51% Attack - Meaning - Definition

[Mounty]

A 51% attack is a situation where more than half of the computing power on a blockchain network is operated by a single entity or group, which gives them complete and total control over the network.

Things that an entity with 51% of the computing power can do:

Halting all mining.

Halting and manipulating all interpersonal transactions.

Double Spending using singular coins over and over (this simply means that they can spend same coin/token money twice by deleting transactions from the Blockchain records).

the cost for doing a 51% attack  on a specific blockchain is  based on calculation by site below on 1/7/2018:

Name    Symbol    Market Cap    Algorithm    Hash Rate    1h Attack Cost    NiceHash-able
Bitcoin    BTC    $109.65 B    SHA-256    38,259 PH/s    $483,816    1%
Ethereum    ETH    $45.83 B    Ethash    231 TH/s    $314,888    4%
Bitcoin Cash    BCH    $12.73 B    SHA-256    4,538 PH/s    $57,382    10%
Litecoin    LTC    $4.60 B    Scrypt    282 TH/s    $47,811    6%
Monero    XMR    $2.10 B    CryptoNightV7    484 MH/s    $16,599    14%
Dash    DASH    $1.91 B    X11    1 PH/s    $12,299    45%
Ethereum Classic    ETC    $1.65 B    Ethash    11 TH/s    $15,484    78%
Zcash    ZEC    $700.54 M    Equihash    570 MH/s    $47,236    12%
Bytecoin    BCN    $549.28 M    CryptoNight    489 MH/s    $574    113%
Bitcoin Gold    BTG    $457.08 M    Equihash    19 MH/s    $1,611    345%
Dogecoin    DOGE    $290.12 M    Scrypt    208 TH/s    $35,339    9%
Bitcoin Private    BTCP    $230.57 M    Equihash    6 MH/s    $464    1,199%
MonaCoin    MONA    $124.57 M    Lyra2REv2    2 TH/s    $2,096    318%
Electroneum    ETN    $76.00 M    CryptoNightV7    76 MH/s    $2,613    89%
ZenCash    ZEN    $73.68 M    Equihash    62 MH/s    $5,175    107%
GameCredits    GAME    $40.95 M    Scrypt    2 TH/s    $290    1,042%
Vertcoin    VTC    $38.64 M    Lyra2REv2    757 GH/s    $644    1,033%
Ubiq    UBQ    $34.66 M    Ethash    200 GH/s    $272    4,430%
ZClassic    ZCL    $32.39 M    Equihash    29 MH/s    $2,363    235%
Unobtanium    UNO    $32.35 M    SHA-256    4,459 PH/s    $56,384    10%
Bitcoin Interest    BCI    $31.34 M    Equihash    2 MH/s    $171    3,259%
Litecoin Cash    LCC    $28.83 M    SHA-256    18 PH/s    $222    2,603%
Gulden    NLG    $28.48 M    Scrypt    1 TH/s    $232    1,300%
Einsteinium    EMC2    $27.39 M    Scrypt    110 GH/s    $19    16,218%

https://www.crypto51.app/ [nofollow]

[backfirst77]

Very good information in the field of mining. This will be very helpful for beginners about the term. So when mining has understood this situation. Thanks for the information.

[Munareal]

Attackers can interfere with the process of recording new blocks.   They disrupt the network and render it insecure. The bad actor could reverse transactions so as to engage in the nefarious act of double-spending.

[Raqeebzy]

Great explanation and spot on.
The era of random 51% attack is far approaching its end. At least to bitcoin and lots of top altcoins. The costs to launch a successful 51% attack for BTC is much more higher than it was back in 2018 and now, it is almost not feasible anymore. And also most projects taking to PoS algorithm is a stumbling block to 51% attack. The network are much more secured.

[Findingnemo]

A 51% attack is a situation where more than half of the computing power on a blockchain network is operated by a single entity or group, which gives them complete and total control over the network.

Things that an entity with 51% of the computing power can do:

Halting all mining.

Halting and manipulating all interpersonal transactions.

Double Spending using singular coins over and over (this simply means that they can spend same coin/token money twice by deleting transactions from the Blockchain records).

While I am exploring the forum I found this thread and I just wanted to say that this isn't accurate in terms of definition.

A 51% attack doesn't necessarily give control of the network completely, there has been lot of instances when a single mining pool of Bitcoin network crossed 51% but they chose to be loyal and focus on the block rewards instead of tampering and altering the network.

And also about double spending the attacker can spend the coins twice but its much more complicated since it requires precision to fork the chain by creating a separate private blockchain and then quickly switch to the other branch (the longer chain) to render the original transaction invalid.

[Z-tight]

And also most projects taking to PoS algorithm is a stumbling block to 51% attack. The network are much more secured.

Pos is not as secure as pow. Proof of stake algorithm is kind of centralized, and validators with a huge amount of staked coins become so powerful in the network and in deciding which tx's should be confirmed. It is easy to see how Ethereum moved from pow to pos and became much more centralized.

[Chilwell]

I also agree with what you said, Proof of stake (poS) is less secure than proof of work (poW), because proof of stake is more accessible to hackers, and it can also be controlled by unauthorized individuals. It gives access to the stakeholders which gives them the ability to dominate the network. Stake pools can become centralized, and it will allow or give access to some group of people to control the large part of network. It can lead to cartel formation, where validators collude to control the network.

[Pablo-wood]

Pos is less secure that pow because it is highly prone to centralisation issues where a users with larger stakes might try to control the network and this will put threats to this set of users trying to control the network.

[Baofeng]

Pos is less secure that pow because it is highly prone to centralisation issues where a users with larger stakes might try to control the network and this will put threats to this set of users trying to control the network.

And that's what happening to Ethereum already as this move to PoS and not it's more centralized and the power is only to those few who have high stakes.

For Bitcoin, I doubt that this 51% of attack will happen, it's too big for that kind as it will really take a lot of power to take over and so it really doesn't make sense for someone to "cleverly" pull it out.