That was the old method - it was too confusing and still could me manipulated with expensive super computers.
"ec" is just part of the hash. Each payment will have a hash 1-9 and a-f. All mixed up. The draw hash is compared to transaction hashes to find the winner. The hash can not be predicted or controlled since mega millions numbers are added after all the payments are in.
Ah alright, just I misinterpreted "digit" as a traditional 0-9 number, not as a hexadecimal digit.
I see you transfer the payment via 1 bitcoin transactions, that's an odd way to do it.
1% is a really small operator's fee, it might be wise to take a bit more to invest in advertising and to put some coins as the jackpot minimum at the start of every round.
both would benefit the players after all