| 1 | /* |
| 2 | * misc.c: Miscellaneous helpful functions. |
| 3 | */ |
| 4 | |
| 5 | #include <assert.h> |
| 6 | #include <stdlib.h> |
| 7 | #include <string.h> |
| 8 | #include <stdio.h> |
| 9 | |
| 10 | #include "puzzles.h" |
| 11 | |
| 12 | void free_cfg(config_item *cfg) |
| 13 | { |
| 14 | config_item *i; |
| 15 | |
| 16 | for (i = cfg; i->type != C_END; i++) |
| 17 | if (i->type == C_STRING) |
| 18 | sfree(i->sval); |
| 19 | sfree(cfg); |
| 20 | } |
| 21 | |
| 22 | /* |
| 23 | * The Mines (among others) game descriptions contain the location of every |
| 24 | * mine, and can therefore be used to cheat. |
| 25 | * |
| 26 | * It would be pointless to attempt to _prevent_ this form of |
| 27 | * cheating by encrypting the description, since Mines is |
| 28 | * open-source so anyone can find out the encryption key. However, |
| 29 | * I think it is worth doing a bit of gentle obfuscation to prevent |
| 30 | * _accidental_ spoilers: if you happened to note that the game ID |
| 31 | * starts with an F, for example, you might be unable to put the |
| 32 | * knowledge of those mines out of your mind while playing. So, |
| 33 | * just as discussions of film endings are rot13ed to avoid |
| 34 | * spoiling it for people who don't want to be told, we apply a |
| 35 | * keyless, reversible, but visually completely obfuscatory masking |
| 36 | * function to the mine bitmap. |
| 37 | */ |
| 38 | void obfuscate_bitmap(unsigned char *bmp, int bits, int decode) |
| 39 | { |
| 40 | int bytes, firsthalf, secondhalf; |
| 41 | struct step { |
| 42 | unsigned char *seedstart; |
| 43 | int seedlen; |
| 44 | unsigned char *targetstart; |
| 45 | int targetlen; |
| 46 | } steps[2]; |
| 47 | int i, j; |
| 48 | |
| 49 | /* |
| 50 | * My obfuscation algorithm is similar in concept to the OAEP |
| 51 | * encoding used in some forms of RSA. Here's a specification |
| 52 | * of it: |
| 53 | * |
| 54 | * + We have a `masking function' which constructs a stream of |
| 55 | * pseudorandom bytes from a seed of some number of input |
| 56 | * bytes. |
| 57 | * |
| 58 | * + We pad out our input bit stream to a whole number of |
| 59 | * bytes by adding up to 7 zero bits on the end. (In fact |
| 60 | * the bitmap passed as input to this function will already |
| 61 | * have had this done in practice.) |
| 62 | * |
| 63 | * + We divide the _byte_ stream exactly in half, rounding the |
| 64 | * half-way position _down_. So an 81-bit input string, for |
| 65 | * example, rounds up to 88 bits or 11 bytes, and then |
| 66 | * dividing by two gives 5 bytes in the first half and 6 in |
| 67 | * the second half. |
| 68 | * |
| 69 | * + We generate a mask from the second half of the bytes, and |
| 70 | * XOR it over the first half. |
| 71 | * |
| 72 | * + We generate a mask from the (encoded) first half of the |
| 73 | * bytes, and XOR it over the second half. Any null bits at |
| 74 | * the end which were added as padding are cleared back to |
| 75 | * zero even if this operation would have made them nonzero. |
| 76 | * |
| 77 | * To de-obfuscate, the steps are precisely the same except |
| 78 | * that the final two are reversed. |
| 79 | * |
| 80 | * Finally, our masking function. Given an input seed string of |
| 81 | * bytes, the output mask consists of concatenating the SHA-1 |
| 82 | * hashes of the seed string and successive decimal integers, |
| 83 | * starting from 0. |
| 84 | */ |
| 85 | |
| 86 | bytes = (bits + 7) / 8; |
| 87 | firsthalf = bytes / 2; |
| 88 | secondhalf = bytes - firsthalf; |
| 89 | |
| 90 | steps[decode ? 1 : 0].seedstart = bmp + firsthalf; |
