Homework on Hash Functions - Questions

[Ayajib]

1. Hash functions are special functions in which each input gives out unique output. You can get out from any input but you cant trace back the input from output in hash functions.

2. Hash functions are used in crypto to generate unique output from a specific input. Hash functions prevents an output hash to be altered or erased after enough chain commands.

3. It means that two different inputs have a different output. Even when there is a slightest change in the input, there is a complete change in output.

[CryptoCredentials]

Hash functions are where a unique input always receives a unique output. Different hash functions produce different outputs even with the same inputs. Modifying the input even a tiny amount completely changes the hash output. Hash functions are used as cryptographic tools to provide security to a network and ensure finality as well as utility. Being collision resistant means that regardless of the obstacle the hash function retains its trustless solidity without having to question if there is an error.

[thehong]

1. hash function is used to create unique digital fingerprint
2. result from google: hashing means taking an input string of any length and giving out an output of a fixed length. In the context of 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.
3. Collision resistance means it’s almost impossible to have the same output in hash function.

[baxjamd]

1. Describe hash functions with your own words. Hash function is a special function takes data and outputs in 256 bit. Its completely unique like a fingerprint and cant be reversed.

2. Hash function are used by miners, whose computer hardware will compete to complete complex mathematical algorithms to produce the 256 bit hash function output. Once a hash functions is solved and confirmed its assigned as part of a block. Unique for storing transactional data.

3. What does it mean when we say that hash functions need to be collision resistant? They need to unique for every input, producing complete random output even in input is very similar ie. extra comma, space etc

[Stitch]

@ivan

• Describe hash functions with your own words

Hash functions are an algorithm that takes any input data provided and allocates it a hash value of a specific length.

@ivan

How are hash functions used in cryptocurrencies like bitcoin?

Blockchains use hash functions maintain the security of their data. This is done by using output hash values to verify transactions within each block and as a way of linking each block to the next block in the chain. In blockchains like Bitcoin hash functions are also used in proof of work consensus to verify when a miner secures a valid block.

@ivan

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

Being collision resistant means that it is extremely hard to find two input values that produce the same output hash value. This needs to be hard enough that a brute force attack is the only feasible option.

[Wevcl]

1. A hash function is a mathematically complex algorithm where only one input will yield a specific output. Hash functions are unidirectional. An output cannot be used to mathematically determine the input.
2. Hash functions are used in Blockchains to verify transactions and create blocks. The characteristics of a hash functions is what ensures Blockchains security.
3. “Collision Resistance” is an important characteristic of hash functions. Hash functions are “collision resistant” in that a hash function output cannot be produced by more than one input.

[phuongn]

1. Hash function accepts an input and produces an output through mathematical calculations. It differs from ordinary function because it’s nearly impossible to reverse the output to have the input.

2. Hash function in bitcoin is used as part of Proof-of-Work mecanism. Miners, in order to confirm bitcoin transactions, have to do a lot of mathematical calculation and each one of those is a hash function. The hash function’s output has to be lower than a target in order for the transaction to be confirmed, which requires a large number of trials.

3. Collision resistant means that it’s impossible to find two different inputs that produce the same output.

[AverageJoe]

1. Hash function are mathematical operations that cannot be reverse-calculated. You cannot start from the output and find out what the input(s) was/were. These can be used to securely verify the integrity of information because any change to the input(s) will result in a completely different output.

2. Hash functions are used in blockchain technology to verify the integrity of a transactions, verify UTXOs, verifying the recipient is who they say they are, etc.

3. They need to be collision resistant in order to stop them from being hacked/worked out. As soon as you have a collision in the hashing algorithm, the parameters of the calculation can be worked out, thus making that hashing algorithm unsecure.

[Maki]

@AverageJoe

verify UTXOs, verifying the recipient is who they say they are, etc.

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

[Gulaman]

1. A hash function is a mathematical process that takes input data of any size, performs an operation on it, and returns output data of a fixed size.
2. In the bitcoin protocol, hash functions are part of the block hashing algorithm which is used to write new transactions into the blockchain through the mining process.

In bitcoin mining, the inputs for the function are all of the most recent, not-yet-confirmed transactions (along with some additional inputs relating to the timestamp and a reference to the previous block).

Of course, solving the hash for a bitcoin block – which at the time of writing must start with 18 zeros – requires an extremely large amount of computation (and so the combined processing power of all the computers in the network still takes approximately 10 minutes to solve a block).

It’s the need for this large amount of processing power that means new bitcoins get mined over a long period of time, not all at once.

In order to earn bitcoins through mining, you need to put in the huge amount of work necessary to solve a block – and by earning that reward, you’re locking in all of the new transactions into a block, which is added to the permanent record of all previous transactions: the blockchain. (https://www.coindesk.com/bitcoin-hash-functions-explained)

3. Collision resistance is the property of a hash function that it is computationally infeasible to find two colliding inputs . This property is related to second preimage resistance, which is also known as weak collision resistance.

[Attiss]

1. Describe hash functions with your own words
   A hash function is a function which a) yields a unique output for every unique input, and b) is “one-way” in that you cannot deduce the input from knowing the output.

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 to write new transactions into the blockchain which are verifiably “random” and use a predictable amount of CPU energy.

