Reading assignment: Hashing

[Mauro]

@acey

2. Why is this hashing algorithm really hard (almost impossible) to brute-force?

An attacker might be interested in ‘rehashing’ a block of transaction data so it can be modified (adding a fraudulent transaction or undoing a payment) and then submitted back to the blockchain. To do this they would have to brute force attack the SHA-256 algorithm which means executing it many times on guesses of what the data could be, to eventually find a matching hash confirming the data. This isn’t impossible but is considered infeasible because of the vast computational power it would require. In addition to this, every subsequent block in the blockchain would need to be re-hashed to hide the modification as they each contain a hash of the previous block.

When you modify a block in bitcoin, you don’t need to brute force SHA-256. You just need to be faster than the rest of the network to preform the attack. Once you catch up with the current chain with a modified block you push your longer chain, which everyone will accept. But trying to know the input that generate a hash is impossible to brute force.

[Mauro]

Yep. Grab yourself a coffee and start on learning. GMC is the best. xD

[Conrad_Swart]

Thank you Fabijanić!

[GabrielCrypto]

He live, he learn You’re welcome Mauro

[syrafa]

1. Sha-256
2. it is infeasible to brute-force Sha-256 because one would need to guess a value for k in the function H(k|x) = Y with a value for Y given as the output from the previous block 2^128 times in the worst case scenario to get to the right answer. This would take multiple generations to achieve.

[vdxART]

1. What is the hashing algorithm called used in Bitcoin?

SHA-256

2. Why is this hashing algorithm really hard (almost impossible) to brute-force?

The amount of ressources (time and hashpower) would be ridiculous in the worst scenario that you would find the private key at the last combination; after 2^128 – 1 times.
Simply said 1 out of 2^128 is the right answer, try finding a specific atom in the whole galaxy.

[vale_dinap]

— My answers —

1. SHA-256
2. It’s pre-image resistant, the amount of values that should be attempted in order to guess the origin of the hash is enormous.

[strenev]

1. SHA256
2. Because the possible inputs are a so many, that it would take so much time to guess that it wouldn’t make sense to do it

[Drift]

1. What is the hashing algorithm called used in Bitcoin?
   Sha256
2. Why is this hashing algorithm really hard (almost impossible) to brute-force?
   Too many possibilities to enter, it would be a waste of time.

[Long]

1. SHA-256 (Secure Hashing Algorithm 256)
2. The brute-force method basically means that you have to pick up a random input, hash it and then compare the output with the target hash and repeat until you find a match. In reality, this would be so astronomically difficult and take so long that it would be infeasible given the amount of data.

[Flaflaflohi]

1. What is the hashing algorithm called used in Bitcoin?

SHA-256

2. Why is this hashing algorithm really hard (almost impossible) to brute-force?

Because the brute force method involves taking some random input and seeing if it matches the output hash, and then repeating until you are successful. Because the amount of data Is so large (256-bit hash), this is too time consuming to do.

[Griz]

1. Secure Hash Algorithm - 256 or SHA-256.

2. Brute force means to literally guess the correct hash out of 2^256 possibilities. It would take so long to guess the correct hash or to find a collision, it would no longer matter.

[Xhosa]

1. What is the hashing algorithm called used in Bitcoin?
   Sha-256
2. Why is this hashing algorithm really hard (almost impossible) to brute-force?
   Small changes in input changes the whole output, this makes the function pre-image resistant. For one person to guess the hash it would take generations guessing 24hrs a day.

[kat55]

What is the hashing algorithm called used in Bitcoin?
SHA256

Why is this hashing algorithm really hard (almost impossible) to brute-force?
Lots of computation and randomness, the possibilities become so huge, unlikely to ever match.

[knottymoose]

1. What is the hashing algorithm called used in Bitcoin?
   SHA-256 (Secure Hashing Algorithm)

2. Why is this hashing algorithm really hard (almost impossible) to brute-force?
   The more data sets that are added to a hashing algorithm, the harder it is the brute force. To brute force, you must know change the input and hash it until the output matches the hash you are attempting to brute force. It is almost impossible as it would be extremely time consuming and potentially you couldn’t crack one in your lifetime, however it is possible that you get lucky and choose the correct combination quickly.

[JennM]

1. SHA 256
2. The hashing algorithm is really hard, almost impossible to brute-force, because you would have to pick up a random input, hash it then compare the output with the target hash, then repeat until you found a match. This could take too long to matter or allow for the efficiency of bitcoin.

[Dhamma]

1. sha 256

2. It will take a very long time .

[MarcusG]

1. What is the hashing algorithm called used in Bitcoin?

SHA-256

2. Why is this hashing algorithm really hard (almost impossible) to brute-force?

The brute-force method implies picking up a random input, hash it and compare the output with the target hash. It is repeated until a match is found.

In SHA-256, a 64 character string output hash has 2^256 possibilities. Hence, finding a match would require massive amount of time and computational power, making it really hard to brute-force.

[Brett_Schor]

1. The hashing algorithm in Bitcoin is SHA-256.
2. Is it practically impossible to brute force because it has extremely high collision resistance.

[Bren509]

1. Bitcoin uses the SHA-256 hashing algorithm
2. Guessing a hashing algorithm with the brute force method is basically impossible because it would take an unrealistic amount of time to come to the right answer.