Homework on Hash Functions - Questions

Blockchain and Bitcoin 101
#1185
  1. A hash function describes a function that computes a variable input and derives a fixed value output.
  2. In Bitcoin transactions, the input data is put through a hashing algorithm called Sha 256. A unique 256 bit string of fixed length is derived. This is a once off address/fingerprint and is irreversible. So any mistake with the address and the stakeholder will not be able to undo it. If a hacker wanted to alter this outcome it is infeasible. This is partly due to the hash pointer in the blockchain. This pointer contains the address and data of the previous block. Any alteration would create a domino effect of change that would be rejected. This renders the data virtually hacker proof. Otherwise Bitcoin would be defunct…
  3. An input in a HASH FUNCTION is variable so there is an infinite number of possibilities. In contrast the outcome is finite. It is mathematically certain that more that one input will produce the same output…
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#1186

  1. Hash function takes unique inputs and produces unique output. With bitcoin’s SHA-256 the input can be any length but the output will be a fixed length.

  2. The new unconfirmed bitcoin transactions are used as inputs and the hashing algorithms encrypts them those transactions into a hash which the miners attempt to calculate to mine bitcoin and the new block is then added to the chain.

  3. Collision resistant means it should be infeasible that to 2 inputs should generate the same output by the hashing algorithm.

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#1187

  1. A hash function takes an input and outputs a unique digital fingerprint (a number on a scale so large it is to all practical purpose unique)

  2. Bitcoin hashes the transactions in a block to create a unique digital fingerprint for that block. Each block will link to the hash of the previous block, hence any attempt to tamper with the data in a block will result in a different hash which will then break the blockchain

  3. Collision resistance means that a hash function must to all practical purposes give a unique output to every input. If two inputs can give the same output, then a collision has occurred. Although this is possible for any hash function, it must be suitably improbable so as to allow users confidence that the hash function can provide a unique digital fingerprint for any data that is hashed.

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#1188

1. Describe hash functions with your own words
Each unique Input produce a unique output.
BUT never output to input.

2. How are hash functions used in cryptocurrencies like bitcoin? (Try to research this on your own, we will cover this later in the course but challenge yourself and see if you can find information on this already now).

cryptocurrencies like bitcoin , the transactions are taken as input and run through a hashing algorithm ( bitcoin uses SHA-256) which gives an output of a fixed length. … So basically, instead of remembering the input data which could be huge, you can just remember the hash and keep track.
3. What does it mean when we say that hash functions need to be collision resistant? (We didn’t use the term “collision resistant” in the lecture, but you will easily find this on Google, we add this question intentionally to make you research information on your own, that’s how you learn best).

Collision resistance is a property of cryptographic hash functions : a hash function H is collision resistant if it is hard to find two inputs that hash to the same output; that is, two inputs a and b such that H(a) = H(b), and a ≠ b. … Cryptographic hash functions are usually designed to be collision resistant .

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#1189
  1. They take an input, compute it, and produce an output.

2.Data from previous block is included in the new block linking them together, this is what gives bitcoin immutability.

  1. The output of two different inputs can not be the same.
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#1190

1.Describe hash functions with your own words

  1. How are hash functions used in cryptocurrencies like bitcoin? (Try to research this on your own, we will cover this later in the course but challenge yourself and see if you can find information on this already now).

  2. What does it mean when we say that hash functions need to be collision resistant? (We didn’t use the term “collision resistant” in the lecture, but you will easily find this on Google, we add this question intentionally to make you research information on your own, that’s how you learn best).

A1. Hash functions is a unique identification like a digital fingerprint. Every input has a unique output that cannot be changed. If any part of the input is changed even by a space the unique output (hash) is changed. It’s only possible to hash from input to output and not in reverse.

A2. Hash functions are used in crypto currencies to create digital signatures. This is done through the process of using a hash algorithm.
When a message is sent through this algorithm it produces a digest value. A digest value is a result of the digest method which in itself is an algorithm used to calculate the digest value.

Once the original message is sent through this process it encrypts the digest to produce a digital signature (SHA256)

The recipient of the message will verify the signature by running it through the same hash algorithm process and decrypt the attached signature to confirm the digest is a match with the original value that was sent.

A3. Hash functions need to be collision resistant in order to prevent a hacker or anyone untoward from breaking the hash with ease.

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#1191

1- Hash functions will take an input and using a base 16 system create a 64 character string. This string is one way, you can always and only go from from input to output, never from output to input.

2- I believe that bitcoin uses hash functions by hashing a block of transactions, adding a nonce,
and then hashing again. The miners will attempt to guess this last hash and the one who guesses correctly wins the reward for verifying that block.

3- Collision resistant means that its highly improbable for two inputs to equal the same hashing output.

#1192

1 - They are functions that generate an unique output for a given input in the form of a string of alphanumeric characters.

2 - Hash functions are used to encode data in the blockchain, be it the pointers or the sequence of the transactions or nonce+key with is used to mine.

