Is there any method to convert a SHA256 hash string to a Java string?

Question

I have the following code and I want a Java string from a SHA256 hash string. Is there a way to convert hex string to its original value?

public class CryptoHash {
    public static void main( String[] args ) throws NoSuchAlgorithmException {
        MessageDigest md = MessageDigest.getInstance( "SHA-256" );
        String text = "Text to hash, cryptographically.";

        // Change this to UTF-16 if needed
        md.update( text.getBytes( StandardCharsets.UTF_8 ) );
        byte[] digest = md.digest();

        String hex = String.format( "%064x", new BigInteger( 1, digest ) );
        System.out.println( hex );
    }
}

Isn't a hash exactly meant to be impossible to convert back to original string? — ernest_k, Aug 29 '18 at 07:47
Could you please clarify whether you want to get your original string back from the hash, or the `[]byte` (digest) from the outputted hex string? — Leon, Aug 29 '18 at 07:48
how do you want to convert for example 0xFF to [ASCII](https://en.wikipedia.org/wiki/ASCIIhttps://en.wikipedia.org/wiki/ASCII)? — pskink, Aug 29 '18 at 07:53
Possible duplicate of [How to decrypt SHA-256 encrypted String?](https://stackoverflow.com/questions/9316437/how-to-decrypt-sha-256-encrypted-string) — Greggz, Aug 29 '18 at 07:54
for example from "f56c3a71b29e28ce7bc8f2f3f1ede0f89a40b25a8857b2bc25023a40a7391fb8" to ASCII — Dhananjay Jatagond, Aug 29 '18 at 07:55
It sounds like you're trying to revert a SHA-256 hashed string back into it's original form. This is not possible, as the SHA-256 hashing function is a so called one-way hash. You can only turn a string into a hashed string, you cannot turn the hashed string back into a normal, readable string. — Sander van't Veer, Aug 29 '18 at 07:58
i have a code to convert hex to ASCII but i am not getting expected output. the code returning ASCII value as õl:q²(Î{Èòóñíàø@²ZW²¼%:@§9¸ — Dhananjay Jatagond, Aug 29 '18 at 07:58
ok so how do you want to convert the first `0xf5` to [ascii](http://www.asciitable.com/)? or you mean "Extended ASCII"? — pskink, Aug 29 '18 at 07:59
`hash` itself is designed **exactly** to make it impossible to get original value from it. — Vladyslav Matviienko, Aug 29 '18 at 08:01
@VladyslavMatviienko i am pretty sure (maybe i'm wrong) that OP is aware of fact that if the original data has for example 10MB and the hash code has 32 bytes it is impossimble to get that 10MB bask from 32 bytes... he probably wants to convert that hex string to 32 binary bytes - for example: "566c6164" is `Vlad` in ASCII — pskink, Aug 29 '18 at 08:06
If this is the case, the title is either wrong or ambiguous. — ProgFroz, Aug 29 '18 at 08:13
@ProgFroz i thought like i have a code for hash password with salt. after that i need to convert it to hex to ASCII — Dhananjay Jatagond, Aug 29 '18 at 08:18
I am afraid that my answer is still the same. When you convert the Hash into Hex and then to ASCII you will find that you simply got your Hash back. — ProgFroz, Aug 29 '18 at 08:22
maybe http://www.java2s.com/Code/Java/File-Input-Output/Givenahexstringthiswillreturnthebytearraycorrespondingtostring.htm ? — pskink, Aug 29 '18 at 08:23
@pskink thank you..but my expected output is somewhat different.. — Dhananjay Jatagond, Aug 29 '18 at 08:26
@pskink i tried that method but getting unexpected output for hash hex — Dhananjay Jatagond, Aug 29 '18 at 08:31
Your question is still unclear. Maybe you are looking at converting a byte array to base64 (as your base64 code seems to do)? In that case, look at: https://stackoverflow.com/questions/2418485/how-do-i-convert-a-byte-array-to-base64-in-java — Mark Rotteveel, Aug 29 '18 at 14:36

ProgFroz · Answer 1 · 2018-08-29T08:27:17.097

Simple Answer: No, there is no way.

Longer Answer: There may be a way using a Brute Force Strategy. But it would take a long time, too long to be efficient.

See, Hash in general is made to make it impossible to reverse. You convert the String into some Hash and this cannot be reversed. You may take a look at how Hashes and Encrypting work.

https://www.cryptocompare.com/coins/guides/how-does-a-hashing-algorithm-work/

If it would be that easy, using just one line of code, the whole idea and process of hashing would be problematic.

Edit: If you want to convert a String to Hash, then to Hex and finally to ASCII your result will be the original Hash. Therefore, the idea won't work out. You cannot decrypt it this way.

Is there any method to convert a SHA256 hash string to a Java string?

1 Answers1