Decrypt the string from the encoded byte string

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; } ...