3 - Collision resistance means that it should be highly improbable (although not completely impossible) to get the same outcome from 2 different incomes in a hash function.

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#1193

  1. it is a function in which an input will generate a unique output, but the output cannot be used to determine the input

  2. hash functions are part of the block hashing algorithm which is used to write new transactions into the blockchain through the mining process

  3. two inputs of a hash function will not have the same output

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#1194

  1. Hash function is a computing algorhytm that produces a unique output for a unique input. It can only go one way i.e. from input to output and never the other way

  2. In the BTC protocol hash functions are used as a part of the blockchain. they’re used to write new transactions into the blockchain by the mining process

  3. collision resistant means that no 2 inputs will hash to the same output. each input will generate a unique output

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#1195
  1. Hash function is a function that produces a unique output (fingerprint), with each unique input. Hash functions are a one way functions meaning you can go from input to output but not other way round.
  2. In cryptocurrencies hash functions are used to take a sequence of letters of any length as input, and return a sequence of letters of a fixed length, whether the input is a single letter, word or sentence the output will always be the same length.
  3. A hash function is collision resistant if it is hard to find two inputs that hash to the same output.
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#1196

I like a lot your replies mate, I can see you have some previous knowledge in Coding!! Your replies helps me a lot to formulate my own anwers, tks and keep the Good work!! :=)

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#1197

  1. A hash function takes a unique input and provides a unique output. This output is like a digital fingerprint for the original input in the form of a hash. Hash functions are one-way functions because you can go from input to output, but not output to input.

  2. Hash functions are used in cryptocurrencies like Bitcoin in order to write new transactions into the blockchain during the mining process. The input are the most recent, not yet confirmed transactions.

  3. Collision resistance means that, for the most part, a unique input will have a unique output, or hash. This is important because an input’s hash is like it’s digital fingerprint. The hash of each input must be different in order to differentiate between them.

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#1198

Hi Mate, can you explain me what it is Pre-image resistant? tks

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#1199

1. Describe hash functions with your own words

  • It is a one way function that creates a unique string of alphanumerical values that comes out of a cryptographic blockbox which you cannot recover an input from an output given. The same input will always give the same output. The data will change drastically if it recognizes any changes in the Bitwise sensitive inputs in the original data set.it’s a real fast method, it’s collision resistant.
  1. How are hash functions used in cryptocurrencies like bitcoin? (Try to research this on your own, we will cover this later in the course but challenge yourself and see if you can find information on this already now).

Hash function are used to

#1200

1. Describe hash functions with your own words

  • A hash function is a mathematical calculation that will take an input and produce a unique output. This is a one way process.

2. How are hash functions used in cryptocurrencies like bitcoin? (Try to research this on your own, we will cover this later in the course but challenge yourself and see if you can find information on this already now).

  • Hash functions are used in the mining process. The block contents are hashed and concatenated with the nonce. This is hashed again and compared to the difficulty level. If it is less, the miner is rewarded bitcoin. If it is more, a new nonce is chosen and the process repeats.

3. What does it mean when we say that hash functions need to be collision resistant? (We didn’t use the term “collision resistant” in the lecture, but you will easily find this on Google, we add this question intentionally to make you research information on your own, that’s how you learn best).

  • Each input will have a unique output after it is hashed.
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#1201

This means that it is infeasible to determine the input based on the output hash. It could be achieved through brute force, but it would take a multiple lifetimes.

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#1202
  1. A hash function gives a unique digital output for any data input. It is a one-way function in that you can find output from input but never find input data from the output. Changing a small part of the input for a hash function results in a completely different output.
  2. Hash functions are used in the block hashing algorithm to write new transactions into the blockchain through the mining. Hash functions are used (with some additional data: the timestamp and a reference to the previous block) in bitcoin mining.
  3. A collision is finding two hashes with the same output from two different sets of data (inputs). It would take all of the computers in the world to work for millions of years to have a 99.8% chance that you could hack a hash algorithm, or rather to find a collision, where H(x)=H(y). But as this is such an infinitesimal period of time it is of no matter, as it is nigh on impossible to achieve.
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#1203

  1. Describe hash functions with your own words
    Hash functions allow us to get an output Y from an input X which considered as a one way and unique fingerprint, it is intended to secure the transaction or the message sent to a particular recipient.

  2. How are hash functions used in cryptocurrencies like bitcoin?
    Hash functions are used in mining in creating blocks, and create what we call a merkle tree where each non-leaf node is the hash of the values of their child nodes, the single node on the highest tier called top hash is the root node, this one is added to the block also the hash of the previous block is added the the current one.

  3. What does it mean when we say that hash functions need to be collision resistant?
    This mean that a function need to always get a unique output.

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#1204

Pre-image is basically the input before it was hashed. So Pre-image resistant means that it’s almost impossible to calculate the input from a given hash. The only way to achieve this is by brute forcing the hash. (Keep guessing and hashing until you find a match)

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