With "meaningful input" one usually means some prime number or the eg. first X digits of a constant like pi. (and if you chose a strange prime or constant, peop

With "meaningful input" one usually means some prime number or the eg. first X digits of a constant like pi. (and if you chose a strange prime or constant, people would also ask questions) This generally narrows down the options to something were relatively little trickery is possible: keep in mind that the eg. hashes used to break some encryption would have to be very specific so that the algorithm isn't trivially broken to begin with. The more important part about nothing-up-my-sleeve is really the justification for choosing a particular hash/number. If, let's say your algorithm needs a prime with at least 10 digits and you pick the first prime with 10 digits nobody asks questions. If you picked the 16th, then people would ask questions. Similarly, if you can pick any arbitrary ten digit number and you pick the first 10 digits of pi, nobody will ask questions. If you picked the million'th to million-and-tenth digit of pi people would asks questions. "meaningful" has to be understood more as "from a pool of constants that leave little room for (mallicious) adjustment". The abstracter the number, the higher the potentially used searchspace.