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131 lines (108 loc) · 4.59 KB
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/* crypt.h -- base code for crypt/uncrypt ZIPfile
Version 1.01e, February 12th, 2005
Copyright (C) 1998-2005 Gilles Vollant
This code is a modified version of crypting code in Infozip distribution
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.
This code support the "Traditional PKWARE Encryption".
The new AES encryption added on Zip format by Winzip (see the page
http://www.winzip.com/aes_info.htm ) and PKWare PKZip 5.x Strong
Encryption is not supported.
*/
#define CRC32(c, b) ((*(pcrc_32_tab+(((int)(c) ^ (b)) & 0xff))) ^ ((c) >> 8))
/***********************************************************************
* Return the next byte in the pseudo-random sequence
*/
static int decrypt_byte(z_crc_t* pkeys, const z_crc_t* pcrc_32_tab)
{
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)(*(pkeys+2)) & 0xffff) | 2;
return (int)(((temp * (temp ^ 1)) >> 8) & 0xff);
}
/***********************************************************************
* Update the encryption keys with the next byte of plain text
*/
static int update_keys(z_crc_t* pkeys,const z_crc_t* 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,z_crc_t* pkeys,const z_crc_t* 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,pcrc_32_tab)))
#define zencode(pkeys,pcrc_32_tab,c,t) \
(t=decrypt_byte(pkeys,pcrc_32_tab), 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,
z_crc_t* pkeys,
const z_crc_t* pcrc_32_tab,
z_crc_t 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