| 91 | steps[decode ? 1 : 0].seedlen = secondhalf; |
| 92 | steps[decode ? 1 : 0].targetstart = bmp; |
| 93 | steps[decode ? 1 : 0].targetlen = firsthalf; |
| 94 | |
| 95 | steps[decode ? 0 : 1].seedstart = bmp; |
| 96 | steps[decode ? 0 : 1].seedlen = firsthalf; |
| 97 | steps[decode ? 0 : 1].targetstart = bmp + firsthalf; |
| 98 | steps[decode ? 0 : 1].targetlen = secondhalf; |
| 99 | |
| 100 | for (i = 0; i < 2; i++) { |
| 101 | SHA_State base, final; |
| 102 | unsigned char digest[20]; |
| 103 | char numberbuf[80]; |
| 104 | int digestpos = 20, counter = 0; |
| 105 | |
| 106 | SHA_Init(&base); |
| 107 | SHA_Bytes(&base, steps[i].seedstart, steps[i].seedlen); |
| 108 | |
| 109 | for (j = 0; j < steps[i].targetlen; j++) { |
| 110 | if (digestpos >= 20) { |
| 111 | sprintf(numberbuf, "%d", counter++); |
| 112 | final = base; |
| 113 | SHA_Bytes(&final, numberbuf, strlen(numberbuf)); |
| 114 | SHA_Final(&final, digest); |
| 115 | digestpos = 0; |
| 116 | } |
| 117 | steps[i].targetstart[j] ^= digest[digestpos++]; |
| 118 | } |
| 119 | |
| 120 | /* |
| 121 | * Mask off the pad bits in the final byte after both steps. |
| 122 | */ |
| 123 | if (bits % 8) |
| 124 | bmp[bits / 8] &= 0xFF & (0xFF00 >> (bits % 8)); |
| 125 | } |
| 126 | } |
| 127 | |
| 128 | /* err, yeah, these two pretty much rely on unsigned char being 8 bits. |
| 129 | * Platforms where this is not the case probably have bigger problems |
| 130 | * than just making these two work, though... */ |
| 131 | char *bin2hex(const unsigned char *in, int inlen) |
| 132 | { |
| 133 | char *ret = snewn(inlen*2 + 1, char), *p = ret; |
| 134 | int i; |
| 135 | |
| 136 | for (i = 0; i < inlen*2; i++) { |
| 137 | int v = in[i/2]; |
| 138 | if (i % 2 == 0) v >>= 4; |
| 139 | *p++ = "0123456789abcdef"[v & 0xF]; |
| 140 | } |
| 141 | *p = '\0'; |
| 142 | return ret; |
| 143 | } |
| 144 | |
| 145 | unsigned char *hex2bin(const char *in, int outlen) |
| 146 | { |
| 147 | unsigned char *ret = snewn(outlen, unsigned char); |
| 148 | int i; |
| 149 | |
| 150 | debug(("hex2bin: in '%s'", in)); |
| 151 | |
| 152 | memset(ret, 0, outlen*sizeof(unsigned char)); |
| 153 | for (i = 0; i < outlen*2; i++) { |
| 154 | int c = in[i]; |
| 155 | int v; |
| 156 | |
| 157 | assert(c != 0); |
| 158 | if (c >= '0' && c <= '9') |
| 159 | v = c - '0'; |
| 160 | else if (c >= 'a' && c <= 'f') |
| 161 | v = c - 'a' + 10; |
| 162 | else if (c >= 'A' && c <= 'F') |
| 163 | v = c - 'A' + 10; |
| 164 | else |
| 165 | v = 0; |
| 166 | |
| 167 | ret[i / 2] |= v << (4 * (1 - (i % 2))); |
| 168 | } |
| 169 | return ret; |
| 170 | } |
| 171 | |
| 172 | void game_mkhighlight(frontend *fe, float *ret, |
| 173 | int background, int highlight, int lowlight) |
| 174 | { |
| 175 | float max; |
| 176 | int i; |
| 177 | |
| 178 | frontend_default_colour(fe, &ret[background * 3]); |
| 179 | |
| 180 | /* |
| 181 | * Drop the background colour so that the highlight is |
| 182 | * noticeably brighter than it while still being under 1. |
| 183 | */ |
| 184 | max = ret[background*3]; |
| 185 | for (i = 1; i < 3; i++) |
| 186 | if (ret[background*3+i] > max) |
| 187 | max = ret[background*3+i]; |
| 188 | if (max * 1.2F > 1.0F) { |
| 189 | for (i = 0; i < 3; i++) |
| 190 | ret[background*3+i] /= (max * 1.2F); |
| 191 | } |
| 192 | |
| 193 | for (i = 0; i < 3; i++) { |
| 194 | ret[highlight * 3 + i] = ret[background * 3 + i] * 1.2F; |
| 195 | ret[lowlight * 3 + i] = ret[background * 3 + i] * 0.8F; |
| 196 | } |
| 197 | } |
| 198 | |
| 199 | /* vim: set shiftwidth=4 tabstop=8: */ |