tanjent@gmail.com | f3b7897 | 2012-03-01 03:38:55 +0000 | [diff] [blame] | 1 | //----------------------------------------------------------------------------- |
| 2 | // Differential collision & distribution tests - generate a bunch of random keys, |
| 3 | // see what happens to the hash value when we flip a few bits of the key. |
| 4 | |
| 5 | #pragma once |
| 6 | |
| 7 | #include "Types.h" |
| 8 | #include "Stats.h" // for chooseUpToK |
| 9 | #include "KeysetTest.h" // for SparseKeygenRecurse |
| 10 | #include "Random.h" |
| 11 | |
| 12 | #include <vector> |
| 13 | #include <algorithm> |
| 14 | #include <stdio.h> |
| 15 | |
| 16 | //----------------------------------------------------------------------------- |
| 17 | // Sort through the differentials, ignoring collisions that only occured once |
| 18 | // (these could be false positives). If we find collisions of 3 or more, the |
| 19 | // differential test fails. |
| 20 | |
| 21 | template < class keytype > |
| 22 | bool ProcessDifferentials ( std::vector<keytype> & diffs, int reps, bool dumpCollisions ) |
| 23 | { |
| 24 | std::sort(diffs.begin(), diffs.end()); |
| 25 | |
| 26 | int count = 1; |
| 27 | int ignore = 0; |
| 28 | |
| 29 | bool result = true; |
| 30 | |
| 31 | if(diffs.size()) |
| 32 | { |
| 33 | keytype kp = diffs[0]; |
| 34 | |
| 35 | for(int i = 1; i < (int)diffs.size(); i++) |
| 36 | { |
| 37 | if(diffs[i] == kp) |
| 38 | { |
| 39 | count++; |
| 40 | continue; |
| 41 | } |
| 42 | else |
| 43 | { |
| 44 | if(count > 1) |
| 45 | { |
| 46 | result = false; |
| 47 | |
| 48 | double pct = 100 * (double(count) / double(reps)); |
| 49 | |
| 50 | if(dumpCollisions) |
| 51 | { |
| 52 | printbits((unsigned char*)&kp,sizeof(kp)); |
| 53 | printf(" - %4.2f%%\n", pct ); |
| 54 | } |
| 55 | } |
| 56 | else |
| 57 | { |
| 58 | ignore++; |
| 59 | } |
| 60 | |
| 61 | kp = diffs[i]; |
| 62 | count = 1; |
| 63 | } |
| 64 | } |
| 65 | |
| 66 | if(count > 1) |
| 67 | { |
| 68 | double pct = 100 * (double(count) / double(reps)); |
| 69 | |
| 70 | if(dumpCollisions) |
| 71 | { |
| 72 | printbits((unsigned char*)&kp,sizeof(kp)); |
| 73 | printf(" - %4.2f%%\n", pct ); |
| 74 | } |
| 75 | } |
| 76 | else |
| 77 | { |
| 78 | ignore++; |
| 79 | } |
| 80 | } |
| 81 | |
| 82 | printf("%d total collisions, of which %d single collisions were ignored",(int)diffs.size(),ignore); |
| 83 | |
| 84 | if(result == false) |
| 85 | { |
| 86 | printf(" !!!!! "); |
| 87 | } |
| 88 | |
| 89 | printf("\n"); |
| 90 | printf("\n"); |
| 91 | |
| 92 | return result; |
| 93 | } |
| 94 | |
| 95 | //----------------------------------------------------------------------------- |
| 96 | // Check all possible keybits-choose-N differentials for collisions, report |
| 97 | // ones that occur significantly more often than expected. |
| 98 | |
| 99 | // Random collisions can happen with probability 1 in 2^32 - if we do more than |
| 100 | // 2^32 tests, we'll probably see some spurious random collisions, so don't report |
| 101 | // them. |
| 102 | |
| 103 | template < typename keytype, typename hashtype > |
| 104 | void DiffTestRecurse ( pfHash hash, keytype & k1, keytype & k2, hashtype & h1, hashtype & h2, int start, int bitsleft, std::vector<keytype> & diffs ) |
| 105 | { |
| 106 | const int bits = sizeof(keytype)*8; |
| 107 | |
| 108 | for(int i = start; i < bits; i++) |
| 109 | { |
| 110 | flipbit(&k2,sizeof(k2),i); |
| 111 | bitsleft--; |
| 112 | |
| 113 | hash(&k2,sizeof(k2),0,&h2); |
| 114 | |
| 115 | if(h1 == h2) |
| 116 | { |
| 117 | diffs.push_back(k1 ^ k2); |
| 118 | } |
| 119 | |
| 120 | if(bitsleft) |
| 121 | { |
| 122 | DiffTestRecurse(hash,k1,k2,h1,h2,i+1,bitsleft,diffs); |
| 123 | } |
| 124 | |
| 125 | flipbit(&k2,sizeof(k2),i); |
| 126 | bitsleft++; |
| 127 | } |
| 128 | } |
| 129 | |
| 130 | //---------- |
| 131 | |
| 132 | template < typename keytype, typename hashtype > |
| 133 | bool DiffTest ( pfHash hash, int diffbits, int reps, bool dumpCollisions ) |
| 134 | { |
| 135 | const int keybits = sizeof(keytype) * 8; |
| 136 | const int hashbits = sizeof(hashtype) * 8; |
| 137 | |
| 138 | double diffcount = chooseUpToK(keybits,diffbits); |
| 139 | double testcount = (diffcount * double(reps)); |
| 140 | double expected = testcount / pow(2.0,double(hashbits)); |
| 141 | |
| 142 | Rand r(100); |
| 143 | |
| 144 | std::vector<keytype> diffs; |
| 145 | |
| 146 | keytype k1,k2; |
| 147 | hashtype h1,h2; |
| 148 | |
