Decryption of string using HMACSHA256 with key in C#

Question

1.00/5 (3 votes)

See more:

I have an encrypted string (encoded with a key using HMACSHA256). Now how can I decrypt it back using the key and HMACSHA256 algorithm?

Posted 24-Feb-15 1:42am

arunkx

Add a Solution

1 solution

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Sergey Alexandrovich Kryukov · Accepted Answer · 2015-02-24T03:12:00

Solution 1

The question make no sense at all. This is not encryption. And your string cannot be decrypted, because nothing was encrypted. I don't know what do you call a "key", but you don't have a key. Probably you have only the hash-based message authentication code, only HMAC value itself, which does not contains the string you thought you "encrypted". You did not. You never mentioned you had "encrypted data".

Please see:
http://en.wikipedia.org/wiki/Hash-based_message_authentication_code[^],
https://msdn.microsoft.com/en-us/library/system.security.cryptography.hmacsha256%28v=vs.110%29.aspx[^].

To understand how something can be hash-based and what cryptographic hash does, please see:
http://en.wikipedia.org/wiki/Cryptographic_hash_function[^],
see also http://en.wikipedia.org/wiki/SHA-2[^].

—SA

Posted 24-Feb-15 3:12am

Sergey Alexandrovich Kryukov

Updated 30-Apr-15 3:52am

v2

Comments

arunkx 25-Feb-15 0:42am

I will explain the process in detail.

public string function(string data,string key)
{
System.Text.UTFEncoding encode=new UTFEncoding ();
byte [] kbyte=encode.GetBytes(key);
byte [] mbyte=encode.GetBytes(data);
HMACSHA256 hmac=new HMACSHA256(kbyte);
byte []hmsg=hmac.ComputeHash(mbyte);
string rslt=Convert.ToBase64String(hmsg,0,hmsg.length);
return rslt;
}

This is how I did my encryption. Now I have the encrypted text and the key. How can I decrypt it back?

Sergey Alexandrovich Kryukov 25-Feb-15 6:39am

Are you serious? Do I have to repeat? You did not do encryption. There is nothing to decrypt.
—SA

arunkx 25-Feb-15 6:47am

Sorry. Doing this for the first time :)

Sergey Alexandrovich Kryukov 25-Feb-15 6:48am

No problem.
Will you accept the answer formally now? I think I explained everything.
—SA

arunkx 25-Feb-15 6:51am

Before that, I have hashed some data here. Can you tell me how to retrieve the data back if I have the key?

Sergey Alexandrovich Kryukov 25-Feb-15 6:53am

You cannot. The purpose of the cryptographic hash requires it to be irreversible.
Listen, I gave you links explaining it all. Did you read anything at all?
—SA

arunkx 25-Feb-15 7:01am

Ah Yes.There lies another of my doubt. What is the purpose of hashing if it cannot be reversed back to meaningful data? Is it like locking some data forever?

Sergey Alexandrovich Kryukov 25-Feb-15 7:10am

Well, again: I provided you some links. Why not reading the referenced articles?
It is not "locking data".

How do you think passwords are stored, for example? Cryptographic hash is stored, never a password. To check validity of a password, hash is compared to hash. This way, nobody knows the password itself, except its creator who types it. The party checking for validity of authentication cannot know original password. There are other uses...

—SA

arunkx 25-Feb-15 7:12am

Cool. Thanks Mr.SA :)

Sergey Alexandrovich Kryukov 25-Feb-15 7:17am

You are welcome.
—SA