[a_tartaruga]

This isn't specified well enough to get detailed criticism. I don't know what you're hashing exactly but I think it includes purchase time. Depending on resolution of {Time of purchase of lottery} it might be very easy to manipulate.

[keepworking]

The idea was to list participants' purchase information in a byte array and hash them. I thought that the more participants there were, the more difficult it would be to induce the desired hash value to come out.