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The 51% Attack Nightmare Scenario (Isn't That Bad)
An accessible, in-depth look at what's really at risk when Proof-of-Work or Proof-of-Stake blockchains suffer the dreaded 51% attack.

On this Speaking of Bitcoin episode, join hosts Adam B. Levine, Andreas M. Antonopoulos, Stephanie Murphy and Jonathan Mohan for an in-depth discussion about what's really at risk when blockchains suffer the dreaded 51% attack.
For more episodes and free early access before our regular releases, subscribe with Apple Podcasts, Spotify, Pocketcasts, Google Podcasts, Castbox, Stitcher, RadioPublica, iHeartRadio or RSS.
This episode is sponsored by Crypto.com, Bitstamp and Nexo.io.
On today's show we're talking 51% attacks, the much discussed, infrequently seen and fairly misunderstood doomsday scenarios. It's a topic of discussion that's recently re-emerged as Ethereum plans its transition to Proof-of-Stake and after fork Ethereum Classic was hit by its third in less than a month.
Although the numbers may change, basically any blockchain you can imagine is vulnerable to some form of the so-called 51% attack. By distributing the power within a protocol, say to miners instead of a corporate board, blockchains and other decentralized systems create and maintain a "Consensus Reality" where what most of the network believes to be true is true, or becomes true for the entirety of the network.
See also: How Does Kraken's New Crypto Bank Work?
If you think about it, this makes sense. Each blockchain creates a game with a distinct set of rules that need to be followed for the thing to work. It requires lots of people who don't know each other to individually follow those rules and get rewarded by the system for doing so. The assumption underlying all of these systems is that most of the people are going to be compelled by the offered rewards to follow the rules. Even if a lot of people aren't following the rules, they're probably breaking them in different ways rather than working together.
In a 51% attack, that assumption is broken as most, or at least enough of the network is overcome by bad actors who aim to rewrite reality in their favor.
It's a real problem, one of the biggest blockchains face, especially less popular ones ... But even if you could pull one off, the outcome might not be as bad as many fear.
But what is actually at risk? What's possible and what's safe? Tune in to find out.
For more episodes and free early access before our regular releases, subscribe with Apple Podcasts, Spotify, Pocketcasts, Google Podcasts, Castbox, Stitcher, RadioPublica, iHeartRadio or RSS.
Adam B. Levine
Adam B. Levine joined CoinDesk in 2019 as the editor of its new audio and podcasts division. Previously, Adam founded the long-running Let's Talk Bitcoin! talk show with co-hosts Stephanie Murphy and Andreas M. Antonopoulos. Finding early success with the show, Adam transformed the podcast's homepage into a full newsdesk and publishing platform, founding the LTB Network in January of 2014 to help broaden the conversation with new and different perspectives. In the Spring of that year, he would go on to launch the first and largest tokenized rewards program for creators and their audience. In what many have called an early influential version of "Steemit"; LTBCOIN, which was awarded to both content creators and members of the audience for participation was distributed until the LTBN was acquired by BTC, Inc. in January of 2017. With the network launched and growing, in late 2014 Adam turned his attention to the practical challenges of administering the tokenized program and founded Tokenly, Inc. There, he led the development of early tokenized vending machines with Swapbot, tokenized identity solution Tokenpass, e-commerce with TokenMarkets.com and media with Token.fm. Adam owns some BTC, ETH and small positions in a number of other tokens.
