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102
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1 /* crypt.h -- base code for crypt/uncrypt ZIPfile
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2
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3
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4 Version 1.01e, February 12th, 2005
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5
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6 Copyright (C) 1998-2005 Gilles Vollant
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7
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8 This code is a modified version of crypting code in Infozip distribution
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9
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10 The encryption/decryption parts of this source code (as opposed to the
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11 non-echoing password parts) were originally written in Europe. The
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12 whole source package can be freely distributed, including from the USA.
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13 (Prior to January 2000, re-export from the US was a violation of US law.)
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14
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15 This encryption code is a direct transcription of the algorithm from
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16 Roger Schlafly, described by Phil Katz in the file appnote.txt. This
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17 file (appnote.txt) is distributed with the PKZIP program (even in the
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18 version without encryption capabilities).
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19
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20 If you don't need crypting in your application, just define symbols
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21 NOCRYPT and NOUNCRYPT.
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22
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23 This code support the "Traditional PKWARE Encryption".
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24
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25 The new AES encryption added on Zip format by Winzip (see the page
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26 http://www.winzip.com/aes_info.htm ) and PKWare PKZip 5.x Strong
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27 Encryption is not supported.
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28 */
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29
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30 #define CRC32(c, b) ((*(pcrc_32_tab+(((int)(c) ^ (b)) & 0xff))) ^ ((c) >> 8))
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31
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32 /***********************************************************************
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33 * Return the next byte in the pseudo-random sequence
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34 */
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35 static int decrypt_byte(unsigned long* pkeys, const unsigned long* pcrc_32_tab)
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36 {
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37 unsigned temp; /* POTENTIAL BUG: temp*(temp^1) may overflow in an
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38 * unpredictable manner on 16-bit systems; not a problem
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39 * with any known compiler so far, though */
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40
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41 temp = ((unsigned)(*(pkeys+2)) & 0xffff) | 2;
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42 return (int)(((temp * (temp ^ 1)) >> 8) & 0xff);
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43 }
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44
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45 /***********************************************************************
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46 * Update the encryption keys with the next byte of plain text
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47 */
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48 static int update_keys(unsigned long* pkeys,const unsigned long* pcrc_32_tab,int c)
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49 {
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50 (*(pkeys+0)) = CRC32((*(pkeys+0)), c);
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51 (*(pkeys+1)) += (*(pkeys+0)) & 0xff;
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52 (*(pkeys+1)) = (*(pkeys+1)) * 134775813L + 1;
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53 {
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54 register int keyshift = (int)((*(pkeys+1)) >> 24);
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55 (*(pkeys+2)) = CRC32((*(pkeys+2)), keyshift);
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56 }
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57 return c;
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58 }
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59
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60
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61 /***********************************************************************
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62 * Initialize the encryption keys and the random header according to
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63 * the given password.
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64 */
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65 static void init_keys(const char* passwd,unsigned long* pkeys,const unsigned long* pcrc_32_tab)
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66 {
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67 *(pkeys+0) = 305419896L;
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68 *(pkeys+1) = 591751049L;
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69 *(pkeys+2) = 878082192L;
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70 while (*passwd != '\0') {
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71 update_keys(pkeys,pcrc_32_tab,(int)*passwd);
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72 passwd++;
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73 }
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74 }
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75
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76 #define zdecode(pkeys,pcrc_32_tab,c) \
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77 (update_keys(pkeys,pcrc_32_tab,c ^= decrypt_byte(pkeys,pcrc_32_tab)))
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78
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79 #define zencode(pkeys,pcrc_32_tab,c,t) \
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80 (t=decrypt_byte(pkeys,pcrc_32_tab), update_keys(pkeys,pcrc_32_tab,c), t^(c))
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81
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82 #ifdef INCLUDECRYPTINGCODE_IFCRYPTALLOWED
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83
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84 #define RAND_HEAD_LEN 12
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85 /* "last resort" source for second part of crypt seed pattern */
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86 # ifndef ZCR_SEED2
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87 # define ZCR_SEED2 3141592654UL /* use PI as default pattern */
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88 # endif
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89
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90 static int crypthead(const char* passwd, /* password string */
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91 unsigned char* buf, /* where to write header */
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92 int bufSize,
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93 unsigned long* pkeys,
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94 const unsigned long* pcrc_32_tab,
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95 unsigned long crcForCrypting)
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96 {
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97 int n; /* index in random header */
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98 int t; /* temporary */
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99 int c; /* random byte */
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100 unsigned char header[RAND_HEAD_LEN-2]; /* random header */
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101 static unsigned calls = 0; /* ensure different random header each time */
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102
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103 if (bufSize<RAND_HEAD_LEN)
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104 return 0;
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105
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106 /* First generate RAND_HEAD_LEN-2 random bytes. We encrypt the
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107 * output of rand() to get less predictability, since rand() is
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108 * often poorly implemented.
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109 */
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110 if (++calls == 1)
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111 {
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112 srand((unsigned)(time(NULL) ^ ZCR_SEED2));
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113 }
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114 init_keys(passwd, pkeys, pcrc_32_tab);
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115 for (n = 0; n < RAND_HEAD_LEN-2; n++)
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116 {
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117 c = (rand() >> 7) & 0xff;
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118 header[n] = (unsigned char)zencode(pkeys, pcrc_32_tab, c, t);
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119 }
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120 /* Encrypt random header (last two bytes is high word of crc) */
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121 init_keys(passwd, pkeys, pcrc_32_tab);
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122 for (n = 0; n < RAND_HEAD_LEN-2; n++)
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123 {
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124 buf[n] = (unsigned char)zencode(pkeys, pcrc_32_tab, header[n], t);
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125 }
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126 buf[n++] = (unsigned char)zencode(pkeys, pcrc_32_tab, (int)(crcForCrypting >> 16) & 0xff, t);
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127 buf[n++] = (unsigned char)zencode(pkeys, pcrc_32_tab, (int)(crcForCrypting >> 24) & 0xff, t);
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128 return n;
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129 }
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130
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131 #endif
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