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Encoding not converting

An ASP.NET page (ashx) receives a GET request with a UTF8 string. It reads a SqlServer database with Windows-1255 data.
I can't seem to get them to work together. I've used information gathered on SO (mainly Convert a string's character encoding from windows-1252 to utf-8) as well as msdn on the subject.
When I run anything through the functions below - it always ends up the same as it started - not converted at all.
Is something done wrong?
EDIT
What I'm specifically trying to do (getData returns a Dictionary<int, string>):
getData().Where(a => a.Value.Contains(context.Request.QueryString["q"]))
Result is empty, unless I send a "neutral" character such as "'" or ",".
CODE
string windows1255FromUTF8(string p)
{
Encoding win = Encoding.GetEncoding(1255);
Encoding utf8 = Encoding.UTF8;
byte[] utfBytes = utf8.GetBytes(p);
byte[] winBytes = Encoding.Convert(utf8, win, utfBytes);
return win.GetString(winBytes);
}
string UTF8FromWindows1255(string p)
{
Encoding win = Encoding.GetEncoding(1255);
Encoding utf8 = Encoding.UTF8;
byte[] winBytes = win.GetBytes(p);
byte[] utfBytes = Encoding.Convert(win, utf8, winBytes);
return utf8.GetString(utfBytes);
}

There is nothing wrong with the functions, they are simply useless.
What the functions do is to encode the strings into bytes, convert the data from one encoding to another, then decode the bytes back to a string. Unless the string contains a character that is not possible to encode using the windows-1255 encoding, the returned value should be identical to the input.
Strings in .NET doesn't have an encoding. If you get a string from a source where the text was encoded using for example UTF-8, once it's decoded into a string it doesn't have that encoding any more. You don't have to do anyting to a string to use it when the destination has a specific encoding, whatever library you are using that takes the string will take care of the encoding.

For some reason this worked:
byte[] fromBytes = (fromEncoding.UTF8).GetBytes(myString);
string finalString = (Encoding.GetEncoding(1255)).GetString(fromBytes);
Switching encoding without the conversion...

get dsa signature value in octect string

I am trying to read the octect string value of attribute dsa-signature. I got the field from default naming context properties. But its in byte array, when I try to convert it into a string it give wrong output.
Does anyone knows how to do correct octect converion?
DirectoryEntry entry = new DirectoryEntry("LDAP://DC=cobra,DC=net");
PropertyValueCollection propCol = entry.Properties["dSASignature"];
Console.WriteLine(propCol.PropertyName + " : " + propCol.Value);
System.Text.UTF8Encoding enc = new System.Text.UTF8Encoding();
string str = enc.GetString((System.Byte[])propCol.Value);
Console.WriteLine("value : " + str);
Thanks in advance

But its in byte array, when I try to convert it into a string it give wrong output.
It's a byte array. Just an arbitrary sequence of bytes. It's not UTF-8-encoded text, which is what you're treating it as.
If you want to display the bytes formatted as hex, you can use:
byte[] data = (byte[]) propCol.Value;
string hex = BitConverter.ToString(data);
If you need to transfer it more efficiently but as text, you could use base64... but ideally you should treat it as a byte array for as long as possible, given that fundamentally it's just binary data.

Encoding strings to and from base-64

I'm trying to encode some strings back and forth from base-64 string and I'm having truble to get the right result.
string text = base64string.... //Here I have a base-64 string.
byte[] encodedByte = System.Text.ASCIIEncoding.ASCII.GetBytes(text);
string base64Encoded = Convert.ToBase64String(encodedByte);
if (text == base64Encoded) //If the new encoded string is equal to its original value
return base64Encoded;
I have tried my ways to do this and I don't seem to get the right result. I have tried both with System.Text.Encoding.Unicode and System.Text.Encoding.UTF8
What could be the problem? Does anyone have a proper solution?

string text = base64string.... //Here I have a base-64 string.
byte[] encodedByte = System.Text.ASCIIEncoding.ASCII.GetBytes(text);
string base64Encoded = Convert.ToBase64String(encodedByte);
You are double encoding the string. You begin with a base64 string, get the bytes, and then encode it again. If you want to compare you will need to begin with the original string.

If text is a base-64 string, then you are doing it backwards:
byte[] raw = Convert.FromBase64String(text); // unpack the base-64 to a blob
string s = Encoding.UTF8.GetString(raw); // assume the blob is UTF-8, and
// decode to a string
which will get you it as a string. Note, though, that this scenario is only useful for representing unicode text in an ascii format. Normally you wouldn't base-64 encode it if the original contents are string.

