[Cryptech Tech] counter data

Bernd Paysan bernd at net2o.de
Thu Aug 21 20:53:08 UTC 2014


Am Donnerstag, 21. August 2014, 22:06:49 schrieb Fredrik Thulin:
> On Thursday, August 21, 2014 09:52:55 PM Bernd Paysan wrote:
> > Am Donnerstag, 21. August 2014, 17:51:28 schrieb Fredrik Thulin:
> > > Here is the private e-mail with raw counter data from my entropy source.
> > 
> > Thanks.
> > 
> > > Sorry for the 14MB e-mail.
> > 
> > Don't worry, that's the e-mail server I maintain myself, so it can handle
> > that stuff.
> 
> Good =).
> 
> I changed the counter to run up to 0xff before resetting, and have been
> gathering about 5.9M values of the timer when the rising edge occurs over
> the last 2.5 hours.
> 
> I'm going to leave it running but I think there might be an
> overrepresentation of about 16 groups of digits. Look at the attached
> histogram - looks suspect to me. I wonder if it is the noise source or the
> MCU that introduces this, or if it will go away with more samples.

I've processed the data you sent me, and there's clearly some pattern to be 
seen.  I've plotted this y axis logarithmic - it's the deltas between 
consecutive counters converted to a histogram.

The 114 is much overrepresented, and that's because that's the bucket for all 
the transitions which are faster than you can measure them.  This also causes 
your low output bandwidth, because repeated 114 will get filtered out.

The remaining pattern looks like the MCU has counter values which are much 
more likely to be detected than others.

This means: You will get much better results if you use a predictable capture 
counter in an FPGA (or a higher end fast microcontroller), i.e. count until 
the intput changes, then store the counter in RAM, increment the pointer and 
reset the counter - until the RAM is full, and you can wait for the external 
readout to take the sampled data.

Apart from these artefacts (controller too slow, high likely/low likely timer 
values), the data looks good; an exponential cutoff for higher delays is 
expected.

Sent also on tech at cryptech.is, so that others can comment.  This is now data 
in a form that doesn't clutter up the mailing list archive.

-- 
Bernd Paysan
"If you want it done right, you have to do it yourself"
http://bernd-paysan.de/
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114 1042259 
115 54665 
116 22403 
117 109308 
118 109237 
119 22523 
120 56162 
121 164091 
122 54259 
123 21975 
124 105728 
125 105582 
126 21076 
127 52173 
128 154483 
129 50850 
130 20465 
131 99260 
132 97830 
133 19659 
134 47915 
135 140859 
136 46019 
137 18732 
138 90451 
139 88372 
140 18024 
141 43992 
142 128133 
143 42097 
144 17061 
145 81292 
146 80138 
147 16297 
148 39483 
149 114901 
150 37664 
151 91251 
152 74070 
153 72046 
154 16877 
155 37869 
156 103974 
157 34639 
158 17212 
159 66365 
160 64016 
161 14943 
162 33467 
163 91554 
164 30670 
165 15259 
166 58752 
167 56632 
168 13418 
169 29559 
170 80906 
171 27038 
172 13410 
173 51152 
174 49773 
175 11788 
176 26168 
177 71015 
178 23510 
179 11830 
180 44701 
181 43578 
182 10339 
183 23152 
184 61654 
185 53433 
186 10764 
187 39322 
188 38161 
189 9584 
190 19971 
191 54294 
192 18735 
193 9526 
194 34356 
195 33764 
196 8607 
197 17620 
198 47066 
199 16235 
200 8237 
201 29607 
202 29266 
203 7653 
204 15087 
205 40732 
206 14450 
207 7456 
208 25846 
209 25366 
210 6638 
211 13276 
212 35357 
213 12488 
214 6361 
215 22580 
216 21888 
217 5723 
218 11496 
219 30541 
220 10873 
221 5758 
222 21213 
223 18933 
224 5053 
225 9973 
226 26348 
227 9433 
228 4884 
229 16403 
230 16435 
231 4357 
232 8767 
233 22435 
234 8091 
235 4332 
236 14343 
237 13990 
238 3791 
239 7422 
240 19367 
241 6933 
242 3815 
243 12255 
244 11858 
245 3291 
246 6436 
247 16523 
248 5806 
249 3258 
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251 10248 
252 2788 
253 5492 
254 14217 
255 5205 
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257 8847 
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259 2413 
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261 12014 
262 4364 
263 2425 
264 7707 
265 7618 
266 2175 
267 4078 
268 10675 
269 3909 
270 2100 
271 6825 
272 6646 
273 1918 
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275 9179 
276 3243 
277 1990 
278 5838 
279 5645 
280 1643 
281 3111 
282 7972 
283 2852 
284 1651 
285 5014 
286 4901 
287 1409 
288 2682 
289 6866 
290 2521 
291 1331 
292 4485 
293 4167 
294 1201 
295 2219 
296 5806 
297 2014 
298 1207 
299 3598 
300 3587 
301 1036 
302 1948 
303 5020 
304 1845 
305 1067 
306 3149 
307 3024 
308 863 
309 1704 
310 4161 
311 1544 
312 938 
313 2693 
314 2645 
315 802 
316 1505 
317 3590 
318 1377 
319 752 
320 2363 
321 2282 
322 710 
323 1252 
324 3176 
325 1223 
326 691 
327 2059 
328 1957 
329 571 
330 1078 
331 2580 
332 1027 
333 638 
334 1675 
335 1662 
336 529 
337 986 
338 2346 
339 885 
340 536 
341 1508 
342 1467 
343 449 
344 843 
345 2074 
346 738 
347 453 
348 1266 
349 1245 
350 393 
351 697 
352 1753 
353 637 
354 392 
355 1058 
356 1005 
357 331 
358 588 
359 1433 
360 564 
361 335 
362 903 
363 873 
364 282 
365 460 
366 1257 
367 472 
368 284 
369 856 
370 822 
371 210 
372 439 
373 1037 
374 414 
375 253 
376 732 
377 676 
378 219 
379 398 
380 888 
381 371 
382 198 
383 555 
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385 169 
386 319 
387 762 
388 317 
389 181 
390 510 
391 536 
392 183 
393 303 
394 707 
395 295 
396 138 
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398 459 
399 130 
400 238 
401 591 
402 221 
403 132 
404 370 
405 377 
406 122 
407 231 
408 522 
409 182 
410 111 
411 326 
412 287 
413 107 
414 187 
415 426 
416 182 
417 104 
418 275 
419 289 
420 88 
421 156 
422 344 
423 157 
424 103 
425 251 
426 239 
427 82 
428 137 
429 306 
430 111 
431 87 
432 204 
433 213 
434 77 
435 107 
436 307 
437 113 
438 67 
439 173 
440 201 
441 54 
442 102 
443 238 
444 94 
445 48 
446 143 
447 130 
448 50 
449 86 
450 194 
451 81 
452 46 
453 120 
454 128 
455 47 
456 82 
457 182 
458 52 
459 31 
460 100 
461 132 
462 34 
463 59 
464 136 
465 61 
466 33 
467 98 
468 78 
469 26 
470 40 
471 129 
472 52 
473 17 
474 78 
475 66 
476 33 
477 46 
478 107 
479 41 
480 32 
481 73 
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483 21 
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487 25 
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491 44 
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