3. Server seed + Roll result method.

Server seed can change every roll or be fixed.

Roll result is pre-generated by the site before bet is made (method for generating roll result may be unknown/unpublished, but it is in the best interests of the site if it is properly random, otherwise someone could predict the patterns and ruin them)

Server seed + roll result are combined, SHA256/512 hash calculated and provided prior to bet being made as proof. NO Client Seed is used or required.

Once bet is submitted the server seed + roll result are shown (along with the previous hash for verification purposes)... new hash for next seed/roll result is generated and provided.

Server knows reach roll result BEFORE you place a bet, BUT CANNOT CHANGE IT, because that would break the server seed hash.

ParaDice.io is using this method.

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In any case, in ALL of these methods, even the ones where the server is pre-generating the result like ParaDice.io... the server cannot possibly change anything that the hash is related to, after it has been provided to the player. The maths of SHA256 (and 512 as applicable) make it, for all intents and purposes, impossible for them to modify anything... as (ironically) pointed out by MafiaCoin in his "Scam" accusation, if they change anything, it breaks the hash calculation.