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Have you ever wondered what Base64 is? Why you need it? Have you ever wanted to write your own Base64 encoder? Base64 is a common way to convert binary data into a text form. This is commonly used to store and transfer data over media that was designed to store and transfer only text, such as including an image in an XML document.
It works by converting the data into a base representation and displaying it using a common character set. The goal is to use a common set of characters that can be represented in most encoding schemes. It works by grouping the bits of the data into chunks 24 bits, treating those as 4 chunks of 6 bits sextets , converting each sextet into base10 and looking up the corresponding character for that decimal number.
A single 24 bit string is represented by 4 encoded characters. For instance, to start encoding the first 3 characters of my name we first have to convert the letters into bytes, and the bytes into bits.
The byte representations for Dav are:. Those numbers, written in 8 bit binary, are , , and respectively. Group those together to form a 24 bit string and you get Next, grab 4 sextets of bits, convert those to decimal and look up the corresponding character in the index table.
Looking those up in the index table gives the string RGF2. We just converted to Base64! But wait… we have a problem. This is where padding comes in. We know that Dav is encoded as RGF2 so we just need to encode the last letter, e. If we attempt to get our sextet groupings out of that, we get and That last sextet is missing a few bits.
What we need to do is pad the last sextet with 0 and note that we have 2 octects missing. That leaves us with and , which are 25 and 16 , which are Z and Q.
NET comes with a respectable Base64 converter. This is a learning exercise. ToBase64String method in the System namespace takes a byte as a parameter and returns a string.
The good part about the method taking a byte parameter is that part of the work is already done for you — getting the byte representation of your data.
We could use one of the Convert. NET, or we could use the one we wrote ourselves! Now that we have our data represented as binary, we need to grab bit chunks at a time. Note that we loop while octectsTaken is less than the length. This will allow us to loop through the end of the string, regardless of whether or not we have full 24 bit chunks. Next we go sextet by sextet, convert the binary to a byte and look it up in the table. We're making use of another LINQ method, Aggregate , which is basically a fancy way of joining the bits into a string again.
If we check the remainder of the length of the full bit string divided by 3, that will tell us how many padding characters are required.