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).
   It is hard (computationally impractical to find two inputs which hash to the same output.

[Ankun]

1. Hash functions are algorithms, which take some unique inputs of different length and produce unique outputs of the same fixed length, which are basically fingerprints of the inputs. Hash functions are one-way functions and there is no way to find the input based on the output.
2. In the bitcoin protocol, hash functions are part of the block hashing algorithm which is used to write new transactions into the blockchain through the mining process.
3. Collision resistance is a property of cryptographic hash functions: a hash function is collision resistant if it is hard to find two inputs that hash to the same output. Every hash function with more inputs than outputs will necessarily have collisions. Collision resistance is very important, because without it, the whole usefulness of a hash function is completely lost. If an attacker is able to create collisions, they can pass off malicious files or data as having a valid hash, and thereby as being legitimate.

[Sarcasshole]

1. Describe hash functions with your own words

a hash function is a computation which can only be solved unilaterally. It takes any input, and reliably outputs the same answer following calculations (if using the same input). Additionally, any change in the input will lead to a different output.

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

I believe hash functions are used for wallets, transactions and block creation for BTC. moreover, BTC uses a variable target for the hash output to coincide with a target of 1 block / 10 min. on average.

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

hash functions ideally give a unique output for most combinations of inputs in order to prevent reliably duplicate outputs. however, in any instance where inputs exceed possible outputs, duplicates will exist. The emphasis being that duplicates are very rare.

[Bourdier_Kidakan]

1. It is a one-way function that can be used to map data. It produces a digital fingerprint so there is never one output that is the same as another.
2. It is used in mining Bitcoin, it is the creation of new transactions that is put into the blockchain.
3. It is where it is difficult to find the same inputs that give us the same outputs.

[MichaelW]

1: Hash functions are a function that can go from input to output but cannot go from output to input this makes it a one way function.
2: Hash functions are used in Bitoin through mining for new transactions.
3: Collision resistant means two different transactions are not getting the same hash

[DvanDijk]

1. A hash function gives an unique output for every unique input and its impossible to reverse the output to input therefore it is safe.

2. It is used to make transactions safe and stored on the blockchain. It is also used in mining. If a miner can solve the puzzle of a new unconfirmed transactions he is able to create a new block and be rewarded in btc. The response string must be run as a hash function to get confirmed.

3. Collision resistant means that it is nearly impossible that 2 different inputs will resolve in the same hash function. If this will happen they have basically cracked btc.

[asheppy]

1. Hash functions take a set of inputs and map to a unique output that is not reversable.
2. Hash functions are used to verify data has not been tampered with in the past. Hashes from previous transactions are part of the next transaction making it possible to verify the entire blockchain past.
3. Collision resistant means that their are not more than one input mapped to the same output. This is important as it creates a unique finger print of a transaction.

[MoonBoy]

1. Describe hash functions with your own words
   Answer: A hash function is a function with an unique input and a unique output (unique finger print)
   with the same unique input you can always retrieve the same unique output but you can 't get the unique input via the unique outcome . In other functions this might be possible.

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).
   Answer: Hash functions in Crypto such as Bitcoin make use of the SHA-256 hash algorithm used by miners to hash blocks in order to make sure the blockchain is secure and safe - by generating verifiably random" numbers in a way that requires a predictable amount of CPU effort . Generating a SHA-256 hash with a value less than the current target solves a block and wins the miner some coins and the block is added to the blockchain.

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).
   Answer: Collision resistance is a property of cryptographic hash functions: a hash function 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). Every hash function with more inputs than outputs will necessarily have collisions.

[Jayman]

1. Hash functions take a input and then put it into a sequence of numbers or letters or both. It is a unique output and it cannot be reverted to see the original input.
2. In bitcoin one way it is used is in unconfirmed transactions which are the inputs and the confirmation which are the outputs. It its transparent and can’t be forged but at the same time is ownerless and trustable.
3. So that no two outputs are the same.

[kylecullen]

1. Describe hash functions with your own words
   • An Input of variable length when put through a hash function produces a unique fixed length output. It’s is statistically improbable that the output can be used to reverse the hash function to derive the input.
   • Hashing is not really encryption
   • One way function
   • Used for passwords and integrity
2. How are hash functions used in cryptocurrencies like bitcoin?
   • In blockchain hashes are used to represent the current state of a blockchain
     • This ensures it’s immutability
   • Each transaction contains certain info
     • Each part of the transaction hashed into transaction ID (TXID)
       • Amount
       • Addresses (send and receive)
       • Time stamp
     • TXID is a hash value used to identify and confirm transaction
   • In the Genesis block all transaction are combined into a unique hash
     • In second block the hash of the Genesis block is added to all the new transactions which combine to form a new hash
       • This process repeats in the same way as blocks are added creating a unique chain which contains all past and current transactions
   • BTC uses SHA256 to create a blockchain that is secure, immutable & transparent
   • Reference: https://www.youtube.com/watch?v=2BldESGZKB8
3. What does it mean when we say that hash functions need to be collision resistant?
   • A collision is referring to a event where 2 different inputs when put through the same hash function produce the same output (message digest)
   • This would break the integrity of the hash function