Daily must-read (2)--base64

What is base64?

As defined by RFC2045, Base64 is defined as: the Base64 content transfer encoding is designed to describe an arbitrary sequence of 8-bit bytes as a form that is not easily recognizable by humans. (The Base64 content-transfer-encoding is designed to represent arbitrary sequences of octets in a form that need not being HU Manly readable.)

The characters used include 26 uppercase and lowercase letters, plus 10 digits, and a plus sign "+", a slash "/", a total of 64 characters, and an equal sign "=" to use as a suffix.

Second, the role of Base64

1. The implementation of simple data encryption, so that users can not see the real data at a glance, the complexity of the Base64 algorithm is small, the efficiency is relatively high.
2. Some systems or applications that use only ASCII characters, such as email, need to encode data using Base64

The above is excerpted from http://www.cnblogs.com/apm70/articles/2358569.html

Three, base64 principle

Base64 requires that every three bytes of 8Bit be converted to four 6Bit bytes (3*8 = 4*6 = 24), and 6Bit is then added two bits high 0, which makes up four 8Bit bytes, that is, the converted string will theoretically be 1/3 longer than the original one. The encoding principle is as follows:

(1) The encoding of Base64 is based on the length of the string, in a group of 3 characters per 8bit,

(2) Then for each group, first get the ASCII encoding for each character,

(3) Then convert the ASCII encoding to 8bit binary to get a set of 3*8=24bit bytes

(4) Then divide the 24bit into 4 6bit bytes, and fill in front of each 6bit byte two high 0, get 4 8bit bytes

(5) then convert the 4 8bit bytes into 10 binary, control the BASE64 encoding table, the corresponding encoded characters.

Four, base64 character mapping table

V. Base64 routines

            //a single byte            byte[] B =New byte[] {0x01}; strings = convert.tobase64string (b,0,1); byte[] be =convert.frombase64string (s); //two bytes            byte[] bs =New byte[] {0x01,0x02}; stringSS = Convert.tobase64string (BS,0,2); //three bytes            byte[] BSS =New byte[] {0x01,0x02,0x03 }; stringSSS = convert.tobase64string (BSS,0,3);

Daily must-read (2)--base64