Over the past week there have been multiple attacks on smaller Ethereum based blockchains like Shift and Krypton. Both blockchains were forked due to 51% attacks combined with DoS attacks against nodes.
The Krypton blockchain was recently hijacked and nearly switched over to a non-Ethereum based POS chain, as an emergency solution. As it turns out, Krypton will be staying as an Ethereum based POW chain because an alternative solution was found.
Recently, Professor Emin Gün Sirer from Cornell University, offered a temporary solution to Krypton founder, Stephanie Kent when she reached out for advice. The fix is called Checkpoint Lockin and was something that Bitcoin used when it was a young network.
Checkpoint Lockin was introduced by Satoshi as a way to defend Bitcoin against DoS attacks on the network. It did this by occasionally hard coding an old block hash into the software. Any fork of the chain that does not include that block hash will become invalid, even if the chain is longer.
Smaller blockchains may want to include these checkpoints to prevent these types of attacks until their networks grow. Bitcoin no longer uses them due to its incredible network size and hash rate.
According to Professor Sirer, checkpoints are only a temporary solution to the problem because they do add an element of centralization. Those who hold the keys to the checkpoints are in a position of authority and can override forks, as well as launch their own double spend attacks.
Fixing the Problem
Both Krypton and Shift developers are working together and sharing upgrades to regain control of their networks. Trading, deposits and withdrawals will resume as soon as the problem is resolved.
Although attacks against smaller blockchains are unfortunate, they can be used as case studies for the entire industry. Smaller altcoins can be grounds for experimentation without placing large sums of capital at risk.