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     (void)pcrc_32_tab;
42     temp = ((unsigned)(*(pkeys+2)) & 0xffff) | 2;
43     return (int)(((temp * (temp ^ 1)) >> 8) & 0xff);
44 }
45 
46 /***********************************************************************
47  * Update the encryption keys with the next byte of plain text
48  */
49 static int update_keys(unsigned long* pkeys,const z_crc_t* pcrc_32_tab,int c)
50 {
51     (*(pkeys+0)) = CRC32((*(pkeys+0)), c);
52     (*(pkeys+1)) += (*(pkeys+0)) & 0xff;
53     (*(pkeys+1)) = (*(pkeys+1)) * 134775813L + 1;
54     {
55       register int keyshift = (int)((*(pkeys+1)) >> 24);
56       (*(pkeys+2)) = CRC32((*(pkeys+2)), keyshift);
57     }
58     return c;
59 }
60 
61 
62 /***********************************************************************
63  * Initialize the encryption keys and the random header according to
64  * the given password.
65  */
66 static void init_keys(const char* passwd,unsigned long* pkeys,const z_crc_t* pcrc_32_tab)
67 {
68     *(pkeys+0) = 305419896L;
69     *(pkeys+1) = 591751049L;
70     *(pkeys+2) = 878082192L;
71     while (*passwd != '\0') {
72         update_keys(pkeys,pcrc_32_tab,(int)*passwd);
73         passwd++;
74     }
75 }
76 
77 #define zdecode(pkeys,pcrc_32_tab,c) \
78     (update_keys(pkeys,pcrc_32_tab,c ^= decrypt_byte(pkeys,pcrc_32_tab)))
79 
80 #define zencode(pkeys,pcrc_32_tab,c,t) \
81     (t=decrypt_byte(pkeys,pcrc_32_tab), update_keys(pkeys,pcrc_32_tab,c), (Byte)t^(c))
82 
83 #ifdef INCLUDECRYPTINGCODE_IFCRYPTALLOWED
84 
85 #define RAND_HEAD_LEN  12
86    /* "last resort" source for second part of crypt seed pattern */
87 #  ifndef ZCR_SEED2
88 #    define ZCR_SEED2 3141592654L       /* use PI as default pattern */
89 #  endif
90 
91 static unsigned crypthead(const char* passwd,       /* password string */
92                           unsigned char* buf,       /* where to write header */
93                           int bufSize,
94                           unsigned long* pkeys,
95                           const z_crc_t* pcrc_32_tab,
96                           unsigned long crcForCrypting)
97 {
98     unsigned n;                  /* index in random header */
99     int t;                       /* temporary */
100     int c;                       /* random byte */
101     unsigned char header[RAND_HEAD_LEN-2]; /* random header */
102     static unsigned calls = 0;   /* ensure different random header each time */
103 
104     if (bufSize<RAND_HEAD_LEN)
105       return 0;
106 
107     /* First generate RAND_HEAD_LEN-2 random bytes. We encrypt the
108      * output of rand() to get less predictability, since rand() is
109      * often poorly implemented.
110      */
111     if (++calls == 1)
112     {
113         srand((unsigned)(time(NULL) ^ ZCR_SEED2));
114     }
115     init_keys(passwd, pkeys, pcrc_32_tab);
116     for (n = 0; n < RAND_HEAD_LEN-2; n++)
117     {
118         c = (rand() >> 7) & 0xff;
119         header[n] = (unsigned char)zencode(pkeys, pcrc_32_tab, c, t);
120     }
121     /* Encrypt random header (last two bytes is high word of crc) */
122     init_keys(passwd, pkeys, pcrc_32_tab);
123     for (n = 0; n < RAND_HEAD_LEN-2; n++)
124     {
125         buf[n] = (unsigned char)zencode(pkeys, pcrc_32_tab, header[n], t);
126     }
127     buf[n++] = (unsigned char)zencode(pkeys, pcrc_32_tab, (int)(crcForCrypting >> 16) & 0xff, t);
128     buf[n++] = (unsigned char)zencode(pkeys, pcrc_32_tab, (int)(crcForCrypting >> 24) & 0xff, t);
129     return n;
130 }
131 
132 #endif
133