Why is sha256 irreversible and how secure is sha256

sha256 It is one of the most popular computer algorithms , It is also one of the strongest encryption functions . because sha256 Very powerful , Therefore, it is used in cryptocurrencies such as bitcoin .sha256 Is an unbreakable function , its 256 The bit key has never been compromised . that ,sha256 How safe is it , Why? sha256 Irreversible ？ This article will discuss these problems .

sha256 Why not reversible

sha256 It's irreversible . because sha256 Is a definite one-way hash function , Developed by the national security agency SHA-2 One of the members of the cryptographic hash function . in other words sha256 It's a mathematical function , Accept input of any size , But return fixed size input , Like a digital fingerprint of a file or string .

meanwhile , It is also deterministic , Because the same input always produces the same output . Irreversibility , When you know x Of HASH value , It's impossible to work out x; The so-called no conflict , When you know x, I can't figure out one y, send x And y Of HASH Same value .

sha256 How to work ？

sha256 Very safe , Even if we change only one digit in the input , The output will also change completely . For messages of any length ,sha256 There will be a 256 bit Long hash value , It's called a message digest . This summary is equivalent to a length of 32 An array of bytes , Usually use a length of 64 Hexadecimal string to represent . in other words , No matter how long the input is , It always comes back 64 A hexadecimal string of characters .

Here are some examples

stay md5、sha256 Online encryption and decryption website ：https://md5.cn/ Perform the following tests .

Input ：Bye

After the hash function SHA256 The resulting hash value is ：128901223aac8df3b89cd75d7ec644f9924ed9dcd01e0c65ae99334a3cf9273a

Input ：bye
After the hash function sha256 The resulting hash value is ：
b49f425a7e1f9cff3856329ada223f2f9d368f15a00cf48df16ca95986137fe8

From the example above , It's not hard to see , No matter what the input length , It will return a 64 Character string . and , Even if a letter becomes lowercase, it will completely change the hash value , We can't pass the hash function , Guess Bye and bye Very similar .

sha256 How safe is it ？

sha256 Very safe , as a result of ： Only by inputting the same file or string can we get the same hash value , Even a small adjustment will completely change the output hash value . You can try some interesting things with this algorithm , Like taking a picture , adopt sha256 function , The output hash value may never appear in this world .

sha256 Is a one-way hash function , Therefore, it is irreversible . meanwhile , Because it has a strong ability to resist strong collisions , And the same input information passes sha256 The output value of is unique , When used SHA256 When the encrypted information is modified , Even small modifications , The results will be completely different . therefore sha256 Very safe .