Homework on Hash Functions - Questions

[Mauro]

@MarcisB

Hashing improves efficiency as you don’t have to drag old data along, you just save the hash.

Every node/miner in the blockchain network saves all data. From the first transaction, until this very moment. You have to save old data, as that is the only way that the hash will have any meaning. Hashing is used to verify that the miners have put the work behind the block, and that block contains the history of what happened. Mining secures the network.

[Mauro]

@Roger_Palomino

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). The hash function must be a one-way street for inputs and receive an output. It is infeasible to go from the output to the input, which makes that hash function collision resistant. If not, then it could be easily feasible to guess the original input, which makes that hash function not collision resistant.

You talked about breaking the hash function. A collision is finding 2 inputs that generate the same output. For example: MD5 hash function has a collision vulnerability, but even with that it is impossible to go from the output to the input.

[Mauro]

@DJ_Wilhelm

1. Hash functions are functions that take an input, and produce an output which is supposed to encrypt the input. Each value input inserted into the hash function produces a unique encrypted code. All encrypted codes are of equal length, but different values, regardless of their input.

@umeshusoda

1. Hash functions allow me to input any given data and it gives an encrypted output of that input. Its a one way function where you cannot guess or figure out the input given the output.

Hash functions only hash. They can’t encrypt. This is important since hashes can’t be reversed, while encryption can. (If you provide the proper decryption key.) Hash function are one way, and encryption is two way. Its okay to mix these terms up if you are new.

[Mauro]

@welowy

3. There are only 21 million bitcoins out there. If the miners are allowed to carry on, at this rate, they will fish out all the bitcoins in existence. On top of that, there needs to be a specific time limit in between the creation of each blocks. For bitcoin the time limit in between block creation is 10 mins. If the blocks were allowed to be created faster, it would result in more collisions: More hash functions will be generated which will inevitably cause more collisions.

We are talking about the collision resistance in the hash functions. Its a general question about hashing. It has nothing to do with the bitcoin. Feel free to answer it again.

Your answer make sense as we do have difficulty adjustments to ensure the 10 minutes block time, but then again that wasn’t the question.

[Mauro]

@HexagonalView

2. The SHA-256 algorithm is used by Bitcoin to generate random numbers which can be mathematically verified.

You answer is correct, here is how I would put the terminology in your sentence.

“The SHA-256 algorithm is used by Bitcoin to generate random numbers (nonces) which can be mathematically verified. (compare if the hash is lower than the current target)”

Don’t worry if you don’t understand the details.The important part is that your answer is correct. I just wanted to add additional information. Feel free to look back at this once you learn about mining in bitcoin. Keep up the great work.

[Mauro]

@coin_digger

MD5 is a hash function which is no longer secure because people have worked out how to derive the input value from the output value.

MD5 has a collision vulnerability. It is still impossible to go from the hash of MD5 to the input. Try to unhash the hash I created: 7c870f0c62d5d07848c52a672ff30f2d

Good luck.

[Diego_BM]

1. conversion string of date to a fixed length output
2. encrypt transaction data to secure and only the recipient can decrypt it.
3. input = transformed to unique output, probability of 2 different inputs transforming to same output is infeasable if not impossible.

[welowy]

3. For the most part each imput will have its own hash.

[Falkon]

1.Hash function is a cryptographic process that in its end gives a unique binary code with the same length for any data structure you will ask it to represent. That been said (guys ) there will be no way to understand the substance of the data from the unique binary code.

2.In cryptocurrencies the hash function represents the transactions.

3.If in a hash function there are more input options then output options then it may give one same output to two different inputs. Meaning the more output options the hash function has the more collision resistant it is.

[EnglishMom]

1. Each unique input will produce a unique output, one way.
2. Mining in Bitcoin uses Hash functions for new transactions on the blockchain. The inputs are
   a. the unconfirmed transactions
   b. additional data recording time and the previous transaction information.
3. Cryptographic hash functions are usually designed to be collision resistant for accuracy. If it is hard to find two inputs that hash to the same output then collision resistance is successful.

[Atlas]

Describe hash functions with your own words.

Hash functions are algorithms to transform inputs into unreversable outputs as like fingerprints.

How are hash functions used in cryptocurrencies like bitcoin? …

In the most known blockchain structures, every block has header as fingerprints gets hashed by previous block’s inputs. Those inputs are the database content which are also hashed (attending ids or fingerprints) as well. Besides cryptographic hash functions make mining and proof of work processes possible.

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

It is infeasible that hash of an input might be equal to another. A possibility called “Birthday Paradox” is a scenario about a chance of an encounter between two persons who may have the same birthday among 23 is 50% in 365. This odd rises with the amount of people, i.e. among 50 it becomes 97%. About the resistance, when considered that SHA-256 has 256 bits encryption makes the chance of an unique input in an assumable manner might have equal hash with another at sqrt(2^256) = 2^127th instance, which is not fun gamble.

[HexagonalView]

Thank you for your intervention, your answer is more comprehensive

[MarcisB]

Thanks for clarifying that, my answer was too brief. What I meant was that each block only contains a hash of the previous block.
However, this got me thinking - as we still have to save old data, it inevitably takes more and more power to run a full node. Are there any estimations how far this would go? Also, the connection speed that each node needs, gets higher, to get sensible processing times.

[BlockTech]

1. Hash functions are *not reversable
2. Transactions work as input and run trough the function which gives a unique key, to keep the track of the transaction you need only the key, not the input to track easier.
3. To not be able to find 2x inputs, with the same key

[Kevko]

1. A hash is an encrypted piece of text.
2. It is used to hash transaction data.
3. Every input has its unique output and it is infeasible if not impossible to have the same output for two different inputs.

[sats4all]

1. You have a unique input and get a unique digital fingerprint as 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. 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).

3. 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 ).

[nick_bell2017]

• A hash function takes an input of any length and returns a unqiue output of fixed length.

• Hash functions are used in cryptos like Bitcoin in mining. The miners are in essence, trying to ‘guess’ the hash of the block for it to be mined and the miner receive the block rewards.

• Collision resistant, refers to the unique output of a hash function. It is a rule that says that the unique output should always be unique. It is possible for hash function to produce the same output for 2 different inputs, but, like trying to brute force an Algo, it will take so long that the risk is negligible or insignificant.

[Changfa_Lin]

thanks, Mauro. I get that hash is different to encryption now. hash is generating a unique value from a string or text of past info by using some mathematical function.

[MarkM]

1. Describe hash functions with your own words

Hash functions produce a unique input which gives a unique 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 part of the block hashing algorithm which is used to write new transactions into the blockchain through the mining process.

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).

Hash functions need to be collision resistant because if one block is changed then it changes every block before it.

[ajwagers]

1. Hash functions convert any number or message to one single long number. This number represents the chosen data.

2. The bitcoin hashing algorithm takes unconfirmed transactions and adds them to the blockchain.

3. Hash functions are collision resistant when it is hard to find two inputs that give the same has result. Otherwise the blockchain would be ambiguous and not very useful.