Convert whatever it is that you need in Base64 into a Byte array then use the FromBase64String and ToBase64String to convert to and from Base64:
Byte[] buffer = Convert.FromBase64String(myBase64String1);
myBase64String2 = Convert.ToBase64String(buffer);
myBase64String1 will be equal to myBase64String2. You will need to use other methods to get your data type into a Byte array and the reverse to get your data type back. I have used this to convert the content of a class into a byte array and then to Base64 string and write the string to the filesystem. Later I read it back into a class instance by reversing the process.

You have the encoding code correctly laid out. To confirm whether the base64-encoded string is correct, you can try decoding it and comparing the decoded contents to the original:
var decodedBytes = Convert.FromBase64String(base64encoded);
var compareText = System.Text.Encoding.ASCII.GetString(decodedText);
if (text == compareText)
{
// carry on...
return base64encoded;
}

Invalid length for a Base-64 char array

I'm getting a "Invalid length for a Base-64 char array." inside of the IF(){...} are variations i have tried to get it to work. it fails in the first line without calling decrypt(...) proving it's not that functions problem. i get the same error inside with the first decrypt(...) call. the last one using the encoding.ascii... will get me inside the function, but then it fails inside the function. I'm getting the proper encrypted info from the database to string SSnum. it's value is: 4+mFeTp3tPF
try
{
string SSnum = dr.GetString(dr.GetOrdinal("Social Security"));
if (isEncrypted)
{
byte[] temp = Convert.FromBase64String(SSnum);
//SSnum = decrypt(Convert.FromBase64String(SSnum), Key, IV);
//SSnum = decrypt(Encoding.ASCII.GetBytes(SSnum), Key, IV);
}
txt_Social_Security.Text = SSnum;
}
catch { txt_Social_Security.Text = ""; }
I've been told to use the Convert.FromBase64String() and not the ASCII method...so why is it failing, how can i fix it?

Base64 data length should be multiple of 4 and with padding char '='
You can change your data as valid base64 data.
string dummyData = imgData.Trim().Replace(" ", "+");
if (dummyData.Length % 4 > 0)
dummyData = dummyData.PadRight(dummyData.Length + 4 - dummyData.Length % 4, '=');
byte[] byteArray = Convert.FromBase64String(dummyData);
https://stackoverflow.com/a/9301545/2024022
This will help you , try once.
Thanks
suribabu.

it's value is: 4+mFeTp3tPF
You are receiving this error because that value, 4+mFeTp3tPF, is in fact not valid Base64.
Is it possible you are simply missing the required padding character, as so 4+mFeTp3tPF=?

Are you certain that you have a Base64 string? Base64 is a means of encoding binary data into a string while only using standard 7-bit ASCII characters. It's not a string encoding like ASCII and has some control bytes present. You have a Base64 string if you're using Convert.ToBase64String to obtain the value (which, if you're trying to store binary data as a string, is your best bet)
Judging by your error (and your example data), I'm assuming that you do not have a Base64 string. If you need to store binary data in the database, you can either create a column using a binary type or encode the string into Base64 by using Convert.ToBase64String.
byte[] inputData = ...;
string base64String = Convert.ToBase64String(inputData);
byte[] outputData = Convert.FromBase64String(base64String);
Here, outputData should contain the same data as inputData.
If what you have is just an ASCII-encoded string, then your original practice of using System.Text.Encoding.ASCII.GetBytes() is correct, but you should change this to use a Base64 string if you can.

Are you sure that string 4+mFeTp3tPF is well-formed Base64 string?
I've tried some online services - no one could convert it.

replace
byte[] temp = Convert.FromBase64String(SSnum);
to this
var temp = UTF8Encoding.UTF8.GetBytes(SSnum);

Input string was not in a correct format?

In my application i write the code like this
byte[] byt = new byte[Convert.ToSbyte(textbox1.Text)];
it is giving the error that input string was not in a correct format.

This is a wild guess, but are you trying to convert the contents of the text box into a byte array? If so, you can do it like this:
byte[] byt = Encoding.UTF8.GetBytes(textbox1.Text);

The text in textbox1 is not a valid numeral for a signed byte.
Does it have spaces? Letters? ...?

What are you trying to do? The new byte[num] creates an array of 'num' bytes, where 'num' is usually an integer. All bytes in the array are then 0.
It doesn't create a filled array, as I suspect you may be trying to do.
What are the contents of that textbox1.Text that gave the error?

what you want in fact is this
// C# to convert a string to a byte array.
public static byte[] StrToByteArray(string str)
{
System.Text.ASCIIEncoding encoding=new System.Text.ASCIIEncoding();
return encoding.GetBytes(str);
}