Decrypt the string from the encoded byte string

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I have converted a string in encrypted form using SHA1 algorithm. How do I decrypt it in the original string?

The code is given below:

byte[] data = Encoding.Unicode.GetBytes(TxtAddress.Text);
               SHA1 sha = new SHA1CryptoServiceProvider();
               byte[] hash = sha.ComputeHash(data);
               DSASignatureFormatter DSAFormatter = new DSASignatureFormatter(DSA);
               DSAFormatter.SetHashAlgorithm("SHA1");

               signature = DSAFormatter.CreateSignature(hash);

               string digiSignature = "";
               foreach (byte b in signature)
               { digiSignature += b; }

Posted 13-Jul-12 18:30pm

Member 8491154

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3 solutions

Solution 2

Hi,
SHA1 is not an encryption algorithm, so it is not possible to decrypt it. As seventheyejosh just stated, it is a hash (checksum.) And it is one-way and cannot be undone.

So, you Can't, Hash Function[^] are one way functions. this is why it is used for passwords, because you can't get the password using some reverse function on the hash value.

You can refer these links for the other solution:
Encryption/Decryption Function in .NET using the TripleDESCryptoServiceProvider Class[^]
Simple encrypting and decrypting data in C#[^]
All the best.
--Amit

Posted 13-Jul-12 20:15pm

_Amy

Updated 13-Jul-12 20:39pm

v2

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Member 8491154 14-Jul-12 2:21am

so what can other solution?

_Amy 14-Jul-12 2:39am

See my updated answer.

Solution 3

As others have stated, you cannot turn a hash back into it's original data - that is not the purpose a hash function

That said, what you appear to be doing is creating a digital signature, which uses an asymmetric key to encrypt the hash

Checking the data is correct is a case of hashing the original data, asymmetrically decrypting the hash, and checking the two hashes

PKI[^]

Posted 13-Jul-12 21:34pm

barneyman

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**AmitGajjar** · Accepted Answer · 2012-07-13T18:39:00

Solution 1

Hi,

Please go through How To: Hash Data Using MD5 and SHA1[^]

This may help you,
Let me know if you have any query.

Thanks
-Amit

Posted 13-Jul-12 18:39pm

AmitGajjar

Comments

Member 8491154 14-Jul-12 1:35am

It does the validation part, but the string is not decrypted back to original string.

AmitGajjar 16-Jul-12 0:02am

Why you need decrypted text ? if you have login functionality then you do not need to decrypt the password. instead you can encrypt user entered password and your database encrypted password.

Member 8491154 18-Jul-12 3:22am

I just want to validate the signature generated

AmitGajjar 18-Jul-12 5:09am

in that case you can compare your stored signature with generated signature.

Member 8491154 18-Jul-12 7:24am

i am asking that only. How do I compare the signature and hash already stored in database

AmitGajjar 18-Jul-12 7:43am

steps
1) get hash value stored in database and store in variable1.
2) compute hash for your input string and store in variable2.
3) compare variable1 and variable2.

Member 8491154 14-Jul-12 2:20am

Can you suggest something else?