How to decrypt a SHA-256 encrypted string?

Question

I have a string that was salted, hashed with SHA-256, then base64 encoded. Is there a way to decode this string back to its original value?

Answer 1

SHA-256 is a cryptographic (one-way) hash function, so there is no direct way to decode it. The entire purpose of a cryptographic hash function is that you can't undo it.

One thing you can do is a brute-force strategy, where you guess what was hashed, then hash it with the same function and see if it matches. Unless the hashed data is very easy to guess, it could take a long time though.

You may find the question "Difference between hashing a password and encrypting it" interesting.

Answer 2

It should be noted - Sha256 does not encrypt the data/content of your string, it instead generates a fixed size hash, using your input string as a seed.

This being the case - I could feed in the content of an encyclopedia, which would be easilly 100 mb in size of text, but the resulting string would still be 256 bits in size.

Its impossible for you to reverse the hash, to get that 100mb of data back out of the fixed size hash, the best you can do, is try to guess / compute the seed data, hash, and then see if the hash matches the hash your trying to break.

If you could reverse the hash, you would have the greatest form of compression to date.