Homework on Hash Functions - Questions

Blockchain and Bitcoin 101
#2231

  1. Can go from input to output but almost impossible to go from output to input. each unique input always produces the same output, it is deterministic.

  2. Used to link blocks together. To verify validity of transactions. To create a proof of work system. To verify data integrity.

  3. So that 2 inputs are unlikely to create the same output.

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#2232

  1. Hash function has a unique input which generates a unique output. Output cannot be use to deduce input due to its “one way traffic” property.

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

  3. It means that input will always generate a different output regardless how minor the differences are in an input. Otherwise one can break/hack Bitcoin which mean it will make Bitcoin unsafe and unreliable as a cryptocurrency.

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#2233

  1. Hash function is a special function that change an input to an output as a fingerprint and can’t be reversed back to the input

  2. Hash function is processed by miners. They calculate the output of the function from the input of the transaction. This is how it is being used in bitcoin. The results are recorded in the block. A series of block is called blockchain

  3. It means that any two inputs should not produce the same output. An output is only a result of an input.

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#2234
  1. Hash function is a mathematical equation that makes it virtually impossible to work back from the output to determine the input.

2… Hash function is used to compact the data stored on the block chain and is also used to easily find a transaction and confirm its validity. it is also an integral part of the security as each hash is connected it makes it virtually impossible to hack. It is also used in the mining process to ensure no underhanded approaches are taken to mining, To me hashing is the backbone of crypto currency as once the hash is broken the currency becomes vulnerable.

  1. collision resistance is more or less determined by the distribution entropy the higher the distribution entropy the higher the collision resistance will be.
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#2235
  1. Describe hash functions with your own words

A hash function is a function that is a one-way street. You put an input (no matter the size) and you get a similar length in characters output. It doesn’t go the other way, especially using SHA-256. It’s a unique finger print on the data that is being brought into the blockchain. And even the smallest of changes, the hash function will generate a brand new string of characters applied to it. And if you revert back to what it was before you’ll get the same hash returned back to you from before. This part of hash functions helps keep the integrity and validity of the data on the blockchain secure.

  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 functions are used in cryptocurrencies, like bitcoin as a way to keep all the transactions secure because a hash function ability to take any sized input and return back the output massively. And also, the hash function is one-way making it infeasible to reverse engineer the transaction on the blockchain. It also plays a big part in mining bitcoin as well.

  1. 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).

A hash function needs to be collision resistant because if a hash contains the same output for numerous different inputs, then it makes the probability of finding what input you are searching for much higher. Also, if it’s not collision resistant it can cause major crashes in systems.

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#2236

Hash functions takes an input of data of any lenght and calculates an output hash of a fixed lenght. The same input will always produce the same output hash. Like an unique fingerprint of some data. It’s practically impossible to calculate the input from the output. Also, if you only change 1 character in the input, the hash will be totally different. These properties are perfect to use in Bitcoin. Because if you would change something in a bitcoin block, the hash of the block will be completely different.

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#2237

  1. Describe hash functions with your own words
    It is a function which converts one value into another. The output is of fixed length.

  2. How are hash functions used in cryptocurrencies like bitcoin?
    The function operates only in one direction. ie inputs resulting in an output of fixed length.
    Also it is a fast operation. It is also collision resistant.

  3. What does it mean when we say that hash functions need to be collision resistant?
    It makes it difficult for to find two values of the same lenght that result in the same hash.
    This means that it is second pre-image resistant.

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#2238
  1. Describe hash functions with your own words

Hash functions are a type of function that produce a unique output for a given string of text. They are uni-directional meaning that for a given output the input can not be determined.

  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 functions are the foundation for cryptocurrencies like Bitcoin. They are used to produce a unique identifiers (that meet a predetermined criteria) for blocks (and subsequent transactions) through computational work to ensure the contents of the ledger are tamper proof. Malicious actors attempting to alter the state of the blockchain would need enough computational power (51%) to alter the state of the longest chain. Hash functions are ensure this work must be completed because the hash functions used in Bitcoin are cryptographic has functions. In Bitcoin, the unique identifier produced for each block is known as proof-of-work.

  1. 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 means that the likelihood of two hashes producing the same input is extremely unlikely. The higher the entropy of the system (i.e. possible inputs), the lower the likelihood of collision, and thus the higher the collision resistance.

