Python SHA1 DECODE函数

Question

I cant find how to decode string encoded in sha1. I'm suprised that i can't find simple function in python docs or google doing sha1 decoding. I give up. I need help..

Answer 1

SHA1 is a hashing algorithm. Hashing is one-way, which means that you can't recover the input from the output for any non-trivial hash function. A simple example of a one-way hash function would be adding together all the digits of a number. 1234 would hash to 1 + 2 + 3 + 4 = 10 , but so would 4321 , 1900 , 5050 , and many other numbers. Given just the hash value of 10 , you can't tell whether the input was 1234 or 5050 because information was lost.

Here's a graphical example:

As you can see, both John Smith and Sandra Dee are mapped to 02 . This means that you can't recover which name was hashed given only 02 .

Hashing is useful because it maps any amount of data to a fixed-size output and, unlike in the above examples, it is extremely difficult to find two inputs that hash to the same output. It took over 6,500 CPU-years to find just a single pair inputs to SHA-1 that have the same hash.

Therefore, if hash(A) == hash(B) , then you can be confident that A == B . If you copy a huge file and the hashes of both the original and the copy are the same, then you can be pretty sure that the file is intact.