105 lines
3.5 KiB
C
105 lines
3.5 KiB
C
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#define CRC32(c, b) ((*(pcrc_32_tab+(((int)(c) ^ (b)) & 0xff))) ^ ((c) >> 8))
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/***********************************************************************
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* Return the next byte in the pseudo-random sequence
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*/
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static int decrypt_byte(unsigned long* pkeys, const unsigned long* pcrc_32_tab)
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{
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unsigned temp; /* POTENTIAL BUG: temp*(temp^1) may overflow in an
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* unpredictable manner on 16-bit systems; not a problem
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* with any known compiler so far, though */
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temp = ((unsigned)(*(pkeys+2)) & 0xffff) | 2;
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return (int)(((temp * (temp ^ 1)) >> 8) & 0xff);
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}
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/***********************************************************************
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* Update the encryption keys with the next byte of plain text
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*/
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static int update_keys(unsigned long* pkeys,const unsigned long* pcrc_32_tab,int c)
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{
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(*(pkeys+0)) = CRC32((*(pkeys+0)), c);
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(*(pkeys+1)) += (*(pkeys+0)) & 0xff;
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(*(pkeys+1)) = (*(pkeys+1)) * 134775813L + 1;
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{
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register int keyshift = (int)((*(pkeys+1)) >> 24);
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(*(pkeys+2)) = CRC32((*(pkeys+2)), keyshift);
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}
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return c;
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}
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/***********************************************************************
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* Initialize the encryption keys and the random header according to
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* the given password.
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*/
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static void init_keys(const char* passwd,unsigned long* pkeys,const unsigned long* pcrc_32_tab)
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{
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*(pkeys+0) = 305419896L;
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*(pkeys+1) = 591751049L;
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*(pkeys+2) = 878082192L;
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while (*passwd != '\0') {
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update_keys(pkeys,pcrc_32_tab,(int)*passwd);
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passwd++;
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}
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}
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#define zdecode(pkeys,pcrc_32_tab,c) \
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(update_keys(pkeys,pcrc_32_tab,c ^= decrypt_byte(pkeys,pcrc_32_tab)))
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#define zencode(pkeys,pcrc_32_tab,c,t) \
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(t=decrypt_byte(pkeys,pcrc_32_tab), update_keys(pkeys,pcrc_32_tab,c), t^(c))
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#ifdef INCLUDECRYPTINGCODE_IFCRYPTALLOWED
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#define RAND_HEAD_LEN 12
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/* "last resort" source for second part of crypt seed pattern */
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# ifndef ZCR_SEED2
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# define ZCR_SEED2 (unsigned long)3141592654L /* use PI as default pattern */
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# endif
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static int crypthead(passwd, buf, bufSize, pkeys, pcrc_32_tab, crcForCrypting)
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const char *passwd; /* password string */
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unsigned char *buf; /* where to write header */
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int bufSize;
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unsigned long* pkeys;
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const unsigned long* pcrc_32_tab;
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unsigned long crcForCrypting;
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{
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int n; /* index in random header */
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int t; /* temporary */
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int c; /* random byte */
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unsigned char header[RAND_HEAD_LEN-2]; /* random header */
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static unsigned calls = 0; /* ensure different random header each time */
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if (bufSize<RAND_HEAD_LEN)
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return 0;
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/* First generate RAND_HEAD_LEN-2 random bytes. We encrypt the
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* output of rand() to get less predictability, since rand() is
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* often poorly implemented.
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*/
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if (++calls == 1)
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{
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srand((unsigned)(time(NULL) ^ ZCR_SEED2));
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}
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init_keys(passwd, pkeys, pcrc_32_tab);
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for (n = 0; n < RAND_HEAD_LEN-2; n++)
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{
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c = (rand() >> 7) & 0xff;
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header[n] = (unsigned char)zencode(pkeys, pcrc_32_tab, c, t);
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}
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/* Encrypt random header (last two bytes is high word of crc) */
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init_keys(passwd, pkeys, pcrc_32_tab);
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for (n = 0; n < RAND_HEAD_LEN-2; n++)
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{
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buf[n] = (unsigned char)zencode(pkeys, pcrc_32_tab, header[n], t);
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}
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buf[n++] = zencode(pkeys, pcrc_32_tab, (int)(crcForCrypting >> 16) & 0xff, t);
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buf[n++] = zencode(pkeys, pcrc_32_tab, (int)(crcForCrypting >> 24) & 0xff, t);
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return n;
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}
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#endif
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