IOS BASE64 Encryption

1, Base64 code description

The BASE64 encoding requires the conversion of 3 8-bit bytes (3*8=24) into 4 6-bit bytes (4*6=24), followed by 6 two in front of 0 bits, forming a 8-bit byte form. If the remaining characters are less than 3 bytes, then 0 is populated with the output character using ' = ', so there may be 1 or 2 ' = ' At the end of the encoded text output.

To ensure the output of the encoded bit-readable characters, BASE64 developed an encoding table for uniform conversion. The size of the encoded table is 2^6=64, which is also the origin of the Base64 name.

2. Base64 Code Table

Code Value	character		Code Value	character		Code Value	character		Code Value	character
0	A		16	Q		32	G		48	W
1	B		17	R		33	H		49	X
2	C		18	S		34	I		50	Y
3	D		19	T		35	J		51	Z
4	E		20	U		36	K		52	0
5	F		21st	V		37	L		53	1
6	G		22	W		38	M		54	2
7	H		23	X		39	N		55	3
8	I		24	Y		40	O		56	4
9	J		25	Z		41	P		57	5
10	K		26	A		42	Q		58	6
11	L		27	B		43	R		59	7
12	M		28	C		44	S		60	8
13	N		29	D		45	T		61	9
14	O		30	E		46	U		62	+
15	P		31	F		47	V		63	/

3, BASE64 encoding use

(1) Use less than three bytes of code

Example: Encryption BS (ASCII b hex 16 binary is 73)

Alternate binary: 0110 0010 0111 0011

Not enough for three bytes with 0 full 0110 0010 0111 0011 0000 0000

Convert to 6 own mode 011000 100111 001100 000000

Find base64 encoding table corresponding to ynm=

(2) Use an encoding greater than or equal to three bytes

For example: Encrypt ASD (ASCII a hexadecimal size s 16 binary to 16 for 64)

Alternate binary: 0110 0001 0111 0011 0110 0100

Convert to 6 own mode 011000 010111 001101 100100

Find base64 encoding table corresponding to Yxnk

IOS BASE64 Encryption