<a href="https:&#x2F;&#x2F;en.bitcoin.it&#x2F;wiki&#x2F;Altcoin#Proof_Of_Stake" rel="nofollow">https:&#x2F;&#x2F;en.bitcoin.it&#x2F;wiki&#x2F;Altcoin#Proof_Of_Stake</a><p><pre><code>  Because these attacks exists, including Peercoin[3] and Blackcoin[4] proof of stake cryptocurrencies have &quot;master&quot; public keys that control the blockchain.
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I wonder who would control that ;)<p><pre><code>  This class of cryptocurrency is either insecure or centralized, however proof of stake (based on a PoW currency) is useful in some systems because gaining stake is costly, but it isn&#x27;t workable for bootstrapping distributed consensus.
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This would be an interesting though experiment. If they implemented proof of stake based on a proof of work currency, like Bitcoin, what would happen if the new currency took off and Bitcoin started to die? Now there&#x27;s a threat model that requires unmotivated miners to still secure the network, both networks.