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encodingbase64
Jack
Jack

Reputation: 7547

What is the real purpose of Base64 encoding?

Why do we have Base64 encoding? I am a beginner and I really don't understand why would you obfuscate the bytes into something else (unless it is encryption). In one of the books I read Base64 encoding is useful when binary transmission is not possible. Eg. When we post a form it is encoded. But why do we convert bytes into letters? Couldn't we just convert bytes into string format with a space in between? For example, 00000001 00000004? Or simply 0000000100000004 without any space because bytes always come in pair of 8?

Upvotes: 109

Views: 51456

Answers (4)

Om Sao
Om Sao

Reputation: 7643

For data transmission, data can be textual or non-text(binary) like image, video, file etc.

As we know, during transmission only a stream of data(textual/printable characters) can be sent or received, hence we need a way encode non-text data like image, video, file.

Binary and ASCII representation of non-text(image, video, file) is easily obtainable. Such non-text(binary) represenation is encoded in textual format such that each ASCII character takes one out of sixty four(A-Z, a-z, 0-9, + and /) possible character set.

                  Table 1: The Base 64 Alphabet

 Value Encoding  Value Encoding  Value Encoding  Value Encoding
     0 A            17 R            34 i            51 z
     1 B            18 S            35 j            52 0
     2 C            19 T            36 k            53 1
     3 D            20 U            37 l            54 2
     4 E            21 V            38 m            55 3
     5 F            22 W            39 n            56 4
     6 G            23 X            40 o            57 5
     7 H            24 Y            41 p            58 6
     8 I            25 Z            42 q            59 7
     9 J            26 a            43 r            60 8
    10 K            27 b            44 s            61 9
    11 L            28 c            45 t            62 +
    12 M            29 d            46 u            63 /
    13 N            30 e            47 v
    14 O            31 f            48 w         (pad) =
    15 P            32 g            49 x
    16 Q            33 h            50 y

These sixty four character set is called Base64 and encoding a given data into this character set having sixty four allowed characters is called Base64 encoding.

Let us take examples of few ASCII characters when encoded to Base64.

1 ==> MQ==

12 ==> MTI=

123 ==> MTIz

1234 ==> MTIzNA==

12345 ==> MTIzNDU=

123456 ==> MTIzNDU2

Here few points are to be noted:

  • Base64 encoding occurs in size of 4 characters. Because an ASCII character can take any out of 256 characters, which needs 4 characters of Base64 to cover. If the given ASCII value is represented in lesser character then rest of characters are padded with =.
  • = is not part of base64 character set. It is used for just padding.

Hence, one can see that the Base64 encoding is not encryption but just a way to transform any given data into a stream of printable characters which can be transmitted over network.

Upvotes: 1

giorgio
giorgio

Reputation: 10202

Base64 is a way to encode binary data into an ASCII character set known to pretty much every computer system, in order to transmit the data without loss or modification of the contents itself. For example, mail systems cannot deal with binary data because they expect ASCII (textual) data. So if you want to transfer an image or another file, it will get corrupted because of the way it deals with the data.

Note: base64 encoding is NOT a way of encrypting, nor a way of compacting data. In fact a base64 encoded piece of data is 1.333… times bigger than the original datapiece. It is only a way to be sure that no data is lost or modified during the transfer.

Upvotes: 147

Ahmed Shah
Ahmed Shah

Reputation: 191

Base64 is a mechanism to enable representing and transferring binary data over mediums that allow only printable characters.It is most popular form of the “Base Encoding”, the others known in use being Base16 and Base32.

The need for Base64 arose from the need to attach binary content to emails like images, videos or arbitrary binary content . Since SMTP [RFC 5321] only allowed 7-bit US-ASCII characters within the messages, there was a need to represent these binary octet streams using the seven bit ASCII characters...

Hope this answers the Question

Upvotes: 19

Denys Séguret
Denys Séguret

Reputation: 382092

Base64 is a more or less compact way of transmitting (encoding, in fact, but with goal of transmitting) any kind of binary data.

See http://en.wikipedia.org/wiki/Base64

"The general rule is to choose a set of 64 characters that is both part of a subset common to most encodings, and also printable."

That's a very general purpose and the common need is not to waste more space than needed.

Historically, it's based on the fact that there is a common subset of (almost) all encodings used to store chars into bytes and that a lot of the 2^8 possible bytes risk loss or transformations during simple data transfer (for example a copy-paste-emailsend-emailreceive-copy-paste sequence).

(please redirect upvote to Brian's comment, I just make it more complete and hopefully more clear).

Upvotes: 4

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