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#2239

  1. A hash function is a mathematical method of providing a unique fingerprint for any given data input.

  2. Cryptocurrencies use hash functions to facilitate peer to peer transactions that are transparent and immutable. They also allow “proof of work” which is essential to mining.

  3. “Collision resistant” means nobody can find the hash of two separate values. Although nobody can find it, it doesn’t mean that the hash does not exist.

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#2240
  1. Hash functions take string as a input and convert it into unique, fixed length output in one-way process.
  2. Hash functions are fundamental for bitcoin. They are used to encrypt data and ensure immutability of transactions. They are also key concept in mining.
  3. Hash functions are collision resistant if there isn’t any significant possibility of the same output from different inputs.
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#2241
  1. Hash function - function which converts input of any size to a fixed unique output which is almost impossible to reverse.
  2. Hash functions are used to write new transactions into the blockchain trough mining process.
  3. So that hashing algorithm will not generate the same key(output) for a and b, two different inputs.
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#2242

Yes yes youre right, it should be INPUT :slight_smile:

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#2243

Hi Fabrice! Thank you for reading my answer and for elaborating. I really appreciate it. I wanted to simplify my answer as much as possible. :sweat_smile:

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#2244

  1. Hash functions are unique digital finger prints. They are functions which take a unique input and produce a unique output however, they can now take an output and give you an input.

  2. Hash function SHA-256 is a secure hashing algorithm used in the bitcoin blockchain. Since it is essentially a unique string of computations which links each block together in chronological order, if even the smallest detail of one hash is tampered with, the next block will be altered, as well as every block that follows after that one. Due to consensus, nodes running the blockchain will notice this immediately and will not verify the modification. Hence, no modification will be validated. This creates immense security for accuracy of data within wallets.

  3. Collision resistance means each input will have its own unique hash. Having two different inputs that result in the same hash is know as a collision.

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#2245

  1. Hash functions are one way functions, easy to calculate the output from given input, impossible to calculate the input from an output. small changes in the input result in completely different output which makes it a one-way function.

  2. hash functions are used to validate all the data in the blocks. any change in the data will result in an invalid hash. hash function is also used in the mining process to randomly select the block producer.

  3. collision resistant means there are very few collision (multiple inputs that generate the same output). the fewer the better, if it take infinite amount of time to find the one and only input, it still takes a near infinite amount of time to find one of the collision inputs that will produce the same output too.

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#2246

  1. a function that can take as an input any alphanumeric string and converts it into a fixed-length, unique “data fingerprint” for that initial string. Small changes in input generate completely different outputs, same input always generates the same output. You can’t guess/find the input from the output.

  2. hash functions are part of the block hashing algorithm which is used to write new transactions into the blockchain through the mining process. To successfully ‘solve’ a block, miners try to combine all of the inputs with their own arbitrary piece of input data in such a way that the resulting hash starts with a certain number of zeroes.

  3. It’s very unlikely to have the same output from two different inputs.

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#2247

Hash functions are taking a string of text and converting it into a 256 bit for Bitcoin SHA or other form made up of numbers and letters.

Hash functions are used to hide your private key transactions by creating unique addresses. Also, used for public addresses too.

You can not have to identical addresses. You can’t have two inputs that produce 1 single output.

#2248

Hash functions are like a digital fingerprint where the hash is linked to the original data or input. The input can be anything and it generates a fixed number of letters and numbers.

They create a unique hash for a transaction.

Collision resistant means you can’t figure the input from the outputted hash.

#2249
  • Describe hash functions with your own words

A hash function converts data of arbitrary length to a fixed length

  • How are hash functions used in cryptocurrencies like bitcoin?

Transactions are taken as input an ran through as HA (SHA-256) which gives a desired output of a fixed length.

  • What does it mean when we say that hash functions need to be collision resistant?

A hash function becomes collision resistant when its too difficult to locate to inputs that hash to the same output.

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#2250
  1. Describe hash functions with your own words.

One-way functions where given an input creates an output that is impossible to calculate the input from the output, it generates a completely different output when you slightly change the input.

  1. How are hash functions used in cryptocurrencies like bitcoin?

They are used to validate transactions in the blocks. If data is changed inside any block it will result in invalid hash.

  1. What does it mean when we say that hash functions need to be collision resistant?

It means that it is very unlikely for two inputs to produce the same output.

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