Base 64 encode

Wiki. We will discuss what is it and why we use it and how is it generated.

What and Why ?

It’s basically a way of encoding arbitrary binary data in ASCII text. It takes 4 characters per 3 bytes of data, plus potentially a bit of padding at the end.

Essentially each 6 bits of the input is encoded in a 64-character alphabet. The “standard” alphabet uses A-Z, a-z, 0-9 and + and /, with = as a padding character. There are URL-safe variants.

When you have some binary data that you want to ship across a network, you generally don’t do it by just streaming the bits and bytes over the wire in a raw format. Why? because some media are made for streaming text. You never know — some protocols may interpret your binary data as control characters (like a modem), or your binary data could be screwed up because the underlying protocol might think that you’ve entered a special character combination (like how FTP translates line endings).

So to get around this, people encode the binary data into characters. Base64 is one of these types of encodings.

Why 64?
Because you can generally rely on the same 64 characters being present in many character sets, and you can be reasonably confident that your data’s going to end up on the other side of the wire uncorrupted.

Spammers use Base64 to evade basic anti-spamming tools, which often do not decode Base64 and therefore cannot detect keywords in encoded messages.
Base64 can be used to transmit and store text that might otherwise cause delimiter collision.

How ? ( 1, Check wiki as well)

Base64 encoding takes three bytes, each consisting of eight bits, and represents them as four printable characters in the ASCII standard. It does that in essentially two steps.

The first step is to convert three bytes to four numbers of six bits. Each character in the ASCII standard consists of seven bits. Base64 only uses 6 bits (corresponding to 2^6 = 64 characters) to ensure encoded data is printable and humanly readable.

None of the special characters available in ASCII are used. The 64 characters (hence the name Base64) are 10 digits, 26 lowercase characters, 26 uppercase characters as well as ‘+’ and ‘/’.

If, for example, the three bytes are 155, 162 and 233, the corresponding (and frightening) bit stream is 100110111010001011101001, which in turn corresponds to the 6-bit values 38, 58, 11 and 41.

Advertisements

Leave a Reply

Please log in using one of these methods to post your comment:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s