|
Title: Understanding about Hash functions Post by: Insufficient on July 20, 2018, 06:07:59 AM Introduction
Hash functions (https://en.m.wikipedia.org/wiki/Hash_function) are the fundamental and vital part of the Blockchain (https://en.m.wikipedia.org/wiki/Blockchain). In summarize if you understand how the Hash functions work, you'll understand too the Blockchain. Hash Function What is it? ??? In the abstract, a Hash function (https://en.m.wikipedia.org/wiki/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. In summarize , a hash function takes an input of any length and creates an output of fixed length. Hash function have a three basic characteristics :
How this relate to the blockchain? ??? Blockchain use hash functions everywhere : i.e In Bitcoin private key ; every public key linked to a private key , private key can generate an essentially unlimited supply of public addresses but you can not reverse it to show the secret key behind it. Title: Re: Understanding about Hash functions Post by: r1s2g3 on July 21, 2018, 07:32:51 AM How this relate to the blockchain? ??? Blockchain use hash functions everywhere : i.e In Bitcoin private key ; every public key linked to a private key , private key can generate an essentially unlimited supply of public addresses but you can not reverse it to show the secret key behind it. I guess, this part is wrong, Private key is used to generate public key by using elliptic curve multiplication. Bitcoin Address are generated by using Hash function on Public key. https://i.imgur.com/5pZkcKZ.png source : https://github.com/bitcoinbook/bitcoinbook/blob/develop/ch04.asciidoc Hash function have a three basic characteristics :
I do not have source but I remember to read that it is very rare scenarios but it is possible that 2 different input can have same hash. Title: Re: Understanding about Hash functions Post by: HCP on July 21, 2018, 09:46:48 AM I do not have source but I remember to read that it is very rare scenarios but it is possible that 2 different input can have same hash. You are indeed correct... this is known as a "collision". Refer: https://en.wikipedia.org/wiki/Collision_(computer_science)Basically, it depends on the size of the output space for your hash function. The larger the space, the smaller the chance of a collision. For example, if you have a 2 bit hash function (as opposed to bitcoins 256 bit hash functions)... then the only possible outputs of your hash function are: Quote 00 01 10 11 Given any two different inputs... there is a 1/4 chance that they'll both generate the same output. A 256 bit hash function on the other hand has 2256 possible outputs... the odds of finding a collision are so small it is generally regarded as zero. Title: Re: Understanding about Hash functions Post by: vphasitha01 on July 21, 2018, 09:52:18 AM I do not have source but I remember to read that it is very rare scenarios but it is possible that 2 different input can have same hash. When we compare to the SHA-2 series of hash functions(SHA-256, SHA-384, SHA 512) has strong collision resistance (https://en.wikipedia.org/wiki/Collision_resistance). so it is hard to find two inputs having the same hash. I think you're talking about MD5 (http://www.iusmentis.com/technology/hashfunctions/md5/) hash function which is vulnerable for collision attacks and also a hacker can produce two colliding hashes in no time with higher CPU power, but not with the SHA-2 series.With SHA-256 function, almost all the time we cannot get Hash(A)=Hash(B) if A≠B <...snip...> |