| 149 | printf("Testing %0.f up-to-%d-bit differentials in %d-bit keys -> %d bit hashes.\n",diffcount,diffbits,keybits,hashbits); |
| 150 | printf("%d reps, %0.f total tests, expecting %2.2f random collisions",reps,testcount,expected); |
| 151 | |
| 152 | for(int i = 0; i < reps; i++) |
| 153 | { |
| 154 | if(i % (reps/10) == 0) printf("."); |
| 155 | |
| 156 | r.rand_p(&k1,sizeof(keytype)); |
| 157 | k2 = k1; |
| 158 | |
| 159 | hash(&k1,sizeof(k1),0,(uint32_t*)&h1); |
| 160 | |
| 161 | DiffTestRecurse<keytype,hashtype>(hash,k1,k2,h1,h2,0,diffbits,diffs); |
| 162 | } |
| 163 | printf("\n"); |
| 164 | |
| 165 | bool result = true; |
| 166 | |
| 167 | result &= ProcessDifferentials(diffs,reps,dumpCollisions); |
| 168 | |
| 169 | return result; |
| 170 | } |
| 171 | |
| 172 | //----------------------------------------------------------------------------- |
| 173 | // Differential distribution test - for each N-bit input differential, generate |
| 174 | // a large set of differential key pairs, hash them, and test the output |
| 175 | // differentials using our distribution test code. |
| 176 | |
| 177 | // This is a very hard test to pass - even if the hash values are well-distributed, |
| 178 | // the differences between hash values may not be. It's also not entirely relevant |
| 179 | // for testing hash functions, but it's still interesting. |
| 180 | |
| 181 | // This test is a _lot_ of work, as it's essentially a full keyset test for |
| 182 | // each of a potentially huge number of input differentials. To speed things |
| 183 | // along, we do only a few distribution tests per keyset instead of the full |
| 184 | // grid. |
| 185 | |
| 186 | // #TODO - put diagram drawing back on |
| 187 | |
| 188 | template < typename keytype, typename hashtype > |
| 189 | void DiffDistTest ( pfHash hash, const int diffbits, int trials, double & worst, double & avg ) |
| 190 | { |
| 191 | std::vector<keytype> keys(trials); |
| 192 | std::vector<hashtype> A(trials),B(trials); |
| 193 | |
| 194 | for(int i = 0; i < trials; i++) |
| 195 | { |
| 196 | rand_p(&keys[i],sizeof(keytype)); |
| 197 | |
| 198 | hash(&keys[i],sizeof(keytype),0,(uint32_t*)&A[i]); |
| 199 | } |
| 200 | |
| 201 | //---------- |
| 202 | |
| 203 | std::vector<keytype> diffs; |
| 204 | |
| 205 | keytype temp(0); |
| 206 | |
| 207 | SparseKeygenRecurse<keytype>(0,diffbits,true,temp,diffs); |
| 208 | |
| 209 | //---------- |
| 210 | |
| 211 | worst = 0; |
| 212 | avg = 0; |
| 213 | |
| 214 | hashtype h2; |
| 215 | |
| 216 | for(size_t j = 0; j < diffs.size(); j++) |
| 217 | { |
| 218 | keytype & d = diffs[j]; |
| 219 | |
| 220 | for(int i = 0; i < trials; i++) |
| 221 | { |
| 222 | keytype k2 = keys[i] ^ d; |
| 223 | |
| 224 | hash(&k2,sizeof(k2),0,&h2); |
| 225 | |
| 226 | B[i] = A[i] ^ h2; |
| 227 | } |
| 228 | |
| 229 | double dworst,davg; |
| 230 | |
| 231 | TestDistributionFast(B,dworst,davg); |
| 232 | |
| 233 | avg += davg; |
| 234 | worst = (dworst > worst) ? dworst : worst; |
| 235 | } |
| 236 | |
| 237 | avg /= double(diffs.size()); |
| 238 | } |
| 239 | |
| 240 | //----------------------------------------------------------------------------- |
| 241 | // Simpler differential-distribution test - for all 1-bit differentials, |
| 242 | // generate random key pairs and run full distribution/collision tests on the |
| 243 | // hash differentials |
| 244 | |
| 245 | template < typename keytype, typename hashtype > |
| 246 | bool DiffDistTest2 ( pfHash hash ) |
| 247 | { |
| 248 | Rand r(857374); |
| 249 | |
| 250 | int keybits = sizeof(keytype) * 8; |
| 251 | const int keycount = 256*256*32; |
| 252 | keytype k; |
| 253 | |
| 254 | std::vector<hashtype> hashes(keycount); |
| 255 | hashtype h1,h2; |
| 256 | |
| 257 | bool result = true; |
| 258 | |
| 259 | for(int keybit = 0; keybit < keybits; keybit++) |
| 260 | { |
| 261 | printf("Testing bit %d\n",keybit); |
| 262 | |
| 263 | for(int i = 0; i < keycount; i++) |
| 264 | { |
| 265 | r.rand_p(&k,sizeof(keytype)); |
| 266 | |
| 267 | hash(&k,sizeof(keytype),0,&h1); |
| 268 | flipbit(&k,sizeof(keytype),keybit); |
| 269 | hash(&k,sizeof(keytype),0,&h2); |
| 270 | |
| 271 | hashes[i] = h1 ^ h2; |
| 272 | } |
| 273 | |
| 274 | result &= TestHashList<hashtype>(hashes,true,true,true); |
| 275 | printf("\n"); |
| 276 | } |
| 277 | |
| 278 | return result; |
| 279 | } |
| 280 | |
| 281 | //---------------------------------------------------------------------------- |