Reading assignment: Hashing

Blockchain and Bitcoin 101
#1447
  1. bitcoin uses SHA256 and RIPEMD160 (as seen in a previous lecture video)
  2. it would require a couple galaxies lifetimes of guessing as amount of possible inputs is bigger than the number of atoms in the universe (just for the SHA256), and thats just for guessing a single input
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#1448

SHA-256
Brute force could potentially take a very long time due to the slim probability of guessing the correct input.

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#1449

The hashing algorithm used in Bitcoin is called SHA-256 (or Secure Hashing Algorithm 256). The purpose of hashing algorithms like SHA-256 are to securely transfer data from one person to another in a way that, if a third party acquires the data, it is useless and uninterpretable.

Blockchain properties like hash pointersā€“a hashed version of the data inside the previous blockā€“make using a brute-force attack or some other hacking method counterproductive as the hacker would have to change the data in all the previous blocks. Such a method to find the correct input of one block would be both time-consuming and energy-intensive.

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#1450
  1. SHA- 256
  2. To select input and hash it then compare to output until you have a match would take same so long it is infeasible unless youā€™re the luckiest person in the galaxy.
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#1451

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?

A string of 256 bits of random characters are far too much, too long to brute force unless you are using quantum computer.

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#1452
  1. What is the hashing algorithm called used in Bitcoin?
  2. Why is this hashing algorithm really hard (almost impossible) to brute-force?
  1. SHA-256
  2. With brute-force method you will be randomly picking up input and comparing the output with the targeting hash for 2^127 times. This is astronomical and changes for it to break pre-image resistance and collision resistance is almost zero.
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#1453
  1. What is the hashing algorithm called used in Bitcoin?

SHA-256

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

the probability to break the hash is 1 / 2^256 technically impossible unless Quantum computing plays a role in it.

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#1454

  1. The hashing algorithm used in Bitcoin is called SHA-256

  2. SHA-256 algorithm is really hard to brute-force because every input has a unique hash function output and slightly changing an input will change the hash function output. It is near impossible to have the same hash function output from two different inputs.

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#1455

Iā€™m not exactly sure if I understand what you mean by that. But if the block hash does not satisfy the difficulty level than the nonce is changed and tried again. This process is repeated until correct hash is found :slight_smile:

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#1456

Hi @Stephen_Modica and welcome to the forum! :slight_smile: I think you have mistaken the question. It is true that we use hashes in that manner to maintain the generation of blocks. But is not the point of the question. :slight_smile:
The reason why hash functions are so hard to brute force is because of the shear amount of possible outcomes of the hash function because it produces such a large number.

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#1457

Homework: Hashing

  1. SHA-256
  2. Hashes are random strings that could be anything. Itā€™s very hard primarily because of the difficulty adjustment thatā€™s adjusting every two weeks to make it easier or harder to generate 10min blocks.
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#1458
  1. SHA-256
  2. Because you may need to guess about 2^127 to 2^128 times. Which is a very big number.
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#1459

  1. SHA-256

  2. It could take multiple lifetimes to come up with the input string that produced the hash using brute force.

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#1460
  1. sha-256
  2. The chances to find input based on output are astronomical.
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#1461
  1. SHA 256
  2. because its 2^256 possiblilities. thats need an much amount of power to bruteforce this
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#1462
  1. SHA 256
  2. To brute-force the hashing algorithm you would have to take to take a random input, hash it, and compare to the actual hashed output. You would have to continue doing this until you got a match. With a 256 bit length to the output, it would require for a middle of the data estimate, 2^256/2 iterations, or 2^257. This is a huge number and multiplied by the average time to do the iteration would result in an unacceptable long period of time.
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#1464

  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 SHA-256 hashing algorithm has pre-image resistance properties and thus is infeasible to ā€œbrute-forceā€. What pre-image resistance states are that given H(A) it is infeasible to determine A, where A is the input and H(A) is the output hash. 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. Your best case scenario of guessing the correct input on the first try would be 1/2^256 chances. Your worst case scenario of guessing the correct input by trying every input would take 2^256-1 attempts. Your average case scenario of finding the correct input in the middle would take 2^255 attempts.

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#1465

  1. SHA 256 is the hashing algorithm used in Bitcoin

  2. The computational possibilities are so great that makes it almost impossible to brute-force.

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#1466

What is the hashing algorithm called used in Bitcoin?

  1. SHA-256

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

  1. Without knowing the input value, it is infeasible to find the output value without
    a huge computational effort
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#1467

1/ SHA 256

2/ Because there are so many possibilities of computations it would be almost impossible to guess the correct result. It would be almost like trying to guess someoneĀ“s fingerprint!

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