unsigned char header[RAND_HEAD_LEN-2]; /* random header */
Chris@4:     static unsigned calls = 0;   /* ensure different random header each time */
Chris@4: 
Chris@4:     if (bufSize<RAND_HEAD_LEN)
Chris@4:       return 0;
Chris@4: 
Chris@4:     /* First generate RAND_HEAD_LEN-2 random bytes. We encrypt the
Chris@4:      * output of rand() to get less predictability, since rand() is
Chris@4:      * often poorly implemented.
Chris@4:      */
Chris@4:     if (++calls == 1)
Chris@4:     {
Chris@4:         srand((unsigned)(time(NULL) ^ ZCR_SEED2));
Chris@4:     }
Chris@4:     init_keys(passwd, pkeys, pcrc_32_tab);
Chris@4:     for (n = 0; n < RAND_HEAD_LEN-2; n++)
Chris@4:     {
Chris@4:         c = (rand() >> 7) & 0xff;
Chris@4:         header[n] = (unsigned char)zencode(pkeys, pcrc_32_tab, c, t);
Chris@4:     }
Chris@4:     /* Encrypt random header (last two bytes is high word of crc) */
Chris@4:     init_keys(passwd, pkeys, pcrc_32_tab);
Chris@4:     for (n = 0; n < RAND_HEAD_LEN-2; n++)
Chris@4:     {
Chris@4:         buf[n] = (unsigned char)zencode(pkeys, pcrc_32_tab, header[n], t);
Chris@4:     }
Chris@4:     buf[n++] = (unsigned char)zencode(pkeys, pcrc_32_tab, (int)(crcForCrypting >> 16) & 0xff, t);
Chris@4:     buf[n++] = (unsigned char)zencode(pkeys, pcrc_32_tab, (int)(crcForCrypting >> 24) & 0xff, t);
Chris@4:     return n;
Chris@4: }
Chris@4: 
Chris@4: #endif