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 */
35 static 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 */
48 static 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 */
65 static 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
90 static 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